COMPARATIVE DOPAMINE-ACETYLCHOLINE INTERACTIONS IN THE VENTRAL AND DORSAL STRIATUM OF RABBIT AND RAT-BRAIN

The dopamine (DA)-acetylcholine (ACh) interactions were investigated i n dorsal (nucleus caudate, NC) and ventral (olfactory tubercle, OT) st riatal regions, of rats and rabbits. Both regions receive a dense dopa minergic innervation and have high ACh concentrations. Brain slices of NC and OT from both animal species were prelabeled with [H-3]choline and superfused. In rat and rabbit OT and NC, higher ACh release per pu lse was elicited by lower than higher stimulation frequencies; in addi tion, rabbit tissues released a greater fraction of tissue [H-3]transm itter than rat tissues. Blockade of D-2 DA-receptors with sulpiride (1 mu M), did not modify ACh release in OT and NC of rats and rabbits; s uggesting that the lower ACh release observed in rat tissues is not du e to an inhibitory dopaminergic tone on cholinergic neurons. Apomorphi ne (APO), a D-2 DA-receptor agonist, inhibited in a concentration-depe ndent manner the evoked release of ACh from rat and rabbit NC (maximal inhibition = 90%). In rabbit OT, maximal inhibition induced by APO wa s 49 +/- 2% and in the rat OT, it was 23 +/- 1%. Sulpiride antagonized APO-induced inhibition of ACh release from rat and rabbit NC; however , it failed to prevent APO-induced inhibition in rat OT, and in the ra bbit OT reduced it from 47% to 20 +/- 5%. These results indicate diffe rences in the wiring of DA and cholinergic neurons and terminals in do rsal and ventral striatal structures, as well as between rat and rabbi t tissues. Cholinergic ventral striatal structures may not receive a d irect DA input, and afferent cholinergic nerve terminals (rather than interneurons) predominate in the ventral striatum.