Anatomical Features and Physiological Properties of Central Serotonin Neurons

Abstract

The authors describe the anatomical features and physiological properties of central serotonergic neurons. The central serotonin neurons (part of which store peptides [substance P, TRF, enkephalins] in addition to 5HT) are highly collateralized reticular-type brain stem neurons receiving multi-modal afferent information from ascending sensory and descending motor pathways. They are under control by noradrenergic, peptidergic and and gaba-ergic projection neurons and interneurons. Furthermore, they establish variable synaptoid and synaptic contacts to neuronal, glial and secretory targets throughout the entire neuraxis and send terminal branches into the ventricular CSF space. Firing rate and transmission activity appear to be controlled in a complex and rather rigid manner by 5HT release-dependent dendrodendritic and dendrosomatic inhibition via autoreceptors (which also regulate release at the axon terminals) and via transsynaptic inhibitory feedback circuits which may involve gabaergic projection and interneurons. 3H-imipramine appears to bind to an "imipramine recognition site" in the vicinity of the 5HT carrier, and to a variety of other transport and (postsynaptic) receptor sites (NA uptake, H1, 5HT2- and alpha 1-binding sites). Circumstantial evidence points to an as yet undetermined role of the postsynaptic 5HT-1-binding sites in neurotransmission. 5HT-2-binding sites fulfil the criteria for receptors: binding affinity of antagonists to these sites correlates significantly with their potency to inhibit behavioral excitation in rats elicited by 5-hydroxytryptophan or 5HT agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

d,l-fenfluramine Response in Impulsive Personality Disorder Assessed with [18F]fluorodeoxyglucose Positron Emission Tomography

“…However, given the multiplicity of serotonin receptors that could mediate the glucose metabolic response to fenfluramine, as well as the possibility raised by studies of serotonin metabolites that pre-synaptic availability may be reduced in impulsive-aggressive patients, further studies will be required to identify the specific serotonergic components altered in impulsive-aggressive patients. Furthermore, serotonergic neurons may have downstream effects on other brain neurotransmitter systems, for example, by activating inhibitory GABAminergic interneurons or even by modulating subcortical dopamine receptor sensitivity (Baumgarten and Lachenmayer 1985). These downstream effects are unlikely to account, however, for the proximal effects of fenfluramine on orbital frontal and cingulate cortex observed in this study.…”

Similar effect on REM sleep but differential effect on slow wave sleep of the two 5-HT uptake inhibitors zimeldine and alaproclate in cats and rats

“…1 and 2). A species difference between cats and rats with regard to 5-HT dependence of sleep control has been suggested (Baumgarten and Lachenmayer, 1985). There are no known species difference in metabolism or uptake inhibition.…”

“…We also wanted to confirm the REM sleep suppressant action in cats. A species difference between cats and rats with regard to 5-HT dependence of sleep control has been suggested (Baumgarten and Lachenmayer, 1985).…”

Demyelination as An Epiphenomenon in Multiple Sclerosis

“…It is of note that 5-HT has been found to function as an inhibitory neurotransmitter in the optic nerve (Gawel et al,198l), optic radiation, and occipital lobes (Baumgarten & Lachenmayer, 1985). Moreover, Holder et al (1980) found a significant correlation between CSF 5-HIAA levels and VEP latency in patients undergoing surgery and Harrer and Fischbach (1973) and Kisser and Harrer (1974) reported that administration of the 5-HT precursor tryptophan in conjunction with tyrosine and L-dopa effectively abolished the negative effect of artificial overheating on the flicker-fusion threshold in MS patients.…”