Abstract
ObjectiveMelanocortin-4 receptors (MC4Rs) are key regulators of energy homeostasis and adipose deposition in the central nervous system. Considering that MC4R expression regions and function-related research mainly focus on the paraventricular nucleus (PVN), little is known about their distribution throughout the mouse brain, although its messenger RNA distribution has been analyzed in the rat. Therefore, MC4R protein localization in mouse neurons was the focus of this study.MethodsMC4R protein distribution was assessed in mice through immunofluorescence and Western blotting.ResultsMC4R was differentially expressed throughout the arcuate nucleus (ARC), nucleus of the solitary tract (NTS), raphe pallidus (RPa), medial cerebellar nucleus, intermediolateral nucleus, and brainstem. The highest MC4R protein levels were found in the ARC and ventromedial hypothalamic nucleus, while they were significantly lower in the parabrachial nucleus and NTS. The lowest MC4R protein levels were found in the PVN; there was no difference in the protein levels between the area postrema and RPa.ConclusionsThese data provide a basic characterization of MC4R-expressing neurons and protein distribution in the mouse brain and may aid further research on its role in energy homeostasis.
Highlights
The melanocortin system in the central nervous system (CNS) plays an important role in regulating appetite and energy homeostasis [1]
A very high density of MC4Rlabeled neurons was detected in the dentate gyrus molecular layer (DG-mo; Figure 1a)
Within the region next to the medulla, homogenous Melanocortin-4 receptors (MC4Rs) staining was found on the cervical enlargement region (Figure 1d) and hypothalamus (Figure 1h and i)
Summary
The melanocortin system in the central nervous system (CNS) plays an important role in regulating appetite and energy homeostasis [1]. The central melanocortin system regulates food intake [2], energy expenditure, and body weight via distinct projection patterns to melanocortin receptors (MCRs) in hypothalamic and extrahypothalamic nuclei [3]. These effects are mediated mainly via G protein-coupled melanocortin-4 receptor (MC4R) activation and stimulated by the α melanocyte-stimulating hormone [4,5]. After an initial blocking step (3% normal donkey serum in 0.01 M PBS containing 1% Triton X-100), the sections were incubated with primary antibodies F rabbit anti-MC4R (1:1,000, ab24233, Abcam) overnight at 4°C. Fluorescent neuronal cells were visualized and imaged using a Nikon C2 confocal microscope (Japan) with 4× and 10× objectives
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