Basic study for application of stress-resistant effect of prolactin to animals

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(1)Effects of rearing with low-prolactin milk on the stress-resistance and maternal behavior of rats at adulthoodEffects of milk-born prolactin on the development of brain function were examined in rats. Bromocriptin, a prolactin secretion inhibitor, was administrated into intraperitoneal cavity at days 20 and 21 of pregnancy, and stress-tolerance and maternal behavior reared by the bromocriptin-administrated mothers were tested at adulthood. Both the extent of gastric ulcer caused by water-restraint stress and latency of maternal behavior to foster pups were significantly increased in the rats reared by the bromocriptin-administrated mothers compared to those in rats reared by control mothers. These results suggest that milk-born prolactin plays an important role in establishment of neural networks for stress tolerance and maternal behavior.(2)Identification of a novel first exon of rat prolactin receptor gene and regulation of the prolactin receptor gene expression in the liver by sex steroid hormonesIn addition to the known four first exones, E1-1,E1-2,E1-3 and E1-4, another first exon, E1-5,was identified in the rat prolactin receptor gene. Analysis of expression of each first exon in the liver revealed that sex steroid hormones specifically regulate the expression of E1-2 first exon(3)Mechanism of brain-specific regulation of prolactin receptor gene expression in the ratThe brain-specific exon 1,E1-4,was found to localize between exons 2 and 3 of rat prolactin receptor gene, and analysis of expression of each first exon in the brain revealed that induction of prolactin gene expression during development depends on the expression of E1-4.