Distribution of serotonin-immunoreactivity in the central nervous system of the rat—Cell bodies and terminals

Abstract The localization and distribution of serotonin (5-hydroxytryptamine, 5-HT) has been studied with the indirect immunofluorescence technique using a highly specific and well-characterized antibody to 5-HT. In neuron systems 5-HT was found to be primarily present with a distribution similar to that observed in basic mappings carried out with the formaldehyde-induced fluorescence method. In addition to the nine areas originally described, several other areas in the mesencephalon and rhombencephalon appeared to contain widely distributed 5-HT-positive perikarya. In the median eminence 5-HT fluorescent mast cells could be visualized. No 5-HT-positive nerve cell bodies could be observed either in the telencephalon or diencephalon. Our results also demonstrate a widespread occurrence of 5-HT-positive nerve terminals throughout the central nervous system. Dense populations of serotonin-immunoreactive nerve terminals are present in the following areas, from rostral to caudal: various parts of the medial forebrain bundle; the ventromedial part of the nucleus suprachiasmaticus: the most ventrolateral part of the caudatus-putamen complex; an area between the rostral part of the nucleus reuniens and the fornix: at that same level of the latter area, a region just ventral of the fornix; the dorsolateral part of the nucleus periventricularis thalami; an area lateral of the claustrum, close to the cortex piriformis; the nucleus amygdaloideus basalis; the dorsomedial part of the nucleus medialis thalami pars medialis, only in the rostral part; the inner part of the nucleus ventromedialis hypothalami; the ventral part of the nucleus mamillaris medialis; the radiatio thalami superior; the nucleus subthalamicus; the caudal part of the nucleus amygdaloideus medialis posterior; the area pretectalis radialis; the dorsal part of the nucleus ventralis corporis geniculati lateralis; the ventromedial part of the substantia nigra reticularis; an area ventral of the decussatio supramammillaris; the substantia nigra pars lateralis; the dorsolateral part of the nucleus reticularis pontis oralis; some parts of the nucleus origines nervi trigemini; the ventromedial part of the nucleus origines nervi facialis; the medial part of the nucleus tractus solitarius and the medial part of the cornu ventrale of the spinal cord. There are only a few areas where no serotonin-immunoreactivity could be found. Within several areas, as, e.g., hippocampus, nucleus caudatus, medial forebrain bundle, the density of serotoninergic fibers appeared to show considerable local differences. Within the same nuclei or area the amount can differ considerably. This immunohistochemical procedure makes it possible to study the distribution of serotonin-containing nerves and their processes in considerable detail. The finding that serotonin-containing neurons are present in many nuclei that also include catecholamine-containing neurons makes it necessary to reconsider the terminology of the monoaminergic cell groups.