Differentiation of hypothalamic GABAergic neurons in vitro: absence of effects of sex and gonadal steroids.

The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is involved in the control of sexually dimorphic brain functions, such as pituitary secretion and reproductive behavior. Hypothalamic GABAergic systems in vivo exhibit sexually dimorphic functional properties. Sexual dimorphisms in the rat brain are currently thought to be brought about by the organizational influence of gonadal steroids during the perinatal developmental period. The present study is concerned with the question of whether developing hypothalamic GABAergic neurons are primary targets of sex hormones. Since it is impossible to distinguish direct from indirect effects of experimental manipulations of the hormonal environment of the in vivo brain, sex-specific primary cultures raised from embryonic day 14 rat diencephalon and cultured for up to 8 days in vitro (DIV) were used as a model system. Effects of sex steroids were investigated on high affinity uptake of [3H]GABA. GABA transport was already mature at 3 DIV. [3H]GABA uptake was sensitive to inhibition by nipecotic acid and the transmitter was taken up by high affinity transport (Km = 15.2 microM). Immunocytochemical preparations demonstrated extensive networks of GABA-immunoreactive fibers at 8 DIV. Concomitantly with the outgrowth of neurites, there was a marked increase in maximum uptake velocity (Vmax). No differences could be detected regarding cell numbers or uptake kinetics between cultures from male and female donors. Neither cell numbers nor GABA uptake were affected by short- and long-term treatment with estradiol-17 beta or testosterone. It appears that hypothalamic GABAergic neurons in vitro do not develop sex differences in cell numbers or GABA transport.(ABSTRACT TRUNCATED AT 250 WORDS)