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

This article is distributed under the terms of the Creative Commons Attribution License (http:// creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed. Alerts: Sign up at eneuro.org/alerts to receive customized email alerts when the fully formatted version of this article is published. Acetylcholine acts through nicotinic receptors to enhance the firing rate of a subset of hypocretin neurons in the mouse hypothalamus through distinct pre-and postsynaptic mechanisms This is a confidential document and must not be discussed with others, forwarded in any form, or posted on websites without the express written consent of eNeuro. Title: Acetylcholine acts through nicotinic receptors to enhance the firing rate of a subset 1 of hypocretin neurons in the mouse hypothalamus through distinct pre-and postsynaptic 2 mechanisms 3 Abstract 31 Hypocretin/orexin neurons regulate many behavioral functions, including 32 addiction. Nicotine acts through nicotinic acetylcholine receptors (nAChRs) to alter firing 33 rate of neurons throughout the brain, leading to addiction-related behaviors. While 34 nAChRs are expressed in the hypothalamus and cholinergic fibers project to this structure, 35 it is unclear how acetylcholine modulates the activity of hypocretin neurons. In this study 36 we stimulated hypocretin neurons in mouse brain slices with ACh in the presence of 37 atropine to dissect pre-and postsynaptic modulation of these neurons through nAChRs. 38 Approximately 1/3 of tested hypocretin neurons responded to pressure application of 39 ACh (1 mM) with an increase in firing frequency. Stimulation of postsynaptic nAChRs 40 with ACh or nicotine resulted in a highly variable inward current in approximately 1/3 of 41 hypocretin neurons. In contrast, ACh or nicotine (1 µM) reliably decreased the frequency 42 of miniature EPSCs (mEPSCs). Antagonism of nAChRs with mecamylamine also 43 suppressed mEPSC frequency, suggesting that an endogenous, tonic activation of 44 presynaptic nAChRs might be required for maintaining functional mEPSC frequency. 45 Antagonism of heteromeric (α4β2) or homomeric (α7) nAChRs alone suppressed 46 mEPSCs to a lesser extent. Finally, blocking internal calcium release reduced the 47 frequency of mEPSCs, occluding the suppressive effect of presynaptic ACh. Taken 48 together, these data provide a mechanism by which phasic ACh release enhances the 49 firing of a subset of hypocretin neurons through postsynaptic nAChRs, but disrupts tonic, 50 presynaptic nAChR-mediated glutamatergic inputs to the overall population of 51 hypocretin neurons, potentially enhancing the signal-to-noise ratio during the response of 52 the …