Distribution of prolactin receptor immunoreactivity in the brain of estrogen-treated, ovariectomized rats

Although there is extensive evidence for effects of prolactin (PRL) on the brain, knowledge about the PRL receptor (PRL-R) in the brain is limited. By using monoclonal antibodies raised against purified rat liver PRL-R, the distribution of PRL-R was investigated by immunohistochemistry in brains of the estrogen-treated ovariectomized (OVX+E) rat and the adult male rat. Immunohistochemistry was performed by using the avidin biotinylated horse radish peroxidase macromolecular complex method. In both male and OVX+E rats, strong immunostaining was detected in the choroid plexus of all cerebral ventricles. This immunostaining was localized predominately on epithelial cell membranes. In the OVX+E female rat, scattered immunoreactive perikarya were observed in the arcuate nucleus, periventricular hypothalamic nucleus, preoptic area, suprachiasmatic nucleus, and supraoptic nucleus of the hypothalamus. Immunostaining in hypothalamic nuclei was localized on neuronal cell bodies as well as on neuronal processes. In addition, there was extensive PRL-R immunoreactivity throughout the globus pallidus and ventral pallidum. Immunostaining in these striatal regions was not associated with neuronal cell bodies but appeared to be localized on processes or glial cells. In the male rat, less immunostaining was observed in the hypothalamus, and there was no immunostaining in the corpus striatum. No significant staining was observed in the cerebral cortex, thalamus, or hindbrain of either male or OVX+E rats. The implication of PRL-R existence in these brain regions remains to be investigated.