Microinjection Of Melanin-concentrating Hormone Research Articles

Melanin-concentrating hormone regulates the hypercapnic chemoreflex by acting in the lateral hypothalamic area.

What is the central question of this study? Melanin-concentrating hormone (MCH) suppresses the hypercapnic chemoreflex: what is the mechanism by which this effect is produced? What is the main finding and its importance? MCH acting in the lateral hypothalamic area but not in the locus coeruleus in rats, in the light period, attenuates the hypercapnic chemoreflex. The data provide new insight into the role of MCH in the modulation of the hypercapnic ventilatory response. Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide involved in a broad range of homeostatic functions including regulation of the hypercapnic chemoreflex. We evaluated whether MCH modulates the hypercapnic ventilatory response by acting in the lateral hypothalamic area (LHA) and/or in the locus coeruleus (LC). Here, we measured pulmonary ventilation ( ), body temperature, electroencephalogram (EEG) and electromyogram (EMG) of unanaesthetized adult male Wistar rats before and after microinjection of MCH (0.4mM) or MCH receptor 1 (MCH1-R) antagonist (SNAP-94847; 63mM) into the LHA and LC, in room air and 7% CO2 conditions during wakefulness and sleep in the dark and light periods. MCH intra-LHA caused a decreased CO2 ventilatory response during wakefulness and sleep in the light period, while SNAP-94847 intra-LHA increased this response, during wakefulness in the light period. In the LC, MCH or the MCH1-R antagonist caused no change in the hypercapnic ventilatory response. Our results suggest that MCH, in the LHA, exerts an inhibitory modulation of the hypercapnic ventilatory response during the light-inactive period in rats.

Microinjection of melanin-concentrating hormone (MCH) into the median raphe nucleus promotes REM sleep in rats.

Melanin concentrating hormone (MCH) is a sleep-promoting neuromodulator synthesized by neurons located in the postero-lateral hypothalamus and incerto-hypothalamic area. MCHergic neurons have widespread projections including the serotonergic dorsal (DR) and median (MnR) raphe nuclei, both involved in the control of wakefulness and sleep. In the present study, we explored in rats the presence of the MCH receptor type 1 (MCHR-1) in serotonergic neurons of the MnR by double immunofluorescence. Additionally, we analyzed the effect on sleep of MCH microinjections into the MnR. We found that MCHR-1 protein was present in MnR serotonergic and non-serotonergic neurons. In this respect, the receptor was localized in the primary cilia of these neurons. Compared with saline, microinjections of MCH into the MnR induced a dose-related increase in REM sleep time, which was related to a rise in the number of REM sleep episodes, associated with a reduction in the time spent in W. No significant changes were observed in non-REM (NREM) sleep time. Our data strongly suggest that MCH projections towards the MnR, acting through the MCHR-1 located in the primary cilia, promote REM sleep.

Lateral hypothalamic Orexin-A-ergic projections to the arcuate nucleus modulate gastric function in vivo.

It has been well-known that hypothalamic orexigenic neuropeptides, orexin-A, and melanin-concentrating hormone (MCH), play important roles in regulation of gastric function. However, what neural pathway mediated by the two neuropeptides affects the gastric function remains unknown. In this study, by way of nucleic stimulation and extracellular recording of single unit electrophysiological properties, we found that electrically stimulating the lateral hypothalamic area (LH) or microinjection of orexin-A into the arcuate nucleus (ARC) excited most gastric distension-responsive neurons in the nuclei and enhanced the gastric function including motility, emptying, and acid secretion of conscious rats. The results indicated that LH-ARC orexin-A-ergic projections may exist and the orexin-A in the ARC affected afferent and efferent signal transmission between ARC and stomach. As expected, combination of retrograde tracing and immunohistochemistry showed that some orexin-A-ergic neurons projected from the LH to the ARC. In addition, microinjection of MCH and its receptor antagonist PMC-3881-PI into the ARC affected the role of orexin-A in the ARC, indicating a possible involvement of the MCH pathway in the orexin-A role. Our findings suggest that there was an orexin-A-ergic pathway between LH and ARC which participated in transmitting information between the central nuclei and the gastrointestinal tract and in regulating the gastric function of rats.

Melanin-concentrating hormone (MCH) modulates the activity of dorsal raphe neurons

Hypothalamic neurons that utilize melanin-concentrating hormone (MCH) as a neuromodulator are localized in the postero-lateral hypothalamus and incerto-hypothalamic area. These neurons send dense projections to the dorsal raphe nucleus (DRN).Serotonergic neurons of the DRN are involved in the control of sleep and play a critical role in major depression. Previously, we demonstrated that microinjections of MCH into the DRN resulted in an increase in REM sleep and produce a depressive-like effect. In the present study we examined the mechanisms that mediate these effects by employing neuroanatomical and electrophysiological techniques.First, we determined that rhodamine-labeled MCH (R-MCH), when microinjected into the lateral ventricle, is internalized in serotonergic and non-serotonergic DRN neurons in rats and cats. These data strongly suggest that these neurons express MCHergic receptors. Second, in rats, we demonstrated that the microinjection of MCH into the lateral ventricle results in a significant decrease in the firing rate in 59% of the neurons recorded in the DRN; the juxtacellular administration of MCH reduced the discharge in 80% of these neurons. Some of the neurons affected by MCH were likely serotonergic on the basis of their electrophysiological and pharmacological properties.We conclude that MCH reduces the activity of serotonergic neurons of the DRN. These and previous data suggest that the MCHergic modulation of serotonergic activity within the DRN is involved in the regulation of REM sleep as well as in the pathophysiology of depressive disorders.

Prodepressive effect induced by microinjections of MCH into the dorsal raphe: time course, dose dependence, effects on anxiety-related behaviors, and reversion by nortriptyline.

Melanin-concentrating hormone (MCH) administered within the rat dorsal raphe nucleus (DRN) has been shown to elicit prodepressive behaviors in the forced-swim test. The present study was designed to evaluate the time course (30 and 60 min) and dose dependence (25-100 ng) of this effect, and whether it would be antagonized by an intra-DRN microinjection of the MCH-1 receptor antagonist ATC0175 (ATC, 1 mmol/l) or intraperitoneal pretreatment with the noradrenergic antidepressant nortriptyline (20 mg/kg). The results showed that the behavioral effect of MCH was time and dose dependent as immobility was increased, and climbing decreased, only by the 50 ng MCH dose at T30. The effect was mediated by MCH-1 receptors as a significant blockade of this behavioral response was observed in ATC-pretreated animals. ATC did not by itself modify animal behavior. Nortriptyline also prevented the prodepressive-like effect of MCH. Concomitantly, the effect of MCH (50 ng) at T30 on anxiety-related behaviors was assessed using the elevated plus-maze. Interestingly, these behaviors were unchanged. In conclusion, MCH administration within the DRN elicits, through the MCH-1 receptor, a depression-related behavior that is not accompanied by changes in anxiety and that is prevented by a noradrenergic antidepressant.

The median raphe nucleus participates in the depressive-like behavior induced by MCH: Differences with the dorsal raphe nucleus

An emerging body of evidence involves the hypothalamic neuropeptide melanin-concentrating hormone (MCH) in the regulation of emotional states. We have reported a pro-depressive effect induced by MCH after its microinjection into the dorsal raphe nucleus (DR) evaluated in the forced swimming test (FST) in rats. Here we extended this study to the median raphe nucleus (MnR). Firstly, the presence of MCH-containing fibers in the rat MnR was analyzed by means of immunohistochemistry. Secondly, the behavioral effect induced by the microinjection of MCH into the MnR was assessed using the FST. Morphological results showed a large density of MCHergic fibers within the MnR. Behavioral results indicated that 100ng of MCH (but not 50ng) significantly increased the immobility time and decreased the swimming time, demonstrating a depressive-like effect. In contrast, climbing behavior was not significantly affected. Present findings revealed that the MnR neurons participate in the MCHergic control of affective-related behavioral responses. However, the behavioral patterns induced by MCH in the MnR and DR were different. This could be explained by anatomical and physiological differences between both nuclei.

Melanin concentrating hormone induces hippocampal acetylcholine release via the medial septum in rats

Among various actions of melanin concentrating hormone (MCH), its memory function has been focused in animal studies. Although MCH neurons project to various areas in the brain, one main target site of MCH is hippocampal formation for memory consolidation. Recent immunohistochemical study shows that MCH neurons directly project to the hippocampal formation and may indirectly affect the hippocampus through the medial septum nucleus (MS). It has been reported that sleep is necessary for memory and that hippocampal acetylcholine (ACh) release is indispensable for memory consolidation. However, there is no report how MCH actually influences the hippocampal ACh effluxes in accordance with the sleep–wake cycle changes. Thus, we investigated the modulatory function of intracerebroventricular (icv) injection of MCH on the sleep–wake cycle and ACh release using microdialysis techniques. Icv injection of MCH significantly increased the rapid eye movement (REM) and non-REM episode time and the hippocampal, not cortical, ACh effluxes. There was a significant correlation between REM episode time and hippocampal ACh effluxes, but not between REM episode time and cortical ACh effluxes. Microinjection of MCH into the MS increased the hippocampal ACh effluxes with no influence on the REM episode time. It appears that the effect sites of icv MCH for prolongation of REM episode time may be other neuronal areas than the cholinergic neurons in the MS. We conclude that MCH actually increases the hippocampal ACh release at least in part through the MS in rats.

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

AimsTo examine the effects of bilateral microinjection of melanin-concentrating hormone (MCH) 50 and 100ng 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 methodsMale 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 6h. 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 findingsMCH 50 and 100ng significantly decreased W during the first 2-h of recording. Moreover, MCH 100ng 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. SignificanceOur 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.

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.