Bimodal effect of progesterone on in vitro dopamine function of the rat corpus striatum

In the present experiment we examined the temporal effects of progesterone (P) upon in vitro dopamine (DA) release from superfused corpus striatum (CS) and medial basal hypothalami (MBH) tissue fragments. In ovariectomized-estrogen-primed adult female rats, P was systemically administered at 0.5, 2, 4, 12 or 24 h prior to sacrifice for CS and at 4 or 24 h for MBH superfusions. Control groups receiving either steroid alone and/or the oil vehicle were included. Progesterone at the 2- to 12-hour periods stimulated spontaneous and amphetamine-evoked DA release and increased post-superfusion tissue concentrations of DA from the CS when compared to controls. At 24 h P apparently produced an active inhibition, with all parameters of DA activity (spontaneous and AMPH-induced DA release), significantly decreased compared to controls. In contrast, P failed to alter the spontaneous or marginal amphetamine response of the MBH but did significantly reduce post-superfusion DA concentration at 24 h. We hypothesize that the dual effect of P upon brain dopaminergic systems (facilitation followed by inhibition), in the CS but not in the MBH represents changes in DA synthesis and release which are coupled in the CS but not in the MBH.