Acetylcholine Acts through Nicotinic Receptors to Enhance the Firing Rate of a Subset of Hypocretin Neurons in the Mouse Hypothalamus through Distinct Presynaptic and Postsynaptic Mechanisms.

Wen-Liang Zhou,Xiao-Bing Gao,Marina R Picciotto

doi:10.1523/eneuro.0052-14.2015

Abstract

Hypocretin/orexin neurons regulate many behavioral functions, including addiction. Nicotine acts through nicotinic acetylcholine receptors (nAChRs) to alter firing rate of neurons throughout the brain, leading to addiction-related behaviors. While nAChRs are expressed in the hypothalamus and cholinergic fibers project to this structure, it is unclear how acetylcholine modulates the activity of hypocretin neurons. In this study, we stimulated hypocretin neurons in mouse brain slices with ACh in the presence of atropine to dissect presynaptic and postsynaptic modulation of these neurons through nAChRs. Approximately one-third of tested hypocretin neurons responded to pressure application of ACh (1 mM) with an increase in firing frequency. Stimulation of postsynaptic nAChRs with ACh or nicotine resulted in a highly variable inward current in approximately one-third of hypocretin neurons. In contrast, ACh or nicotine (1 μM) reliably decreased the frequency of miniature EPSCs (mEPSCs). Antagonism of nAChRs with mecamylamine also suppressed mEPSC frequency, suggesting that an endogenous, tonic activation of presynaptic nAChRs might be required for maintaining functional mEPSC frequency. Antagonism of heteromeric (α4β2) or homomeric (α7) nAChRs alone suppressed mEPSCs to a lesser extent. Finally, blocking internal calcium release reduced the frequency of mEPSCs, occluding the suppressive effect of presynaptic ACh. Taken together, these data provide a mechanism by which phasic ACh release enhances the firing of a subset of hypocretin neurons through postsynaptic nAChRs, but disrupts tonic, presynaptic nAChR-mediated glutamatergic inputs to the overall population of hypocretin neurons, potentially enhancing the signal-to-noise ratio during the response of the nAChR-positive subset of neurons.

Highlights

A small group of neurons that express hypocretin (Hcrt, known as orexin) resides in the perifornical and lateral hypothalamus, and these neurons project throughout the brain and spinal cord (Peyron et al, 1998; van den Pol, 1999; Bayer et al, 2002)
Nicotinic stimulation boosts spontaneous action potential firing in hypocretin neurons To determine whether phasic nicotinic stimulation modulates the electrical output of Hcrtϩ neurons, we patched the cells with an ATP-rich (5 mM, vs 3 mM in other experiments) intracellular solution and investigated the effect of pressure-applied ACh on spontaneous action potential firing
Hypocretin/orexin neurons are involved in multiple behaviors, including those related to arousal and addiction (Mahler et al, 2012; de Lecea and Huerta, 2014)

Summary

Introduction

A small group of neurons that express hypocretin (Hcrt, known as orexin) resides in the perifornical and lateral hypothalamus (de Lecea et al, 1998; Sakurai et al, 1998), and these neurons project throughout the brain and spinal cord (Peyron et al, 1998; van den Pol, 1999; Bayer et al, 2002). Hcrtϩ neurons play important roles in modulating. Received November 6, 2014; accepted February 5, 2015; First published February 12, 2015. W.-L.Z. performed research; W.-L.Z. and X.-B.G. analyzed data; W.-L.Z., X.-B.G., and M.R.P. wrote the paper Received November 6, 2014; accepted February 5, 2015; First published February 12, 2015. 1The authors declare no competing financial interests. 2Author contributions: W.-L.Z., X.-B.G., and M.R.P. designed research;

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