Anatomical distribution of serotonin‐containing neurons and axons in the central nervous system of the cat

Abstract

By using a monoclonal antibody to serotonin (5-HT), an immunohistochemical study was undertaken to provide a comprehensive description of the 5-HT-containing neurons and of the distribution of their axonal processes in the cat brain and spinal cord. The localization of cell bodies was comparable to that previously reported in studies using formaldehyde-induced fluorescence and other 5-HT antibodies, with a large proportion of labeled neurons in the raphe nuclei and a minor, yet not negligible number, in the ventral, lateral, and dorsal reticular formation. The ascending efferent non-varicose axons were best visualized in sagittal sections and mainly seen taking a rostroventral direction through the tegmentum. The varicose axons could be grossly classified into thin and large fibers, according to the size and shape of the immunoreactive varicosities, which were elongated (up to 2 microm in length and 1 microm in width) or round (2-4 microm in diameter). Varicose axonal arborizations invaded almost every region of the gray matter and avoided large myelinated bundles except in the spinal cord. Variations in the density of the plexuses of immunoreactive fibers generally followed the anatomical divisions and were also observed within nuclei, especially in laminated structures. Only the superior olivary complex could be regarded as devoid of 5-HT-containing axons. A few areas contained extremely rich fiber plexuses. These were the olfactory tubercle, nucleus accumbens, ventral mesencephalon, periventricular gray from the hypothalamus to the pons, facial nucleus, subdivisions of the inferior olive, and the intermediolateral nucleus in the spinal cord. Varicose axons formed tight pericellular arrays in the neocortex, mainly the ectosylvian gyrus, and in the lateral septum and medullar magnocellular nucleus. These data, combined with those of the literature concerning the synaptic versus non-synaptic mode of termination of the 5-HT-immunoreactive varicosities and the high number of distinct receptors, are indicative of the multiple possible actions of serotonin in the central nervous system.

Distribution and morphology of serotonin‐immunoreactive axons in the hippocampal region of the New Zealand white rabbit. I. Area dentata and hippocampus

“…Three morphologically different serotonergic fiber types are seen in the rabbit, which correspond to the findings by others in different species: rat (Molliver, 1987;Swanson et al, 1987), cat (Mulligan and Törk, 1988;Törk et al, 1989;Léger et al, 2001), monkey Wilson and Molliver, 1991), and human (Törk, 1990). We call these fine fibers, beaded fibers, and stem-axons, according to the nomenclature established previously (Kosofsky and Molliver, 1987;Molliver, 1987;Wilson and Molliver, 1991).…”

“…Studies conducted in several species have thus shown that serotonergic neurons in the dorsal raphe nucleus, the median raphe nucleus and the B9/supralemniscal area dispatch numerous serotonergic axons that primarily reach the diencephalon and telencephalon by the medial forebrain bundle in the rat (Azmitia and Segal, 1978;Moore et al, 1978;Parent et al, 1981;Steinbusch and Nieuwenhuys, 1983;Törk, 1985), cat (Jacobs et al, 1984;Léger et al, 2001), rabbit (Bjarkam et al, 1997), marmoset (Hornung and Fritschy, 1988) and man ).…”

Sudden Infant Death Syndrome and Sudden Intrauterine Unexplained Death: Correlation Between Hypoplasia of Raphé Nuclei and Serotonin Transporter Gene Promoter Polymorphism

“…Yet, studies describing the topography and the histopathology of the human raphé nuclei, where the serotonin producing and containing neurons are located, are few in number (2,(22)(23)(24). The anatomical organization of the 5-HT neurons and their projections in the brain and spinal cord, in fact, has been intensely studied only in experimental animals (25)(26)(27)(28). A first value of this study was therefore the morphologic identification in the human brainstem of all nuclei of the raphé complex, i.e., the caudal linear raphé nucleus, the dorsal raphé nucleus and the median raphé nucleus forming the rostral group, and the raphé magnus nucleus, the raphé obscurus nucleus, and the raphé pallidus nucleus forming the caudal group.…”

Plasticity of tyrosine hydroxylase and serotonergic systems in the regenerating spinal cord of adult zebrafish

“…1G, 5B), which is typical of serotonergic and dopaminergic terminals (Leger et al, 2001;Mrini et al, 1995;Takeoka et al, 2009). Our manual and semiautomatic quantification method counts mostly profiles of varicosities.…”