Organization of neural systems expressing melanocortin‐3 receptors in the mouse brain: Evidence for sexual dimorphism

Abstract

The central melanocortin system is fundamentally important for controlling food intake and energy homeostasis. Melanocortin-3 receptor (MC3R) is one of two major receptors of the melanocortin system found in the brain. In contrast to the well-characterized melanocortin-4 receptor (MC4R), little is known regarding the organization of MC3R-expressing neural circuits. To increase our understanding of the intrinsic organization of MC3R neural circuits, identify specific differences between males and females, and gain a neural systems level perspective of this circuitry, we conducted a brain-wide mapping of neurons labeled for MC3R and characterized the distribution of their projections. Analysis revealed MC3R neuronal and terminal

Melanocortin receptor 3 and 4 mRNA expression in the adult female Syrian hamster brain

“…The expression of MC4R mRNA was greatest in the midbrain. These observations are consistent with those described in previous mapping studies (Roselli-Rehfuss et al, 1993;Gantz et al, 1993a,b;Mountjoy et al, 1994;Kishi et al, 2003;Bedenbaugh et al, 2022). Finally, with the exception of the MPOA and the ARC, there was very little co-expression of MC3R and MC4R mRNA in female Syrian hamsters in this study.…”

“…There are species differences in MC3R mRNA expression in the PVN and the MePD of the amygdala, where the expression levels in hamsters are lower than that reported for the rat (Roselli-Rehfuss et al, 1993). The VMH of the hamster had similar expression levels of MC3R mRNA with that of the rat and mouse (Roselli-Rehfuss et al, 1993;Bedenbaugh et al, 2022). Melanocortin 3 receptor mRNA expression in the hamster ARC was equal to that in the rat and greater than the expression in the mouse (Roselli-Rehfuss et al, 1993;Bedenbaugh et al, 2022).…”

“…The plus scale was used to compare the expression of MC3R and MC4R in hamsters with data reported for other species (Table 2). A plus scale was utilized for the MC3R distribution study conducted by Bedenbaugh et al (2022). The plus scale was generated from the intensity color of MC3R expression, with each color having a natural break in the numbers of labeled cells (Table 2).…”

“…The distribution of MC3R and MC4R expression in the brain has been mapped by Roselli-Rehfuss et al (1993), Mountjoy et al (1994), and Kishi et al (2003) in rats, and Gantz et al (1993a,b), Liu et al (2003), and Sweeney et al (2021) in mice. Furthermore, a study was recently published that provided a more extensive description of the distribution of the cells that express MC3R mRNA in the central nervous system of mice (Bedenbaugh et al, 2022). The expression of MC3R tends to be isolated in the hypothalamus and thalamus in mice and rats (Roselli-Rehfuss et al, 1993;Bedenbaugh et al, 2022).…”

“…Furthermore, a study was recently published that provided a more extensive description of the distribution of the cells that express MC3R mRNA in the central nervous system of mice (Bedenbaugh et al, 2022). The expression of MC3R tends to be isolated in the hypothalamus and thalamus in mice and rats (Roselli-Rehfuss et al, 1993;Bedenbaugh et al, 2022). On the other hand, MC4Rs are expressed more broadly across the central nervous system in mice and rats (Mountjoy et al, 1994;Liu et al, 2003;Tao, 2010).…”