Effect of neuroactive peptides on labeled 5-hydroxytryptamine release from rat spinal cord.

The effects of neuroactive peptides on the release of 5-HT were studied. The 5-HT released from the spinal cord was significantly increased by somatostatin, substance P and peripheral pain stimulation (tail pinch), but not affected by neurotensin, beta-endorphin and met-enkephalin. The somatostatin-evoked 5-HT release was inhibited by baclofen and met-enkephalin in vivo but not in vitro. The substance P-evoked 5-HT release was strongly inhibited by baclofen, and slightly potentiated by met-enkephalin in vivo but not in vitro. The tail pinch-induced 5-HT release was inhibited by met-enkephalin and baclofen, but potentiated by naloxone. These findings provide further evidence on the important role of neuropeptides and suggest that the descending serotonergic neurones are modulated by neuropeptide interneurones in the spinal cord.