ABSTRACT: To determine the global changes in hypothalamic gene expression that may occur at the time of female puberty in this species, animals were euthanized at three different stages, juvenile (25-days of age), early puberty (30-35 days of age) and on the day of the first proestrus (32-37 days of age). According to criteria previously established (Ojeda,S.R.; Urbanski,H.F. Puberty in the rat pp.363-409. The Physiology of Reproduction, 2nd Edition, Vol 2. Edited by Knobil,E.; Neill,J.D. Raven Press, 1994), 25-day-old animals are in the mid- juvenile phase of prepubertal development (JUV). At this time, the vagina is not yet patent and the uterine weight is 60 mg or less, with no accumulation of intrauterine fluid. Older rats showing a closed vagina, accumulation of intrauterine fluid and an uterine weight less that 180 mg are considered to be in the early proestrous (EP) phase of puberty. Finally, rats still exhibiting a closed vagina, but showing a uterus ballooned with fluid and a uterine weight of at least 200 mg are considered to be in late proestrus (LP), i.e., the phase of puberty when the first preovulatory surge of LHRH and gonadotropins takes place. The first ovulation occurs the following day. All animals were sacrificed between 1600-1700 h, and the medial basal hypothalamus (MBH) was immediately dissected, as previously described (Rogers,L.C.; Junier,M-P.; Farmer,S.R.; Ojeda,S.R. A sex-related difference in the developmental expression of class II -tubulin messenger RNA in rat hypothalamus. Mol.Cell.Neurosci., 2: 130-138, 1991) and stored in RNAlater according to manufacturer’s instructions. Keywords: comparison between Early pubertal and Juvenile or Late pubertal and Juvenile stages of sexual development in the female rat
