Publications by authors named "Nissi Varghese"

3 Publications

  • Page 1 of 1

Loss of KCNQ2 or KCNQ3 leads to multifocal time-varying activity in the neonatal forebrain .

eNeuro 2021 Apr 15. Epub 2021 Apr 15.

Dept. of Physiology and Neurobiology, University of Connecticut, Storrs, CT 06269, USA

Early neonatal epileptic encephalopathy represents a group of epilepsies often characterized by refractory seizures, regression in cognitive development, and typically poor prognosis. Dysfunction of KCNQ2 and KCNQ3 channels has emerged as a major cause of neonatal epilepsy. However, our understanding of the cellular mechanisms that may both explain the origins of epilepsy and inform treatment strategies for KCNQ2 and KCNQ3 dysfunction is still lacking. Here, using mesoscale calcium imaging and pharmacology, we demonstrate that in mouse neonatal brain slices, conditional loss of from forebrain excitatory neurons ( mice) or constitutive deletion of leads to sprawling hyperactivity across the neocortex. Surprisingly, the generation of time-varying hypersynchrony in slices from mice does not require fast synaptic transmission. This is in contrast to control littermates and constitutive knockout mice where activity is primarily driven by fast synaptic transmission in the neocortex. Unlike in the neocortex, hypersynchronous activity in the hippocampal formation from conditional and constitutive knockout mice persists in the presence of synaptic transmission blockers. Thus, we propose that loss of KCNQ2 or KCNQ3 function differentially leads to network hyperactivity across the forebrain in a region- and macro-circuit-specific manner.Neocortical hypersynchrony is a hallmark of neonatal epilepsy but its cellular mechanisms are unclear. This study shows that hypersynchrony in the neocortex can stem from the loss of KCNQ2 function in excitatory neurons even in the absence of fast synaptic transmission, unlike the hypersynchrony in response to KCNQ3 loss in the neocortex. This points to unique network dysfunctions involving potassium KCNQ2 channels as a mechanism for neonatal epilepsy.
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http://dx.doi.org/10.1523/ENEURO.0024-21.2021DOI Listing
April 2021

Flexible Stoichiometry: Implications for KCNQ2- and KCNQ3-Associated Neurodevelopmental Disorders.

Dev Neurosci 2021 Apr 1:1-10. Epub 2021 Apr 1.

Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut, USA.

KCNQ2 and KCNQ3 pathogenic channel variants have been associated with a spectrum of developmentally regulated diseases that vary in age of onset, severity, and whether it is transient (i.e., benign familial neonatal seizures) or long-lasting (i.e., developmental and epileptic encephalopathy). KCNQ2 and KCNQ3 channels have also emerged as a target for novel antiepileptic drugs as their activation could reduce epileptic activity. Consequently, a great effort has taken place over the last 2 decades to understand the mechanisms that control the assembly, gating, and modulation of KCNQ2 and KCNQ3 channels. The current view that KCNQ2 and KCNQ3 channels assemble as heteromeric channels (KCNQ2/3) forms the basis of our understanding of KCNQ2 and KCNQ3 channelopathies and drug design. Here, we review the evidence that supports the formation of KCNQ2/3 heteromers in neurons. We also highlight functional and transcriptomic studies that suggest channel composition might not be necessarily fixed in the nervous system, but rather is dynamic and flexible, allowing some neurons to express KCNQ2 and KCNQ3 homomers. We propose that to fully understand KCNQ2 and KCNQ3 channelopathies, we need to adopt a more flexible view of KCNQ2 and KCNQ3 channel stoichiometry, which might differ across development, brain regions, cell types, and disease states.
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http://dx.doi.org/10.1159/000515495DOI Listing
April 2021

KCNQ3 is the principal target of retigabine in CA1 and subicular excitatory neurons.

J Neurophysiol 2021 04 17;125(4):1440-1449. Epub 2021 Mar 17.

Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut.

Retigabine is a first-in-class potassium channel opener approved for patients with epilepsy. Unfortunately, several side effects have limited its use in clinical practice, overshadowing its beneficial effects. Multiple studies have shown that retigabine acts by enhancing the activity of members of the voltage-gated KCNQ (Kv7) potassium channel family, particularly the neuronal KCNQ channels KCNQ2-KCNQ5. However, it is currently unknown whether retigabine's action in neurons is mediated by all KCNQ neuronal channels or by only a subset. This knowledge is necessary to elucidate retigabine's mechanism of action in the central nervous system and its adverse effects and to design more effective and selective retigabine analogs. In this study, we show that the action of retigabine in excitatory neurons strongly depends on the presence of KCNQ3 channels. Deletion of severely limited the ability of retigabine to reduce neuronal excitability in mouse CA1 and subiculum excitatory neurons. In addition, we report that in the absence of KCNQ3 channels, retigabine can enhance CA1 pyramidal neuron activity, leading to a greater number of action potentials and reduced spike frequency adaptation; this finding further supports a key role of KCNQ3 channels in mediating the action of retigabine. Our work provides new insight into the action of retigabine in forebrain neurons, clarifying retigabine's action in the nervous system. Retigabine has risen to prominence as a first-in-class potassium channel opener approved by the Food and Drug Administration, with potential for treating multiple neurological disorders. Here, we demonstrate that KCNQ3 channels are the primary target of retigabine in excitatory neurons, as deleting these channels greatly diminishes the effect of retigabine in pyramidal neurons. Our data provide the first indication that retigabine controls neuronal firing properties primarily through KCNQ3 channels.
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http://dx.doi.org/10.1152/jn.00564.2020DOI Listing
April 2021