Similarities of the effects of apomorphine and 3-PPP on serotonin neurons.

Acute administration of 3-3-hydroxyphenyl-N-n-propyl-piperidine (3-PPP), selectively increased intracellular serotonin (5-HT) fluorescence in the dorsal raphe and 5-HT as well as 5-hydroxyindoleacetic acid (5-HIAA) in the corresponding projection site of the dorsal raphe, the striatum. These effects are similar to those produced by systemic treatments with apomorphine (APO). Serotonin neurons in the median raphe and its corresponding terminal area hippocampus were not affected by either APO or 3-PPP. Haloperidol at a dose having no significant effect alone, antagonized the APO-induced elevation of striatal 5-HT. The differential effects of 3-PPP on the mesostriatal and mesolimbic serotonergic systems further confirm that the dorsal and median raphe nuclei constitute two anatomically and functionally distinct cell groups and the similarities of the effects of APO and 3-PPP indicate that dopamine autoreceptors may mediate the observed effects of APO on 5-HT neurons.