Alterations in noradrenaline nerve terminals in the periventricular hypothalamus of the rat during regeneration after administration of 6-OH dopamine.

The alterations in noradrenaline (NA) nerve terminals fixed by KMnO4 have been studied electron microscopically during regeneration after an injection of 6-OH dopamine (6-OHDA), a specific neurotoxin of aminergic fibers, in the periventricular region of the rat hypothalamus. In non-treated rats, only 7% of the total number of NA terminals had obvious synaptic structures with neighboring dendrites. In rats 30 days after 6-OHDA treatment, NA terminals, though rarely found, showed synaptic contacts with dendrites. In rats 60 days after the neurotoxin injection, NA terminals increased remarkably in number, and half of the total number of NA terminals observed had a membrane specialization between NA terminals and dendrites. Thereafter, NA terminals with synaptic structure decreased in incidence. In rats 90 days after 6-OHDA treatment, NA terminals were found in a cluster which sometimes contained huge axonal bulgings in peri- and paraventricular areas of the hypothalamus. Results obtained by fluorescence histochemistry indicated that giant fluorescent varicosities corresponded to the clusters of NA terminals.