Publications by authors named "Fu-Quan Huo"

29 Publications

  • Page 1 of 1

Paclitaxel Induces Sex-biased Behavioral Deficits and Changes in Gene Expression in Mouse Prefrontal Cortex.

Neuroscience 2020 02 14;426:168-178. Epub 2019 Dec 14.

Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi 710061, PR China; Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University), Ministry of Education, Beijing, PR China.

Paclitaxel (PTX) is one of the most commonly used chemotherapeutic agents for various cancer diseases. Despite its advantages, PTX also causes behavioral deficits related to nervous-system dysfunction, such as neuropathic pain, depression, anxiety, and cognitive impairments. The prefrontal cortex (PFC) is one of the areas that is susceptible to adverse effects of chemotherapeutic agents. Therefore, the present study was designed to examine sex-biased behavioral deficits and whole-transcriptome changes in gene expression in the PFC of mice treated with vehicle or PTX. In this study, PTX (4 mg/kg) was injected intraperitoneally four times in mice every other day. Three weeks later, both PTX-treated male and female mice developed mechanical pain hypersensitivities, as indicated by increased paw withdrawal responses to 0.16-g von Frey filaments. Additionally, PTX-treated mice exhibited depression-like symptoms, as they exhibited increased immobility times in the forced swim test. PTX also induced cognitive impairment, as demonstrated via results of a novel object recognition (NOR) test and anxiety-like behavior in an elevated plus-maze test in male mice, but not in female mice. RNA sequencing and in-depth gene expression analysis of the PFC in paired vehicle and PTX-treated mice showed that PTX induced 1755 differentially expressed genes in the PFCs of male and female mice. Quantitative real-time RT-PCR verified that some gene expressions in the medial PFC (mPFC) were related to neurotransmission. In conclusion, this study identified a sex-biased effect of PTX on PFC function and gene expression, which provides a foundation for future studies to explore the precise mechanisms of PTX-induced behavioral deficits.
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http://dx.doi.org/10.1016/j.neuroscience.2019.11.031DOI Listing
February 2020

Involvement of 5-HT2A, 5-HT2B and 5-HT2C receptors in mediating the ventrolateral orbital cortex-induced antiallodynia in a rat model of neuropathic pain.

Neuroreport 2020 01;31(2):167-173

Department of Blood Purification, the First Affiliated Hospital of Xi'an Jiaotong University.

The present study examined the roles of 5-HT2A, 5-HT2B and 5-HT2C receptor subtypes in mediating the ventrolateral orbital cortex (VLO)-induced antiallodynia in a rat model of neuropathic pain induced by spared nerve injury (SNI). Change of mechanical paw withdrawal threshold (PWT) was measured using von-Frey filaments. Microinjection of preferential or selective 5-HT2A/C, 5-HT2B and 5-HT2C receptor agonists, (±)-1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI), α-methyl-5-(2-thienylmethoxy)-1H-Indole-3-ethanamine hydrochloride (BW723C86) and 1-(3-Chlorophenyl)-piperazine hydrochloride (m-CPP) into the VLO significantly depressed allodynia induced by SNI, and the inhibitory effect of DOI was blocked or attenuated by selective 5-HT2A/C receptor antagonists ketanserin (+)-tartrate salt (ketanserin) and 5-HT2A receptor antagonist R-(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidinemethanol (M100907); the effects of BW723C86 and m-CPP were antagonized by 5-HT2B receptor antagonists N-(1-Methyl-1H-5-indolyl)-N'-(3-methyl-5-isothiazolyl)urea (SB204741) and 5-HT2C receptor antagonist RS102221 hydrochloride hydrate (RS-102221), respectively. These results suggest that 5-HT2A, 5-HT2B, 5-HT2C receptor subtypes are involved in mediating the VLO-induced antiallodynia in the neuropathic pain state.
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http://dx.doi.org/10.1097/WNR.0000000000001377DOI Listing
January 2020

The pronociceptive role of 5-HT receptors in ventrolateral orbital cortex in a rat formalin test model.

Neurochem Int 2019 12 30;131:104562. Epub 2019 Sep 30.

College of Forensic Medicine, Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi, 710061, China; The Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University), Ministry of Education, China. Electronic address:

Recent studies have shown the 5-HT receptors are expressed in regions which are important in pain processing such as the cortex, amygdala, thalamus, PAG, spinal cord and dorsal root ganglia (DRG), suggesting a putative role of 5-HT receptors in pain modulation. The ventrolateral orbital cortex (VLO) is part of an endogenous analgesic system, consisting of the spinal cord - thalamic nucleus submedius (Sm) - VLO - periaqueductal gray (PAG) - spinal cord loop. The present study assessed the possible role of 5-HT receptors in the VLO in formalin-induced inflammatory pain model. Firstly we found that microinjection of selective 5-HT receptor agonists EMD-386088 (5 μg in 0.5 μl) and WAY-208466 (8 μg in 0.5 μl) both augmented 5% formalin-induced nociceptive behavior. Microinjection of selective 5-HT receptor antagonist SB-258585 (1,2 and 4 μg in 0.5 μl) significantly reduced formalin-induced flinching. Besides, the pronociceptive effects of EMD-386088 and WAY-208466 were dramatically reduced by SB-258585, implicating 5-HT receptor mechanisms in mediating these responses. In addition, the pronociceptive effect of EMD-386088 was also prevented by the adenylate cyclase (AC) inhibitor SQ-22536 (2 nmol in 0.5 μl) and the protein kinase A (PKA) inhibitor H89 (10 nmol in 0.5 μl), respectively. We further confirmed the above results with quantification of spinal c-fos expression. Taken together, our results suggested that 5-HT receptors play a pronociceptive role in the VLO in the rat formalin test due to its activation of AC - PKA pathway. Therefore, cerebral cortical 5-HT receptors could be a new target to develop analgesic drugs.
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http://dx.doi.org/10.1016/j.neuint.2019.104562DOI Listing
December 2019

Peripheral ionotropic glutamate receptors contribute to Fos expression increase in the spinal cord through antidromic electrical stimulation of sensory nerves.

Neurosci Lett 2018 06 26;678:1-7. Epub 2018 Apr 26.

Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, Research Center of Stomatology, Xi'an Jiaotong University College of Stomatology, 98 West 5th Road, Xi'an, Shaanxi 710004, P. R. China. Electronic address:

Previous studies have shown that peripheral ionotropic glutamate receptors are involved in the increase in sensitivity of a cutaneous branch of spinal dorsal ramus (CBDR) through antidromic electrical stimulation (ADES) of another CBDR in the adjacent segment. CBDR in the thoracic segments run parallel to each other and no synaptic contact at the periphery is reported. The present study investigated whether the increased sensitivity of peripheral sensory nerves via ADES of a CBDR induced Fos expression changes in the adjacent segments of the spinal cord. Fos expression increased in the T8 - T12 segments of the spinal cord evoked by ADES of the T10 CBDR in rats. The increased Fos expression in the T11 and T12, but not T8 - T10 spinal cord segments, was significantly blocked by local application of either N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine maleate (MK-801) or non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) into the receptive field of T11 CBDR. The results suggest that endogenous glutamate released by ADES of sensory nerve may bind to peripheral ionotropic glutamate receptors and activate adjacent sensory nerve endings to increase the sensitivity of the spinal cord. These data reveal the potential mechanisms of neuron activation in the spinal cord evoked by peripheral sensitization.
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http://dx.doi.org/10.1016/j.neulet.2018.04.051DOI Listing
June 2018

Non-canonical Opioid Signaling Inhibits Itch Transmission in the Spinal Cord of Mice.

Cell Rep 2018 Apr;23(3):866-877

Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110, USA. Electronic address:

Chronic itch or pruritus is a debilitating disorder that is refractory to conventional anti-histamine treatment. Kappa opioid receptor (KOR) agonists have been used to treat chronic itch, but the underlying mechanism remains elusive. Here, we find that KOR and gastrin-releasing peptide receptor (GRPR) overlap in the spinal cord, and KOR activation attenuated GRPR-mediated histamine-independent acute and chronic itch in mice. Notably, canonical KOR-mediated G signaling is not required for desensitizing GRPR function. In vivo and in vitro studies suggest that KOR activation results in the translocation of Ca-independent protein kinase C (PKC)δ from the cytosol to the plasma membrane, which in turn phosphorylates and inhibits GRPR activity. A blockade of phospholipase C (PLC) in HEK293 cells prevented KOR-agonist-induced PKCδ translocation and GRPR phosphorylation, suggesting a role of PLC signaling in KOR-mediated GRPR desensitization. These data suggest that a KOR-PLC-PKCδ-GRPR signaling pathway in the spinal cord may underlie KOR-agonists-induced anti-pruritus therapies.
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http://dx.doi.org/10.1016/j.celrep.2018.03.087DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5937707PMC
April 2018

Microinjection of histone deacetylase inhibitor into the ventrolateral orbital cortex potentiates morphine induced behavioral sensitization.

Brain Res 2016 09 14;1646:418-425. Epub 2016 Jun 14.

College of Forensic Medicine, Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi 710061, China; Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University), Ministry of Education, China. Electronic address:

Accumulating evidence indicates that epigenetic regulation, such as changes in histone modification in reward-related brain regions, contributes to the memory formation of addiction to opiates and psychostimulants. Our recent results suggested that the ventrolateral orbital cortex (VLO) is involved in the memories of stress and drug addiction. Since addiction and stress memories share some common pathways, the present study was designed to investigate the role of histone deacetylase (HDAC) activity in the VLO during morphine induced-behavioral sensitization. Rats received a single exposure to morphine for establishing the behavioral sensitization model. The effect of HDAC activity in the VLO in morphine induced-behavioral sensitization was examined by microinjection of HDAC inhibitor Trichostatin A (TSA). Furthermore, the protein expression levels of extracellular signal-regulated kinase (ERK) and phosphorylated ERK (p-ERK), histone H3 lysine 9 acetylation (aceH3K9) and brain-derived neurotrophic factor (BDNF) in the VLO in morphine-induced behavioral sensitization were examined. The results showed that the bilateral VLO lesions suppressed the expression phase, but not the developmental phase of morphine-induced behavioral sensitization. Microinjection of TSA into the VLO significantly increased both the development and expression phases. Moreover, the protein levels of p-ERK, aceH3K9 and BDNF except ERK in the VLO were significantly upregulated in morphine-treated rats in the expression phase. These effects were further strengthened by intra-VLO injection of TSA. Our findings suggest that HDAC activity in the VLO could potentiate morphine-induced behavioral sensitization. The upregulated expression of p-ERK, aceH3K9 and BDNF in the VLO might be the underlying mechanism of histone acetylation enhancing the morphine-induced behavioral sensitization.
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http://dx.doi.org/10.1016/j.brainres.2016.06.019DOI Listing
September 2016

Activation of α1 adrenoceptors in ventrolateral orbital cortex attenuates allodynia induced by spared nerve injury in rats.

Neurochem Int 2016 10 11;99:85-93. Epub 2016 Jun 11.

College of Forensic Medicine, Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi 710061, China; Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University), Ministry of Education, China. Electronic address:

Recent studies have demonstrated that noradrenaline acting in the ventrolateral orbital cortex (VLO) can potentially reduce allodynia induced by spared nerve injury (SNI), and this effect is mediated by α2 adrenoceptor. The present study examined the effect of the α1 adrenoceptors in the VLO on allodynia induced by SNI in the rats. The mechanical paw withdrawal threshold (PWT) was measured using von-Frey filaments. Microinjection of selective α1 adrenoceptor agonist methoxamine (20, 50, 100 μg in 0.5 μl) into the VLO, contralateral to the site of nerve injury, increased PWT in a dose-dependent manner. This effect was antagonized by pre-microinjection of the selective α1 adrenoceptor antagonist benoxathian into the same VLO site, and blocked by electrolytic lesion of the ventrolateral periaqueductal gray (PAG). Furthermore, pre-administration of non-selective glutamate receptor antagonist kynurenic acid, phospholipase C (PLC) inhibitor U73122, and protein kinase C (PKC) inhibitor chelerythrine to the VLO also blocked methoxamine-induced inhibition of allodynia. These results suggest that activation of α1 adrenoceptors in the VLO can potentially reduce allodynia induced by SNI. This effect may be direct excitation of the VLO neurons, via PLC-PKC signaling pathway, projecting to the PAG or facilitating glutamate release and then indirectly exciting the VLO output neurons projecting to the PAG, leading to activation of the PAG-brainstem descending inhibitory system which depresses the nociceptive transmission at the spinal cord level.
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http://dx.doi.org/10.1016/j.neuint.2016.06.006DOI Listing
October 2016

Analgesic effect of total flavonoids from Sanguis draxonis on spared nerve injury rat model of neuropathic pain.

Phytomedicine 2015 Nov 16;22(12):1125-32. Epub 2015 Sep 16.

College of Pharmacy, South-Central University for Nationalities, Wuhan, Hubei 430074, PR China. Electronic address:

Background: Sanguis draxonis (SD) is a kind of red resin obtained from the wood of Dracaena cochinchinensis (Lour.) S. C. Chen (D. cochinchinensis). The active components of total flavonoids from SD (SDF) have analgesic effect.

Aim: The aim of this study is to evaluate the analgesic effects and potential mechanism of SDF on mechanical hypersensitivity induced by spared nerve injury (SNI) model of neuropathic pain in the rat.

Methods: SNI model in rats was established and then the rats were treated with SDF intragastric administration for 14 days. Paw withdrawal mechanical threshold (PMWT) in response to mechanical stimulation was measured by von Frey filaments on day 1 before operation and days 1, 3, 5, 7, 9, 11, 14 after operation, respectively. After 14 days, we measured the levels of nitric oxide (NO), nitric oxide synthase (NOS), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-10 (IL-10) in the spinal dorsal horn. In addition, the expression of fibroblast growth factor receptor 3 (FGFR3), phosphorylated cyclic AMP response element-binding protein (p-CREB) and glial fibrillary acidic protein (GFAP) of the spinal dorsal horn was evaluated by western blotting and an immunofluorescence histochemical method, respectively.

Results: Intragastric administration of SDF (100, 200, 400 mg/kg) alleviated significantly SNI-induced mechanical hypersensitivity, as PMWT increased in a dose-dependent manner. Moreover, SDF not only reduced the level of NO, NOS, TNF-α and IL-1β, but also upregulated the level of IL-10 in the spinal dorsal horn of SNI rats. At the same time, SDF (100, 200, 400 mg/kg) could inhibit the expression of FGFR3, GFAP and p-CREB in the spinal dorsal horn.

Conclusion: SDF has potentially reduced mechanical hypersensitivity induced by SNI model of neuropathic pain which may be attributed to inhibition of astrocytic function (like release pro-inflammatory cytokines) and NO release as well as p-CREB activation in the spinal dorsal horn.
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http://dx.doi.org/10.1016/j.phymed.2015.08.011DOI Listing
November 2015

The α1 adrenoceptors in ventrolateral orbital cortex contribute to the expression of morphine-induced behavioral sensitization in rats.

Neurosci Lett 2016 Jan 28;610:30-5. Epub 2015 Oct 28.

College of Forensic Medicine, Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi 710061, China; Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University), Ministry of Education, China. Electronic address:

The aim of the present study was to investigate the effect of microinjection of benoxathian, selective α1 adrenoceptor antagonist, into the ventrolateral orbital cortex (VLO) on morphine-induced behavioral sensitization and its underlying molecular mechanism in rats. A single morphine treatment protocol was used in establishing the behavioral sensitization model. The effect of bilateral intra-VLO benoxathian injection on locomotor activity was examined and the protein expression levels of α1 adrenoceptors and activation of extracellular signal-regulated kinase (ERK) in the VLO were detected after locomotor test. The results showed that a single injection of morphine could induce behavioral sensitization by a low challenge dosage of morphine after a 7-days drug free period. Benoxathian significantly suppressed the expression but not the development of morphine-induced behavioral sensitization. Morphine treatment significantly elicited ERK phosphorylation and downregulated the expression level of α1 adrenoceptors in the VLO. In addition, intra-VLO benoxathian injection enhanced the expression levels of α1 adrenoceptors and phosphorylated ERK. These results suggest that α1 adrenoceptors in the VLO are involved in regulating the expression of morphine-induced behavioral sensitization. The effect of decreased locomotor activity by blocking α1 adrenoceptors might be associated with activation of ERK in the VLO.
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http://dx.doi.org/10.1016/j.neulet.2015.10.057DOI Listing
January 2016

Mechanism Underlying the Analgesic Effect Exerted by Endomorphin-1 in the rat Ventrolateral Periaqueductal Gray.

Mol Neurobiol 2016 Apr 16;53(3):2036-2053. Epub 2015 Apr 16.

Department of Anatomy, Histology and Embryology, K. K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, 710032, China.

The ventrolateral periaqueductal gray (vlPAG) is an important brain area, in which 5-HTergic neurons play key roles in descending pain modulation. It has been proposed that opioid peptides within the vlPAG can excite the 5-HTergic neurons by alleviating tonic inhibition from GABAergic neurons, the so-called disinhibitory effect. However, no direct morphological evidence has been observed for the micro-circuitry among the opioid peptide-, GABA-, and 5-HT-immunoreactive (ir) profiles nor for the functional involvement of the opioid peptides in the intrinsic properties of GABAergic and 5-HTergic neurons. In the present study, through microscopic observation of triple-immunofluorescence, we firstly identified the circuitry among the endomorphin-1 (EM1, an endogenous ligand for the μ-opioid receptor)-ir terminals and GABA-ir and 5-HT-ir neurons within the rat vlPAG. The synaptic connections of these neurons were further confirmed by electron microscopy. Through the in vitro whole-cell patch-clamp method, we showed that EM1 has strong inhibitory effects on the spiking of GABAergic neurons. However, although the resting membrane potential was hyperpolarized, EM1 actually increased the firing of 5-HTergic neurons. More interestingly, EM1 strongly inhibited the excitatory input to GABAergic neurons, as well as the inhibitory input to 5-HTergic neurons. Finally, behavioral results showed that pretreatment with a GABA(A) receptor antagonist potentiated the analgesic effect of EM1, while treatment with a GABA(A) receptor agonist blocked its analgesic effect. In summary, by utilizing morphological and functional methods, we found that the analgesic effect of EM1 is largely dependent on its potent inhibition on the inhibitory inputs to 5-HTergic neurons, which overwhelms EM1's direct inhibitory effect on 5-HTergic neurons.
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http://dx.doi.org/10.1007/s12035-015-9159-5DOI Listing
April 2016

Activation of mu-opioid receptors in the ventrolateral orbital cortex inhibits the GABAergic miniature inhibitory postsynaptic currents in rats.

Neurosci Lett 2015 Apr 21;592:64-9. Epub 2015 Feb 21.

Department of Physiology and Pathophysiology, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an Jiaotong University School of Medicine, Xi'an 710061, China.

Previous studies have indicated that mu-opioid receptors in the ventrolateral orbital cortex (VLO) are involved in antinociception in tail flick tests and GABAergic neurons or terminals express mu-opioid receptors in the VLO. The current study examined the effect of selective mu-opioid receptor agonist DAMGO on the GABAergic miniature inhibitory postsynaptic currents (mIPSCs) in the VLO in rats using the whole-cell patch clamp. The results demonstrated that 5 μM DAMGO application into the rat VLO slices significantly reduced the GABAergic mIPSCs frequency, without any effect on its amplitude, and this effect of DAMGO was reversed by pretreatment with selective mu-opioid receptor antagonist 1 μM CTOP. Importantly, application of CTOP alone into the VLO slices did not produce any effect on the frequency and amplitude of GABAergic mIPSCs. These results indicate a presynaptic effect of mu-opioid receptor activation on the GABAergic neurons in the VLO. The current data suggests that a presynaptic inhibition of the GABA release may contribute to the mu-opioid receptor mediated effects in the VLO and provides novel electrophysiological evidence for the underlying mechanisms of mu-opioid receptors in the VLO.
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http://dx.doi.org/10.1016/j.neulet.2015.02.045DOI Listing
April 2015

Descending control of itch transmission by the serotonergic system via 5-HT1A-facilitated GRP-GRPR signaling.

Neuron 2014 Nov 30;84(4):821-34. Epub 2014 Oct 30.

Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110, USA. Electronic address:

Unlabelled: Central serotonin (5-hydroxytryptophan, 5-HT) modulates somatosensory transduction, but how it achieves sensory modality-specific modulation remains unclear. Here we report that enhancing serotonergic tone via administration of 5-HT potentiates itch sensation, whereas mice lacking 5-HT or serotonergic neurons in the brainstem exhibit markedly reduced scratching behavior. Through pharmacological and behavioral screening, we identified 5-HT1A as a key receptor in facilitating gastrin-releasing peptide (GRP)-dependent scratching behavior. Coactivation of 5-HT1A and GRP receptors (GRPR) greatly potentiates subthreshold, GRP-induced Ca(2+) transients, and action potential firing of GRPR(+) neurons. Immunostaining, biochemical, and biophysical studies suggest that 5-HT1A and GRPR may function as receptor heteromeric complexes. Furthermore, 5-HT1A blockade significantly attenuates, whereas its activation contributes to, long-lasting itch transmission. Thus, our studies demonstrate that the descending 5-HT system facilitates GRP-GRPR signaling via 5-HT1A to augment itch-specific outputs, and a disruption of crosstalk between 5-HT1A and GRPR may be a useful antipruritic strategy.

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http://dx.doi.org/10.1016/j.neuron.2014.10.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4254557PMC
November 2014

Cross-inhibition of NMBR and GRPR signaling maintains normal histaminergic itch transmission.

J Neurosci 2014 Sep;34(37):12402-14

Center for the Study of Itch, and Departments of Anesthesiology, Psychiatry, Developmental Biology,

We previously showed that gastrin-releasing peptide receptor (GRPR) in the spinal cord is important for mediating nonhistaminergic itch. Neuromedin B receptor (NMBR), the second member of the mammalian bombesin receptor family, is expressed in a largely nonoverlapping pattern with GRPR in the superficial spinal cord, and its role in itch transmission remains unclear. Here, we report that Nmbr knock-out (KO) mice exhibited normal scratching behavior in response to intradermal injection of pruritogens. However, mice lacking both Nmbr and Grpr (DKO mice) showed significant deficits in histaminergic itch. In contrast, the chloroquine (CQ)-evoked scratching behavior of DKO mice is not further reduced compared with Grpr KO mice. These results suggest that NMBR and GRPR could compensate for the loss of each other to maintain normal histamine-evoked itch, whereas GRPR is exclusively required for CQ-evoked scratching behavior. Interestingly, GRPR activity is enhanced in Nmbr KO mice despite the lack of upregulation of Grpr expression; so is NMBR in Grpr KO mice. We found that NMB acts exclusively through NMBR for itch transmission, whereas GRP can signal through both receptors, albeit to NMBR to a much lesser extent. Although NMBR and NMBR(+) neurons are dispensable for histaminergic itch, GRPR(+) neurons are likely to act downstream of NMBR(+) neurons to integrate NMB-NMBR-encoded histaminergic itch information in normal physiological conditions. Together, we define the respective function of NMBR and GRPR in itch transmission, and reveal an unexpected relationship not only between the two receptors but also between the two populations of interneurons in itch signaling.
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http://dx.doi.org/10.1523/JNEUROSCI.1709-14.2014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4160775PMC
September 2014

B-type natriuretic peptide is neither itch-specific nor functions upstream of the GRP-GRPR signaling pathway.

Mol Pain 2014 Jan 18;10. Epub 2014 Jan 18.

Center for the Study of Itch, Washington University School of Medicine Pain Center, St, Louis, MO 63110, USA.

Background: A recent study by Mishra and Hoon identified B-type natriuretic peptide (BNP) as an important peptide for itch transmission and proposed that BNP activates spinal natriuretic peptide receptor-A (NPRA) expressing neurons, which release gastrin releasing peptide (GRP) to activate GRP receptor (GRPR) expressing neurons to relay itch information from the periphery to the brain (Science 340:968-971, 2013). A central premise for the validity of this novel pathway is the absence of GRP in the dorsal root ganglion (DRG) neurons. To this end, they showed that Grp mRNA in DRG neurons is either absent or barely detectable and claimed that BNP but not GRP is a major neurotransmitter for itch in pruriceptors. They showed that NPRA immunostaining is perfectly co-localized with Grp-eGFP in the spinal cord, and a few acute pain behaviors in Nppb-/- mice were tested. They claimed that BNP is an itch-selective peptide that acts as the first station of a dedicated neuronal pathway comprising a GRP-GRPR cascade for itch. However, our studies, along with the others, do not support their claims.

Findings: We were unable to reproduce the immunostaining of BNP and NPRA as shown by Mishra and Hoon. By contrast, we were able to detect Grp mRNA in DRGs using in situ hybridization and real time RT-PCR. We show that the expression pattern of Grp mRNA is comparable to that of GRP protein in DRGs. Pharmacological and genetic blockade of GRP-GRPR signaling does not significantly affect intrathecal BNP-induced scratching behavior. We show that BNP inhibits inflammatory pain and morphine analgesia.

Conclusions: Accumulating evidence demonstrates that GRP is a key neurotransmitter in pruriceptors for mediating histamine-independent itch. BNP-NPRA signaling is involved in both itch and pain and does not function upstream of the GRP-GRPR dedicated neuronal pathway. The site of BNP action in itch and pain and its relationship with GRP remain to be clarified.
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http://dx.doi.org/10.1186/1744-8069-10-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3930899PMC
January 2014

Chronic itch development in sensory neurons requires BRAF signaling pathways.

J Clin Invest 2013 Nov;123(11):4769-80

Chronic itch, or pruritus, is associated with a wide range of skin abnormalities. The mechanisms responsible for chronic itch induction and persistence remain unclear. We developed a mouse model in which a constitutively active form of the serine/threonine kinase BRAF was expressed in neurons gated by the sodium channel Nav1.8 (BRAF(Nav1.8) mice). We found that constitutive BRAF pathway activation in BRAF(Nav1.8) mice results in ectopic and enhanced expression of a cohort of itch-sensing genes, including gastrin-releasing peptide (GRP) and MAS-related GPCR member A3 (MRGPRA3), in nociceptors expressing transient receptor potential vanilloid 1 (TRPV1). BRAF(Nav1.8) mice showed de novo neuronal responsiveness to pruritogens, enhanced pruriceptor excitability, and heightened evoked and spontaneous scratching behavior. GRP receptor expression was increased in the spinal cord, indicating augmented coding capacity for itch subsequent to amplified pruriceptive inputs. Enhanced GRP expression and sustained ERK phosphorylation were observed in sensory neurons of mice with allergic contact dermatitis– or dry skin–elicited itch; however, spinal ERK activation was not required for maintaining central sensitization of itch. Inhibition of either BRAF or GRP signaling attenuated itch sensation in chronic itch mouse models. These data uncover RAF/MEK/ERK signaling as a key regulator that confers a subset of nociceptors with pruriceptive properties to initiate and maintain long-lasting itch sensation.
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http://dx.doi.org/10.1172/JCI70528DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3809799PMC
November 2013

The role of α₂ adrenoceptor in mediating noradrenaline action in the ventrolateral orbital cortex on allodynia following spared nerve injury.

Exp Neurol 2013 Oct 18;248:381-6. Epub 2013 Jul 18.

Department of Physiology and Pathophysiology, Xi'an Jiaotong University College of Medicine, Yanta Road W. 76#, Xi'an, Shaanxi 710061, PR China; Department of Physiology, Xi'an Medical University, Xinwang Road 1#, Xi'an, Shaanxi 710021, PR China.

The present study examined the role of α₂ adrenoceptor in mediating noradrenaline action in the ventrolateral orbital cortex (VLO) on allodynia induced by spared nerve injury (SNI) in the rat. The mechanical paw withdrawal threshold (PWT) was measured using von-Frey filaments. Microinjection of noradrenaline (1, 2, 4 μg in 0.5 μl) into the VLO, contralateral to the site of nerve injury, reduced allodynia; PWT increased in a dose-dependent manner. Similar to noradrenaline, microinjection of selective α₂ adrenoceptor agonist clonidine into the same VLO site also reduced allodynia, and was blocked by selective α₂ adrenoceptor antagonist yohimbine. Furthermore, administration of γ-aminobutyric acid A (GABAA) receptor antagonist bicuculline or picrotoxin to the VLO significantly enhanced clonidine-induced inhibition of allodynia, while GABAA receptor agonist muscimol or THIP (2,5,6,7-retrahydroisoxazolo(5,4-c)pyridine-3-ol hydrochloride) attenuated clonidine-induced inhibition. These results suggest that noradrenaline acting in the VLO can potentially reduce allodynia induced by SNI, and this effect is mediated by α₂ adrenoceptor. Moreover, GABAergic disinhibition may participate in α₂ receptor mediating effects in neuropathic pain in the central nervous system.
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http://dx.doi.org/10.1016/j.expneurol.2013.07.004DOI Listing
October 2013

Tea polyphenol-induced neuron-like differentiation of mouse mesenchymal stem cells.

Chin J Physiol 2011 Apr;54(2):111-7

Department of Kidney Transplantation of Nephropathy Center, First Affiliated Hospital, Xi'an Jiaotong University School of Medicine, Xi'an 710061, Shaanxi, People's Republic of China.

Bone marrow mesenchymal stem cells (BMSCs) can be induced to differentiate into neuron-like cells under appropriate conditions often involving toxic reagents that are not applicable for clinical transplantation. The present study investigated whether tea polyphenol (TP), a native nontoxic antioxidant, could induce mouse neuron-like cell differentiation of BMSCs in vitro. BMSCs, dissected from mouse femur bone marrow, were amplified in culture and treated with TP or beta-mercaptoethanol (BME, control). Morphological changes were observed under light microscopy. After 12 h treatment with 50 microg/ml TP or 5 mM BME, most cells differentiated into neuron-like cells exhibiting neuronal morphological characteristics, cellular shrinkage and neurite growth. Immunocytochemistry and reverse transcription (RT)-PCR results demonstrated neuronal marker expression in the induced cells with no glial fibrillary acidic protein expression. Taken together, TP induced mouse BMSCs to differentiate into neuron-like cells in vitro. These findings provide a potential source for the treatment of various neurological diseases.
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http://dx.doi.org/10.4077/cjp.2011.amm003DOI Listing
April 2011

The role of dopamine receptors in ventrolateral orbital cortex-evoked antinociception in a rat formalin test model.

Eur J Pharmacol 2011 Apr 17;657(1-3):97-103. Epub 2011 Feb 17.

Department of Forensic Medicine, Key Laboratory of Environment and Genes Related to Diseases of Ministry of Education, Xi'an Jiaotong University School of Medicine, Yanta Road West 76#, Xi'an, Shaanxi 710061, China.

The present study examined the roles of dopamine and D(1)- and D(2)-like dopamine receptors in ventrolateral orbital cortex (VLO)-evoked antinociception in rats with persistent inflammatory pain. Following formalin injection into the rat unilateral hindpaw pad, the effects of dopamine receptor agonist and antagonist microinjections into the VLO on nociceptive behavior were observed. Results demonstrated that VLO microinjection of the non-selective dopamine receptor agonist apomorphine (R(-)-apomorphine hydrochloride, 1.0, 2.5 and 5.0μg) depressed later-phase nociceptive behavior induced by formalin injection; this effect was attenuated by the D(2)-like dopamine receptor antagonist S(-)-raclopride(+)-tartrate salt (raclopride, 3.0μg), but not by the D(1)-like dopamine receptor antagonist R(+)-SCH-23390 hydrochloride (SCH-23390, 1.0μg). Apomorphine-induced antinociception was mimicked by microinjection of the D(2)-like dopamine receptor agonist (-)-quinpirole hydrochloride (2.0 and 5.0μg) into the same VLO site, and this effect was antagonized by raclopride (3.0μg). In addition, microinjection of the D(1)-like dopamine receptor agonist R(+)-SKF-38393 hydrochloride (5.0μg) had no effect on formalin-induced nociceptive behavior during the later phase. However, the D(1)-like dopamine receptor antagonist SCH-23390 (2.5, 5.0 and 10μg) depressed nociceptive behavior in a dose-dependent manner. These results suggested that dopamine mediated VLO-induced antinociception via different mechanisms in the persistent inflammatory pain model; D(2)-like receptors mediated dopamine-induced antinociception, while D(1)-like dopamine receptors exhibited tonic facilitatory action on nociceptive behavior, thereby blocking D(1)-like dopamine receptors could induce antinociception.
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http://dx.doi.org/10.1016/j.ejphar.2011.01.064DOI Listing
April 2011

Activation of serotonin 1A receptors in ventrolateral orbital cortex depresses persistent nociception: a presynaptic inhibition mechanism.

Neurochem Int 2010 Dec 8;57(7):749-55. Epub 2010 Sep 8.

Department of Physiology and Pathophysiology, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an Jiaotong University School of Medicine, Xi'an, China.

The present study examined the effect of serotonin 1A (5-HT(1A)) receptor activation in the ventrolateral orbital cortex (VLO) upon formalin-evoked flinching behavior and spinal Fos expression, and further determined whether activation of 5-HT(1A) receptors affected the spontaneous GABAergic miniature inhibitory postsynaptic currents (mIPSCs) in rat VLO slice by pharmacologically separated neurons to understand the possible mechanism underlying this effect. Microinjection of the 5-HT(1A) receptors agonist 8-OH-DPAT (8-hydro-2-(di-n-propylamino) tetralin) into the VLO depressed the formalin-evoked nociceptive behavior flinching response and the Fos expression in the lumbar spinal cord dorsal, which was antagonized by pre-treatment with 5-HT(1A) receptors antagonist NAN-190 (1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine hydrobromide). Furthermore, application of 8-OH-DPAT into VLO slice inhibited GABAergic mIPSC frequency in a dose-dependent manner without effects on amplitude of the GABAergic mIPSCs, this effect was blocked by NAN-190. These results provide evidence for the involvement of 5-HT(1A) receptors in VLO in the modulation of persistent inflammatory nociception, and suggest that a presynaptic inhibition of the GABA release may contribute to the 5-HT(1A) receptor-mediated descending antinociception.
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http://dx.doi.org/10.1016/j.neuint.2010.08.011DOI Listing
December 2010

Topographical distributions of endomorphinergic pathways from nucleus tractus solitarii to periaqueductal gray in the rat.

J Chem Neuroanat 2010 May 18;39(3):166-74. Epub 2009 Nov 18.

Department of Anatomy, Histology and Embryology, K. K. Leung Brain Research Centre, The Fourth Military Medical University, No. 17 West Changle Road, Xi'an, PR China.

In the central nervous system (CNS), endomorphin 1 (EM1)- and endomorphin 2 (EM2)-containing neuronal cell bodies have been found in the nucleus tractus sollitarii (NTS) and the hypothalamus, and EMergic fibers and terminals are distributed widely in many regions of the CNS, including the periaqueductal gray (PAG). The aim of the present study was to examine whether EM-expressing neurons in the NTS of the rat send their axons to the PAG, and determine whether the EMergic pathway from the NTS to the PAG is topographic by using. Immunofluorescent staining for EM1 or EM2 combined with retrograde and anterograde tract-tracing methods. The results showed that after injecting tetramethyl rhodamine dextran-amine (TMR) into the ventrolateral or lateral column of the PAG, some EM1- or EM2-immunoreactive (IR) neurons in the NTS were retrogradely labeled with TMR, and the majority of the EM-IR/TMR double-labeled neurons were mainly distributed in the medial and commissural subnuclei of the NTS. Following injection of biotinylated dextran amine (BDA) into the medial or commissural subnucleus of the NTS, EM1-IR/BDA and EM2-IR/BDA double-labeled fibers and terminals were mainly distributed in the ventrolateral or lateral column of the PAG, respectively. The results indicate that EMergic pathway from the NTS to PAG is topographically organized, and suggest that EMs released from NTS to PAG projecting terminals may bind to mu-opioid receptor on the PAG neurons, and thereby contribute to various functions.
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http://dx.doi.org/10.1016/j.jchemneu.2009.11.001DOI Listing
May 2010

The thalamic nucleus submedius and ventrolateral orbital cortex are involved in nociceptive modulation: a novel pain modulation pathway.

Prog Neurobiol 2009 Dec 9;89(4):383-9. Epub 2009 Oct 9.

Department of Physiology and Pathophysiology, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an Jiaotong University School of Medicine, Yanta Road W. 76#, Xi'an, Shaanxi 710061, PR China.

Recently, a series of studies have given rise to and provided evidence for the hypothesis that the nucleus submedius (Sm) in the medial thalamus is involved in modulation of nociception. The Sm, ventrolateral orbital cortex (VLO) and the periaqueductal gray (PAG) constitute a pain modulatory pathway, activation of which leads to activation of the PAG-brainstem descending inhibitory system and depression of the nociceptive inputs in the spinal cord and trigeminal nucleus. Other studies have indicated that the Sm-VLO-PAG pathway plays an important role in the analgesia induced by electroacupuncture stimulation of the acupuncture point (acupoint) for exciting small diameter fiber (A-delta and C group) afferents. Opioid peptides, serotonin, dopamine, glutamate and their related receptors are involved in Sm- and/or VLO-mediated descending antinociception, and a GABAergic disinhibitory mechanism participates in mediating the antinociception induced by activation of mu-opioid receptors, serotonin 1(A) receptors, and dopamine D(2)-like receptors. This review describes these findings, which provide important new insights into the roles of the thalamus and cerebral cortex in descending pain modulation.
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http://dx.doi.org/10.1016/j.pneurobio.2009.10.002DOI Listing
December 2009

Endomorphin 1- and endomorphin 2-containing neurons in nucleus tractus solitarii send axons to the parabrachial nuclei in the rat.

Anat Rec (Hoboken) 2009 Apr;292(4):488-97

Department of Anatomy, Histology and Embryology and K. K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, People's Republic of China.

Endomorphin-1 (EM1) and endomorphin-2 (EM2) are the selective endogenous ligands for the mu-opioid receptor (MOR). Since EMs-expressing neuronal cell bodies or axonal components have been observed, respectively, in the nucleus tractus solitarii or the parabrachial nuclei, we examined if EMs-expressing neurons in the NTS of the rat might send their axons to the PBN. Immunofluorescent stainings for EM1 or EM2 were combined with retrograde or anterograde tract-tracing method. After injecting tetramethyl rhodamine dextran-amine (TMR) into the parabrachial nuclei of rats, some EM1- or EM2-immunoreactive neurons in the nucleus tractus solitarii were labeled retrogradely with TMR. The majority of the EM1/TMR and EM2/TMR double-labeled neurons were observed in the medial, commissural, and dorsolateral subnuclei of the nucleus tractus solitarii. Following injection of biotinylated dextran amine (BDA) into the medial, commissural, or dorsolateral subnuclei of the nucleus tractus solitarii, EM1- or EM2-immunopositive axons and axon terminals were anterogradely labeled with BDA mainly in the lateral parabrachial nucleus. The present results have indicated that endomorphinergic neurons in the nucleus tractus solitarii project to the parabrachial nuclei. This suggests that EMs released from NTS-PBN projection fibers may bind to MOR on the PBN neurons to be implicated in processing of visceral information within the parabrachial nuclei.
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http://dx.doi.org/10.1002/ar.20847DOI Listing
April 2009

Cerebral cortex modulation of pain.

Acta Pharmacol Sin 2009 Jan 15;30(1):31-41. Epub 2008 Dec 15.

Department of Physiology and Pathophysiology, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an Jiao-tong University, Xi'an 710061, China.

Pain is a complex experience encompassing sensory-discriminative, affective-motivational and cognitiv e-emotional components mediated by different mechanisms. Contrary to the traditional view that the cerebral cortex is not involved in pain perception, an extensive cortical network associated with pain processing has been revealed using multiple methods over the past decades. This network consistently includes, at least, the anterior cingulate cortex, the agranular insular cortex, the primary (SI) and secondary somatosensory (SII) cortices, the ventrolateral orbital cortex and the motor cortex. These cortical structures constitute the medial and lateral pain systems, the nucleus submedius-ventrolateral orbital cortex-periaqueductal gray system and motor cortex system, respectively. Multiple neurotransmitters, including opioid, glutamate, GABA and dopamine, are involved in the modulation of pain by these cortical structures. In addition, glial cells may also be involved in cortical modulation of pain and serve as one target for pain management research. This review discusses recent studies of pain modulation by these cerebral cortical structures in animals and human.
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http://dx.doi.org/10.1038/aps.2008.14DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4006538PMC
January 2009

Synaptic connections between GABAergic elements and serotonergic terminals or projecting neurons in the ventrolateral orbital cortex.

Cereb Cortex 2009 Jun 2;19(6):1263-72. Epub 2008 Nov 2.

Department of Physiology and Pathophysiology, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an Jiaotong University School of Medicine, Xi'an 710061, PR China.

The ventrolateral orbital cortex (VLO) is part of an endogenous analgesic system, consisting of the spinal cord-thalamic nucleus submedius-VLO periaqueductal gray (PAG)-spinal cord loop. The present study examined morphological connections of GABAergic (gamma-aminobutyric acidergic) neurons and serotonergic projection terminals from the dorsal raphe nucleus (DR), as well as the relationship between GABAergic terminals and VLO neurons projecting to the PAG, by using anterograde and retrograde tracing combined with immunofluorescence, immunohistochemistry, and electron microscopy methods. Results indicate that the majority (93%) of GABAergic neurons in the VLO also express the 5-HT(1A) (5-hydroxytryptamine 1A) receptor, and serotonergic terminals originating from the DR nucleus made symmetrical synapses with GABAergic neuronal cell bodies and dendrites within the VLO. GABAergic terminals also made symmetrical synapses with neurons expressing GABA(A) receptors and projecting to the PAG. These results suggest that a local neuronal circuit, consisting of 5-HTergic terminals, GABAergic interneurons, and projection neurons, exists in the VLO, and provides morphological evidence for the hypothesis that GABAergic modulation is involved in 5-HT(1A) receptor activation-evoked antinociception.
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http://dx.doi.org/10.1093/cercor/bhn169DOI Listing
June 2009

D2-like but not D1-like dopamine receptors are involved in the ventrolateral orbital cortex-induced antinociception: a GABAergic modulation mechanism.

Exp Neurol 2009 Jan 8;215(1):128-34. Epub 2008 Oct 8.

Department of Physiology and Pathophysiology, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an Jiaotong University School of Medicine, Xi'an, Shaanxi 710061, People's Republic of China.

The ventrolateral orbital cortex (VLO) is part of an endogenous analgesic system consisting of an ascending pathway from the spinal cord to VLO via the thalamic nucleus submedius (Sm) and a descending pathway to the spinal cord relaying in the periaqueductal gray (PAG). This study examines whether activation of D(1)-like and D(2)-like dopamine receptors in VLO produces antinociception and whether GABAergic modulation is involved in the VLO, D(2)-like dopamine receptor activation-evoked antinociception. The radiant heat-evoked tail flick (TF) reflex was used as an index of nociceptive response in lightly anesthetized rats. Microinjection of the D(2)-like (D(2)/D(3)) dopamine receptor agonist quinpirole (0.1-2.0 microg), but not D(1)-like (D(1)/D(5)) receptor agonist SKF-38393 (1.0, 5.0 microg), into VLO produced dose-dependent antinociception which was antagonized by the D(2)-like (D(2)/D(3)) receptor antagonist raclopride (1.5 microg). We also found that VLO application of the GABA(A) receptor antagonist bicuculline or picrotoxin (100 ng) enhanced the quinpirole-induced inhibition of the TF reflex, whereas the GABA(A) receptor agonist muscimol (250 ng) or THIP (1.0 microg) significantly attenuated the quinpirole-induced inhibition. These results suggest that D(2)-like, but not D(1)-like, dopamine receptors are involved in VLO-induced antinociception and that GABAergic disinhibitory mechanisms participate in the D(2)-like receptor mediated effect. These findings provide support for the hypothesis that D(2)-like receptor activation may inhibit the inhibitory action of the GABAergic interneurons on the output neurons projecting to PAG leading to activation of the brainstem descending inhibitory system and depression of nociceptive inputs at the spinal dorsal horn.
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http://dx.doi.org/10.1016/j.expneurol.2008.09.018DOI Listing
January 2009

GABAergic modulation is involved in the ventrolateral orbital cortex 5-HT 1A receptor activation-induced antinociception in the rat.

Pain 2008 Oct 24;139(2):398-405. Epub 2008 Jun 24.

Department of Physiology and Pathophysiology, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an Jiaotong University School of Medicine, Xi'an Yanta Street, W. 76#, Xi'an, Shaanxi 710061, China Department of Anatomy and K.K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, Shaanxi 710032, China.

The ventrolateral orbital cortex (VLO) is a component of an endogenous analgesic system consisting of an ascending pathway from the spinal cord to VLO via the thalamic nucleus submedius (Sm) and a descending pathway relaying in the periaqueductal gray matter (PAG). This study examines whether the activation of 5-HT 1A receptors in VLO produces antinociception and whether GABAergic modulation is involved in the VLO 5-HT 1A receptor activation-evoked antinociception. The radiant heat-evoked tail flick (TF) reflex was used as an index of nociceptive response in lightly anesthetized rats. Microinjection of the 5-HT 1A receptor agonist 8-OH-DPAT (1.0, 2.0, 5.0 microg) into VLO produced dose-dependent antinociception, which was reversed by the 5-HT 1A receptor antagonist (NAN-190, 20 mug). We also found that VLO application of the GABA A receptor antagonist bicuculline or picrotoxin (100 ng) enhanced the 8-OH-DPAT-induced inhibition of the TF reflex, whereas the GABA A receptor agonist muscimol (250 ng) or THIP (1.0 microg) significantly attenuated the 8-OH-DPAT-induced inhibition. These results suggest that 5-HT 1A receptors are involved in VLO-induced antinociception and that GABAergic disinhibitory mechanisms participate in the 5-HT 1A receptor-mediated effect. These findings provide support for the hypothesis that 5-HT 1A receptor activation may inhibit the inhibitory action of the GABAergic interneurons on the output neurons projecting to PAG leading to activation of the brainstem descending inhibitory system and depression of nociceptive inputs at the spinal cord level.
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http://dx.doi.org/10.1016/j.pain.2008.05.013DOI Listing
October 2008

GABAergic neurons express mu-opioid receptors in the ventrolateral orbital cortex of the rat.

Neurosci Lett 2005 Jul;382(3):265-8

Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Department of Physiology, School of Medicine, Xi'an Jiaotong University, Xi'an 710061, China.

Behavioral studies have indicated that GABAergic modulation is involved in the opioid-induced antinociception in the ventrolateral orbital cortex (VLO). The aim of the current study was to examine whether the GABAergic neurons in the rat VLO expressed mu-opioid receptor subtype 1 (MOR1). This study employed immunofluorescence histochemical double-staining technique and showed that a considerable amount of GABA- and MOR1-like immunoreactive neurons existed in layers II-VI in the VLO. Of these GABA-like immunoreactive neurons, 92.0% of them showed MOR1-like immunoreactivities. Similarly, 80.2% of MOR1-like immuoreactive neurons also exhibited GABA-like immunoreactivities. These results provide morphological evidence that opioid-induced antinociception in the VLO might be due to an inhibitory effect by opioid via MOR1 on GABAergic neurons, resulting in disinhibition of VLO projection neurons and leading to activation of the VLO-PAG brainstem descending pain control system to depress the nociceptive inputs at the spinal cord level.
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http://dx.doi.org/10.1016/j.neulet.2005.03.070DOI Listing
July 2005

Validation of a simple automated movement detection system for formalin test in rats.

Acta Pharmacol Sin 2005 Jan;26(1):39-45

Department of Physiology, School of Medicine, Xi'an Jiaotong University, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an 710061, China.

Aim: To investigate the validity and sensitivity of an automatic movement detection system developed by our laboratory for the formalin test in rats.

Methods: The effects of systemic morphine and local anesthetic lidocaine on the nociceptive behaviors induced by formalin subcutaneously injected into the hindpaw were examined by using an automated movement detection system and manual measuring methods.

Results: Formalin subcutaneously injected into the hindpaw produced typical biphasic nociceptive behaviors (agitation). The mean agitation event rate during a 60-min observation period increased linearly following increases in the formalin concentration (0.0%, 0.5%, 1.5%, 2.5%, and 5%, 50 microL). Systemic application of morphine of different doses (1, 2, and 5 mg/kg) 10-min prior to formalin injection depressed the agitation responses induced by formalin injection in a dose-dependent manner, and the antinociceptive effect induced by the largest dose (5 mg/kg) of morphine was significantly antagonized by systemic application of the opioid receptor antagonist naloxone (1.25 mg/kg). Local anesthetic lidocaine (20 mg/kg) injected into the ipsilateral ankle subskin 5-min prior to formalin completely blocked the agitation response to formalin injection. These results were comparable to those obtained from manual measure of the incidence of flinching or the duration time of licking/biting of the injected paw.

Conclusion: These data suggest that this automated movement detection system for formalin test is a simple, validated measure with good pharmacological sensitivity suitable for discovering novel analgesics or investigating central pain mechanisms.
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http://dx.doi.org/10.1111/j.1745-7254.2005.00001.xDOI Listing
January 2005