The Melanin-Concentrating Hormone as an Integrative Peptide Driving Motivated Behaviors

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Neurones expressing the melanin‐concentrating hormone (MCH) can be found in the medial preoptic area (mPOA) and ventral aspects of the periventricular preoptic nucleus of rats by mid‐to‐late lactation and this expression disappears after weaning. The transitory expression of MCH in the preoptic area suggests a role for these neurones in the control of the end of lactation. However, the neurochemical identity of mPOA MCH neurones and the regulatory factors that control the transient MCH expression remain largely unknown, especially in the mouse. In the present study, we showed that mice also present the transitory expression of MCH in the mPOA at late lactation. mPOA MCH cells did not colocalise significantly with markers of GABAergic (VGAT), glutamatergic (VGLUT2 and VGLUT3) or dopaminergic (tyrosine hydroxylase) neurones. mPOA MCH cells also did not express Kiss1 or oxytocin. By contrast, approximately 70% and 90% of mPOA MCH neurones colocalised with oestrogen receptor α and prolactin‐induced phosphorylated signal transducer and activator of transcription 5 (STAT5), respectively. Finally, we demonstrated that the number of MCH neurones in the mPOA is significantly higher in females during the first lactation, compared to mice on the second lactation or pregnant mice during the first lactation or brain‐specific STAT5 knockout mice during the first lactation. In summary, our findings indicate that MCH neurones in the mPOA of lactating mice are sensitive to oestrogens and prolactin. Thus, mPOA MCH expression is possibly influenced by hormonal variations. Furthermore, the STAT5 signalling pathway is likely involved in the regulation of MCH expression in the mPOA of lactating mice.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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

Teixeira

Wasinski

Lima

et al. 2019

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“…After more than 20 years of research subsequent to the discovery of the melanin‐concentrating hormone (MCH) in mammals, an extensive list of roles involving this family of neuropeptides has been described, including reproductive functions and the drive for motivated behaviours . Among the motivated behaviours is maternal behaviour, an essential component for the survival of mammalian species, granting nourishment and protection for the litter until the pups become autonomous.…”

Section: Introductionmentioning

confidence: 99%

Characterisation and origins of melanin‐concentrating hormone immunoreactive fibres of the posterior lobe of the pituitary and median eminence during lactation in the Long‐Evans rat

Costa

Da-Silva

Diniz

et al. 2019

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Although the melanin‐concentrating hormone (MCH) and its coding mRNA are predominantly found in the tuberal hypothalamus, there is detectable synthesis of MCH in the preoptic hypothalamus exclusively in lactating dams, suggesting a participation of MCH in the alterations that take place after parturition. Also implicated in the dam physiology is oxytocin, a neurohormone released from the posterior pituitary that is necessary for milk ejection. Because the projection fields from oxytocin‐immunoreactive (‐IR) neurones and the mediobasal preoptic hypothalamus overlap and MCH‐IR neurones are found in proximity to oxytocin neurones, we investigated the spatial relationship between MCH and oxytocin fibres. Accordingly, we employed multiple immunohistochemistry labelling for MCH and oxytocin for light and electron microscopy techniques, in addition to i.v. tracer injection combined with in situ hybridisation to identify MCH neurones that project to neurosecretory areas. As described for other strains, lactating Long‐Evans dams also display immunoreactivity for MCH in the preoptic hypothalamus on days 12 and 19 of lactation. The appearance of these neurones is contemporaneous with an increase in MCH‐IR fibres in both the internal layer of the median eminence and the posterior pituitary. In both regions, MCH‐ and oxytocin‐IR fibres were found in great proximity, although there was no evidence for synaptic interaction between these two populations at the ultrastructural level. The tracer injection revealed that only mediobasal preoptic MCH neurones project to the posterior pituitary, suggesting a neuroendocrine‐modulatory role for this population. When taken together, the results obtained in the present study indicate that neuroplasticity events at the mediobasal preoptic hypothalamus that occur during late lactation may be part of a neuroendocrinology control loop involving both MCH and oxytocin.

“…Melanin‐concentrating hormone (MCH) is a neuropeptide predominately expressed in the incerto‐hypothalamus and lateral hypothalamus and has roles in a wide variety of physiological functions, including energy balance and reproduction. () Additional expression of prepro‐MCH ( Pmch ) in the medial part of the medial preoptic area (mPOA) and the paraventricular nucleus (PVN) during lactation was first described by Knollema et al In virgin or pregnant rats, Pmch expression is not detected in these regions . The Pmch / MCH‐immunopositive cells first appear in the medial part of the mPOA and PVN in mid‐lactation (days 8‐14) in the rat, and the highest number has been reported on days 15‐21 .…”

Section: Introductionmentioning

confidence: 96%

Prolactin maintains transient melanin‐concentrating hormone expression in the medial preoptic area during established lactation

Kokay

Grattan

Murray

2020

A population of neurones in the medial part of the medial preoptic area (mPOA) transiently express melanin‐concentrating hormone (MCH) in mid to late lactation in the rat, and this expression disappears on weaning. Prolactin is known to mediate many of the physiological adaptations that occur within the dam associated with lactation and the mPOA is well endowed with prolactin receptors (Prlr); hence, we hypothesised that these transiently MCH‐expressing cells may be regulated by prolactin. By in situ hybridisation, we show that approximately 60% of the cells expressing prepro‐MCH (Pmch) mRNA in the medial part of the mPOA on day 19 of lactation also express Prlr mRNA. To demonstrate that these transiently MCH‐expressing cells can acutely respond to prolactin, dams were treated with bromocriptine on the morning of day 19 of lactation and then given vehicle or prolactin 4 hours later. In the prolactin‐treated animals, over 80% of the MCH‐immunopositive cells were also immunopositive for phosphorylated signal transducer and activator of transcription 5, an indicator of prolactin receptor activation: double immunopositive cells were rare in vehicle‐treated animals. Finally, the effect of manipulating the circulating concentrations of prolactin on days 17, 18 and 19 on the number of MCH‐immunopositive cells on day 19 was determined. Reducing circulating concentrations of prolactin over days 17, 18 and 19 of lactation with or without a suckling stimulus resulted in a reduction (P < 0.05) in the number of MCH‐immunopositive cells in the medial part of the mPOA on day 19 of lactation. Further research is required to determine the functional role(s) of these prolactin‐activated transiently MCH‐expressing neurones; however, we suggest the most likely role involves adaptations in maternal metabolism to support the final week of lactation.