Progesterone enhances L-dopa-stimulated dopamine release from the caudate nucleus of freely behaving ovariectomized-estrogen-primed rats.

In the present experiment we examined the effect of progesterone upon dopamine (DA) release induced by a direct infusion of unlabeled L-dihydroxyphenylalanine (L-DOPA) into the caudate nucleus of freely behaving rats. Ovariectomized rats were implanted with a push-pull cannula directed at the caudate nucleus and subjected to perfusion under 3 different hormonal conditions: (1) following 4 days of treatment with estradiol benzoate (EB), (2) following 4 days of treatment with estradiol benzoate plus progesterone at 4-6 h prior to perfusion (EB + P-4-6 h) and (3) following 4 days of treatment with estradiol benzoate plus progesterone at 28 h prior to perfusion (EB + P-28 h). During each perfusion session and under each of the 3 hormonal treatment conditions, L-DOPA was infused through the push side of the cannula. Three increasing doses of L-DOPA (10(-6), 10(-5) and 10(-4) M) were infused with a 45-75 min interval between infusions. Regardless of hormonal treatment condition, a clear dose-response increase in DA and 3,4-dihydroxyphenylacetic acid (DOPAC), but not 5-HIAA, output was observed in response to the increasing doses of L-DOPA infusion. For each of the 3 doses of L-DOPA, maximal DA output was observed for animals tested under the EB + P-4-6 h hormonal condition, with statistically significant differences in the areas under the L-DOPA-stimulated DA response curves obtained following the 10(-6) and 10(-5) M doses of L-DOPA infusion.(ABSTRACT TRUNCATED AT 250 WORDS)