Cholecystokinin affects the neuronal discharge mode in the rat lateral geniculate body

Neurons of the dorsal lateral geniculate body (dLGB) discharge either continuously with single spikes or in bursts, that is, groups of action potentials with an interspike interval < or = 4 ms. The influence of the sulphated octapeptide of cholecystokinin (CCK-8S) on the discharge mode of dLGB neurons was studied in rats anesthetized with urethane. Unit activity was recorded during repeated stimulation with diffuse light. The occurrence of bursts was determined during control conditions and during iontophoretic administration of CCK-8S and its antagonists. CCK-8S frequently increased the number of bursts. The percentage of spikes involved in bursts was mainly augmented in neurons that responded after short latency to light or were excited by light-off. It was predominantly reduced in units responding to light after long latency with a primary excitation. CCKA receptors seem to contribute to burst induction, since CCK-8S reduced bursting in the presence of the CCKA receptor antagonist Ge 410 and increased bursting when applied with the CCKB receptor antagonist PD 135,158. These bursts were frequently related to light stimuli.