Melanin-concentrating hormone peptidergic system: Comparative morphology between muroid species.

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 and morphological features may have been determinant to species-specific phenotypes in rodent evolution.

Suckling-induced Fos activation and melanin-concentrating hormone immunoreactivity during late lactation.

AIMS: Melanin-concentrating hormone (MCH) is implicated in the control of food intake, body weight regulation and energy homeostasis. Lactation is an important physiological model to study the hypothalamic integration of peripheral sensory signals, such as suckling stimuli and those related to energy balance. MCH can be detected in the medial preoptic area (MPOA), especially around the 19th day of lactation, when this hormone is described as displaying a peak synthesis followed by a decrease after weaning. The physiological significance of this phenomenon is unclear. Therefore, we aimed to investigate hypothalamic changes associated to sensory stimulation by the litter, in special its influence over MCH synthesis. MAIN METHODS: Female Wistar rats (n=56) were euthanized everyday from lactation days 15-21, with or without suckling stimulus (WS and NS groups, respectively). MCH and Fos immunoreactivity were evaluated in the MPOA and lateral and incerto-hypothalamic areas (LHA and IHy). KEY FINDINGS: Suckling stimulus induced Fos synthesis in all regions studied. An increase on the number of suckling-induced Fos-ir neurons could be detected in the LHA after the 18th day. Conversely, the amount of MCH decreased in the MPOA from days 15-21, independent of suckling stimulation. No colocalization between MCH and Fos could be detected in any region analyzed. SIGNIFICANCE: Suckling stimulus is capable of stimulating hypothalamic regions not linked to maternal behavior, possibly to mediate energy balance aspects of lactation. Although dams are hyperphagic before weaning, this behavioral change does not appear to be mediated by MCH.

Gonadotrophin-Inhibitory Hormone in the Cichlid Fish Cichlasoma dimerus: Structure, Brain Distribution and Differential Effects on the Secretion of Gonadotrophins and Growth Hormone.

The role of gonadotrophin-inhibitory hormone (GnIH) in the inhibition of the reproductive axis has been well-established in birds and mammals. However, its role in other vertebrates, such as the teleost fish, remains controversial. In this context, the present study aimed to evaluate whether GnIH modulates the release of gonadotrophins and growth hormone (GH) in the cichlid fish Cichlasoma dimerus. First, we partially sequenced the precursor polypeptide for GnIH and identified three putative GnIH peptides. Next, we analysed the expression of this precursor polypeptide via a polymerase chain reaction in the reproductive axis of both sexes. We found a high expression of the polypeptide in the hypothalamus and gonads of males. Immunocytochemistry allowed the observation of GnIH-immunoreactive somata in the nucleus posterioris periventricularis and the nucleus olfacto-retinalis, with no differences between the sexes. GnIH-immunoreactive fibres were present in all brain regions, with a high density in the nucleus lateralis tuberis and at both sides of the third ventricle. Finally, we performed in vitro studies on intact pituitary cultures to evaluate the effect of two doses (10(-6)  m and 10(-8)  m) of synthetic C. dimerus (cd-) LPQRFa-1 and LPQRFa-2 on the release of gonadotrophins and GH. We observed that cd-LPQRFa-1 decreased ß-luteinising hormone (LH) and ß-follicle-stimulating hormone (FSH) and also increased GH release to the culture medium. The release of ß-FSH was increased only when it was stimulated with the higher cd-LPQRFa-2 dose. The results of the present study indicate that cd-LPQRFa-1, the cichlid fish GnIH, inhibits ß-LH and ß-FSH release and stimulates GH release in intact pituitary cultures of C. dimerus. The results also show that cd-LPQRF-2 could act as an ß-FSH-releasing factor in this fish species.

Dopamine and melanin-concentrating hormone neurons are distinct populations in the rat rostromedial zona incerta.

Zona incerta (ZI) is a controversial diencephalic area with a variety of cytoarchitectonic subdivisions, neurotransmitters and related functions. Medial ZI synthesizes dopamine (A13 group) and tyrosine hydroxylase (TH, a catecholamine synthesizing enzyme), which has been considered a neurochemical marker for this region. The rostromedial ZI also expresses melanin-concentrating hormone (MCH), but it is not known whether dopamine and MCH are colocalized. By using double label immunohistochemistry we analyzed the distribution of TH and MCH in the rat ZI. We found that MCH and TH neurons are intermingled but are not colocalized.

Melanin-concentrating hormone system in the brain and skin of the cichlid fish Cichlasoma dimerus: anatomical localization, ontogeny and distribution in comparison to alpha-melanocyte-stimulating hormone-expressing cells.

Distribution and development of the melanin-concentrating hormone (MCH) system were examined by immunocytochemistry of the brain, pituitary gland and skin of the South American cichlid fish Cichlasoma dimerus. In adults, the most prominent group of MCH-ir perikarya was located in the nucleus lateralis tuberis (NLT). Outside the NLT, in the posterior hypothalamic region, a group of small neurons was found between the third ventricle and the lateral ventricular recess with delicate immunoreactive fibers that did not seem to contribute to the pituitary innervation. MCH-ir perikarya were identified at day 4 after hatching (AH) in a proliferating zone of the hypothalamic floor. Pituitary innervation could be detected at this stage. Another group of small MCH-ir neurons, only detected in pre-juvenile stages, originated close to the third ventricle in the medial hypothalamic region by day 6 AH. alphaMSH-ir neurons were localized in similar regions of the NLT and in the nucleus periventricularis posterior (NPP). Free MCH-ir neuromasts were detected in the ventral and dorsal skin of larval heads. These epidermal sensory organs were in close association with blood vessels and dermal melanocytes, suggesting that MCH synthesized in larval skin might act in an endocrine way reaching different targets and/or in a paracrine mode regulating melanin concentration in dermal melanocytes.

Study of the origins of melanin-concentrating hormone and neuropeptide EI immunoreactive projections to the periaqueductal gray matter.

Previous studies have described the distribution of melanin-concentrating hormone (MCH) and neuropeptide EI (NEI) in the rat central nervous system (CNS), and revealed this peptidergic system to be primarily localized in neurons within the lateral hypothalamic area (LHA) and zona incerta (ZI). Moreover, an extensive MCH- and NEI-immunoreactive (ir) fiber distribution has been described throughout the CNS, including a dense innervation within the periaqueductal gray matter (PAG). MCH and NEI have become important markers for the LHA, which harbors a variety of neuronal types as well as the medial forebrain bundle, a complex system of fibers which extends rostrocaudally throughout this area. In the present study, the projection patterns of MCH- and NEI-ir fibers within the PAG were characterized using a diamino benzidine immunoperoxidase procedure to localize each of these peptides in normal rat brain sections. MCH- and NEI-ir fibers were seen coursing through all of its subdivisions the entire length of the PAG, with a more condensed number of fibers in the periaqueductal medial zone. The primary origin(s) of these PAG afferents were determined in combined retrograde tracing immunofluorescent studies in which true blue (TB) was injected into various subdivisions of the PAG. TB-filled MCH-ir neurons were identified mainly in the rostral portion of the medial ZI (ZIm) and in the tuberal LHA (LHAt). Studies confirming this MCH-ir projection in which anterograde tracer (Phaseolus vulgaris leucoagglutinin) was injected into various regions in and around the LHA and ZI revealed a distinction in the PAG projections arising from these nuclei. ZIm injections resulted in labeled fibers mainly within the rostral dorsomedial and dorsolateral regions of the PAG, whereas injections in the LHAt revealed an innervation at intermediate and caudal levels in the ventrolateral region. Since the MCH and NEI fiber distribution patterns in the PAG are identical, this would suggest that these peptides are colocalized within the hypothalamus. Sequential immunofluorescent staining for MCH and NEI on tissue from rats who had received TB injections into the PAG confirmed this, and revealed that approximately 15% of all tracer-filled neurons in the LHA and ZI were both MCH- and NEI-ir. In fact, the vast majority of MCH-ir neurons within these regions also colocalize with NEI. Therefore, the MCH/NEI projection patterns within the PAG arise from two major sources: the ZIm which supplies afferents via a medial pathway that enters the PAG dorsally at rostral levels, and a pathway originating in the LHA that enters the PAG ventrally at more caudal levels. The ZIm and LHA are believed to be the primary, if not the only, sources of MCH and NEI projections to the PAG.

Projeçöes diencefálicas para o córtex motor e o núcleo pedunculopontino do tegmento, imunorreativas ao hormônio concentrador de melanina (MCH) e/ou ao neuropeptídeo EI (NEI): um estudo com múltiplos traçadores neuronais / Diencephalic origns of melanin-concentrating hormone-and neuropeptide EI - immunoreactive projections to pedunculopontine nucleous and motor cortex: a study with multiple neuronal tracers

O hormônio concentrador de melanina (MCH) é um heptadecapeptídeo cíclico descrito pela primeira vez em hipófise de salmäo e posteriormente em alguns mamíferos. Os corpos celulares McH-ir encontram-se localizados em regiöes específicas do sistema nervoso central (SNC) do rato, como a Zona Incerta (EI) e a Área Hipotalâmica Lateral (AHL) enquanto que as fibras apresentam-se espalhadas por todo o neuro-eixo. Indica que a inervaçäo cortical é densa e homogênea por todo o neocórtex, assim como, a inervaçäo de várias regiöes da formaçäo reticular, como o núcleo pedunculopontino do tegmento (PPTg). Faz um estudo com múltiplos traçadores neuronais em ratos albinos machos (Wistar) usando 6 procedimentos distintos. Utiliza injeçöes de Diamidino Yellow (DY) no córtex motor (CxM) e de True Blue (TB) no PPTg. Demonstra a existência de neurônios MCH-ir marcados com ambos os traçadores distintamente, tanto na ZI quanto na AHL. Realiza controle com leucoaglutimina do Phaseolus vulgaris (PHA-L) injetado nestes territórios, demonstrando a inervaçäo do CxM e do PPTg originários das regiöes onde as células dupla e triplamente marcada foram encontradas. Conclui que estas células säo também NEI-ir; os resultados envidenciam a presença de colaterais de AHL e ZI para 2 regiöes de SNC envolvidas com o comportamento locomotor. Discute a pesquisa em termos de envolvimento do MCH com o comportamento alimentar, que justamente com o locomotor indica uma atuaçäo na busca do alojamento (a maior quantidade de células marcadas säo originárias de fibras localizadas na regiäo motora das vibrissas), e no sistema reticular ativador ascendente