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 presynaptic action at the CA3-CA1 synapse of rat hippocampus. We have examined the relationship between [Ca-pre](t) via presynaptic, voltage-dependent calcium channels (VDCCs), measured optically by using the fluorescent calcium indicator fura-2, and transmitter release, measured electrophysiologically. Activation of presynaptic NPY Y-2 receptors reduced [Ca-pre](t) and thereby inhibited synaptic transmission. Multiple calcium channels are involved in synaptic transmission at this synapse. Activation of Y-2 receptors inhibits N-type, P/Q-type, and unidentified presynaptic VDCCs. The inhibition of each of these calcium channel types contributes to the reduction of [Ca-pre](t) by Y-2 receptors. Activation of adenosine receptors fully occluded the inhibition of presynaptic calcium influx by Y-2 receptors but not the inhibition by GABA(B) receptors, suggesting a convergent action for Y-2 and adenosine receptors, probably by coupling to the same G-protein.