Prolactin receptor mRNA localization in the hypothalamus by in situ hybridization

Prolactin receptors may mediate the action of prolactin in the brain to influence behavior and neuroendocrine secretions. We recently demonstrated prolactin receptor gene expression in the anterior and medial basal hypothalamus and not in the cortex by the reverse transcription-polymerase chain reaction. In this paper, we localize the prolactin receptor gene expression to individual cells with in situ hybridization. Several steps in the in situ hybridization method were modified to increase sensitivity by using (i) probes complementary to the coding sequence of the extracellular binding domain common to both long and short prolactin receptor, (ii) more stringent hybridization and wash conditions to reduce background and (iii) higher specific activity, more complex and saturating amounts of probe. We detected prolactin receptor gene expression in cells of the periventricular area of the preoptic nucleus, medial preoptic nucleus, supraoptic nucleus, rostral arcuate nucleus and choroid plexus. Cortical brain tissue, which has been demonstrated previously by reverse-transcription polymerase chain reaction to be lacking in prolactin receptor mRNA, did not have any detectable signal for the receptor mRNA and was used as an indication of background levels of signal. The mean area of silver grains over labeled cells in periventricular area of the preoptic nucleus, medial preoptic nucleus, supraoptic nucleus, arcuate nucleus, lateral ventromedial nucleus was at least 10 times greater than the background in the cortex of the same brain section.