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Expression of mRNA for Prolactin Receptor (Long Form) in Dopamine and Pro‐Opiomelanocortin Neurones in the Arcuate Nucleus of Non‐Pregnant and Lactating Rats
Author(s) -
Kokay I. C.,
Grattan D. R.
Publication year - 2005
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/j.1365-2826.2005.01374.x
Subject(s) - prolactin , medicine , endocrinology , arcuate nucleus , hypothalamus , lactation , tyrosine hydroxylase , prolactin receptor , dopamine , biology , messenger rna , receptor , in situ hybridization , hormone , pregnancy , gene , biochemistry , genetics
Under most conditions, prolactin secretion from the pituitary gland is subject to negative‐feedback regulation. Prolactin stimulates dopamine release from tuberoinfundibular (TIDA) neurones in the arcuate nucleus of the hypothalamus, which in turn suppresses the production of prolactin. However, during late pregnancy and continuing into lactation, this feedback mechanism becomes less responsive to prolactin and, as a result, a hyperprolactinaemic state develops. We investigated whether long‐form prolactin receptor (PRL‐R L ) mRNA is present on TIDA neurones in nonpregnant and lactating rats. In addition, we examined whether PRL‐R L mRNA is colocalised on hypothalamic pro‐opiomelanocortin (POMC) neurones. Dual‐label in situ hybridisations using an 35 S‐labelled cRNA probe specific for long‐form PRL‐R, together with a digoxigenin‐labelled RNA probe that encoded either tyrosine hydroxylase (TH) or POMC mRNA, were performed on brain sections. In both nonpregnant and lactating rats, the majority of TH mRNA‐positive cells (> 90%) were found to express long‐form PRL‐R mRNA. In sections from nonpregnant rats, few non‐TH positive cells expressed PRL‐R L mRNA. By contrast, during lactation, the proportion of PRL‐R L mRNA‐positive cells that were not TH mRNA‐positive increased to approximately 70%. Only a small number of neurones in this subpopulation of PRL‐R L mRNA‐positive neurones were found to be positive for POMC mRNA. These data show that the loss of responsiveness to prolactin occuring during lactation is not due to down regulation of long‐form PRL‐R gene expression on TIDA neurones. Moreover, the persistent expression of PRL‐R L in arcuate neuroendocrine circuits suggests that PRL‐R‐mediated signalling continues to be important in these neurones during lactation.