Authors: Divya Sachidanandan Haritha P Reddy Anitha Mani Geoffrey J Hyde Amal Kanti Bera
Publish Date: 2017/01/19
Volume: 61, Issue: 4, Pages: 459-467
Abstract
OrexinA and orexinB OxA OxB are neuropeptides produced by a small number of neurons that originate in the hypothalamus and project widely in the brain Only discovered in 1998 the orexins are already known to regulate several behaviours Most prominently they help to stabilise the waking state a role with demonstrated significance in the clinical management of narcolepsy and insomnia Orexins bind to Gproteincoupled receptors predominantly postsynaptic of two subtypes OX1R and OX2R The primary effect of OxOXR binding is a direct depolarising influence mediated by cell membrane cation channels but a wide variety of secondary effects both pre and postsynaptic are also emerging Given that inhibitory GABAergic neurons also influence orexinregulated behaviours crosstalk between the two systems is expected but at the cellular level little is known and possible mechanisms remain unidentified Here we have used an expression system approach to examine the feasibility and nature of possible postsynaptic crosstalk between OxA and the GABAA receptor GABAAR the brain’s main inhibitory neuroreceptor When HEK293 cells transfected with OX1R and the α1 β1 and γ2S subunits of GABAAR were exposed to OxA GABAinduced currents were inhibited in a calciumdependent manner This inhibition was associated with increased phosphorylation of the β1 subunit of GABAAR and the inhibition could itself be attenuated by 1 kinase inhibitors of protein kinase C and CaM kinase II and 2 the mutation to alanine of serine 409 of the β1 subunit a site previously identified in phosphorylationdependent regulation in other pathways These results are the first to directly support the feasibility of postsynaptic crosstalk between OxA and GABAAR indicating a process in which OxA could promote phosphorylation of the β1 subunit reducing the GABAinduced hyperpolarising current In this model OxA/GABAAR crosstalk would cause the depolarising influence of OxA to be boosted a type of positive feedback that could for example facilitate the ability to abruptly awakeWe express our sincere gratitude to Dr Takeshi Sakurai and Dr Neil Harrison for providing the orexin receptor and GABA receptor clones respectively We are also grateful to Sucheta Sridhar for her critical comments on the manuscript DS and HPR are thankful to IIT Madras and the Department of Biotechnology India DBT respectively for the fellowships provided during the course of their PhD studies The study was supported by the Council of Scientific and Industrial Research CSIR India
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