The effects of iontophoretically applied cholecystokinin fragments and
cholecystokinin antagonists on neurons of the dorsal lateral genicula
te nucleus were investigated with extracellular recordings in rats ane
sthetized with urethane. The peptide cholecystokinin-8S, which has aff
inity for both cholecystokinin-A and -B receptors, altered the baselin
e firing as well as the responses to visual stimuli of about one half
of the investigated neurons (90 out of 190). Excitatory effects predom
inated (P < 0.01, Wilcoxon test), although inhibitory effects were als
o observed. The effects of cholecystokinin-8S were dose-dependent. Neu
rons sensitive to cholecystokinin-8S could be found in all regions of
the dorsal lateral geniculate nucleus, but they differed in their susc
eptibility to cholecystokinin in relation to their location. The B-ago
nist, BOC-cholecystokinin-4, also changed the baseline firing as well
as the light-evoked activity of dorsal lateral geniculate nucleus neur
ons. The effects were either excitatory or inhibitory. Changes induced
by cholecystokinin-8S could be effectively blocked by the cholecystok
inin-B antagonist; CAM 1028 (19 out of 22 cholecystokinin-sensitive ne
urons tested); The cholecystokinin-A antagonist, Ge 410, blocked chole
cystokinin-induced effects in 10 out of 16 neurons. These results indi
cate that the modulation of geniculate cell firing by cholecystokinin
is mediated by both A-and B-receptor types.