The present study investigated whether acetylcholine, a transmitter of
striatal interneurons, modulates responses of neostriatal neurons to
agonists of the neuropeptide cholecystokinin (CCK). Single unit activi
ty was recorded in rats anesthetized with urethane. Acetylcholine and
CCK agonists (the CCKA receptor agonists A-71378 and A-71623; the CCKB
receptor agonist Suc-CCK-4) were iontophoretically administered alone
and in combination. The CCK agonists excited about one third of the n
eurons. The excitatory effects of both the CCKB and the CCKA receptor
agonists were mainly reduced or changed to suppression of activity by
acetylcholine (Wilcoxon test p < 0.001). Atropine did not significantl
y change the neuronal responses to the CCK agonists. The suppressive a
ction of acetylcholine could be diminished by additional administratio
n of atropine. The results suggest that the modulatory action of chole
cystokinin does not only depend on the actual state of excitability in
striatal neurons, but could be changed by acetylcholine released from
interneurons. (C) 1997 Elsevier Science Inc.