Progesterone Receptor Gene and Protein Expression in the Anterior Preoptic Area and Hypothalamus of Defeminized Rats Isabel Arrieta, 1 Leticia Berenice Dı ´az-Iba ´n ˜ ez, 1 Teresa Morales, 2 Luciano Mendoza-Garce ´ s, 1 Sumiko Morimoto, 3 Norma Moreno-Mendoza, 4 Marco A. Cerbo ´n 1 1 Departamento de Biologı´a, Facultad de Quı´mica, Universidad Nacional Auto ´ noma de Me ´ xico, 04510 Me ´ xico D.F., Me ´ xico 2 Centro de Neurobiologı´a, Universidad Nacional Auto ´ noma de Me ´ xico, Campus UNAM-UAQ, 76230 Juriquilla, Qro., Me ´ xico 3 Departamento de Biologı´a de la Reproduccio ´ n, Instituto Nacional de Ciencias Me ´ dicas y Nutricio ´n Salvador Zubira ´ n, 14000 Me ´ xico D.F., Me ´ xico 4 Instituto de Investigaciones Biome ´ dicas, Universidad Nacional Auto ´ noma de Me ´ xico, 04510 Me ´ xico, D.F., Me ´ xico Received 22 November 2002; accepted 3 March 2003 ABSTRACT: Progesterone receptor (PR) plays an important role during sexual differentiation of the rat brain. The objective of the present study was to deter- mine PR protein and gene expression pattern in preop- tic-anterior hypothalamic area (POA-AHA) and hypo- thalamus (HYP), after estradiol or testosterone treatment during the postnatal critical period of sexual differentiation of the rat brain (defeminized animals). Three-day-old female rats were subcutaneously (s.c.) injected with a single dose of 17-estradiol (200 g), or testosterone enanthate (200 g), or vehicle (corn oil). POA-AHA and HYP were dissected 3 h, 24 h, and 14 days, as well as on the day of vaginal opening (VO) after treatments. Other animals, previously treated as above, were acutely injected with 17-estradiol (5 g) on the day of VO; POA-AHA and HYP were obtained 3 h later. Total RNA was extracted and processed for semiquan- titative RT-PCR and tissue slices were prepared for protein detection by immunohistochemistry. We ob- served that PR mRNA expression was increased in POA-AHA and HYP of the animals treated with estra- diol or testosterone 3 hours after treatments, compared with the vehicle-treated control group. We also found a significant increase in PR mRNA and protein expression in POA-AHA and HYP on the day of VO in both estra- diol and testosterone defeminized rats. Interestingly, the acute administration of estradiol on the day of VO (VO  E 2 ) did not increase PR mRNA or protein expression in POA-AHA and HYP of either estradiol or testoster- one defeminized animals, as opposed to the marked induction observed in the intact animals of the control group. The overall results suggest that estradiol and testosterone treatment during the postnatal critical pe- riod of sexual differentiation of the brain modifies the regulation of the PR mRNA and protein expression during early onset of maturity. © 2003 Wiley Periodicals, Inc. J Neurobiol 56: 338 –346, 2003 Keywords: sexual differentiation; defeminization; pro- gesterone receptor; brain differentiation; estradiol Correspondence to: M. Cerbo ´n (mcerbon85@hotmail.com or macer@servidor.unam.mx). Contract grant sponsor: CONACyT; contract grant number: 34861-N. Contract grant sponsor: PAIP, Facultad de Quı ´mica, Univer- sidad Nacional Auto ´noma de Me ´xico (UNAM). © 2003 Wiley Periodicals, Inc. DOI 10.1002/neu.10241 338