Contribution of voltage-gated Ca2+ channels to homosynaptic long-term depression in the CA1 region in vitro.

Homosynaptic long-term depression (LTD) of synaptic efficacy was induced in field excitatory postsynaptic potentials by administration of 900 pulses at either 1 or 3 Hz in 2- to 3-wk-old Sprague-Dawley rats. The stimulation was administered via a bipolar stimulating electrode placed immediately adjacent to the recording electrode in the stratum radiatum region of the hippocampal CA1 subfield. Equivalent LTD induction occurred whether the slices were maintained at room temperature or at 32 degrees C. Lowering bath Ca2+ to 0 mM, or increasing it to 4 mM, prevented the induction of the depression. The NMDA receptor antagonist D,L-2-amino-5-phosphonovaleric acid (50 microM) reversibly blocked the induction of homosynaptic LTD. In addition, the L-type voltage-gated calcium channel (VGCC) antagonist nimodipine (10 microM) and the R- and T-type VGCC antagonist NiCl2 (25 microM) also prevented homosynaptic LTD induction. These results indicate that in addition to N-methyl-D-aspartate receptor activity, Ca2+ influx via VGCCs can play an important role in the induction and expression of LTD induced by low-frequency stimulation in the hippocampal formation.