Serotoninergic Agonists Research Articles

Serotoninergic modulation of cell volume response to estramustine: an image-analysis study on perifused individual glioma cells

A technique of microscopy with computerised detection of early morphological changes during continuous perifusion was used to monitor the geometry changes of cultured glioma cells (MG-251) when exposed to 40 mg/L estramustine phosphate (EMP) alone or in combination with granisetron (0.1 μmol/L), ondansetron (0.1 μmol/L), or serotonin (1 μmol/L). When the cells were exposed to EMP, cell volume measured as projected cell area (PCA) rapidly increased. Serotonin and ondansetron, but not granisetron, prevented the acute EMP response (PCA). Serotonin, but none of the 5-HT 3 receptor antagonists, protected against the cytotoxicity of EMP to the glioma cells as measured by a fluorometric microculture assay. Our results demonstrate hitherto unknown differences between selective 5-HT 3 receptor antagonist on the cellular response to EMP and shows the necessity to study the receptor antagonists from viewpoint of interference with the antitumour drug effects on malignant cells. The perifusion technique could be used to study the effects of serotoninergic agonists and antagonists on cell volume regulation of cells exposed to anticancer drugs.

Regulation of glial Na+/K+-ATPase by serotonin: identification of participating receptors.

The purpose of the present study was the characterization of the receptors participating in the regulatory mechanism of glial Na+/K+-ATPase by serotonin (5-HT) in rat brain. The activity of the Na+ pump was measured in four brain regions after incubation with various concentrations of serotoninergic agonists or antagonists. A concentration-dependent increase in enzyme activity was observed with the 5-HT1A agonist R (+)-2-dipropylamino-8-hydroxy-1,2,3, 4-tetrahydronaphthalene hydrobromide (8-OH-DPAT) in homogenates or in glial membrane enriched fractions from cerebral cortex and in hippocampus. Spiperone, a 5-HT1A antagonist, completely inhibited the response to 8-OH-DPAT but had no effect on Na+/K+-ATPase activity in cerebellum where LSD, a 5-HT6 agonist, elicited a dose-dependent response similar to that of 5-HT. In brainstem, a lack of response to 5-HT and other agonists was confirmed. Altogether, these results show that serotonin modulates glial Na+/K+-ATPase activity in the brain, apparently not through only one type of 5-HT receptor. It seems that the receptor system involved is different according to the brain region. In cerebral cortex, the response seems to be mediated by 5-HT1A as well as in hippocampus but not in cerebellum where 5-HT6 appears as the receptor system involved.

Comparative biochemical and pharmacological characterization of the mouse 5HT5A 5-hydroxytryptamine receptor and the human beta2-adrenergic receptor produced in the methylotrophic yeast Pichia pastoris.

Over the last few years, Pichia pastoris has been developed into a powerful expression system for a multitude of foreign genes. Here, we demonstrate that the P. pastoris expression system has similar power to the baculovirus expression system in high-level production of two G-protein-coupled receptors, the mouse 5HT5A 5-hydroxtryptamine receptor and the human beta2-adrenergic receptor. Different expression plasmids were constructed in which the cDNAs of the two receptors were cloned under the transcriptional control of the highly inducible promoter of the P. pastoris alcohol oxidase 1 (AOX1) gene. In three expression plasmids, the receptors were fused to the Saccharomyces cerevisiae alpha-factor prepropeptide and also to the c-myc tag or the FLAG tag to permit immunological detection of the receptors. After transformation into P. pastoris strains KM71 and SMD 1163, recombinant clones were selected and tested for the production of the 5HT5A receptor and the beta2-adrenergic receptor by radioligand binding using [N-methyl-3H]lysergic acid diethylamide and [5,7-3H](-)CGP-12177 respectively. The production level of the 5HT5A receptor was improved by a factor of three by fusion with the alpha-factor prepropeptide. Also, the higher gene dosage resulting from multiple insertions of the expression cassette led to an improvement in production by a factor of two for both receptors. The addition of the adrenergic antagonist alprenolol to the culture medium had a positive effect on the number of specific binding sites detectable in clones producing the beta2-adrenergic receptor. For the 5HT5A receptor the addition of yohimbine resulted in a similar but smaller effect. Binding assays revealed that approx. 25 pmol of beta2-adrenergic receptor and approx. 40 pmol of 5HT5A receptor per mg of membrane protein in crude membrane preparations were produced. The pharmacological profiles for the heterologously produced receptors, estimated by ligand-displacement analysis using certain adrenergic and serotoninergic agonists and antagonists, were comparable with those reported for the receptors expressed in mammalian systems. Immunoblot analysis of the 5HT5A receptor revealed an apparent molecular mass about 20 kDa higher than expected from the amino acid sequence. Here, the Kex2 endopeptidase failed to process the alpha-factor leader correctly. Blocking glycosylation in vivo by tunicamycin or in vitro deglycosylation of membranes by endoglycosidase H resulted in correct processing. In contrast, the beta2-adrenergic receptor fusion to the alpha-factor leader was correctly processed by the internal Kex2 endopeptidase. The Kex2-processed beta2-adrenergic receptor was not glycosylated. In conclusion, the high-level production of the two receptors in P. pastoris will allow their purification in quantities sufficient for subsequent biophysical and structural studies.

The m-chlorophenylpiperazine test in cluster headache: a study on central serotoninergic activity.

The central serotoninergic agonist m-chlorophenylpiperazine (m-CPP) stimulates several 5HT receptor subtypes. It induces the release of both cortisol and prolactin (PRL). In this study we investigated central serotoninergic responsiveness in cluster headache by monitoring cortisol and PRL responses to m-CPP administration. Twenty-three patients with episodic cluster headache and 17 sex-matched and age-matched healthy subjects were studied. The cluster headache patients were tested during a cluster period, and none were receiving prophylaxis. A single oral dose of m-CPP, 0.5 mg/kg, was given at time 0. Blood samples were drawn at -30, 0, 30, 60, 90, 120, 150 and 180 min. PRL and cortisol levels were assayed in the samples. PRL and cortisol delta maxima (delta maximum = maximum response - baseline level at time 0/baseline level at time 0) were evaluated in each patient and mean values compared. Serum levels of m-CPP were detected by HPLC and correlated to hormonal responses. Reduced cortisol (p < 0.02) and increased PRL (p < 0.05) delta maxima were observed in cluster headache patients. Increased basal cortisol plasma levels (p < 0.05) and reduced basal PRL plasma levels (p = 0.06) also characterized cluster headache patients. This is the first study evaluating central serotoninergic responsiveness to m-CPP in cluster headache and these data suggest impaired central serotoninergic function in this pathology.

Microdialysis monitoring of variations in extracellular levels of serotonin, GABA and excitatory amino acids in the frontal cortex of awake rats in response to a single peripheral or central administration of dexfenfluramine

The effects of a single dexfenfluramine ( d-fen) administration on the release of endogenous serotonin (5-hydroxytryptamine, 5-HT), excitatory (glutamate, Glu, aspartate, Asp) and inhibitory (γ-aminobutyric acid, GABA) amino acids from the frontal cortex were studied by using in vivo microdialysis in freely-moving rats. Extracellular levels of these neurotransmitters were measured with HPLC coupled to electrochemical detection or with capillary electrophoresis coupled to laser-induced fluorescence detection (CE-LIFD). In a first study, single intraperitoneal administration of d-fen (0.5, 1.3, 5 and 10 mg/kg) increased extracellular 5-HT levels in a dose-dependent manner (maximal increase by 982% over baseline for the highest dose) while changes in Glu, Asp or GABA never reached statistical significance. In a second study, 73 nM of d-fen applied locally through the frontocortical dialysis probe, at a flow rate of 1.5 μl/min in 30 μl of perfusion fluid for 20 min, increased extracellular 5-HT and Asp levels [the maximal increases were to 1804% and 280% of the respective basal values (100%)] without altering extracellular levels of Glu and GABA. Thus, the order of magnitude of the changes induced by systemic administration or local infusion of d-fen on frontocortical extracellular levels of several neurotransmitters (5-HT ≫ Asp > GABA = Glu) demonstrate that d-fen, an indirect serotoninergic agonist, mainly increases 5-HT release while producing slight (Asp) or no (Glu, GABA) short-term in vivo variations in amino acid extracellular levels in the rat frontal cortex.

Reduced prolactin release during immobilization stress in thyrotoxic rats: role of the central serotoninergic system.

Adult Wistar male rats in a thyrotoxic state T4 increases rats) induced by administration of T4 (350 micrograms/kg/day, i.p. for 7 days) as well as their euthyroid controls were submitted to immobilization stress during forty minutes. Prolactin (PRL) secretion during stress was significantly lower in T4 increases rats as compared to control animals. Treatment with MK 212, a serotoninergic agonist, entirely reverts this situation. The effect of MK 212 seems to be due to its interaction with 5-HT2 receptors since it is blocked by LY 53857, a selective 5-HT2 antagonist. Furthermore, the blockade of 5-HT2 receptors by LY 53857, a selective 5-HT2 antagonist, significantly diminishes prolactin (PRL) response to stress in euthyroid rats but has no effect in T4 increases animals. It is suggested that an increased concentration of thyroid hormone in plasma disrupts an endogenous serotoninergic brain input necessary to trigger stress-induced PRL rise.

Calcium Currents in Diseased Human Cardiac Cells

Isolated atrial or ventricular human cardiomyocytes were dissociated from the heart of patients undergoing either open heart surgery (CS) or cardiac transplantation (CT). L-type Ca currents were recorded on cardiomyocytes from CS or CT by whole-cell voltage clamp technique. Although the electrophysiologic properties of L-type Ca current were similar in atrial and ventricular myocytes from CS and CT patients, cells from CT had larger capacitance and lower current density. Whereas isoprenaline (Iso) induced an increase in the Ca current amplitude both in atrial and ventricular cells, a serotoninergic agonist (5-HT4) enhanced Ca current only in atrial cells. Although the affinity for Iso and 5-hydroxytryptamine (5-HT) was not modified between CS and CT (K0.5 = 0.1 microM), the amplitude of the response to both Iso and 5-HT were altered in CT. Some electrophysiologic and pharmacological properties of Ca current are altered in cardiomyopathic human hearts. These alterations correspond to (a) a reduction in the number of functional L-type Ca channels, and (b) a decreased response to both beta-adrenergic and serotoninergic agonists indicating that potentiation of Ca channel activity through the cyclic AMP pathway is altered.

Effect of Acute Administration of the Serotoninergic 5-HT1A Agonist Flesinoxan on Feeding in the Rat: could the Hyperphagia be Mediated by Neuropeptide Y?

Effect of Acute Administration of the Serotoninergic 5-HT1A Agonist Flesinoxan on Feeding in the Rat: could the Hyperphagia be Mediated by Neuropeptide Y?

Evidence for downregulation of hypothalamic 5-hydroxytryptamine receptor function in endurance-trained athletes.

Serum prolactin (PRL) was used as a hormone marker of serotoninergic function following oral administration of an acute dose of a serotoninergic agonist. Five male endurance-trained athletes (ET) and five healthy non-endurance-trained controls (NT) were studied. The peak PRL concentration was lower (P = 0.031) for the ET athletes (486 +/- 208 mU l-1; mean +/- S.D.) than for the NT controls (1000 +/- 385 mU l-1); the total release of PRL was also lower (P = 0.042) for the ET subjects. The lower neuroendocrine response to a serotoninergic agonist in the endurance-trained athletes suggests a downregulation of central serotoninergic receptor function in response to endurance training in man.

ChemInform Abstract: Synthesis of 8‐Dipropylamino‐7,8,9,10‐tetrahydrophenanthridines as Potential Serotoninergic Agonists.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of 8‐dipropylamino‐7,8,9,10‐tetrahydrophenanthridines as potential serotoninergic agonists

AbstractA number of 8‐dipropylamino‐7,8,9,10‐tetrahydrophenanthridines have been prepared as analogs of the known serotoninergic agonist 8‐hydroxy‐2‐(dipropylamino)tetralin (8‐OH‐DPAT) and their affinity for the 5‐HT1A receptor subtype evaluated by radioligand binding assay.

The effect of serotoninergic 1A agonists on rotating behavior in rats with raphe lesions

This work is devoted to the study of CPK BB content in nuclear fraction of nervous cells in normal brain and in brains of mental (schizophrenia and Alzheimer disease) patients. With the help of the immunocytochemistry and immunoblotting was detected, that the nuclear membrane fraction of brain contains significant amount of CPK BB. On the contrary, in the nuclear membrane fractions of schizophrenic and Alzheimer disease brains the content of this isoenzyme decreased. Therefore in the brain of schizophrenic and Alzheimer disease patients the content of CPK BB decreased not only in cytosolic fractions, but also in the fractions of nuclear membranes. We demonstrated also, that cytosolic CPK BB associates not only with nuclear membranes, but with synaptosomal and microsomal fractions and mitochondrias of normal brain cells.

Synthesis of the Naphthalenic Bioisostere of Indorenate. Synthese des Naphthalin‐Bioisosters von Indorenat

AbstractThe relationships between some physiological processes and central nervous system or peripheral activity of serotonin (5‐HT; A) has resulted in extensive studies of the chemistry and biological properties of many serotoninergic (agonists or antagonists) compounds1) and the existence of multiple serotoninergic receptors subtypes is supported by pharmacological evidence2). So, central 5‐HT binding sites can be classified into 5‐HT1 (1A, 1B, 1C, 1D), 5‐HT2, 5‐HT3 and 5‐HT4 subtypes3,4) There is some basis for considering that central serotoninergic agonists might be antihypertensives acting via 5‐HT1A receptors5,6,7) Indorenate (B), a synthetic indole. closely related to serotonin, has antihypertensive properties resulting from agonist activity at central serotoninergic receptors with a relatively high affinity for 5‐HT1A sites8).A possible approach in the design of new serotoninergic ligands and more generally new drug candidates may consist in the application of the bioisosteric theory. So, the NH group is a classical bioisostere of the vinyl increment and the naphthalene nacleus could be considered as a bioisostere of the indole ring. Few examples of the naphthalene‐indole bioisosterism have emerged in the lit.9,10,11) Here we describe the synthesis of the naphthalenic bioisostere C of B (Scheme 1).

Beta-endorphin concentrations in resting peripheral mononuclear cells and after treatment with PHA or serotoninergic drugs in human aging, Alzheimer's disease, and Down's syndrome.

We measured the concentrations of beta-endorphin in resting peripheral blood mononuclear cells obtained from normal subjects of different ages and from age-matched patients with Down's syndrome or Alzheimer's disease. We also measured beta-endorphin concentrations in peripheral blood mononuclear cells obtained from subjects of different ages after treatment with PHA or serotoninergic drugs. The results show that in normal subjects the concentrations of the peptide increase after 30 years of age and remain constant up to 99 years. After stimulation with PHA, the release of beta-endorphin in cells from subjects older than 30 years increases, leading to a decrease in contents, whereas it is unchanged in younger subjects. In patients with Down's syndrome or Alzheimer's disease, beta-endorphin concentrations in peripheral blood mononuclear cells behave similarly to those in age-matched normal subjects. Treatment in vivo with the serotoninergic agonist chlorimipramine induces an increase in beta-endorphin concentrations in peripheral blood mononuclear cells that is significantly greater in subjects over 30 years old than in younger subjects.

Serotoninergic depression of auditory evoked responses recorded in the rat hippocampus: effect of repeated buspirone treatment

Auditory evoked middle latency responses recorded in the hippocampus (HAER), were monitored in alert, gently restrained rats with chronic indwelling electrodes and cannulae. Intrahippocampal (i.h.) injection of 5-hydroxytryptamine (5-HT, 10 μg) reduced the amplitude and increased the latency of the P28 and N55 peaks of the HAER. An early (N18) negative peak was unaffected. Buspirone (1 μg, i.h. and 3 mg/kg, i.p.) had similar effects to those produced by i.h. 5-HT. RU 24969 (1 mg/kg, s.c.) also reduced the amplitude of the P28 peak of the HAER. Long-term treatment with buspirone for 14 days at a dose (0.5 mg/kg, i.p.) which when applied acutely did not produce any observable effect, caused an increase in the latency of both the P28 and N55 peaks. Direct i.h. injection of 5-HT into these chronically treated animals did not have any additional depressant effect on the HAER peaks. It is concluded that these serotoninergic agonists can modulate the later peaks of the HAER possibly via 5-HT 1A receptors. In the case of buspirone there was evidence of an enhanced depressant effect following chronic treatment.

Pharmacological modulation of neuropeptides in peripheral mononuclear cells

The concentrations of β-endorphin and cholecystokinin were measured in fresh resting peripheral mononuclear cells obtained from rats and human subjects in basal conditions and after different pharmacological treatments. Both in the human and the rat, β-endorphin concentrations in mononuclear cells increased after treatment with serotoninergic agonists, decreased after dopaminergic or GABAergic drugs, while the respective antagonists exerted the opposite effect. In vitro, serotoninergic and GABAergic compounds confirmed their roles in the modulation of β-endorphin in mononuclear cells. Cholecystokinin was never affected by the pharmacological treatments.

Effects of 8-OH-DPAT and fluoxetine on activity and attack by female mice towards lactating intruders

1. 1. The impact of the serotoninergic receptor on the attack directed by female mice towards lactating intruders was assessed by studying the effects of 8-OH-DPAT (a serotoninergic agonist) and fluoxetine (an inhibitor of serotonin reuptake) on this paradigm at a range of doses and post-injection durations. 2. 2. The specificity of these drug actions behaviour were examined by studying their effects on wheel running activity and performance in the open field. Non-sedative doses of 200 and 250 μg/kg of 8-OH-DPAT reduced attack by resident females on lactating intruders. 3. 3. Higher doses (12–16 mg/kg) of fluoxetine reduced activity measures whereas lower non-sedative doses (up to 8 mg/kg) were without action on this aggression paradigm. 4. 4. Additional studies with specific serotoninergic drugs are needed to clarify the role of this transmitter in attack by female mice on lactating intruders.

Postmortem- and cryostability of the potassium-evoked release of [3H]5-hydroxytryptamine from rat cerebral cortical miniprisms.

A prerequisite for the study of neurotransmitter release from human brain autopsy samples with histories of different diseases is that the cryo- and postmortem stability of the release process is good. In the present study, the effect of post-mortem delay and of storage at -70 degrees C by the "slow freeze--fast thaw" method of Hardy et al. [J Neurochem (1983) 40: 608-614] (which allows for the retention of metabolic activity of the tissue after the storage and thawing) of rat cerebral cortex samples upon the release of [3H]5-hydroxytryptamine ([3H]5-HT) from prelabelled miniprisms has been investigated. Storage of samples at -70 degrees C by this method resulted in samples that accumulated less [3H]5-HT but showed an increased sensitivity to the Ca2+-dependent releasing properties of K+ when compared with "fresh" samples. On the other hand, the sensitivity of the K+-evoked release to the inhibitory effects of the serotoninergic agonist 5-methoxy-N,N-dimethyltryptamine were reduced by storage. The effects on [3H]5-HT accumulation and on K+-evoked release were due mainly to the freeze-thaw procedure, the length of storage at -70 degrees C having only a minor influence on these parameters. A post-mortem interval of 5 hours at either +4 or +22 degrees C prior to storage of the tissue reduced the K+-evoked release of tritium, but did not affect the accumulation of [3H]5-HT or the inhibitory effects of 5-methoxy-N,N-dimethyltryptamine on the K+-evoked release over and above the effects produced by the storage per se.

Effects of dexfenfluramine on the feeding behavior of rats foraging in the cold for palatable bait

An alimentary/thermic conflict of motivation was used to explore the effects of very low doses of dexfenfluramine (dFF), an anorectic serotoninergic agonist, on the parameters of food motivation, drive and incentive (or palatavility). Six rats trained to feed 2 hr/day, were given the possibility to feed on chow in a shelter (25°C), and to get a snack of shortcake, a highly palatable bait, from a feeder placed 16 m away in a very cold environment (− 15°C). dFF at 0.6 or 1.25 mg/kg decreased neither the chow intake in the shelter, nor the mean duration of the snacks in the cold, which is the parameter believed to be the best indicator of incentive. In contrast, dFF reduced the number of trips to the bait in the cold as well as the total mass of palatable bait ingested and the mean amount ingested by snack. Such an effect was no longer observed after a food restriction had reduced the body weight of the rats to 90% of its initial value. It is concluded that, even at doses too small to reduce the consumption of basic food, dFF decreases the drive to get palatable food.

Neuroendocrine response to fenfluramine in patients with idiopathic pain syndromes

In chronic pain patients, a long series of studies indicate disturbances in the serotoninergic systems as one important pathogenetic factor. One way of studying the function of the serotoninergic system would be to study the neuroendocrine responses to serotoninergic agonists. In the present study, twelve healthy volunteers and 17 chronic pain patients were given fenfluramine, 60 mg, at 8 a.m. Serum Cortisol and serum prolactin were measured at 8 a.m., 9 a.m., 10 a.m., 11 a.m. and at noon. The symptomatology was at the same time determined using visual analogue scales (VAS). Fenfluramine, a drug that releases intraneuronal serotonin and blocks the reuptake of serotonin, seems to have a stimulatory effect on the release of Cortisol and prolactin. As concerns serum Cortisol, the chronic pain patients had significantly lower values at 8 a.m. than the healthy volunteers. From 8 a.m. to 10 a.m. the values increased in the chronic pain patients but decreased in the healthy volunteers. The difference between the...