N- and P/Q-type Ca2+ channels regulate synaptic efficacy between spinal dorsolateral funiculus terminals and motoneurons

Abstract Ca 2+ influx through voltage-gated Ca 2+ channels mediates synaptic transmission at numerous central synapses. However, electrophysiological and pharmacological evidence linking Ca 2+ channel activity with neurotransmitter release in the vertebrate mature spinal cord is scarce. In the current report, we investigated in a slice preparation from the adult turtle spinal cord, the effects of various Ca 2+ channel antagonists on neurotransmission at terminals from the dorsolateral funiculus synapsing motoneurons. Bath application of tetrodotoxin or NiCl 2 prevented the monosynaptic excitatory postsynaptic potentials (EPSPs), and this effect was mimicked by exposure to a zero-Ca 2+ solution. Application of polypeptide toxins that block N- and P/Q-type channels (ω-CTx-GVIA and ω-Aga-IVA) reduced the EPSP amplitude in a dose-dependent manner. By analyzing the input resistance and the EPSP time course, and using a paired pulse protocol we determined that both toxins act at presynaptic level to modulate neurotransmitter release. RT-PCR studies showed the expression of N- and P/Q-type channel mRNAs in the turtle spinal cord. Together, these results indicate that N- and P/Q-type Ca 2+ channels may play a central role in the regulation of neurotransmitter release in the adult turtle spinal cord.