N- and P/Q-type Ca2+ channels are involved in neurotransmitter release butnot in synaptic depression in the spinal cord of the neonatal rat

This study investigated the involvement of N- and P/Q-type Ca2+ channels in sensorimotor transmission and synaptic depression in the in vitro neonatal rat spinal cord preparation. Postsynaptic potentia Is were intracellularly recorded from spinal motoneurones during stimulation of the dorsal roots. We found that omega -agatoxin-IVA (P/Q-type Ca2+ channels blocker), omegaw- conotoxin-GVIA (N-type Ca2+ channel blocker) and omega -conotoxin-MVIIC (N- , P/Q-type Ca2+ channel blocker) markedly decreased both poly- and monosyna ptic potentials. We also found that the frequency-dependent depression whic h occurred in the monosynaptic response, for stimulus intervals shorter tha n 30 s, persisted in the presence of the various Ca2+ channels blockers. Hy perpolarizing the motoneurons significantly reduced depression, suggesting contribution from some additional postsynaptic mechanisms: We conclude that at birth, as in adult central nervous system (CNS) synapses, several types of voltage dependent calcium channels mediate sensorimotor neurotransmissi on and that synaptic depression, which is characteristic of neonatal sensor imotor transmission, does not involve these Ca2+ channels. (C) 2000 Elsevie r Science Ireland Ltd. All rights reserved.