Effects of estrogen on cognitive strategy and striatal dopamine transmission in female rats : the role of reproductive experience

Estrogen (E) influences the cognitive strategy used by female rats when solving a maze. Nulliparous rats with high levels of E tend to use an allocentric (place) strategy whereas rats with low E levels are biased towards an egocentric (response) strategy. Furthermore, striatal-dependent response learning is sensitive to dopamine (DA) transmission in that brain area, and E changes DA release in the striatum. Recent findings suggest that reproductive experience may alter how E affects DA transmission. Here the effects of E on cognitive strategy was explored in nulliparous and primiparous rats solving at-maze task, and striatal DA release was measured after administration of an indirect DA agonist (amphetamine; 0.5 & 1 mg/kg) and an autoreceptor-activating dose of the DA agonist (apomorphine; 50 & 80 og/kg). As expected, ovariectomized (OVX) nulliparous rats receiving low 17Ý estradiol (E2) predominantly used a response strategy, whereas high E2 OVX rats did not; this pattern changed in low E2 primiparous rats. High E2 rats receiving the lower AMPH dose exhibited greater DA release than low E2 rats. Interestingly, there were also hemispheric differences in striatal DA response, which suggests possible lateralization in DA function. These findings suggest that parity changes how E affects the cognitive strategy used by females. They also show that E2 affects DA transmission in the dorsal striatum in a lateralized manner