Expression of prolactin receptor mRNA is increased in the preoptic area of lactating rats.

This study investigated expression of prolactin receptor (PRL-R) mRNA in the preoptic area in midlactating rats compared with diestrous rats. Tissues from specific nuclei were micropunched from 300-microm thick rat brain sections with 300- or 500-microm diameter needles. After total RNA was extracted, the two forms of PRL-R mRNA were evaluated by reverse transcriptase polymerase chain reaction and Southern hybridization. The results showed that levels of long-form PRL-R mRNA in the ventrolateral preoptic nucleus and lateroanterior nucleus in lactating rats were significantly higher (p < 0.05) than in diestrous rats. The ventromedial and medial preoptic nuclei in lactating rats also expressed moderately high levels of long-form mRNA when compared with (p = 0.0547) diestrous rats. The ventromedial and ventrolateral preoptic nuclei, and ventrolateral hypothalamic nucleus in lactating rats expressed significantly higher levels of short-form mRNA than in diestrous rats. The increased expression of both forms of PRL-R mRNA helps explain numerous effects of PRL on brain functions during lactation.