RAPID COMMUNICATION Contribution of Voltage-Gated Ca Channels to Homosynaptic Long- Term Depression in the CA1 Region In Vitro

Christie, Brian R., Lalania K. Schexnayder, and Daniel John(Christie et al. 1995; Magee and Johnston 1995). Calcium ston. Contribution of voltage-gated Ca channels to homosynaptic entry in the proximal dendrites of CA1 neurons is mainly long-term depression in the CA1 region in vitro. J. Neurophysiol. due to the activity of L-type VGCCs (Christie et al. 1995; 77: 1651–1655, 1997. Homosynaptic long-term depression (LTD) Jaffe et al. 1992). As one progresses further out into the of synaptic efficacy was induced in field excitatory postsynaptic apical dendrites (ú150 mm), the contribution of Rand Tpotentials by administration of 900 pulses at either 1 or 3 Hz in type VGCCs increases (Christie et al. 1995; Magee and 2to 3-wk-old Sprague-Dawley rats. The stimulation was adminisJohnston 1995). Unlike high-threshold VGCCs, these lowtered via a bipolar stimulating electrode placed immediately adjathreshold T channels can be activated by synaptically acticent to the recording electrode in the stratum radiatum region of vated excitatory postsynaptic potentials (EPSPs) (Magee et the hippocampal CA1 subfield. Equivalent LTD induction occurred whether the slices were maintained at room temperature or at 327C. al. 1995), indicating that they can provide a source of Ca Lowering bath Ca to 0 mM, or increasing it to 4 mM, prevented in the absence of back-propagating action potentials. The the induction of the depression. The NMDA receptor antagonist aims of the present experiments were to examine further the D,L-2-amino-5-phosphonovaleric acid (50 mM) reversibly blocked sensitivity of homosynaptic LTD to different VGCC blockthe induction of homosynaptic LTD. In addition, the L-type volters. Portions of this work have been presented previously in age-gated calcium channel (VGCC) antagonist nimodipine (10 abstract form (Schexnayder et al. 1995). mM) and the Rand T-type VGCC antagonist NiCl2 (25 mM) also prevented homosynaptic LTD induction. These results indicate that M E T H O D S in addition to N-methyl-D-aspartate receptor activity, Ca influx Hippocampal slices were prepared from young Sprague-Dawley via VGCCs can play an important role in the induction and expresrats (14–28 days) with the use of procedures we have described sion of LTD induced by low-frequency stimulation in the hippopreviously (Christie et al. 1995). Briefly, rats were decapitated campal formation. and the brain was rapidly dissected in cold artificial cerebrospinal