Synaptic morphology in the neostriatum of the rat: Possible serotonergic synapse.

Electron-microscopic examination of the striatum of rats 2-3 days after intraperitoneal injection of 10-15 mg/kgp-chloroamphetamine (PCA) indicated two types of terminal degeneration: a light, filamentous degeneration of symmetrical boutons, and a dark, electron-dense degeneration of asymmetrical boutons. The latter was identical to that seen 2-3 days after 6-hydroxydopamine hydrochloride (6-OHDA), and its frequency after PCA was decreased if the animal had been pretreated 10 days previously with 6-OHDA. The same two morphological types of striatal synapses were preferentially labeled by intraventricularly administered [(3)H]5-HT. No structural specificity in labeling in the striatum was seen after raphe injections of labeled 5-HTP or 5-HT. The probable morphology of striatal dopaminergic, cholinergic, GABAnergic, and serotonergic synapses is discussed, with a review of the pertinent evidence.