6-Hydroxydopamine produces lesions of serotonin-containing Retzius cells in the leech nervous system.

The neurotoxin 6-hydroxydopamine (6-OHDA) is reported to selectively ablate neurons which contain catecholamines. Leeches were injected with 6-OHDA over a 4-month period in an attempt to destroy their identified dopamine neurons. Ganglionic Retzius cells (RZ), which contain serotonin, were the first to be rendered brown, misshapen, and non-fluorescent. Continued injections of 6-OHDA had similar, but less substantial, morphological and histochemical effects on the dopamine-containing neurosomata within the anterior roots. Toxin treatment reduced RZ serotonin by 75-90%, but these depleted cells retained normal electrophysiological properties. Serotonin and dopamine within ganglia, as well as dopamine within anterior roots, were reduced significantly by 6-OHDA.