The striato-nigro-collicular pathway and explosive running behaviour: functional interaction between neostriatal dopamine and collicular GABA.

The nature of the functional interaction between neostriatal dopamine activity and collicular GABA activity was studied. To this end we analyzed the ability of apomorphine injections into the neostriatum (50-500 ng/0.5 microliters per side) to reinitiate explosive running behaviour in rats pretreated with a subthreshold dose of picrotoxin into the colliculus superior (30-80 ng/0.5 microliters per side). Apomorphine was found to reinitiate the former behaviour dose dependently and its effect could be antagonized by a very low dose of neostriatally applied haloperidol (250 ng/0.5 microliters per side). It was possible to delineate the most critical region within the structures studied. Evidence is presented in favour of the previously reported hypothesis that increasing dopaminergic neostriatal activity within the terminal region of the nitrostriatal pathway results in a decreasing GABAergic activity within the terminal region of the GABAergic striato-nigro-collicular pathway.