Comparative dopamine-acetylcholine interactions in the ventral and dorsal striatum of rabbit and rat brain

The dopamine (DA)-acetylcholine (ACh) interactions were investigated in dorsal (nucleus caudate, NC) and ventral (olfactory tubercle, OT) striatal regions, of rats and rabbits. Both regions receive a dense dopaminergic innervation and have high ACh concentrations. Brain slices of NC and OT from both animal species were prelabeled with [3H]choline and superfused. In rat and rabbit OT and NC, higher ACh release per pulse was elicited by lower than higher stimulation frequencies; in addition, rabbit tissues released a greater fraction of tissue [3H]transmitter than rat tissues. Blockade of D2 DA-receptors with sulpiride (1 microM), did not modify ACh release in OT and NC of rats and rabbits; suggesting that the lower ACh release observed in rat tissues is not due to an inhibitory dopaminergic tone on cholinergic neurons. Apomorphine (APO), a D2 DA-receptor agonist, inhibited in a concentration-dependent manner the evoked release of ACh from rat and rabbit NC (maximal inhibition = 90%). In rabbit OT, maximal inhibition induced by APO was 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 rabbit OT reduced it from 47% to 20 +/- 5%. These results indicate differences in the wiring of DA and cholinergic neurons and terminals in dorsal and ventral striatal structures, as well as between rat and rabbit tissues. Cholinergic ventral striatal structures may not receive a direct DA input, and afferent cholinergic nerve terminals (rather than interneurons) predominate in the ventral striatum.