Distribution Of Serotonergic Neurons Research Articles

Serotonergic elements in the nervous system of parasite of acipenserid fishes, Acrolichanus auriculatus (Digenea: Allocreadiidae)

The trematode Acrolichanus auriculatus is a widely distributed intestine parasite of acipenserid fishes. For the first time the localization and distribution of the serotonergic nerve elements in A. auriculatus was studied using immunocytochemical method and confocal laser scanning microscopy. The study revealed the presence of biogenic amine, serotonin, in the central and peripheral nervous systems of A. auriculatus, that is in the neurons and neurites of the brain ganglia, brain commissure, the longitudinal nerve cords, and the connective nerve commissures. The innervation of the attachment organs, pharynx, oesophagus and distal regions of the reproductive system by the serotonergic nerve elements is observed. The distribution of serotonergic neurons in A. auriculatus is schematically marked. The comparative analysis of findings obtained in A. auriculatus with those recorded for other digeneans reveals the presence of both conservative and distinctive features in the organization of the serotonergic nervous system in various representatives of trematodes.

Behavior and serotonergic disorders in rats exposed prenatally to valproate: A model for autism

In order to explore whether some aspects of the autistic phenotype could be related to impairment of the serotonergic system, we chose an animal model which mimics a potential cause of autism, i.e. rats exposed to valproate (VPA) on the 9th embryonic day (E9). Previous studies have suggested that VPA exposure in rats at E9 caused a dramatic shift in the distribution of serotonergic neurons on postnatal day 50 (PND50). Behavioral studies have also been performed but on rats that were exposed to VPA later (E12.5). Our aim was to test whether VPA exposure at E9 induces comparable behavioral impairments than at E12.5 and causes serotonergic impairments which could be related to behavioral modifications. The results showed significant behavioral impairments such as a lower tendency to initiate social interactions and hyperlocomotor activity in juvenile male rats. The serotonin levels of these animals at PND50 were decreased (−46%) in the hippocampus, a structure involved in social behavior. This study suggests that VPA could have a direct or indirect action on the serotonergic system as early as the progenitor cell stage. Early embryonic exposure to VPA in rats provides a good model for several specific aspects of autism and should help to continue to explore pathophysiological hypotheses.

Embryonic and postnatal development of the serotonergic raphe system and its target regions in 5-HT 1A receptor deletion or overexpressing mouse mutants

The neurotransmitter 5-HT regulates early developmental processes in the CNS. In the present study we followed the embryonic and postnatal development of serotonergic raphe neurons and catecholaminergic target systems in the brain of 5-HT 1A receptor knockout (KO) and overexpressing (OE) in comparison with wild-type (WT) mice from embryonic day (E) 12.5 to postnatal day (P) 15.5. Up to P15.5 no differences were apparent in the differentiation and distribution of serotonergic neurons in the raphe area as revealed by the equal number of serotonergic neurons in the dorsal raphe in all three genotypes. However, the establishment of serotonergic projections to the mesencephalic tegmentum and hypothalamus was delayed at E12.5 in KO and OE animals and projections to the cerebral cortex between E16.5 and E18.5 were delayed in OE mice. This delay was only transient and did not occur in other brain areas including septum, hippocampus and striatum. Moreover, OE mice caught up with WT and KO animals postnatally such that at P1.5 serotonergic innervation of the cortex was more extensive in the OE than in KO and WT mice. Tissue levels of 5-HT and of its main metabolite 5-hydroxyindoleacetic acid as well as 5-HT turnover were considerably higher in brains of OE mice and slightly elevated in KO mice in comparison with the WT, starting at E16.5 through P15.5. The initial differentiation of dopaminergic neurons and fibers in the substantia nigra at E12.5 was transiently delayed in KO and OE mice as compared with WT mice, but no abnormalities in noradrenergic development were apparent in later stages. The present data indicate that 5-HT 1A receptor deficiency or overexpression is associated with increased 5-HT synthesis and turnover in the early postnatal period. However, they also show that effects of 5-HT 1A KO or OE on the structural development of the serotonergic system are at best subtle and transient. They may nonetheless contribute to the establishment of increased or reduced anxiety-like behavior, respectively, in adult mice.

On the serotonergic nervous system of two planktonic rotifers, Conochilus coenobasis and C. dossuarius (Monogononta, Flosculariacea, Conochilidae)

The serotonergic nervous systems of two non-colonial species of Conochilus were examined to obtain the first immunohistochemical insights into the neuroanatomy of species of Flosculariacea (Rotifera, Monogononta). Species of Conochilus, subgenus Conochiloides, were examined using serotonin (5-HT) immunohistochemistry, epifluorescence and confocal laser scanning microscopy, and 3D computer imaging software. In specimens of C. coenobasis and C. dossuarius, the serotonergic nervous system is defined by a dorsal cerebral ganglion, apically directed cerebral neurites, and paired nerve cords. The cerebral ganglion contains approximately four pairs of small 5-HT-immunoreactive perikarya; one pair innervates the posterior nerve cords and three pairs innervate the apical field. The most dorsal pair innervates a coronal nerve ring that encircles the apical field. Within the apical field is a second nerve ring that outlines the inner border of the coronal cilia. Together, both the inner and outer nerve rings may function to modulate ciliary activity of the corona. The other two pairs of perikarya innervate a region around the mouth. Specific differences in the distribution of serotonergic neurons between species of Conochilus and previously examined ploimate rotifers include the following: (a) a lack of immunoreactivity in the mastax; (b) a greater number of apically directed serotonergic neurites; and (c) a complete innervation of the corona in both species of Conochilus. These differences in nervous system immunohistochemistry are discussed in reference to the phylogeny of the Monogononta.

Distribution of NADPH-Diaphorase-Positive Neurons in the Mouse Brain: Differences from Previous Findings in the Rat Brain and Comparison with the Distribution of Serotonergic Neurons.

The distribution of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) enzyme-containing neurons in the mouse brain was studied and a schematic map of the entire mouse brain was obtained. NADPH-d-positive cell bodies and fibers were detected in almost all brain regions, while the neurons varied in form and staining pattern, and the fibers in density, shape and staining pattern. Significant differences in the localization of NADPH-d-positive neurons were detected and compared to the results of previous studies in rats, in such areas as the lateral globus pallidus, the red nucleus, the locus coeruleus and the principal sensory trigeminal nucleus. Possible causes for the differences between NADPH-d staining in rat and mouse are discussed. Similar to serotonin (5-hydroxytryptamine, 5-HT) fibers, as NADPH-d-positive neurons were found in almost all areas of the brain suggesting the existence of some interaction between NADPH-d-positive neurons and 5-HT neurons. Therefore, the distributions of NADPH-d-positive neurons and 5-HT neurons were compared. To elucidate the relationship between NADPH-d-positive neurons and 5-HT neurons, we analyzed histochemical changes in NADPH-d-positive neurons after injection of 5,7-dihydroxytryptamine (5,7-DHT), a 5-HT neurotoxin, into the lateral ventricle of the mouse brain. Changes in NADPH-d-positive neurons were found in the medial septal nucleus, the diagonal band of Broca, and the dorsal raphe nucleus after injection. The observations suggest a potential relationship between NADPH-d-positive neurons and 5-HT neurons.

Distribution of serotonergic neurons in the eyestalk and brain of the crab, Cancer antennarius

1. Serotonin-containing neurons were localized immunocytochemically in crab cerebral ganglia and their extensions in the eyestalk. 2. Approximately 155 serotonergic cells were found in identifiable regions of the brain, the largest number being localized in the anterior cell cluster (40 reactive cells) and the bilateral anterior olfactory cell clusters (40 cells each). 3. Serotonin immunoreactive cells were found in all three ganglionic divisions of the eyestalk. The medulla terminalis contains up to 15 reactive cells, of which only one occurs in the X-organ (origin of neurosecretory axons in the sinus gland nerve). The m. terminalis also contains three identifiable cells in the mediolateral border adjacent to the sinus gland nerve, of which one is a giant (up to 100 μm diameter), designated MT-1. The axon of MT-1 branches profusely after entering the m. terminalis neuropil. 4. No serotonin immunoreactivity was apparent within the sinus gland, the sinus gland nerve or the organ of Bellonci. 5. These findings are discussed in relation to the known serotonergic control of peptide hormone secretion by the eyestalk X-organ-sinus gland complex.

Distribution of serotonergic neurons and processes in the lamprey spinal cord

The distribution of serotonin in the spinal cord in two species of lamprey, Ichthyomyzon unicuspis and Petromyzon marinus, was studied by indirect immunofluorescence techniques. Multipolar cell bodies containing serotonin-like immunoreactivity were found along the length of the spinal cord, along the midline and slightly ventral to the central canal. These cell bodies send a diffuse projection of processes throughout the spinal cord, including: (1) a dense projection to the ventral surface; (2) a strong projection to the ventromedial longitudinal fiber tracts; (3) a less intense projection to the dorsal longitudinal fiber tracts; and (4) a weak projection to the lateral fiber tracts. Lesion experiments showed that processes descending from the brain or rostral spinal cord provide a major projection to the lateral fiber tracts and smaller contributions to the dorsal and ventromedial fiber tracts. Fluorescent processes were also observed in the dorsal roots and serotonergic peripheral cell bodies were seen adjacent to the dorsal roots. Our results suggest that the serotonergic innervation of the lamprey spinal cord arises from three sources: spinal interneurons, descending tracts and peripheral (possibly sensory) input. This provides an anatomical substrate for our recent finding 12,13 that serotonin modulates the central pattern generator for locomotion in the lamprey spinal cord.

Immunohistochemical Study on the Distribution of Serotonin-Containing Cell Bodies in the Brain Stem of the Dog

The distribution of serotonin-containing neurons in the brain of the dog was studied by use of PAP immunohistochemistry. The lower brain stem was endowed with extensively scattered serotonergic cell bodies, a large portion of which was located in the raphe nuclei. At the same time, prominent distribution of serotonergic neurons in lateral areas outside the raphe nuclei was also demonstrated. Our observations on the brain stem were, in principle, consistent with those on rats, cats and monkeys, with only minor differences.