Experimental Studies on the Development of Sex Differences in the Release of Dopamine from Striatal Tissue Fragments in vitro

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Abstract
Sex differences have been reported in the amphetamine-stimulated release of dopamine from rat striatal tissue fragments in vitro. The present experiments were conducted to further investigate these sex differences. Employing an in vitro perifusion system, we examined the amphetamine-stimulated release of dopamine from striatal tissue of male and female rats: (1) at 4, 19, and 31 days of age; (2) as adults, after receiving hormone treatments neonatally that are known to alter the pattern of gonadotropin release, and (3) as adults, following postpubertal ovariectomy (OVX) or castration (CAST). There were no sex differences in dopamine release at 4, 19 or 31 days of age. Amphetamine elicited significant dopamine release from striatal tissue at all of these ages, regardless of the sex of the donor. There was significant amphetamine-stimulated dopamine release from striatal tissue obtained from both feminized males (CAST at day 2, tested as adults) and control males (CAST at day 15, tested as adults). Striatal tissue obtained from both androgenized females (500 µg testosterone propionate on day 2, OVX day 15, tested as adults) and control females (OVX day 15, tested as adults) also showed significant amphetamine-stimulated dopamine release. These later results are in marked contrast to the results obtained when female rats were ovariectomized postpubertally. Striatal tissue obtained from female rats, OVX as adults, fails to show significant dopamine release when stimulated with amphetamine. In adult OVX females, this attenuation of amphetamine-stimulated dopamine release is seen as early as 11 days after OVX and persists for at least 45 days. However, the effect of CAST in adult males does not differ from its effects in immature males. Striatal tissue obtained from adult males 45 days after CAST, shows significant amphetamine-stimulated release of dopamine. The experiments reported here confirm our previous results of a sex difference in the responsiveness of striatal tissue to amphetamine stimulation. We conclude that this sex difference in amphetamine-stimulated dopamine release from the striatum is not a function of the organizational effects of neonatal androgen exposure, but develops later in life, perhaps in association with puberty.