This study investigated the involvement of N- and P/Q-type Ca(2+) channels in sensorimotor transmission and synaptic depression in the in vitro neonatal rat spinal cord preparation. Postsynaptic potentials were intracellularly recorded from spinal motoneurones during stimulation of the dorsal roots. We found that omega-agatoxin-IVA (P/Q-type Ca(2+) channels blocker), omega-conotoxin-GVIA (N-type Ca(2+) channel blocker) and omega-conotoxin-MVIIC (N-, P/Q-type Ca(2+) channel blocker) markedly decreased both poly- and monosynaptic potentials. We also found that the frequency-dependent depression which occurred in the monosynaptic response, for stimulus intervals shorter than 30 s, persisted in the presence of the various Ca(2+) channels blockers. Hyperpolarizing 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 neurotransmission and that synaptic depression, which is characteristic of neonatal sensorimotor transmission, does not involve these Ca(2+) channels.