Further evidence for the possible relationship between neuropeptides and serotonergic neurones in rat spinal cord

The relationship between neuropeptides and serotonergic neurones was investigated in rat spinal cord, in vivo, using a subarachnoidal perfusion technique. The 5-hydroxytryptamine (5-HT) release from the spinal cord could be evoked by substance P and peripheral pain stimulation (tail pinch), but not by methionine-enkephalin (met-EK). The substance P-evoked 5-HT release was slightly potentiated by met-EK. The tail pinch-evoked 5-HT release was inhibited by met-EK and baclofen, but potentiated by naloxone. These findings may infer a possible mechanism by which neuroactive peptides regulate 5-HT release from serotonergic neurones in the spinal cord.