THE EFFECT OF 5-AND 6-HYDROXYDOPAMINE ON THE CENTRAL MONOAMINERGIC NEURONS OF THE RAT AND THE CAT: FLUORESCENCE HISTOCHEMISTRY AND ELECTRON MICROSCOPY

Abstract

The influence of 5-hydroxydopamine (5-OHDA) and 6-hydroxydopamine (6-OHDA) upon the aminergic neurons of the central nervous system was investigated by fluorescence histochemistry and electron microscopy using the neostriatum, the hypothalamus, including the median eminence, and the substantia nigra of albino rats and cats. After the administration of 5-OHDA into the lateral ventricle or third ventricle, aminergic terminals containing small dense-cored vesicles (400-600Å in diameter) and large cored vesicles (700-1, 000Å in diameter) appeared in the structures listed above. A number of dense-cored vesicles (600-800Å in diameter) were found in the perikarya of some nerve cells of the substantia nigra after treatment with 5-OHDA. It was established that 5-OHDA can be utilized as a marker of both central noradrenaline and dopamine neurons and that endogenous amines are stored in the small vesicles as well as in the large densecored veiscles. On the other hand, intensive depletion of both noradrenaline and dopamine fluorescence occurred in all regions except the external layer of the median eminence after treatment with 6-OHDA. The nerve cell bodies of the substantia nigra, containing dopamine in their perikarya, were less affected by 6-OHDA than the terminals. The administration of 6-OHDA in excess of 500μg produced degeneration of aminergic terminals in animals surviving more than 2 days. However, for short survival times of 1hr, we observed terminals containing small dense cored vesicles similar to those seen after administration of 5-OHDA. A marked depletion of amine fluorescence without ultrastructural damage was also observed in the aminergic terminals.