Reinnervation of dopamine neurons by regenerating serotonin axons in the rat medial zona incerta. A combined radioautographic and immunocytochemical ultrastructural study.
Cellular relationships between serotonin (5-HT) axons and tyrosine hydroxylase (TH)-containing neurons were examined by combined (3H)5-HT uptake radioautography and TH immunocytochemistry in the medial zona incerta (ZI) of adult rats, 7 and 50 days after an intracerebral injection of 5,7-Dihydroxytryptamine (5,7-DHT). Seven days post-lesion, only rare, scattered (3H)5-HT-labeled axon terminals were apparent in the zone of the medial ZI accessible to intraventricularly injected (3H)5-HT. In contrast, in sham-injected animals (3H)5-HT-labeled varicosities were numerous and often observed adjacent to TH-immunoreactive perikarya and dendrites. Fifty days post 5,7-DHT injection, the density of (3H)5-HT-labeled terminals approximated that seen in sham-treated animals. At the ultrastructural level, these regenerated 5-HT axons were similar in size, shape and content to those observed in sham-operated rats. Also, as in sham, some of the (3H)5-HT-labeled axons were directly apposed to TH-immunopositive labeled profiles. The latter included large dendritic shafts and dendritic spines, but only rare perikarya. In both sham- and 5,7-DHT-treated animals a few of the contacts between (3H)5-HT-labeled and TH-immunoreactive profiles exhibited an asymmetric synaptic differentiation. These results indicate that 5-HT fibers in the medial ZI, following regeneration, can reestablish normal relationships and even synapses with a given population of chemically identified cells.
Frankfurt
M
M
Montreal Neurological Institute, Montreal, Quebec, Canada.
Beaudet
A
A
D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D004298:Dopamine / Q000502:physiology*; D008297:Male; D008854:Microscopy, Electron; D009416:Nerve Regeneration; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000032:analysis*; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis*
D015116:5,7-Dihydroxytryptamine; D012701:Serotonin; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine