Differential expression of the two forms of prolactin receptor mRNA within microdissected hypothalamic nuclei of the rat.

The prolactin receptor (PRL-R) has recently been identified in various hypothalamic nuclei of female rats. In this study, expression of both the short- and long-forms of PRL-R mRNA was investigated in 11 microdissected hypothalamic nuclei of ovariectomized, estrogen-treated rats. Specific nuclei were micropunched from 300-micrometer thick frozen coronal sections with autoclaved stainless steel needles of 300 or 500 micrometer diameter. Total RNA was extracted from the punched tissue, and the two forms of PRL-R mRNA were detected by reverse transcription polymerase chain reaction (RT-PCR) using specific primers. The RT-PCR product was verified by Southern hybridization with a digoxigenin-labelled oligonucleotide probe common to both forms. The results showed that both forms of PRL-R mRNA were expressed to varying degrees in the choroid plexus, cerebral cortex and various hypothalamic nuclei, including: ventromedial preoptic nucleus, ventrolateral preoptic nucleus, medial preoptic nucleus, suprachiasmatic nucleus, supraoptic nucleus, paraventricular hypothalamic nucleus, periventricular hypothalamic nucleus, arcuate nucleus, ventromedial hypothalamic nucleus, and median eminence. Of these brain regions, the choroid plexus expressed the highest level while the suprachiasmatic nucleus contained the lowest level of mRNA. There was no expression detected in the dorsomedial hypothalamic nucleus. The choroid plexus, supraoptic nucleus and paraventricular hypothalamic nucleus had higher levels of the short-form of the PRL-R mRNA than the long-form, whilst other hypothalamic nuclei preferentially expressed the long-form of the PRL-R mRNA. The differential expression of PRL-R gene suggests that the two forms may be differentially regulated in specific brain regions and may mediate different functions of PRL.