L-type calcium channels mediate dynorphin neuropeptide release from dendrites but not axons of hippocampal granule cells.

Granule cells in the guinea pig dentate gyrus release kappa opioid neuropeptides, dynorphins, from dendrites as well as from axon terminals. We have found that both L- and N-type calcium channel antagonists inhibited dendritic dynorphin release. In contrast, N-type but not L-type calcium channel antagonists inhibited axonal dynorphin release. Neither L- nor N-type channel antagonists directly altered the effects of kappa opioid receptor activation. By inhibiting dynorphin release, L-type channel antagonists also facilitated the induction of long-term potentiation of the perforant path-granule cell synapse. These studies establish that a single cell type can release a transmitter from two different cellular domains and provide new distinction between axonal and dendritic transmitter release mechanisms.