ON THE ORIGIN OF STRIATAL CHOLECYSTOKININ RELEASE - STUDIES WITH IN-VIVO MICRODIALYSIS

In the present study, extracellular levels of the neuropeptide cholecy stokinin (CCK), of the monoamine dopamine and its metabolites 3,4-dihy droxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA), and of th e excitatory amino acids glutamate and aspartate were simultaneously m onitored by microdialysis in the neostriatum of halothane-anesthetized rats under basal and K+-depolarizing conditions. Extracellular CCK an d dopamine levels, but not glutamate and aspartate levels, were decrea sed by perfusion with a Ca2+-free medium, under both basal and K+-depo larizing conditions. HPLC revealed that the majority of the CCK-like i mmunoreactivity in the perfusates coeluted with CCK octapeptide. Stria tal extracellular CCK levels were decreased by decortication plus call osotomy, with a parallel decrease in glutamate levels. Striatal extrac ellular levels of dopamine, DOPAC, and HVA were significantly decrease d in animals treated previously with a unilateral B-hydroxydopamine in jection into the medial forebrain bundle. In these animals, however, t he effect of decortication plus callosotomy on CCK and glutamate level s was not further augmented. Thus, this study supports the hypothesis of a neuronal origin of extracellular CCK and dopamine monitored with microdialysis in the striatum of the rat, and also supports the idea o f a partly contralateral origin of corticostriatal CCK and glutamate i nputs.