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Most brain neurons are active in waking, but hypothalamic neurons that synthesize the neuropeptide melanin-concentrating hormone (MCH) are claimed to be active only during sleep, particularly rapid eye movement (REM) sleep. Here we use deep-brain imaging to identify changes in fluorescence of the genetically encoded calcium (Ca2+) indicator GCaMP6 in individual hypothalamic neurons that contain MCH. An in vitro electrophysiology study determined a strong relationship between-depolarization and Ca2+ fluorescence in MCH neurons. In 10 freely behaving MCH-cre mice (male and female), the highest fluorescence occurred in all recorded neurons (n = 106) in REM sleep relative to quiet waking or non-REM sleep. Unexpectedly, 70% of the MCH neurons had strong fluorescence activity when the mice explored novel objects. Spatial and temporal mapping of the change in fluorescence between pairs of MCH neurons revealed dynamic activation of MCH neurons during REM sleep and activation of a subset -of the same neurons during exploratory behavior. Functional network activity maps will facilitate comparisons of not only single-neuron activity, but also network responses in different conditions and disease. [ABSTRACT FROM AUTHOR]

Kisspeptin plays an important role in puberty and subsequent fertility by activating its receptor, G-protein-coupled receptor 54 (GPR54), and increasing cytoplasmic free Ca2+ concentration ([Ca2+]i) and gonadotropin-releasing hormone (GnRH) secretion in GnRH neurons. Yet the mechanism by which kisspeptin increases [Ca2+]i in GnRH neurons remains to be fully elucidated. In other neurons, voltage-gated Ca2+ channel (VGCC) activity has been shown to be inversely related to [Ca2+]i. We used whole-cell patch-clamp recording to examine the effects of kisspeptin-10 (KP-10) on VGCC activity evoked by step depolarizations in GnRH neurons in brain slices from pubertal male GnRH-green fluorescent protein transgenic mice. Prolonged (>30 s) KP-10 application inhibited Ca2+ currents. The GPR54 antagonist peptide 234, chelation of intracellular Ca2+ by 1,2-bis(2-aminophenoxy)ethane N,N,N′,N′-tetraacetic acid, substitution of Ba2+ for Ca2+, the calmodulin antagonists calmidazolium and trifluoperazine, the phospholipase C inhibitor edelfosine, the canonical transient receptor potential (TRPC) channel and inositol 1,4,5-trisphosphate receptor (IP3R) antagonist 2-APB, the TRPC channel antagonist BTP2 and the endoplasmic reticulum Ca2+-ATPase blocker cyclopiazonic acid each prevented inhibition. The IP3R antagonists caffeine (10 μM), heparin and intracellular 2-APB prevented inhibition to a lesser extent. The ryanodine receptor (RyR) antagonists ryanodine and dantrolene prevented inhibition, and the RyR agonist caffeine (30 mM) mimicked the effects of KP-10 on Ca2+ currents. Our results suggest that kisspeptin induces Ca2+ influx through TRPC channels and Ca2+ release via IP3Rs and RyRs, and that this is followed by Ca2+/CaM-dependent inhibition of VGCCs. Copyright © 2012 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]