SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Explore the source record for details and available documents.
Substituted amphetamines such as p-chloroamphetamine and the abused drug methylenedioxymethamphetamine cause selective destruction of serotonin axons in rats, by unknown mechanisms. Since some serotonin neurones also express neuronal nitric oxide synthase, which has been implicated in neurotoxicity, the present study was undertaken to determine whether nitric oxide synthase expressing serotonin neurones are selectively vulnerable to methylenedioxymethamphetamine or p-chloroamphetamine. Using double-labeling immunocytochemistry and double in situ hybridization for nitric oxide synthase and the serotonin transporter, it was confirmed that about two thirds of serotonergic cell bodies in the dorsal raphé nucleus expressed nitric oxide synthase, however few if any serotonin transporter immunoreactive axons in striatum expressed nitric oxide synthase at detectable levels. Methylenedioxymethamphetamine (30 mg/kg) or p-chloroamphetamine (2 x 10 mg/kg) was administered to Sprague-Dawley rats, and 7 days after drug administration there were modest decreases in the levels of serotonin transporter protein in frontal cortex, and striatum using Western blotting, even though axonal loss could be clearly seen by immunostaining. p-Chloroamphetamine or methylenedioxymethamphetamine administration did not alter the level of nitric oxide synthase in striatum or frontal cortex, determined by Western blotting. Analysis of serotonin neuronal cell bodies 7 days after p-chloroamphetamine treatment, revealed a net down-regulation of serotonin transporter mRNA levels, and a profound change in expression of nitric oxide synthase, with 33% of serotonin transporter mRNA positive cells containing nitric oxide synthase mRNA, compared with 65% in control animals. Altogether these results support the hypothesis that serotonin neurones which express nitric oxide synthase are most vulnerable to substituted amphetamine toxicity, supporting the concept that the selective vulnerability of serotonin neurones has a molecular basis.
Tracking serotonergic pathways in the brain through immunodetection of serotonin has widely been used for the anatomical characterization of the serotonergic system. Immunostaining for serotonin is also frequently applied for the visualization of individual serotonin containing fibers and quantification of serotonin positive fibers has been widely used to detect changes in the serotonergic innervation. However, particularly in conditions with enhanced serotonin metabolism the detection level of serotonin may lead to an underestimation of the true number of serotonergic fibers. The serotonin transporter (SERT) protein, on the other hand, is less liable to metabolism and for that reason we hypothetized that SERT immunostaining is a more stable marker of serotonergic fibers. Rats were pretreated with monoamine oxidase (MAO) inhibitor and compared with placebo treated rats. Brains were double immunostained for serotonin and SERT protein and colocalization was quantified in several brain areas by confocal microscopy. In comparison with untreated rats, MAO inhibitor treated rats had a significantly higher number (almost 200% increase) of serotonin immunopositive fibers whereas no difference was observed in the number of the SERT positive fibers. Colocalization between serotonin and SERT positive fibers was close to 100% in MAO inhibitor treated animals but only 30% in untreated rats. We conclude that the rapid metabolism of serotonin leads to an underestimation of immunodetected serotonergic fibers and that in many instances, SERT immunostaining may be a better indicator of serotonergic fibers.
We used an immunocytochemical approach to study the localization of serotonin and its termination system, serotonin transporter (SET), in the taste buds of rats using specific antibodies against serotonin and SET. Under confocal laser scanning microscopy, both serotonin and SET immunoreactivity were detected in the taste buds of rat vallate papillae. Serotonin immunoreactivity was seen in the spindle-shaped cells with apical processes that seemed to be light (Type II) taste cells. SET-immunoreactivity was mainly localized in the periphery or interfaces between the taste cells. Double staining studies revealed that all serotonin-containing taste cells were immunoreactive for SET, while a subclass of SET-positive cells showed serotonin immunoreactivity. These data support the hypothesis that serotonin plays a transmitter role in taste receptor cells and suggest that the serotonin-induced sensation of taste is terminated by serotonin uptake through serotonin transporter.
A series of 60 fore-gut carcinoid tumours was examined with regard to serotonin content after application of three different techniques, namely: the argentaffin reaction, formalin-induced fluorescence according to Falck-Hillarp and immunocytochemistry with monoclonal antibodies to serotonin. To evaluate the staining-fluorescence of individual tumour cells, the methods were applied to identical tumour sections. Twelve tumours demonstrated serotonin-immunoreactive cells, six of which were also argentaffin. Four tumours contained argentaffin cells but no serotonin-immunoreactivity. With the use of all three techniques, three types of tumour cells occurred, namely: serotonin-immunoreactive, non-argentaffin and non-fluorescence cells, serotonin-immunoreactive, argentaffin and fluorescent cells, and non-serotonin immunoreactive, argentaffin and non-fluorescent cells. The first (serotonin-immunoreactive) cell type was most frequently found in the tumours. One gastric carcinoid in which the argentaffin cells exceeded the serotonin-immunoreactive cells, a positive reaction was found with the modified Warthin-Starry reaction for demonstrating melanin. Since none of the techniques used for visualization of serotonin in endocrine tumours is unquestionably specific and since they do not give identical results, it is indicated that for a more accurate identification of serotonin in fore-gut carcinoid tumours, a positive reaction with at least two of the applied techniques is desirable.
The distribution of serotonin and serotonin-containing neurons was studied in the ganglia of the CNS of the snail Lymnaea stagnalis. Results of the application of three different labelling techniques on wholemount preparations were compared with each other and with the serotonin content of the ganglia, measured by high-performance liquid chromatography. Serotonin immunocytochemistry resulted in the highest number of labelled neurons, but the more recently developed in vivo method of 5,6- or 5,7-dihydroxytryptamine-induced pigmentation also proved to be a reliable technique for the visualization of serotonin-containing cell bodies. In comparison with these two techniques, the glyoxylic acid fluorescence method appeared to be less sensitive. The distribution and number of serotonin-containing neurons and biochemically measured serotonin in specific ganglia showed a close correlation. By combining the results of the three labelling techniques, a detailed map of serotonin-containing neurons was constructed, and this was compared with maps of identified neurons prepared from earlier electrophysiological studies. Previously described serotonergic neurons were consistently found, as well as several new serotonin-containing cell types in the cerebral, visceral and parietal ganglia. A network of serotonin-containing inter- and intraganglionic axon tracts, and thin serotonergic fibres in the perineurium were also demonstrated. This in vivo and in vitro identification of serotonin-containing neurons will facilitate further neurophysiological analysis of serotonergic neural mechanisms in Lymnaea.
Serotonin is a vital neurotransmitter for the functioning of the nervous system in species throughout the animal phyla. Despite its ubiquitous nature, the metabolism of this molecule has yet to be completely elucidated in even the most basic of organisms. Two novel serotonin catabolites, serotonin-O-sulfate and gamma-glu-serotonin-O-sulfate, are chemically characterized using capillary electrophoresis with wavelength-resolved fluorescence detection and electrospray mass spectrometry, and the formation of gamma-glu-serotonin in Aplysia californica is confirmed. These novel compounds appear to be synthesized enzymatically, and known mammalian enzymes exist for all serotonin transformations observed here. The pathway of serotonin inactivation depends upon the type of neuronal tissue subjected to neurotransmitter incubation, with assorted serotonin products observed in distinct locations. Initially demonstrated to be in the metacerebral cell (MCC) soma, the new serotonin metabolite serotonin-O-sulfate may contribute to important functions in the serotonergic system beyond simple serotonin inactivation.
Exogenous serotonin has been shown to induce an elevated, flexed posture in crustaceans and has also been hypothesized to enhance aggressive behavior. We conducted three experiments to further investigate the effects of serotonin and serotonin analogs on posture and agonistic behavior in the crayfish Procambarus clarkii. In the first experiment, we recorded behavioral responses to five different concentrations of serotonin injected into the ventral hemolymph sinus. The amine elicited a series of behaviors including the characteristic high, flexed posture, but none were clearly associated with aggression. In our second experiment, we tested serotonin and four serotonin receptor agonists [1-(3-chlorophenyl)piperazine dihydrochloride, 2-methyl-5-hydroxytryptamine maleate, 5-carboxamidotryptamine maleate and alpha-methyl-5-hydroxytryptamine maleate] and measured the ability of each agonist to mimic the actions of the amine. High concentrations of 1-(3-chlorophenyl)piperazine dihydrochloride most closely mimicked the actions of serotonin; 5-carboxamidotryptamine maleate induced a high stance, but did not otherwise induce effects similar to serotonin. In our third experiment, we conducted an analysis of fighting behavior between pairs of crayfish that had received injections of control saline, serotonin, or 5-carboxamidotryptamine maleate. Serotonin generally reduced the level of aggression between opponents, whereas 5-carboxamidotryptamine maleate enhanced the performance of several agonistic behaviors.
OBJECTIVES: We have previously reported that acute administration of the specific serotonin reuptake inhibitor (SSRI), fluoxetine, resulted in a decrease in mitogen-induced blood lymphocyte proliferation. The present studies further examine the specificity of this response to serotonin reuptake systems and the potential role of endogenous serotonin in mediating these effects. METHODS: Male Sprague-Dawley rats were treated intraperitoneally with the SSRIs, fluoxetine (6-10 mg/kg) or sertraline (20 mg/kg), dopamine and norepinephrine reuptake inhibitors, GBR 12909 and desipramine, respectively (6 mg/kg) or the serotonin precursor, 5-hydoxytryptophan (5-HTP, 50 mg/kg) 2 h prior to sacrifice. The serotonin-depleting agents, p-chlorophenylalanine (PCPA, 2 x 200 mg/kg) or the serotonin-lesioning agent, p-chloroamphetamine (PCA, 2 x 10 mg/kg) were administered intraperitoneally 5-7 days prior to fluoxetine (10 mg/kg) administration. RESULTS: Unlike the SSRIs, which significantly suppressed lymphocyte proliferation responses, selective norepinephrine or dopamine reuptake inhibition had no effect on lymphocyte proliferation. Elevation of extracellular serotonin levels with the serotonin precursor, 5-HTP, resulted in a similar decrease in lymphocyte proliferation as that seen with SSRI administration. Conversely, decreases in endogenous serotonin following PCA or PCPA treatment prevented the fluoxetine-induced decreases in lymphocyte proliferation. CONCLUSIONS: These results suggest that decreases in mitogen-induced lymphocyte proliferation following acute fluoxetine administration were due to elevations in extracellular serotonin following reuptake inhibition.
BACKGROUND: Serotonin is one of the factors regulating mesangial cell proliferation, and convergent evidence supports its involvement in the development of glomerulonephritis. In this study, we identified a serotonin transporter and the amine-degrading enzyme monoamine oxidases (MAOs) in mesangial cells, and we studied their involvement in serotonin degradation. METHODS: MAOs were characterized in membrane preparations and intact mesangial cells by enzyme assay using [14C]5-hydroxytryptamine and [14C]beta-phenylethylamine as specific substrates for MAO-A and MAO-B, respectively, and by Western blot analysis. The expression of a serotonin transporter was determined by [14C]5-hydroxytryptamine uptake experiments and Western blot. Mesangial cell proliferation was measured by BrdU incorporation. RESULTS: Quantitation of the MAO isoforms by enzyme assay and Western blot analysis showed that MAO-A was largely predominant in mesangial cells, accounting for approximately 90% of the total enzyme population. The MAO substrate [14C]serotonin was transported into mesangial cells by a saturable uptake system (Vmax 310 +/- 36 pmol/30 min/mg protein; Km 5.9 +/- 1.4 microM) displaying the pharmacological properties of a serotonin transporter. The expression of a serotonin transporter was confirmed by Western blot analysis. MAO activity measured in intact cells showed that after accumulation into mesangial cells, [14C]serotonin was metabolized by MAO-A. Finally, serotonin-mediated mesangial cell proliferation was significantly increased after irreversible MAO inhibition. CONCLUSIONS: Our results suggest that serotonin concentration and function in glomeruli may be regulated in part by its transport into mesangial cells and degradation by MAO-A.
Serotonin uptake carriers occur on serotonin neurons, on glial cells and on blood platelets. The uptake carrier on serotonin neurons inactivates serotonin that has been released into the synaptic cleft by transporting it back into the nerve terminal. The serotonin uptake carrier is the means by which blood platelets acquire serotonin, since they do not synthesize it. The function of the serotonin uptake carrier on glial cells is poorly understood. Selective inhibitors of serotonin uptake enhance neurotransmission via serotonergic neurons and have been useful pharmacologic tools for studying physiologic roles of serotonin neurons. Some serotonin uptake inhibitors are finding therapeutic uses in mental depression and other psychiatric disorders and in treating obesity and bulimia; other therapeutic applications continue to be evaluated.
It has been suggested that serotonin serves as a neurotransmitter in the horseshoe crab, Limulus polyphemus. While some studies of identified groups of central neurons have been conducted, little is known concerning the neuronal organization in Limulus central ganglia. This study was undertaken to determine the localization of serotoninergic neurons in the opisthosomal ventral nerve cord of Limulus and to construct a basis for further comparative biochemical and pharmacological studies of the specific function of these neurons. Endogenous serotonin was detected in the ventral nerve cord (chain of abdominal ganglia) by high-performance liquid chromatography and electrochemical detection (HPLC-EC). Endogenous serotonin was quantified in the 9th through 13th ganglia, anterior (hemal) nerves, posterior (branchial) nerves, and connectives. The serotonin content in the abdominal ganglia was significantly reduced when the ganglia were incubated for 24 hours in Leibovitz's (L-15) medium containing reserpine or 5,7-dihydroxytryptamine (5,7-DHT), neurotoxins that block the uptake of serotonin into storage vesicles. The distribution of serotonin-immunoreactive neurons in the ventral nerve cord was determined by indirect immunocytochemistry. Treatment of the chain of ganglia with an anti-serotonin antiserum followed by treatment with a fluorescent-labeled antiserum raised against the primary antibody demonstrated specific staining in each ganglion, the ganglionic roots, and connectives. Clusters of serotonin-immunoreactive neurons were observed anteriolaterally and posteriorly in each ganglion. Processes from dense fiber bundles extended from these clusters of neurons to the central region of each ganglion. These results demonstrate that serotonin-immunoreactive neurons are present in the opisthosomal ventral nerve cord of the horseshoe crab and that serotonin may function as a neurotransmitter.
It has been proposed that considerable DNA damage may be caused by endogenous metabolites produced during the body's normal metabolic processes. 5-hydroxytryptamine (serotonin) is an important neurotransmitter in brain and spinal cord. We have previously shown that serotonin induces oxidative cleavage of DNA strands in the presence of copper ions. In the present paper we have examined the mechanism of copper binding by serotonin using absorption spectroscopy, Cu(II)-mediated lipid peroxidation and by determining the oxidation of the serotonin molecule. Addition of increasing concentrations of Cu(II) to serotonin leads to a progressive enhancement in the absorption band and is accompanied by a shift towards a lower wavelength indicative of the formation of an oxidised species of serotonin. Studies with the structurally related molecules tryptophan and melatonin showed that only serotonin is able to reduce Cu(II) to Cu(I). Similarly, only serotonin was found to be able to abolish the copper-mediated peroxidation of mitochondria. These results suggested the involvement of the phenolic group in copper binding. Further, it was also shown that the binding of copper to serotonin leads to the formation of a quinone in the absence of molecular oxygen. Based on these results, a model has been proposed in which serotonin reduces two molar equivalents of Cu(II) to Cu(I) through a reaction involving two electron oxidation of the phenolic ring to a quinone methide.
1. Serotonin has been shown to be an important neurohormone that modulates behavioral output in lobsters. This study explores the neurochemical identity of excitatory and inhibitory inputs to a pair of identified serotonin-containing neurons in the first abdominal ganglion (A1) of the lobster that also contain the pentapeptide proctolin. These neurons are spontaneously active, appear to be driven by an endogenous pacemaking mechanism, and have been shown to play a role in circuits that control behaviorally relevant postures. 2. To explore the exogenous control of neuronal activity, a number of putative neuroactive compounds were superfused over the A1 serotonin-containing neurons in isolated ventral nerve cords. Three amines, gamma-aminobutyric acid (GABA), octopamine, and serotonin, were found to be potent inhibitors in a dose-dependent manner. GABA inhibition had a rapid onset and termination and yielded a transient postinhibitory rebound activity immediately after amine washout; activity eventually returned to the preinhibition level. Octopamine inhibition had a less rapid onset and termination, and the steady-state activity after inhibition was higher than preinhibition firing in most cells (22% of which were statistically significantly increased). Serotonin inhibition had a relatively slow onset and termination, and the steady-state activity after inhibition remained low in most cells (19% significantly decreased). 3. Repeated or prolonged exposure to these three amines reduced the efficacy of inhibition. Three types of desensitization have been empirically defined: 1) rapid desensitization, which tended to dampen the initial inhibition; this was particularly strong for GABA inhibition; 2) low-dose desensitization, in which the A1 serotonin containing neurons became less sensitive to inhibition by a particular concentration of amine after prior exposure to a lower concentration, although the lower concentration may not by itself have had inhibitory effects; this was seen with octopamine inhibition; and 3) long-term desensitization, in which the efficacy of inhibition of a particular amine concentration dwindled with repeated applications (even with up to 160 min washout between applications); this was seen with octopamine and serotonin inhibition, although not for every A1 serotonin-containing neuron analyzed. 4. Bath application of these three amines was still capable of inhibiting the A1 serotonin-containing neurons when inhibitory synaptic transmission was blocked by use of low Ca2+/high Mg2+ solutions. 5. The pentapeptide proctolin excited the A1 serotonin-containing neurons: it activated silent neurons and increased the firing rate of spontaneously active neurons. The excitatory effect outlasted the presence of the peptide.(ABSTRACT TRUNCATED AT 400 WORDS)
Using high-performance liquid chromatography and gas chromatography, we reevaluated the 24-h influence of a serotonin- and dopamine-rich diet on platelet serotonin and serotonin, 5-hydroxyindoleacetic acid (5-HIAA), and major catecholamine metabolites in the urine of 15 healthy adults. Although there were significant responses in urinary free serotonin and catecholamine metabolites, their concentrations did not exceed the upper limits of the reference ranges for any of the participants. For urinary 5-HIAA, pronounced effects were observed within 2-4 h. After 6-8 h, results for 11 participants exceeded the upper limit of the reference range. The median recovery of dietary serotonin as urinary 5-HIAA was 20% and subject to a large range (1-50%). There was no significant change in platelet serotonin. We conclude that, using specific analytical methods, no dietary restrictions need be imposed to diagnose catecholamine (metabolite)-producing tumors. For diagnosis of carcinoids on the basis of urinary 5-HIAA it is appropriate to completely abstain from serotonin-containing foods for greater than or equal to 12 h before testing. Platelet serotonin is a more sensitive marker for carcinoids that produce only small amounts of serotonin, and is unaffected by dietary serotonin.
The involvement of serotonin and its receptor subtype in the induction of hepatocyte DNA synthesis was investigated in primary cultures of adult rat hepatocytes. Serotonin caused a dose-dependent increase in DNA synthesis in primary cultures of rat hepatocytes in the presence of epidermal growth factor (EGF) and insulin, as measured by [3H]thymidine incorporation. The serotonin S2 receptor antagonists, ketanserin (10(-6) mol/L) and spiperone (10(-6) mol/L), blocked stimulation of DNA synthesis by serotonin. Displacement studies on [3H]5-hydroxytryptamine (5-HT) binding to crude membranes from control and regenerating liver tissue, using cold ketanserin and spiperone, showed an increased involvement of S2 receptors of serotonin in the regenerating liver during the DNA-synthetic phase. Serotonin enhanced the phosphorylation of a 40-kd substrate protein of protein kinase C (PKC) in the regenerating liver during the DNA synthetic phase of the hepatocyte cell cycle. This was blocked by ketanserin, indicating that serotonin S2 receptor activates PKC, an important second messenger in cell growth and division, during rat liver regeneration. Our results show that serotonin can act as a potent hepatocyte comitogen and induce DNA synthesis in primary cultures of rat hepatocytes, which is suggested to be mediated through the serotonin S2 receptors of hepatocytes.
Serotonin selective reuptake inhibitors (SSRIs) are currently among the most frequently prescribed therapeutic agents in all of medicine. Their therapeutic actions are diverse, ranging from efficacy in depression to obsessive-compulsive disorder, panic disorder, bulimia and other conditions as well. The plethora of biological substrates, receptors and pathways for serotonin are candidates to mediate not only the therapeutic actions of SSRIs, but also their side effects. Specifically, the immediate actions of SSRIs are mostly side effects, and may be mediated by the initiating actions of SSRIs, namely negative allosteric modulation of the serotonin transporter. A leading hypothesis to explain these immediate side effects is that serotonin is increased at specific serotonin receptor subtypes in discrete regions of the body where the relevant physiologic processes are regulated. Desensitization of post-synaptic receptors in these same discrete brain regions may explain the development of tolerance to these same side effects. The explanation for therapeutic effects characteristic of SSRIs may be found in delayed neurochemical adaptations. A leading hypothesis for this action is desensitization of somatodendritic serotonin 1A autoreceptors in the midbrain raphe. The hypothesis to explain why SSRIs have such diverse therapeutic actions is that somatodendritic 5HT1A autoreceptor desensitization increases serotonin in those critical brain regions and at those key serotonin receptor subtype(s) which may mediate the pathophysiologies of the various disorders. Understanding the topography of serotonin receptor subtypes in discrete anatomical pathways may enhance our understanding of both the therapeutic actions and side effects of these important pharmaceutical agents.
Tyramine and dopamine are taken up by rat platelets through the serotonin uptake mechanism while phenethylamine is not taken up. This indicates that an aromatic hydroxyl group is a structural requirement for the uptake of phenethylamine derivatives by rat platelets. Although none of these phenethylamine derivatives induce platelet shape change, they inhibit serotonin-induced shape change and serotonin uptake with the same relative potency (tyramine greater than phenethylamine greater than or equal to dopamine). This suggests that the receptors controlling serotonin uptake and serotonin-induced shape change have a common structural component that binds phenethylamine derivatives. However, the fact that phenethylamine derivatives activate the serotonin uptake mechanism but do not induce platelet shape change suggests that serotonin uptake and serotonin-induced shape change are mediated by two distinct activation sites of serotonin receptors.