Role of Sex Steroids on the Survival, Neuritic Outgrowth of Neurons, and Dopamine Neurons in Cultured Preoptic Area and Hypothalamus

Morphological sex differences in some discrete brain regions are thought to be developed by the influence of circulating androgen during the perinatal period. In order to know whether the effect of androgen is a direct one, cells derived from neonatal rat preoptic area (POA) and/or hypothalamus were cultured in a serum-free medium, and the effects on survival, process growth of neurons, and dopaminergic function were examined. When the POA cells were exposed to testosterone (T), neuronal survival was greater than the controls, and the frequency distribution of total process length and the number of process branchings were significantly deviated from the controls. Estradiol-17β (E₂) and 5α-dihydrotestosterone had less significant effects on these parameters than T. Moreover, the addition of T increased the dopamine (DA) contents of cells and medium DA in the hypothalamic culture. E₂ also greatly increased DA content of the medium. These steroids failed to alter the DA levels in the POA cell cultures. These results generally conform to the notion of previous investigators that T has direct effects on the expansion of dendritic elements of the POA and the development of sex difference in the hypothalamic DA neurons, although the effect of T after conversion to E₂ cannot be excluded.