MECHANISM OF PRESYNAPTIC INHIBITION BY NEUROPEPTIDE-Y AT SYMPATHETIC-NERVE TERMINALS

CALCIUM influx through voltage-sensitive Ca2+ channels is the normal p hysiological stimulus for the activity-dependent release of neurotrans mitters at synaptic contacts. It has been postulated that presynaptic inhibition of transmitter release is due to a reduction in Ca2+ influx at the nerve terminal, which could result from the direct inhibition of Ca2+ channels. Neuropeptide Y and noradrenaline act as cotransmitte rs at many sympathetic synapses. Both of these substances produce pres ynaptic inhibition and can inhibit Ca2+ currents in the soma of sympat hetic neurons1-5. Here we provide direct evidence that presynaptic inh ibition produced by neuropeptide Y at sympathetic nerve terminals is a ssociated with a reduction in Ca2+ influx and that this is due to the selective inhibition of neuronal N-type Ca2+ channels.