Expression pattern of Tau in the rat brain during pregnancy and the beginning of lactation.

Pregnancy involves changes in brain function that implicate a re-organization in neuronal cytoskeleton. We analyzed the content of the microtubule associated protein Tau (65kDa isoform) and its phosphorylated form (PhosphoTau) in several rat brain regions throughout pregnancy and on day 2 of lactation by Western blot. In hypothalamus the content of Tau increased on days 2 and 18 of gestation compared with days 14, 21 and in lactation. PhosphoTau content increased throughout pregnancy. In preoptic area Tau content did not show significant changes throughout pregnancy or lactation, however, the content of PhosphoTau presented a decrease on day 21 of gestation. In hippocampus Tau content decreased on day 14 until day 21 compared with day 2 of gestation, however, in lactation day 2 the content of Tau increased meanwhile PhosphoTau content progressively increased throughout pregnancy. In frontal cortex Tau content decreased on day 21 of gestation compared with days 2, 14 and 18, with an increase in lactation, whereas PhosphoTau did not show significant changes. In cerebellum Tau protein decreased on days 14, 18 and 21 of pregnancy with an increase in lactation. PhosphoTau content increased throughout pregnancy and on day 2 of lactation. PhosphoTau/Tau ratio changes in each brain area along pregnancy and in lactation. Our data suggest that Tau expression and its phosphorylation pattern change in a tissue-dependent manner throughout pregnancy and the beginning of lactation in the rat brain.

Effects of RU486 in the expression of progesterone receptor isoforms in the hypothalamus and the preoptic area of the rat during postpartum estrus.

In several mammalian species females undergo postpartum estrus, a brief period of ovulation and sexual receptivity that in rats usually occurs during the first 24h following parturition. The maximal lordotic expression occurs at 12h after the initiation of parturition and depends on intracellular progesterone receptor (PR). We studied the regulation of PR expression by its antagonist, RU486 in the hypothalamus and the preoptic area of the rat during postpartum estrus by Western blot. Adult female rats were treated with RU486 (1.25 and 5mg) 3h after parturition, and Western blot was performed to assess the expression of PR-A and PR-B at 12h postpartum. RU486 (1.25 and 5mg) reduced the expression of PR-A (63% and 95%) and that of PR-B (75% and 99%), respectively in the preoptic area whereas it had no effects in the hypothalamus. These results suggest a differential regulation of PR expression in the rat brain during postpartum estrus.

Role of progesterone receptors during postpartum estrus in rats.

We studied the role of progesterone receptor (PR) in the display of female sexual behavior during postpartum estrus in rats. Adult female rats were treated with the PR antagonist, RU486 (1.25 and 5 mg), 3 h after parturition and sexual behavior was evaluated throughout the first postpartum day. Estradiol and progesterone serum levels changed during the first 24 h postpartum. The highest estradiol and progesterone levels were found at 9 and 12 h postpartum, respectively. The predominant PR isoform in the hypothalamus and the preoptic area was PR-A during postpartum day. The content of PR-A increased at 6 h postpartum in the hypothalamus and the preoptic area, and decreased in both regions at 9 h. PR-B content only increased in the preoptic area at 12 h postpartum. The highest display of lordotic and proceptive behaviors were found at 12 h postpartum. The treatment with 1.25 and 5 mg of RU486 respectively reduced lordosis by 61% and 92% at 12 h postpartum. These results suggest that PR is essential in the display of postpartum estrus in rats.