t" ~ NHIIIISgtK[ LLTTEKS ELSEVIER Neuroscience Letters 180 (1994) 155-158 ...... Quantitative microdialysis determination of extracellular striatal dopamine concentration in male and female rats: effects of estrous cycle and gonadectomy Li Xiao a'b, Jill B. Becker a-~'* aPsychology Department, bReproductive Sciences Program and CNeuroscience Program, University of Michigan, Ann Arbor, MI, USA Received 29 June 1994; Revised version received 25 August 1994; Accepted 25 August 1994 AMtract Sex differencesin basal extracellular striatal dopamine concentrations in gonadectomizedmale and female rats have been reported previously. In the current experiment, estrous cycle-dependent variation, sex differencesand the effect of gonadectomy on extracel- lular striatal dopamine concentrations were determined using quantitative microdialysis.Female rats were found to have significantly higher extracellular striatal dopamine concentrations in proestrus and estrus than in diestrus or after ovariectomy. In contrast, castration of male rats had no effect on extracellular striatal dopamine concentrations. Thus, endogenous ovarian hormones, but not testicular hormones, modulate extracellular striatal dopamine concentrations in rats. Key words: Estrous cycle; Ovariectomy; Castration; Ovarian hormone; Extracellular striatal dopamine; Quantitative microdialysis Ovarian hormones have been shown to modulate be- havioral and neurochemical indices of activity in the nigrostriatal dopamine (DA) system. For example, DA agonist-stimulated behaviors, such as rotational behav- ior, general activity and stereotypy, vary with the estrous cycle [1-7,13,18]. Female rats in estrus exhibit less gen- eral activity and greater intensity of stereotyped behavior after amphetamine (AMPH) treatment than do animals in diestrus [4]. Estrous females also show a greater num- ber of AMPH-induced rotations than do animals 24 h later on the 1 st day of diestrus [7]. Ovariectomy (OVX) attenuates rotational behavior induced by AMPH, com- pared with the response of estrous females, and estrogen treatment in OVX rats potentiates AMPH-induced rota- tional behavior [1,2]. The hormonal modulation of AMPH-induced behav- iors in female rats is correlated with changes in striatal DA release. AMPH-induced DA release from striatal tissue in vitro varies with the phase of the estrous cycle *Corresponding author. Address. Neuroscience Laboratory Building, 1103 East Huron Street, Ann Arbor, MI 48104-1687, USA. Fax: (11 (313) 936-2690. E-mail: JBBecker@umich.edu 0304-3940/94/$7.00 © 1994 Elsevier Science Ireland Ltd. All rights reserved SSDI 0304-3940(94)00671-7 [4,5], OVX attenuates AMPH-induced DA release [5] and estrogen treatment enhances AMPH-induced DA release from striatal tissue in vitro [2]. Studies using in vivo microdialysis also find that AMPH-stimulated DA release in striatum is enhanced on estrus compared with other days of the female rat's estrous cycle [4] and a single estrogen treatment enhances striatal DA release induced by AMPH 30 rain later [1,10]. By contrast, cas- tration (CAST) of male rats either has no effect or en- hances striatal DA-mediated behaviors [9,11] and AMPH-induced striatal DA release [5]. In a previous study, when CAST and OVX rats were compared, there was a sex difference in basal DA con- centrations in striatum determined by in vivo quantita- tive microdialysis [10]. CAST males had significantly higher basal striatal DA than OVX females. The current experiment examines whether there are sex differences in the extracellular striatal DA concentrations in intact male and female rats and whether there is estrous cycle- dependent variation in extracellular striatal DA concen- trations in female rats. To answer these questions, the present experiment applied the quantitative in vivo mi- crodialysis technique (the 'no net flux' method [14,15]) to examine extracellular striatal DA concentrations in