Effects of androgens and estrogens on sexual differentiation of sex behavior, scent marking, and the sexually dimorphic area of the gerbil hypothalamus.

Mating, marking and the sexually dimorphic area (SDA) were studied in male gerbils that were castrated or sham-operated on the day of birth and in females given testosterone (T) propionate or oil 1 day later. Other females received dihydrotestosterone (DHT), R1881, estradiol benzoate (EB), R2858, DHT and EB, or DHT and R2858. Females and control males were castrated as adults. Then half of each group was given T and tested for marking and male sex behavior. They were still exposed to T at perfusion. The rest were given EB and progesterone and were tested for marking and lordosis. They were perfused 1 month after hormone treatment ended. Neonatal castration eliminated mounting, decreased T-induced marking and increased lordosis in males. Neonatal exposure to TP decreased lordosis and increased mounting, intromission patterns and T-induced marking in females. DHT and R1881 did not affect marking or mating when given alone. EB and R2858 decreased lordosis and increased mounting. DHT enhanced the former effect but not the latter. Only combined treatments increased T-induced marking. Total SDA volume was not affected by neonatal treatments, but "dark volume" was largest in control males. The SDA pars compacta (SDApc) was seldom seen in females unless they received steroid neonatally but was present in males that were castrated neonatally. SDApcs of neonatal castrates and steroid-treated females differed, though, from SDApcs of control males in that they were smaller in the absence of T and did not enlarge when exposed to T. Another cell group, the cmSDApc, was affected by T neonatally but was not seen consistently in either sex. SDApc volume correlated positively with T-induced marking and an index of male sex behavior. Both SDApc and cmSDApc volumes correlated negatively with lordosis. The correlations with marking and male sex behavior probably reflect constraints on sexual differentiation rather than causal relationships since these behaviors persist when the SDApc is gone. The effects of direct manipulations of the SDApc on lordosis have not been studied.