INHIBITION OF SYNAPTIC TRANSMISSION BY NEUROPEPTIDE-Y IN RAT HIPPOCAMPAL AREA CA1 - MODULATION OF PRESYNAPTIC CA2+ ENTRY

Neuropeptide Y (NPY) agonists inhibit glutamate release by a presynapt ic action at the CA3-CA1 synapse of rat hippocampus. We have examined the relationship between [Ca-pre](t) via presynaptic, voltage-dependen t calcium channels (VDCCs), measured optically by using the fluorescen t calcium indicator fura-2, and transmitter release, measured electrop hysiologically. Activation of presynaptic NPY Y-2 receptors reduced [C a-pre](t) and thereby inhibited synaptic transmission. Multiple calciu m channels are involved in synaptic transmission at this synapse. Acti vation of Y-2 receptors inhibits N-type, P/Q-type, and unidentified pr esynaptic VDCCs. The inhibition of each of these calcium channel types contributes to the reduction of [Ca-pre](t) by Y-2 receptors. Activat ion of adenosine receptors fully occluded the inhibition of presynapti c calcium influx by Y-2 receptors but not the inhibition by GABA(B) re ceptors, suggesting a convergent action for Y-2 and adenosine receptor s, probably by coupling to the same G-protein.