Inhibition of Synaptic Transmission by Neuropeptide Y in Rat Hippocampal Area CA1: Modulation of Presynaptic Ca2+Entry

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Abstract
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 [Capre]tvia 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 Y2 receptors reduced [Capre]t and thereby inhibited synaptic transmission. Multiple calcium channels are involved in synaptic transmission at this synapse. Activation of Y2 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 [Capre]t by Y2receptors. Activation of adenosine receptors fully occluded the inhibition of presynaptic calcium influx by Y2 receptors but not the inhibition by GABAB receptors, suggesting a convergent action for Y2 and adenosine receptors, probably by coupling to the same G-protein.