L-TYPE VOLTAGE-SENSITIVE CALCIUM-CHANNEL ANTAGONISTS BLOCK HETEROSYNAPTIC LONG-TERM DEPRESSION IN THE DENTATE GYRUS OF ANESTHETIZED RATS

We examined the role of dihydropyridine-sensitive Ca2+ channels in lon g-term potentiation (LTP) and long-term depression (LTD) in the dentat e gyrus of pentobarbital-anaesthetized rats. Intrahippocampal infusion s (1.0 mu 1) of nimodipine (20 mM) and nifedipine (20 mM), two antagon ists of L-type voltage-sensitive calcium channels (VSCC), 60 min prior to medial perforant path tetanization, completely blocked the appeara nce of LTD in the lateral perforant path, without significantly affect ing the simultaneous induction of medial path LTP. Heterosynaptic LTD was not significantly different from control animals following infusio ns of the L-type calcium channel agonist BAY-K8644 (1 mM). These resul ts suggest that L-type VSCC activity is necessary for the induction of heterosynaptic LTD in the dentate gyrus in vivo.