CHOLECYSTOKININ-INDUCED ACTIVITY CHANGES OF DORSAL LATERAL GENICULATENEURONS IN RATS

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.