The Melanin-Concentrating Hormone (MCH) System: A Tale of Two Peptides.

Giovanne B Diniz,Jackson C Bittencourt

doi:10.3389/fnins.2019.01280

Abstract

The melanin-concentrating hormone (MCH) system is a robust integrator of exogenous and endogenous information, modulating arousal and energy balance in mammals. Its predominant function in teleosts, however, is to concentrate melanin in the scales, contributing to the adaptive color change observed in several teleost species. These contrasting functions resulted from a gene duplication that occurred after the teleost divergence, which resulted in the generation of two MCH-coding genes in this clade, which acquired distinctive sequences, distribution, and functions, examined in detail here. We also describe the distribution of MCH immunoreactivity and gene expression in a large number of species, in an attempt to identify its core elements. While initially originated as a periventricular peptide, with an intimate relationship with the third ventricle, multiple events of lateral migration occurred during evolution, making the ventrolateral and dorsolateral hypothalamus the predominant sites of MCH in teleosts and mammals, respectively. Substantial differences between species can be identified, likely reflecting differences in habitat and behavior. This observation aligns well with the idea that MCH is a major integrator of internal and external information, ensuring an appropriate response to ensure the organism’s homeostasis. New studies on the MCH system in species that have not yet been investigated will help us understand more precisely how these habitat changes are connected to the hypothalamic neurochemical circuits, paving the way to new intervention strategies that may be used with pharmacological purposes.

Highlights

The Melanin-Concentrating Hormone SystemThe melanin-concentrating hormone (MCH) system is a robust integrator of exogenous and endogenous information, modulating arousal, promoting motivated behaviors, and controlling energy balance (Diniz and Bittencourt, 2017; Chee et al, 2019), contributing to the appropriate sleep architecture (Ferreira et al, 2017a; Gao, 2018), and tethering energy status and reproductive physiology (Naufahu et al, 2013)
While certain aspects of this system have been explored in length, such as its neuroanatomical aspects (Bittencourt and Diniz, 2018), several others are still open to investigation, including its role in parental behavior (Benedetto et al, 2014; Alachkar et al, 2016; Alhassen et al, 2019), or the mechanisms through which MCH is used to convey information within the central nervous system (CNS) (Noble et al, 2018)
MCH is strongly linked to the roles above, its discovery, and its name is linked to an additional function performed in Teleosts: the control of skin color through the modulation of chromatophore activity (Kawauchi et al, 1983)

Summary

Introduction

The Melanin-Concentrating Hormone SystemThe melanin-concentrating hormone (MCH) system is a robust integrator of exogenous and endogenous information, modulating arousal, promoting motivated behaviors, and controlling energy balance (Diniz and Bittencourt, 2017; Chee et al, 2019), contributing to the appropriate sleep architecture (Ferreira et al, 2017a; Gao, 2018), and tethering energy status and reproductive physiology (Naufahu et al, 2013). Polypteriforms were likely the first clade to split, at around 407 MYA (Kumar S. et al, 2017), and the distribution of MCH-immunoreactivity in these animals closely resemble that of Petromyzontids and Elasmobranchii. An evolutive advantage of a direct NH innervation (interpreted as MCH release directly in the bloodstream) may have paved the way for the split between periventricular/dorsomedial and tuberal lateral groups to be positively selected, with NLT neurons becoming a magnocellular group that preferentially innervates the NH, which was itself followed by the acquisition of adaptive color change.

Results

Conclusion