Differences in reserpine-induced striatal dopamine output and content between female and male mice: Implications for sex differences in vesicular monoamine transporter 2 function

Abstract

In this report a series of six in vitro experiments in which reserpine-evoked dopamine output and two in vivo experiments in which the effects of reserpine injections upon dopamine content from striatal tissue of female and male mice were performed as a means to assess possible sex differences in vesicular monoamine transporter 2 (VMAT2) function. Significantly greater amounts of dopamine were obtained from striatal tissue of female mice in response to either a brief (experiment 1) or continuous (experiment 2) infusion of reserpine. Similarly, reserpine-evoked dopamine output from striatal tissue of gonadectomized females was significantly greater that that of gonadectomized males (experiment 3). When reserpine-evoked dopamine responses were compared directly between intact versus gonadectomized females (experiment 4) or males (experiment 5) no statistically significant differences were obtained. Finally, comparisons of gonadectomized females treated or not with estrogen revealed no statistically significant differences in reserpine-evoked dopamine output (experiment 6). Injections of reserpine produced significantly greater depletions of striatal dopamine content within intact female versus male mice (experiment 7). Dopamine contents of gonadectomized females treated or not with estrogen did not differ following treatment with reserpine, but were significantly greater than that of gonadectomized males (experiment 8). Taken together, these results show that female striatal tissue is more responsive to reserpine-evoked dopamine output, and this sex difference appears to be estrogen independent. Similarly, the dopamine depleting effects of reserpine are greater in intact female mice, however, gonadectomy reverses this effect in an estrogen independent manner. The data suggest that female mice may have a greater amount/activity of VMAT2 function as revealed by the increased responsiveness to the VMAT2 blocking drug, reserpine. Such differences in VMAT2 function may be related to the gender differences observed in conditions like Parkinson's disease and drug addiction.