Patricia Lagos

Effects on sleep of melanin-concentrating hormone (MCH) microinjections into the dorsal raphe nucleus.

Neurons that utilize melanin-concentrating hormone (MCH) as a neuromodulator are located in the lateral hypothalamus and incerto-hypothalamic area, and project diffusely throughout the central nervous system, including areas that participate in the generation and maintenance of the states of sleep and wakefulness. Recent studies have shown that the hypothalamic MCHergic neurons are active during rapid eye movements (REM) sleep, and that intraventricular microinjections of MCH induce slow wave sleep (SWS) and REM sleep. There are particular dense MCHergic projections to the dorsal raphe nucleus (DR), a neuroanatomical structure involved in several functions during wakefulness, and in the regulation of sleep variables. Because of this fact, we analyzed the effect of microinjections of MCH into this nucleus on sleep and waking states in the rat. Compared to control microinjections, MCH (100 ng) produced a moderate increase in SWS (243.7+/-6.0 vs. 223.2+/-8.8 min, p<0.05) and an important increment in REM sleep (35.5+/-2.5 vs. 20.8+/-3.4 min, p<0.01) due to an increase in the number of REM sleep episodes. The increase of REM sleep was accompanied by a reduction in the time spent in light sleep and wakefulness. We therefore conclude that the hypothalamic MCHergic system, via its action in the DR, plays an important role in the generation and/or maintenance of the states of sleep.

Effects of the D3 preferring dopamine agonist pramipexole on sleep and waking, locomotor activity and striatal dopamine release in rats.

Abstract Quantitation of 2 h sessions after administration of the D 3 preferring dopamine (DA) agonist pramipexole (10–500 μg/kg) showed dose-related effects on wakefulness (W), slow wave sleep (SWS) and REM sleep in rats. The 30 μg/kg dose of the DA agonist increased SWS and REM sleep and reduced W during the first recording hour, while the 500 μg/kg dose augmented W. On the other hand, W was increased while SWS and REMS were decreased after the 500 μg/kg dose during the second recording hour. The mixed D 2 - and D 3 receptor antagonist YM-09151-2 (30–500 μg/kg), which per se affected sleep variables prevented the increase of REMS induced by pramipexole. Furthermore, the highest doses (500–1000 μg/kg) of the DA antagonist effectively antagonized the increase of W and reduction of SWS induced by the 500 μg/kg dose of the DA agonist. Pramipexole (30–100 μg/kg) induced a decrease of locomotor activity during the 2 h recording period. In addition, the 500 μg/kg dose gave rise to an initial reduction of motor behavior which was reverted 2 h later. Pramipexole (30 and 500 μg/kg) did not significantly affect striatal DA release during the first two hours following drug administration, as measured by microdialysis. It is tentatively suggested that D 3 receptor could be involved in the pramipexole-induced increase of sleep and reduction of locomotor activity. On the other hand, the increase of W and of motor behavior after relatively high doses could be related to activation of postsynaptic D 2 receptor.

Melanin-concentrating hormone control of sleep–wake behavior

The melanin-concentrating hormone (MCH) is a 19 aminoacid peptide found in mammals predominantly in neurons located in the lateral hypothalamus and incerto-hypothalamic area. The biological function of MCH is mediated by two G-protein-coupled receptors known as MCHR1 and MCHR2, although the latter is expressed only in carnivores, primates and man. The MCHR1 couples to Gi, Gq and Go proteins, with Gi leading to the inhibition of both excitatory and inhibitory synaptic events. Within the central nervous system (CNS) MCH participates in a number of functions including sleep-wake behavior. In this respect, MCHergic neurons project widely throughout the CNS to brain regions involved in the regulation of behavioral states. MCHergic neurons are silent during wakefulness (W), increase their firing during slow wave sleep (SWS) and still more during REM sleep (REMS). Studies in knockout mice for MCH (MCH(-/-)) have shown a reduction in SWS and an increase of W during the light and the dark phase of the light-dark cycle. Moreover, in response to food deprivation a marked reduction in REMS time was observed in these animals. Conflicting effects on sleep variables have been reported in MCHR1(-/-) mice by different authors. The i.c.v. administration of MCH increases REMS and SWS in the rat. In addition, an enhancement of REMS has been described following the microinjection of the neuropeptide into the nucleus pontis oralis of the cat, while its infusion into the dorsal raphe nucleus (DR) and the basal forebrain (horizontal limb of the diagonal band of Broca) is followed by an increase of REMS and a reduction of W in the rat. Immunoneutralization of MCH in the DR augmented W and suppressed REMS in the rat, as did the s.c. injection of selective MCHR1 antagonists. The robust REMS-inducing effect of MCH is likely related to the deactivation of monoaminergic, orexinergic, glutamatergic, cholinergic (W-on) and GABAergic (REM-off) neurons involved in the generation of W and the inhibition of REMS. On the basis of preclinical studies, it can be proposed that selective MCHR1 receptor agonists could constitute potential therapeutic modalities in the arsenal of insomnia pharmacotherapy. Due to the lack of adequate animal models, the role of the MCHR2 on sleep is still unknown.

Melanin-concentrating hormone: a new sleep factor?

Neurons containing the neuropeptide melanin-concentrating hormone (MCH) are mainly located in the lateral hypothalamus and the incerto-hypothalamic area, and have widespread projections throughout the brain. While the biological functions of this neuropeptide are exerted in humans through two metabotropic receptors, the MCHR1 and MCHR2, only the MCHR1 is present in rodents. Recently, it has been shown that the MCHergic system is involved in the control of sleep. We can summarize the experimental findings as follows: (1) The areas related to the control of sleep and wakefulness have a high density of MCHergic fibers and receptors. (2) MCHergic neurons are active during sleep, especially during rapid eye movement (REM) sleep. (3) MCH knockout mice have less REM sleep, notably under conditions of negative energy balance. Animals with genetically inactivated MCHR1 also exhibit altered vigilance state architecture and sleep homeostasis. (4) Systemically administered MCHR1 antagonists reduce sleep. (5) Intraventricular microinjection of MCH increases both slow wave sleep (SWS) and REM sleep; however, the increment in REM sleep is more pronounced. (6) Microinjection of MCH into the dorsal raphe nucleus increases REM sleep time. REM seep is inhibited by immunoneutralization of MCH within this nucleus. (7) Microinjection of MCH in the nucleus pontis oralis of the cat enhances REM sleep time and reduces REM sleep latency. All these data strongly suggest that MCH has a potent role in the promotion of sleep. Although both SWS and REM sleep are facilitated by MCH, REM sleep seems to be more sensitive to MCH modulation.

Immunoneutralization of melanin-concentrating hormone (MCH) in the dorsal raphe nucleus: effects on sleep and wakefulness.

Hypothalamic neurons that utilize melanin-concentrating hormone (MCH) as a neuromodulator exert a positive control over energy homeostasis, inducing feeding and decreasing metabolism. Recent studies have shown also that this system plays a role in the generation and/or maintenance of sleep. MCHergic neurons project to the serotonergic dorsal raphe nucleus (DR), a neuroanatomical structure involved in several functions during wakefulness (W), and in the regulation of rapid-eye movements (REM) sleep. Recently, we determined the effect of MCH microinjected into the DR on sleep variables in the rat. MCH produced a marked increment of REM sleep, whereas slow wave sleep (SWS) showed only a moderate increase. In the present study, we analyze the effect of immunoneutralization of MCH in the DR on sleep and W in the rat. Compared to the control solution, microinjections of anti-MCH antibodies (1/100 solution in 0.2 μl) induced a significant increase in REM sleep latency (31.2±7.1 vs. 84.2±24.8 min, p<0.05) and a decrease of REM sleep time (37.8±5.4 vs. 17.8±2.9 min, p<0.05) that was related to the reduction in the number of REM sleep episodes. In addition, there was an increase of total W time (49.8±4.6 vs. 72.0±5.7 min, p<0.01). Light sleep and SWS remained unchanged. The intra-DR administration of a more diluted solution of anti-MCH antibodies (1/500) or rabbit pre-immune serum did not modify neither W nor REM sleep variables. Our findings strongly suggest that MCH released in the DR facilitates the occurrence of REM sleep.

Microinjection of melanin concentrating hormone into the lateral preoptic area promotes non-REM sleep in the rat

The ventrolateral preoptic area (VLPO) has been recognized as one of the key structures responsible for the generation of non-REM (NREM) sleep. The melanin-concentrating hormone (MCH)-containing neurons, which are located in the lateral hypothalamus and incerto-hypothalamic area, project widely throughout the central nervous system and include projections to the VLPO. The MCH has been associated with the central regulation of feeding and energy homeostasis. In addition, recent findings strongly suggest that the MCHergic system promotes sleep. The aim of the present study was to determine if MCH generates sleep by regulating VLPO neuronal activity. To this purpose, we characterized the effect of unilateral and bilateral microinjections of MCH into the VLPO on sleep and wakefulness in the rat. Unilateral administration of MCH into the VLPO and adjacent dorsal preoptic area did not modify sleep. On the contrary, bilateral microinjections of MCH (100 ng) into these areas significantly increased light sleep (LS, 39.2±4.8 vs. 21.6±2.5 min, P<0.05) and total NREM sleep (142.4±23.2 vs. 86.5±10.5 min, P<0.05) compared to control (saline) microinjections. No effect was observed on REM sleep. We conclude that MCH administration into the VLPO and adjacent dorsal lateral preoptic area promotes the generation of NREM sleep.

Depressive-like profile induced by MCH microinjections into the dorsal raphe nucleus evaluated in the forced swim test

Antagonism of the melanin-concentrating hormone (MCH) receptor 1 (MCH-R1) has been recently shown to have antidepressant-like profile in rats. However, the mechanisms by which the MCHergic system participates in the modulation of emotional states are still to be determined. In the present study we confirmed the presence of MCHergic fibers within the dorsal raphe nucleus (DRN), a serotonergic nucleus involved in the physiopathology of major depression. We also assessed the effects of the administration of MCH and anti-MCH antibody (immunoneutralization) into the DRN using the forced swim test in rats, an animal model to screen antidepressant drugs. We found that a low dose of MCH (50 ng) evoked a depressive-like behavior indicated by a significant increase in the immobility time as well as a decrease in climbing behavior. Furthermore, the depressive-like response was prevented by pretreatment with fluoxetine. Consistent with these results, the immunoneutralization of MCH produced an antidepressant-like effect. By means of the open field test we discarded that these effects were related to unspecific changes in motor activity. Our results suggest that the MCHergic neurons are involved in the regulation of emotional behaviors through the modulation of the serotonergic neuronal activity within the DRN. In addition, the present results are in agreement with previous reports showing that antagonism of the MCHergic system may be a novel therapeutic strategy for the treatment of depressive disorders.

Microinjection of the melanin-concentrating hormone into the lateral basal forebrain increases REM sleep and reduces wakefulness in the rat

AIMS To examine the effects of bilateral microinjection of melanin-concentrating hormone (MCH) 50 and 100 ng into the horizontal limb of the diagonal band of Broca (HDB) on sleep variables during the light phase of the light-dark cycle of the rat. MAIN METHODS Male Wistar rats were implanted for chronic sleep recordings. In addition, a guide cannula was implanted above the right and left HDB. Following the microinjection of MCH or control solution the electroencephalogram and the electromyogram were recorded for 6 h. Data was collected and classified as either wakefulness (W), light sleep, slow wave sleep (SWS) or REM sleep (REMS). Latencies for SWS and REMS, as well as the number of REM periods and the mean duration of REM episodes were also determined. KEY FINDINGS MCH 50 and 100 ng significantly decreased W during the first 2-h of recording. Moreover, MCH 100 ng significantly reduced REMS latency and increased REMS time during the first 2-h block of the recording, due to an increase in the number of REM periods. SIGNIFICANCE Our findings tend to suggest that the basal forebrain participates in the effects of MCH on W and REMS through the deactivation of cholinergic, glutamatergic and γ-aminobutyric acid (GABA)-ergic cells.

Increased REM sleep after intra-locus coeruleus nucleus microinjection of melanin-concentrating hormone (MCH) in the rat.

A study was carried out on the effects of unilateral microinjection of melanin-concentrating hormone (MCH) into the right locus coeruleus (LC) on the sleep-wake cycle in rats prepared for chronic sleep recordings. MCH 200 ng significantly augmented rapid-eye-movement sleep (REMS) time during the first, second and third 2-h of recording. Furthermore, MCH 100 ng induced a significant increase of REMS during the first 2-h period after treatment. The increment of the behavioral state was related to a greater number of REMS episodes. It is suggested that MCH deactivation of noradrenergic neurons located in the LC facilitates the occurrence of REMS.

Melanin-Concentrating Hormone (MCH): Role in REM Sleep and Depression

The melanin-concentrating hormone (MCH) is a peptidergic neuromodulator synthesized by neurons of the lateral sector of the posterior hypothalamus and zona incerta. MCHergic neurons project throughout the central nervous system, including areas such as the dorsal (DR) and median (MR) raphe nuclei, which are involved in the control of sleep and mood. Major Depression (MD) is a prevalent psychiatric disease diagnosed on the basis of symptomatic criteria such as sadness or melancholia, guilt, irritability, and anhedonia. A short REM sleep latency (i.e., the interval between sleep onset and the first REM sleep period), as well as an increase in the duration of REM sleep and the density of rapid-eye movements during this state, are considered important biological markers of depression. The fact that the greatest firing rate of MCHergic neurons occurs during REM sleep and that optogenetic stimulation of these neurons induces sleep, tends to indicate that MCH plays a critical role in the generation and maintenance of sleep, especially REM sleep. In addition, the acute microinjection of MCH into the DR promotes REM sleep, while immunoneutralization of this peptide within the DR decreases the time spent in this state. Moreover, microinjections of MCH into either the DR or MR promote a depressive-like behavior. In the DR, this effect is prevented by the systemic administration of antidepressant drugs (either fluoxetine or nortriptyline) and blocked by the intra-DR microinjection of a specific MCH receptor antagonist. Using electrophysiological and microdialysis techniques we demonstrated also that MCH decreases the activity of serotonergic DR neurons. Therefore, there are substantive experimental data suggesting that the MCHergic system plays a role in the control of REM sleep and, in addition, in the pathophysiology of depression. Consequently, in the present report, we summarize and evaluate the current data and hypotheses related to the role of MCH in REM sleep and MD.