Melanin-concentrating hormone (MCH) reverts the behavioral effects induced by inescapable stress

Hypothalamic MCH Neuron Activity Dynamics during Cataplexy of Narcolepsy

Hypothalamic orexin (hypocretin, HCRT) deficiency causes sleep disorder narcolepsy with cataplexy in humans and murine. As another integral group of sleep/wake-regulating neurons in the same brain area, the melanin-concentrating hormone (MCH) neurons' involvement in cataplexy remains ambiguous. Here we used the live animal deep-brain calcium (Ca2+) imaging tool to record MCH neuron dynamics during cataplexy by expressing calcium sensor GCaMP6s into genetically defined MCH neurons in orexin knock-out mice, which are a model of human narcolepsy. Similar to wild-type mice, MCH neurons of the narcoleptic mice displayed significantly higher Ca2+ transient fluorescent intensity during rapid eye movement (REM) sleep and active waking (AW) episodes compared with non-REM (NREM) sleep. Moreover, MCH neurons displayed significantly lower Ca2+ signals during cataplexy. Importantly, a pre-cataplexy elevation of Ca2+ signals from MCH neurons was not a prerequisite for cataplexy initiation. Our results demonstrated the inactivation status of MCH neurons during cataplexy and suggested that MCH neurons are not involved in the initiation and maintenance of cataplexy in orexin knock-out mice.

The melanin-concentrating hormone1 receptor antagonists, SNAP-7941 and GW3430, enhance social recognition and dialysate levels of acetylcholine in the frontal cortex of rats

Melanin-concentrating hormone (MCH)1 receptors are widely expressed in limbic structures and cortex. Their inactivation is associated with anxiolytic and antidepressive properties but little information is available concerning cognition. This issue was addressed using the selective antagonists, SNAP-7941 and GW3430, in a social recognition paradigm in rats. The muscarinic blocker, scopolamine (1.25 mg/kg s.c.), reduced social recognition, an action dose-dependently blocked by SNAP-7941 and GW3430 (0.63-10.0 and 20.0-80.0 mg/kg i.p., respectively) which did not themselves display amnesic properties. Further, in a protocol where a spontaneous deficit was induced by a prolonged inter-session delay, SNAP-7941 and GW3430 dose-dependently enhanced social recognition. In dialysis studies, SNAP-7941 (0.63-40.0 mg/kg i.p.) and GW3430 (10.0-40.0 mg/kg i.p.) elevated extracellular levels of acetylcholine (ACh) in the frontal cortex (FCX) of freely moving rats. The SNAP-7941 effect was specific, as it did not increase levels of ACh in ventral and dorsal hippocampus: moreover, it did not modify levels of noradrenaline, dopamine, serotonin and glutamate in FCX. Active doses of SNAP-7941 and GW3430 corresponded to doses (2.5-40.0 and 10.0-80.0 mg/kg i.p., respectively) exerting anxiolytic properties in Vogel conflict and ultrasonic vocalization tests, and antidepressant actions in forced swim, isolation-induced aggression and marble-burying procedures. In contrast to SNAP-7941 and GW3430, the benzodiazepine, diazepam, decreased social recognition and dialysate levels of ACh, while the tricyclic, imipramine, reduced social recognition and failed to enhance cholinergic transmission. In conclusion, at anxiolytic and antidepressant doses, SNAP-7941 and GW3430 improve social recognition and elevate extracellular ACh levels in FCX. This profile differentiates MCH1 receptor antagonists from conventional anxiolytic and antidepressant agents.

Melanin-concentrating hormone MCH1 receptor antagonists: a potential new approach to the treatment of depression and anxiety disorders

Melanin-concentrating hormone (MCH) is a cyclic 19-amino-acid neuropeptide that has been considered to play a key role in the regulation of feeding and energy homeostasis. To date, two receptor subtypes for MCH (designated MCH(1) and MCH(2)) have been identified; the MCH(1) receptor has been proposed to mediate the physiological functions of MCH in rodents. In addition to the crucial roles of MCH in feeding behaviour, anatomical and neurochemical studies suggest that the MCH/MCH(1) system is involved in the regulation of emotion and stress responses. This assumption has been supported by a recent series of neurochemical and behavioural studies. Indeed, several lines of evidence show that MCH activates stress responses and induces depressive- and anxiety-like behaviours, while the blockade of MCH(1) receptors results in antidepressant and anxiolytic effects in various rodent models. Moreover, MCH may decrease reward activity while increasing hypothalamus-pituitary adrenal axis activity, both of which may underlie the neurochemical mechanisms of the depression and anxiety-like effects induced by MCH. The effects of MCH(1) receptor antagonists in animal models, together with their rapid onset of effect and lack of adverse CNS effects, suggest that they deserve further investigation as potential new treatments for depression and anxiety disorders.