CHOLECYSTOKININ EXCITES NEOSTRIATAL NEURONS IN RATS VIA CCKA OR CCKB RECEPTORS

The effect of iontophoretically applied cholecystokinin (CCK) on neuro ns of the neostriatum was studied in rats anaesthetized with urethane. The most frequently observed effect of the sulphated octapeptide (CCK -8S) on striatal neurons was excitation. Spontaneously active neurons responded more often to CCK-8S than quiescent cells. Silent, primarily non-responsive neurons could often be stimulated with CCK-8S using gl utamate to induce an ongoing discharge. Thus, 45.8% of the 177 neurons studied changed their discharge rate by more than 30%, Certain CCK re ceptor antagonists could prevent the effect of CCK-8S, fully or at lea st partly, in the majority of CCK-responsive neurons. The data suggest that cholecystokinin modulates the firing of active neostriatal neuro ns via the CCKA or the CCKB receptor type. Furthermore, we compared ne uronal responses to glutamate with those recorded during concomitant a dministration of CCK-8S in order to study the interaction of both tran smitters, which may be colocalized in striatal afferents, CCK-8S mainl y enhanced the excitatory effect of glutamate on striatal neurons, but in several neurons the response to glutamate was reduced. The CCKB re ceptor antagonist could prevent CCK-8S from increasing the glutamate-i nduced activation.