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 neu ropeptides, dynorphins, from dendrites as well as from axon terminals. We have found that both L- and N-type calcium channel antagonists inh ibited dendritic dynorphin release. In contrast, N-type but not L-type calcium channel antagonists inhibited axonal dynorphin release. Neith er L- nor N-type channel antagonists directly altered the effects of k appa opioid receptor activation. By inhibiting dynorphin release, L-ty pe channel antagonists also facilitated the induction of long-term pot entiation of the perforant path-granule cell synapse. These studies es tablish that a single cell type can release a transmitter from two dif ferent cellular domains and provide new distinction between axonal and dendritic transmitter release mechanisms.