Localization of Indolealkylamines in CNS

Abstract

This chapter provides an account of recent studies on central 5-HT neurons using histochemical and biochemical techniques. Little was known about the cellular localization of 5-HT in the central nervous system until the development of the histochemical fluorescence method for the demonstration of catecholamines (CA) and 5-HT. Tryptamine and melatonin are the indolealkylamines normally present in brain. Tryptamine is found only in low amounts with an unknown regional distribution, and melatonin is highly concentrated in the pineal gland. The 5-HT nerve cell bodies are mainly localized to the raphe nuclei of the lower brainstem (nuc.raphe pallidus, obscurus, pontis, dorsalis, and medianus). Some are also found surrounding the pyramidal tract and in the medioventral part of the caudal tegmentum. No 5-HT cell bodies are found in the spinal cord, the diencephalon, or the telencephalon. The highest amount of 5-HT nerve terminals are so far found in the lumbar enlargement and especially in the sacral part of the spinal cord, where the terminals are fine and have strongly yellow fluorescent varicosities, the average varicosity being about 1 p thick as seen in the fluorescence microscope. There are two different ways of mapping out the 5-HT neurons, which complement one another excellently. One is by way of monoamine oxidase (MAO) inhibition, the other by way of lesions, after which the anterograde and retrograde degenerative changes are observed.