Melanin‐concentrating hormone peptidergic system: Comparative morphology between muroid species

Abstract

Melanin-concentrating hormone (MCH) is a conserved neuropeptide, predominantly located in the diencephalon of vertebrates, and associated with a wide range of functions. While functional studies have focused on the use of the traditional mouse laboratory model, critical gaps exist in our understanding of the morphology of the MCH system in this species. Even less is known about the nontraditional animal model Neotomodon alstoni (Mexican volcano mouse). A comparative morphological study among these rodents may, therefore, contribute to a better understanding of the evolution of the MCH peptidergic system. To this end, we employed diverse immunohistochemical protocols to identify key aspects of the MCH system, including its spatial relationship to another neurochemical population of the tuberal hypothalamus, the orexins. Three-dimensional (3D) reconstructions were also employed to convey a better sense of spatial distribution to these neurons. Our results show that the distribution of MCH neurons in all rodents studied follows a basic plan, but individual characteristics are found for each species, such as the preeminence of a periventricular group only in the rat, the lack of posterior groups in the mouse, and the extensive presence of MCH neurons in the anterior hypothalamic area of Neotomodon. Taken together, these data suggest a strong anatomical substrate for previously described functions of the MCH system, and that particular neurochemical

Regulation and neurochemical identity of melanin‐concentrating hormone neurones in the preoptic area of lactating mice

“…On the other hand, an average of 26.5 ± 2.6 MCH cells per section was visualised in the mPOA of mice on day 19 of lactation (Figure B). As seen in rats, MCH cells in the preoptic area were basically distributed in the medial part of the mPOA and ventral aspects of the periventricular preoptic nucleus, whereas no MCH cell was observed in the rostral paraventricular nucleus of the hypothalamus. Thus, the transient MCH expression in the mPOA during lactation is also observed in mice.…”

“…MCH is a phylogenetically conserved peptide and has a wide range of functions, although, in the brain, MCH is strongly implicated in the control of motivated behaviours . Consequently, MCH expression in the mPOA at late lactation may drive behavioural changes associated with the transition between lactation and weaning, particularly the suppression of maternal behaviours . In the present study, we provide new information about possible regulatory factors that control the transient MCH expression in the mPOA.…”

“…Although MCH expression is predominantly found in the LHA, previous studies have identified a transitory MCH expression in the preoptic area of rats and mice at the end of lactation. MCH is a phylogenetically conserved peptide and has a wide range of functions, although, in the brain, MCH is strongly implicated in the control of motivated behaviours . Consequently, MCH expression in the mPOA at late lactation may drive behavioural changes associated with the transition between lactation and weaning, particularly the suppression of maternal behaviours .…”

“…By contrast, some neuropeptides are transiently expressed in the POA, probably to regulate specific functions at certain times of life. In this regard, a group of melanin‐concentrating hormone (MCH)‐expressing neurones only emerge during mid‐to‐late lactation in the medial preoptic area (mPOA) and ventral aspects of the periventricular preoptic nucleus of rats and, more recently, these cells were also identified in mice . Of note, MCH expression in the mPOA disappears after weaning suggesting a role for these neurones in the control of the end of lactation …”

“…Melanin‐concentrating hormone‐expressing neurones are mainly found in the lateral hypothalamic area (LHA), incerto‐hypothalamic area and zona incerta . MCH regulates several motivated behaviours, including feeding, aggression, sexual and maternal care .…”