SEX-DIFFERENTIATION OF RAT HIPPOCAMPAL GABAERGIC NEURONS

In order to analyse mechanisms of sex differentiation of the hippocamp us at the cellular level, the differentiation of hippocampal GABAergic neurons was studied in vitro. Serum-supplemented and serum-free disso ciated cell cultures were raised from the hippocampus of embryonic day 17 male and female rat embryos for up to 14 days in vitro. This time period roughly corresponds to the critical phase for sex differentiati on of the rat brain as determined in vivo. Serum-free cultures were tr eated with testosterone and/or 17 beta-oestradiol for the entire cultu re period. Control cultures from male donors contained twice as many G ABA-immunoreactive neurons as those from female donors, while there wa s no sex difference in overall counts of neurons stained for microtubu le-associated protein 5. Measurements of high-affinity uptake of [H-3] GABA essentially confirmed this sex difference. The development of the sex difference could not be influenced by long-term treatment with an drogen or oestrogen. it is concluded that sex differentiation of a spe cific subpopulation of hippocampal neurons may take place independentl y of the environment provided by gonadal steroids and in the absence o f extrinsic connections with the hypothalamus or other relays of the l imbic circuit.