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

Abstract

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.

Dissociated Pmch and Cre Expression in Lactating Pmch-Cre BAC Transgenic Mice

“…Pmch mRNA in the MPO, PVH, LS, and AD colocalized primarily with Vgat-Cre;eGFP and not Vglut2-eGFP (Figures 8A-C). Because this result contradicts recent studies (Teixeira et al, 2019), we performed fluorescent ISH using RNAscope to further examine colocalization of Pmch with Slc32a1 (VGAT). The findings were unambiguous and demonstrated that virtually all Pmch expressing neurons co-express Slc32a1 (Figures 8D-F).…”

“…In lactating mice, Pmch expression is clearly different from rats ( Knollema et al, 1992 ). While in rats, Pmch expression is triggered at mid-lactation and becomes dense in the MPN and PVH, in mice, Pmch is observed only at the end of lactation (day 19) at low to moderate levels specifically in the MPNm ( Teixeira et al, 2019 ) and anterior PVH. Notably, the mice also show lactation-induced Pmch in previously unreported brain sites, including the LS, the ADP, the ventral BSTpr and the anterior AD.…”

“…It has been suggested that prolactin-induced phosphorylation of STAT5 (pSTAT5) has a role in the lactation-induced MCH-ir in the MPO. STAT5 is a known activator protein for hundreds of enhancers, particularly those implicated in pregnancy- and lactation-associated genes ( Yamaji et al, 2013 ; Teixeira et al, 2019 ). The seven STAT family proteins are all believed to target the same palindromic core motif, TTC N 2 – 4 GAA.…”

Differences between rats and mice in the leptin action on the paraventricular nucleus of the hypothalamus: Implications for the regulation of the hypothalamic‐pituitary‐thyroid axis

“…However, mice are becoming the dominant experimental model in neuroanatomical and physiological studies, especially because of the enormous variety of genetically modified mouse models that allow detailed mechanistic studies 55‐58 . Although there are many similar aspects between rats and mice regarding the cyto‐ and chemoarchitecture of the hypothalamus, some important differences were already noted 40,44,45 . In the present study, we aimed to investigate possible species‐specific differences in the direct and indirect mechanisms used by leptin to regulate the HPT axis.…”

“…Fab fragments secondary antibodies cover the surface of immunoglobulins, blocking the access of the second secondary antibody to the first primary antibody. Consequently, Fab antibodies allow double‐labelling immunofluorescence reactions using primary antibodies from the same host species 38‐40 . Subsequently, brain sections were incubated overnight in anti‐proTRH antibody raised in rabbit (dilution 1:1000), followed by incubation in AlexaFluor 594 ‐conjugated whole IgG donkey anti‐rabbit (dilution 1:1000; Jackson ImmunoResearch Laboratories) for 30 minutes.…”