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At least 19 recordsLinked to original sources
PubMed1978

Release of endogenous serotonin from two identified serotonin-containing neurones and the physiological role of serotonin re-uptake.

1. The amounts of endogenous serotonin (5-HT) released into the medium by the cerebro-buccal ganglionic ring of Aplysia californica incubated in artificial sea water (ASW) were measured. The rate of spontaneous 5-HT release varied between 0.4 and 1.2 p-mole per hour, which is less than 1% of the total 5-HT present in this preparation.2. Direct stimulation of the ordinarily silent 5-HT-containing giant cerebral neurones resulted in a 80-100% increase of the 5-HT released, but only when the 5-HT uptake was blocked by chlorimipramine (1-10 muM).3. High K(+) media (50 mM) also caused a significant increase in the amount of 5-HT released from the preparation provided that chlorimipramine (1-10 muM) was present in the incubation fluid.4. Co(2+) ions (10-30 mM) added to the incubating medium blocked the spontaneous leak of endogenous 5-HT as well as the release, in the presence of chlorimipramine, evoked either by stimulation of the 5-HT-giant cerebral neurones or high K(+)-media.5. In the presence of chlorimipramine or desmethylimipramine, the duration and/or the amplitude of the excitatory or the inhibitory synaptic potentials evoked in the buccal neurones by the stimulation of the 5-HT giant cerebral neurones were markedly enhanced.6. These results strongly support the idea that 5-HT is the synaptic transmitter released at the excitatory and inhibitory junctions established by the 5-HT giant cerebral neurones in the ipsilateral buccal ganglia. In addition, they underline the role of amine re-uptake in the physiological inactivation of 5-HT as a transmitter.

Action Potentials↗
PubMed1977

Serotonin and dopamine as neurotransmitters in mytilus: block of serotonin receptors by an organic mercurial.

The effects of mersalyl, bromo-LSD (BOL) and methysergide (UML) on the relaxation of catch by certain indole and catechol derivatives were studied in the anterior byssus retractor muscle of Mytilus. Mersalyl antagonized relaxation in response to serotonin whereas BOL and UML were less effective. Two other indole derivatives, ergotamine and gramine, were also blocked by mersalyl; BOL and UML antagonized relaxation in response to dopamine more effectively than did mersalyl. Two other catechols, epinephrine and norepinephrine, were also blocked more effectively by BOL and UML than by mersaly. Relaxation in response to neural stimulation was blocked more effectively by mersalyl than by BOL. The blocking action of mersalyl on neural relaxation reversed very poorly after washing the drug, but complete reversal was induced by brief exposure to dithiothreitol. It is concluded that the evidence supports an hypothesis that the transmitter released by relaxing nerves is serotonin. It is suggested that mersalyl blocks serotonin by combining with a sulfhydryl group at or near the site on the receptor to which the indole nitrogen attaches.

Acetylcholine↗
PubMed1979

Corticosteroidogenesis by isolated human adrenal cells: effect of serotonin and serotonin antagonists.

The direct effect of serotonin and antiserotonin agents on adrenal steroid biosynthesis was studied in isolated adrenal cells derived from patients with Cushing's syndrome. The results indicate that serotonin increases corticosterone production, while the serotonin antagonists cyproheptadine and methysergide depress adrenal steroid - particularly cortisol and aldosterone - biosynthesis.

Adrenal Cortex↗
PubMed1979

Reduction of whole blood serotonin in depressed patients treated with a new, selective serotonin-uptake inhibitor, femoxetine.

Femoxetine, a phenylpiperidine derivative with potent serotonin (5-HT)-uptake inhibitory properties, was investigated in 12 depressive patients for its clinical effect as well as its effect on 5-HT concentration in whole blood. The global evaluation after 6 weeks showed a good effect in six patients. The 5-HT concentration was found to be reduced from a mean value of 0.21 to about 0.05 micrograms/ml, indicating a total depletion of 5-HT from the thrombocytes. The steady-state concentrations of femoxetine resulted in reduction of 5-HT to the same level in all patients. No correlation between degree of 5-HT reduction and therapeutic effect was found.

Anisoles↗
PubMedDate not supplied

The effect of serotonin receptor blocking agents--cyproheptadine and danitracen--on serotonin turnover in the rat brain.

Cyproheptadine (CPH), 0.5 mg/kg ip, did not affect the cerebral serotonin (5-HT) level, but elevated the level of 5-hydroxyindoleacetic acid (5-HIAA). Danitracen (DN), 1 mg/kg ip, depressed the cerebral 5-HT level and elevated the 5-HIAA level, but at a dose 10 mg/kg did not affect the levels of either the amine, or its metabolite. Both CPH and DN, 1 mg/kg, significantly potentiated the disappearance of 5-HT after administration of p-chlorophenylalanine. DN, in a low dose, accelerated the disappearance of 5-HT after inhibition of 5-HT synthesis by alpha-propyldopacetamide. The rate of accumulation of 5-HIAA after probenecid, was increased only by CPH. CPH did not affect the 5-HT accumulation after pargyline, while DN depressed its accumulation. The results of experiments on the levels of 5-HT and 5-HIAA, and on the rate of disappearance of 5-HT after inhibition of tryptophan decarboxylase suggest that CPH and DN increase the 5-HT turnover. The results of studies on the turnover rate of 5-HT after administration of probenecid and parygline do not corroborate fully this assumption. Possibly, this discrepancy may depend on differences in the action of 5-HT in various brain areas and interaction of serotoninolytics tested with effects of the MAO inhibitor.

Amides↗
PubMed1978

Effect of p-chlorophenylalanine on cerebral serotonin binding, serotonin concentration and motor activity in the rat.

The effect of p-chlorophenylalanine (PCPA) on the specific binding of 3H-serotonin (5-HT) was investigated in crude membrane preparations of the rat forebrain. The level of cerebral 5-HT and 5-hydroxyindoleacetic acid were concomitantly determined. A single dose of PCPA (300 mg/kg i.p.) increased specific binding at a low concentration of 3H-5-HT within 24 h by more than 100%. The time course of the elevation of specific binding was mirrored by the reduction in the 5-HT level. However, 8--10 days after drug administration, specific binding was close to the control level, while 5-HT was still significantly reduced. A Scatchard analysis revealed that the apparent affinity was significantly increased (KD reduced) during the initial period after PCPA administration, whereas the number of binding sites (BMax) was little changed. In contrast, after reported injections of PCPA (3 injections of 300 mg/kg at 6--8 day intervals, or 100 mg/kg/day for up to 12 days) leading to a prolonged 5-HT depletion, BMax was significantly increased, while KD tended to be restored towards the baseline level. Daily injections of PCPA (100 mg/kg) for 12 days resulted in a transitory increase in day-time motor activity with a maximum on drug day 3, and in a persistent reduction of night-time activity. It is concluded that the initial PCPA-induced decrease in KD was due to a reduced competition for binding sites by the endogenous 5-HT, whereas the increase of BMax after a prolonged 5-HT depletion may reflect a 5-HT receptor supersensitivity.

Animals↗
PubMed1978

Effects of serotonin, of its biosynthetic precursors and of the anti-serotonin agent metergoline on the release of glucagon and insulin from rat pancreas.

We have evaluated the effect of serotonin (5-HT) and of its biosynthetic precursors 5-Hydroxytryptophan (5-HTP) and tryptophan (TRP) on the release of immunoreactive glucagon (IRG) and insulin (IRI) from isolated islets and pieces of pancrease of the rat. In isolated islets, 5-HT inhibited the IRI response to a high glucose concentration (3.0 mg/ml), without affecting the IRG response to either a low (0.5 mg/ml) or a high glucose concentration; TRP stimulated the IRG and IRI response to the low glucose concentration, while 5-HTP was ineffective. When pieces of pancreas were used, 5-HT and 5-HTP inhibited IRG response to both glucose concentrations, while IRI release was inhibited only by 5-HT. The anti-5-HT agent metergoline enhanced the release of IRG and IRI by pieces of pancreas at both glucose concentrations. The results indicate that exogenous and endogenous 5-HT inhibit basal as well as glucose-mediated IRG and IRI release; that isolated islets are less sensitive than pieces of pancreas to the inhibitory effect of 5-HT and that TRP acts as an amino acid and not as a precursor of 5-HT.

5-Hydroxytryptophan↗
PubMed1978

Participation of serotonin in thyrotropin release. I. Evidence for the action of serotonin on thyrotropin releasing hormone release.

Injection of serotonin (5-HT) into the third ventricle of the rat resulted in a rapid increase of serum TSH; a significant effect was observed 5 min after injection, whereas the maximal effect appeared 10 min after the injection of 1 microgram 5-HT. This stimulating effect of 5-HT was completely prevented by pretreatment with cyproheptadine, a blocker of 5-HT receptors, whereas fluphenazine, a dopamine receptor blocker, was unable to block it. Third venticle injection of 5-HT in rats bearing anterior hypothalamic lesions (which did not affect the suprachiasmatic nucleus or the medio-basal hypothalamus) also induced an increase of serum TSH similar to that observed in normal rats despite the fact that these animals show a lower basal TSH. In vitro, the addition of 5-HT to an incubation medium containing one hemi-anterior pituitary did not modify medium TSH, whereas 5-HT addition induced an increase of medium TSH in the system containing one hemi-anterior pituitary and two hypothalami. We conclude that 5-HT acts on TSH function probably through a stimulation of TRH release.

Animals↗
PubMed1979

Participation of serotonin in thyrotropin release. II. Evidence for the action of serotonin on the phasic release of thyrotropin.

During a 12-h light 12-h dark schedule (lights off at 1900 h), male Sprague-Dawley rats show a circadian rhythm of plasma TSH with a zenith near midday. The participation of serotonin (5HT) in the phasic release of TSH was studied using both pharmacological and surgical-stereotaxical approaches. Animals treated with parachlorophenylalanine methyl ester (pCPA), an inhibitor of 5HT synthesis (one or two injections of 250 mg/kg each) showed a reduction or a disappearance of the diurnal peak of TSH, respectively. Additional treatment by 5-hydroxytryptophan, a precursor of 5HT, completely, restored the diurnal TSH peak. Treatment with 5,6-dihydroxytryptamine creatine sulfate, a neurotoxin which selectively destroys 5HT terminals, also induced alterations of the diurnal peak of TSH. There were no major modifications observed in the low nocturnal levels of TSH in rats treated with pCPA, 5-hydroxytryptophan, or 5,6-dihydroxytryptamine. The major serotoninergic innervation of the hypothalamus originates from the raphe dorsalis or centralis; destruction of these two nuclei caused a quasiabolition of the diurnal TSH peak (only a low amplitude TSH circadian rhythm persisted). Hypothalamic 5HT content was measured in the majority of these experiments; the greatest depletions (near 90%) were observed after two injections of pCPA or in rats bearing raphe lesions. We conclude that the diurnal peak of TSH, observed during the physiological circadian rhythm, is serotoninergic dependent.

5,6-Dihydroxytryptamine↗