Evidence for a degeneration of indoleamine containing nerve terminals in rat brain, induced by 5,6-dihydroxytryptamine

5,6-dihydroxytryptamine (5,6-DHT) has been found to induce a substantial degree of “chemical degeneration” of indoleamine containing nerve terminals in the rat brain following a single intraventricular injection of 75 μg 5,6-DHT per animal. The disintegration of varicose terminal portions of serotonin containing neurons is reflected 1. by a loss of yellow fluorescent varicosities in certain defined parts of the rat CNS, despite a mild inhibition of the serotonin catabolizing enzyme monoamine oxidase with nialamide in the pretreated animals, 2. by a significant drop of the chemically measurable 5-hydroxytryptamine content in nearly all parts of the rat brain and spinal cord, 3. by the appearance of highly, orange or brownish fluorescent axons provided with numerous unusually large, distorted and intensely fluorescent swellings (“droplets”), resembling proximal stumps of mechanically severed indoleamine containing axons, 4. a temporary increase in the amount of indoleamine fluorophores stored in some neuronal pericarya, and 5. the electron microscopical demonstration of degenerating synaptic swellings of unmyelinated axons at all sites investigated.