CHOLINERGIC MODULATION OF NEURONAL RESPONSES TO CHOLECYSTOKININ IN ANESTHETIZED RATS

The aim of this study was to investigate whether the effects of the ne uropeptide cholecystokinin on neuronal firing can be changed by acetyl choline in various structures of the brain. Single unit activity was e xtracellularly recorded in rats anesthetized with urethane, The neuron s were located in several nuclei of the thalamus, the basal ganglia an d the cerebral cortex. Neurons responding to the sulfated octapeptide of cholecystokinin (CCK-8S) were mainly activated by the drug [Wilcoxo n test (Wt) p < 0.0001, n = 113]. Thalamic neurons could also increase the number of burst discharges (Wt p < 0.005, n = 39). Iontophoretica lly administered acetylcholine could reduce the activating effects of CCK-8S on firing and burst discharges. In its presence, even inhibitor y effects of CCK-8S predominated (Wt p < 0.0001, n = 113), The suppres sive action seemed not to depend on the direction of the effect of ace tylcholine itself and concerned neurons of all locations studied. Atro pine could diminish or block the suppressive action of acetylcholine. In the presence of both drugs, CCK-8S mainly activated the neurons (Wt p < 0.005, n = 43), Atropine itself did not significantly change the responses to CCK-8S (Wt p > 0.05), It can be concluded that cholecysto kinin may reduce neuronal firing instead of increasing it during activ ation of the cholinergic system. (C) 1998 Elsevier Science Inc.