BILATERAL CHANGES IN STRIATAL DOPAMINE METABOLISM AFTER UNILATERAL INTRACAROTID AND INTRASTRIATAL ADMINISTRATION OF APOMORPHINE

Following cannulation of the common carotid artery of female Sprague-D awley rats, 3 mu Ci (10 mu g) of [H-3]apomorphine were infused. At var ious time intervals, drug concentrations were determined in the right and left striata, anterior forebrains, posterior forebrains and cerebe lla. One minute following intracarotid infusion of apomorphine, approx imately a 65-fold right/left difference in apomorphine concentrations was attained in all forebrain structures, and this difference steadily diminished with time as a result of declining drug levels in the infu sed hemisphere. The concentrations of dopamine and its metabolites (DO PAC, HVA and 3-MT) were quantified by gas chromatography-mass spectrom etry in the right and left striata at 5 and 15 min after unilateral in tracarotid infusion of 1 mu g apomorphine. At both time intervals and regardless of the side infused, the metabolites of dopamine increased ipsilateral to the side of infusion. Moreover, 3-MT levels were signif icantly decreased in the contralateral striatum. After direct intrastr iatal injection of either 0.1 or 1.0 mu g apomorphine into the right s triatum, the levels of dopamine metabolites were again increased in th e ipsilateral striatum. 3-MT levels were also decreased significantly in the left striatum. In contrast to the effects observed after system ic administration of apomorphine, these results demonstrate that dopam ine release in the striatum is increased by selectively delivering hig her concentrations of apomorphine to the nerve terminals of the nigros triatal neurons. The effects of unilateral apomorphine on dopamine met abolism in the contralateral striatum are most likely the effect of in terhemispheric communication.