Abstract
Melanin concentrating hormone (MCH), a neuropeptide produced mainly in neurons localized to the lateral hypothalamic area (LHA), has been implicated in the regulation of food intake, energy balance, sleep state, and the cardiovascular system. Hypothalamic MCH neurons also have multisynaptic connections with diaphragmatic motoneurons and project to many central chemoreceptor sites. However, there are few studies of MCH involvement in central respiratory control. To test the hypothesis that MCH plays a role in the central chemoreflex, we induced a down regulation of MCH in the central nervous system by knocking down the MCH precursor (pMCH) mRNA in the LHA using a pool of small interfering RNA (siRNA), and measured the resultant changes in breathing, metabolic rate, body weight, and blood glucose levels in conscious rats. The injections of pMCH-siRNA into the LHA successfully produced a ∼62% reduction of pMCH mRNA expression in the LHA and a ∼43% decrease of MCH levels in the cerebrospinal fluid relative to scrambled-siRNA treatment (P = 0.006 and P = 0.02 respectively). Compared to the pretreatment baseline and the scrambled-siRNA treated control rats, knockdown of MCH resulted in: 1) an enhanced hypercapnic chemoreflex (∼42 & 47% respectively; P < 0.05) only in wakefulness; 2) a decrease in body weight and basal glucose levels; and 3) an unchanged metabolic rate. Our results indicate that MCH participates not only in the regulation of glucose and sleep-wake homeostasis but also the vigilance-state dependent regulation of the central hypercapnic chemoreflex and respiratory control.
Highlights
Melanin concentrating hormone (MCH), a 17-amino acid neuropeptide, was originally isolated from the pituitary gland of salmon where it controls skin pigmentation [1]
There was no significant difference in pMCH messenger RNA (mRNA) expression between the scrambled small interfering RNA (siRNA) group and the aCSF group (N = 5, P.0.05). pMCH mRNA levels in the pMCH siRNA group were: mean, 37.5% of the controls; range, 26.3%–48.7%; controls being the scrambled siRNA group: mean, 100%; range, 69.7%–131.7%; in the aCSF group: mean, 107.3% of the controls; range, 66.85%–146.15%
We tested whether knocking down pMCH has non-specific effects on the adjacent neuronal groups, e.g., orexin neurons, since MCH and orexin neurons are intermingled within the lateral hypothalamic area (LHA) (Van den Pol, et al 2004; Rao et al, 2008)
Summary
Melanin concentrating hormone (MCH), a 17-amino acid neuropeptide, was originally isolated from the pituitary gland of salmon where it controls skin pigmentation [1]. Recent studies showed that central administration of MCH into lateral ventricle (i.c.v.) or nucleus tractus solitarius (NTS) caused depressor and bradycardiac responses in both anesthetized and conscious rats [8,9]. Intrathecal injection of MCH produced a dose-dependent hypotension, bradycardia, and sympathetic depression, and attenuated the sympathetic response to stimulation of peripheral (anoxia, ,4.4% O2) or central (hyperoxic hypercapnia 10% CO2/93% O2) chemoreceptors [10]. This evidence suggested a role of MCH in autonomic functions
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