The present study investigated the effects of agonists of the neuropep
tide cholecystokinin (CCK) on neostriatal neurons in order to confirm
the existence of CCK-A receptors in the rat caudate-putamen. Single un
it activity was recorded in rats anaesthetized with urethane. The CCK-
A receptor agonists A-71378 -Tyr(SO3H)-Nle-Gly-Trp-Nle-(N-methyl)Asp-P
he-NH2), and A-71623 ys(epsilon-N-2-methylphenylamino-carbonyl)-Asp-(N
- methyl)Phe-NH2, as well as the CCK-B receptor agonist Suc-CCK-4 (Suc
-Trp-(N-methyl)Nle-Asp-Phe-NH2) were iontophoretically administered wi
th multibarrel capillaries. About one-third of the neurons responded t
o the CCK-A receptor agonists. Excitatory effects predominated. The CC
K-B receptor agonist also induced mainly increases in the neuronal fir
ing. Several neurons were affected by both types of agonists. The resu
lts suggest that in the rat neostriatum not only CCK-B receptors, but
also CCK-A receptors seem to mediate the effects of cholecystokinin.