Raphé nucleus-evoked release of acetylcholinesterase from guinea-pig substantia nigra.

Acetylcholinesterase (AChE) is released from dopaminergic dendrites in the guinea-pig substantia nigra. This release, measured by a chemiluminescent assay, is increased following electrical stimulation of the dorsal raphé nucleus, which sends a 5-hydroxytryptaminergic input to the substantia nigra. Application of exogenous 5-hydroxytryptamine (5-HT) directly to the substantia nigra similarly enhanced release of AChE, whilst local application of cinanserin, a 5-HT antagonist, inhibited electrically-evoked release. Although the substantia nigra posseses a dense localization of 5-HT1D receptors, application of the 5-HT1D agonist sumatriptan did not effect AChE release. The results indicate that 5-HT, released from raphé-nigral afferent nerves, enhances the dendritic release of AChE, although this effect is unlikely to be mediated via 5-HT1D receptors.