C-FOS EXPRESSION PATTERN IN THE HYPOTHALAMUS AND THE PREOPTIC AREA OFTHE RAT DURING PROESTRUS

c-fos gene expression in the hypothalamus, the preoptic area, the hipp ocampus and the frontal cerebral cortex of the rat was determined ever y two hours from 09:00 h to 19:00 h on the day of proestrus by using r everse transcription coupled to polymerase chain reaction. Rats under a 14:10 h light-dark cycle, with lights on at 06:00 h were used. We fo und a marked increase in c-fos gene expression in the studied regions but the hippocampus at 13:00 h, followed by a significant diminution i n the subsequent hours of proestrus day. The high expression of c-fos gene at 13:00 could be associated to the increase in estradiol seric l evels observed both at 11:00 h and at 13:00 h. Our results correlate w ith the increase in the number of FOS immunoreactive cells in some for ebrain areas in proestrus afternoon related to gonadotropin releasing hormone secretion.