INTERACTION OF CHOLECYSTOKININ AND GLUTAMATE AGONISTS WITHIN THE DLGN, THE DENTATE GYRUS, AND THE HIPPOCAMPUS

The interaction of sulfated cholecystokinin (CCK-8S) with excitatory a mino acids (EAA) was studied on single units of the dorsal lateral gen iculate nucleus (dLGN), the dentate gyrus, and the hippocampal CA3 reg ion in rats anaesthetized with urethane. lontophoretic co-administrati on of small, individually ineffective currents of CCK-8S and kainic ac id or N-methyl-D-aspartate repeatedly elicited an increase of the disc harge rate in nearly all geniculate and half of the dentate neurons bu t not in those of the CA3 region. The effect could be reduced by the C CKB receptor antagonist PD 135,158 more often than by the CCKA antagon ist KL 1001. The inreased firing due to co-administration of CCK and k ainate could also be suppressed by the non-NMDA antagonist CNQX but no t by the NMDA antagonists CPP or AP-5, which were otherwise able to pr event the neuron from responding to co-administration of CCK and NMDA. It is suggested that in distinct brain regions the effectivity of the ''low level'' EAA transmission may be enhanced by small amounts of CC K-8S. This is thought to be mediated by a coactivation of CCK and EAA receptors.