Galanin: a potent modulator of excitatory neurotransmission in the human urinary bladder

Galanin (GAL) produced a concentration (0.3-100 nM)-related inhibition of the atropine-sensitive component of the contractions induced by field stimulation of detrusor strips from the dome of the human urinary bladder. GAL had an ED50 of 2 nM for the inhibition. The effect of GAL was prevented by atropine (1 microM) and was not seen when the strips were stimulated with a cholinomimetic or KCl. These data suggest a possible neuromodulator role of GAL in the human urinary bladder.     

In vivo presynaptic modulation of serotonergic neurotransmission in the rat hippocampus by diazepam

The effect of the benzodiazepine agonist, diazepam, on serotonergic (5-HT) neurotransmission was assessed in in vivo electrophysiological experiments. Diazepam enhanced, in a dose-dependent manner (0.05-2 mg/kg i.v.), the effect of electrical stimulation of the ascending 5-HT pathway on the firing activity of dorsal hippocampus pyramidal neurons. This effect was blocked by the benzodiazepine antagonist, flumazenil. Diazepam did not modify the efficacy of microiontophoretic application of 5-HT and GABA. The results indicate that the activation of benzodiazepine receptors facilitates of 5-HT neurotransmission, presumably through a presynaptic modulatory mechanism.     

Human hallucinogen interactions with drugs affecting serotonergic neurotransmission.

The absence of relevant human research studies of hallucinogenic drugs has not curtailed their unsupervised use. Two cases are presented that suggest decreased sensitivity to the serotonergic hallucinogens psilocybin and LSD induced by drugs with effects on serotonergic neurotransmission, allopurinol and fluoxetine. These reports suggest that hallucinogens' effects in humans are mediated by serotonergic receptors.     

Fluvoxamine is a potent inhibitor of tacrine metabolism in vivo

Objective: In vitro studies have shown that tacrine is metabolized by cytochrome P4501A2 (CYP1A2). One of the monohydroxy-metabolites has been incriminated with tacrine-induced hepatotoxicity. The aim of this study was to establish whether the potent CYP1A2 inhibitor fluvoxamine in clinically relevant doses could inhibit tacrine metabolism. Methods: Eighteen healthy young men were enrolled in an open, randomized crossover study. In the first study period a single oral dose of tacrine 40 mg was given. In the second period the volunteers were randomized to maintenance doses of fluvoxamine 50 or 100 mg per day, and a single oral dose of tacrine 20 mg was given. Results: Fluvoxamine was found to be a very potent inhibitor of tacrine metabolism. A fractional decrement in tacrine clearance of approximately 85% was found with both fluvoxamine doses, which was in good agreement with a prediction based on in vitro data. The medians of the steady-state concentration of fluvoxamine were 43 nM (range 25–49) and 70 nM (range 44–124) in the 50 mg per day and 100 mg per day groups, respectively. The steady-state concentration of fluvoxamine correlated with the fractional decrement in tacrine clearance (Spearman R_s = 0.53, P < 0.05). Modest, but statistically significant, reductions in the formation of the metabolites 1- and 2-hydroxytacrine were found during concomitant fluvoxamine treatment. Conclusion: Fluvoxamine at clinically relevant doses is a potent inhibitor of tacrine metabolism. This interaction is very likely to have clinical relevance. Whether concomitant fluvoxamine treatment reduces tacrine-induced hepatotoxicity needs further study. Received: 16 September 1998 / Accepted in revised form: 27 January 1999     

Mechanisms of dopaminergic and serotonergic neurotransmission in Tourette syndrome: clues from an in vivo neurochemistry study with PET.

Tourette syndrome (TS) is a neuropsychiatric disorder with childhood onset characterized by motor and phonic tics. Obsessive-compulsive disorder (OCD) is often concomitant with TS. Dysfunctional tonic and phasic dopamine (DA) and serotonin (5-HT) metabolism may play a role in the pathophysiology of TS. We simultaneously measured the density, affinity, and brain distribution of dopamine D2 receptors (D2-R's), dopamine transporter binding potential (BP), and amphetamine-induced dopamine release (DA(rel)) in 14 adults with TS and 10 normal adult controls. We also measured the brain distribution and BP of serotonin 5-HT2A receptors (5-HT2AR), and serotonin transporter (SERT) BP, in 11 subjects with TS and 10 normal control subjects. As compared with controls, DA rel was significantly increased in the ventral striatum among subjects with TS. Adults with TS+OCD exhibited a significant D(2)-R increase in left ventral striatum. SERT BP in midbrain and caudate/putamen was significantly increased in adults with TS (TS+OCD and TS-OCD). In three subjects with TS+OCD, in whom D2-R, 5-HT2AR, and SERT were measured within a 12-month period, there was a weakly significant elevation of DA rel and 5-HT2A BP, when compared with TS-OCD subjects and normal controls. The current study confirms, with a larger sample size and higher resolution PET scanning, our earlier report that elevated DA rel is a primary defect in TS. The finding of decreased SERT BP, and the possible elevation in 5-HT2AR in individuals with TS who had increased DA rel, suggest a condition of increased phasic DA rel modulated by low 5-HT in concomitant OCD.     

Increased serotonergic neurotransmission is not responsible for the anticompulsive effect of berberine in a murine model of obsessive-compulsive disorder

Berberine, an isoquinoline alkaloid, is being extensively explored in several clinical trials for the treatment of metabolic disorder and cancer. It is also reported to be a potent inhibitor of prolyl oligopeptidase, which makes it a potential candidate for the treatment of neuropsychiatric disorders. We have previously shown the potential of berberine in the control of seizures in various murine models of epilepsy, diabetes-induced memory dysfunction, and ethanol-induced hyperexcitability. We have now examined the effects of acute and subchronic (7 days) administration of berberine on a murine model of obsessive-compulsive disorder - the marble-burying behavior of male mice, because berberine administration is reported to increase brain monoamine levels - a desirable endpoint in the treatment of obsessive-compulsive disorder. The studies showed that an acute administration of berberine [1-25 mg/kg, intraperitoneally (i.p.)] dose-dependently inhibited marble burying in male mice without altering locomotor activity. This effect was retained after its subchronic administration. Furthermore, coadministration of a subeffective dose of berberine (1 mg/kg) and fluoxetine (5 mg/kg, i.p.) significantly reduced marble burying in mice. Pretreatment with p-chlorophenylamine (300 mg/kg, i.p. ×3 days), a tryptophan hydroxylase inhibitor and serotonin-depleting agent, completely blocked the effect of fluoxetine on marble burying, whereas it failed to alter the effect of berberine. In conclusion, the findings of the present investigation indicate that the anticompulsive and/or anxiolytic effect of berberine observed in the present investigation may be attributed to its effect on other neurotransmitter systems, such as the nitrergic or the dopaminergic system rather than to increased serotonin turnover in the brain.     

Fluconazole is a potent inhibitor of antipyrine metabolism in vivo in mice

Fluconazole, a bis-triazole antifungal, is distinguished from imidazole antifungals (e.g. ketoconazole) by its potency and pharmacokinetic characteristics. Imidazole-containing compounds are well documented to inhibit the hepatic cytochrome P-450-dependent enzyme system; whether this effect occurs with a bis-triazole agent is unknown. The [14C]antipyrine breath test was employed to investigate the effects of fluconazole on this enzyme system in CD-1 male mice. Control, ketoconazole (100 mg/kg), and fluconazole (1 and 10 mg/kg) were studied in single- and multiple-dose experiments. Fluconazole had potent inhibitory effects on the total (mean = -73% +/- 2%), demethylase (mean = -90% +/- 2%), and nondemethylase (mean = -60% +/- 4%) elimination rate constants (all p less than 0.001). The fraction of the administered radioactivity excreted as 14CO2 was decreased by 50-80% in the fluconazole groups (p less than 0.001). These effects were seen after single- and multiple-dose studies; however, return to baseline occurred more quickly in the multiple-dose group. These effects were significantly more pronounced than those observed with equipotent doses of ketoconazole. These results provide evidence that fluconazole is a potent, partially selective, and reversible inhibitor of the cytochrome P-450-dependent enzyme system in mice. Future studies will be required to assess this property and possible interactions with drugs metabolized by this enzyme system in humans.     

Relationship between central serotonergic neurotransmission and reduction in alcohol intake by citalopram.

The relationship between the effect of citalopram on alcohol intake and central serotonergic neurotransmission, as assessed by prolactin (PRL) response to fenfluramine, was investigated in 17 male heavy drinkers. A positive correlation was obtained, suggesting that the status of central serotonergic neurotransmission in individuals is associated with the treatment response to citalopram. When the group of subjects were divided into those with high and low PRL response (above and below median, respectively) to fenfluramine, those with high PRL response had a significant reduction in alcohol intake during citalopram treatment, whereas those with low PRL response had no such effect. Thus, in subjects with evidence of unimpaired or only slightly impaired central serotonergic neurotransmission (high PRL response) citalopram may have beneficial effect on alcohol consumption, whereas in those with more evidently impaired serotonergic neurotransmission (low PRL response) citalopram treatment may have no effect on or may even increase the alcohol consumption.     

Agmatine, an endogenous modulator of noradrenergic neurotransmission in the rat tail artery.

1. We investigated the vascular effects of agmatine (decarboxylated arginine), an endogenous ligand for alpha 2-adrenoceptors and non-adrenoceptor imidazoline (I-) receptors, present in endothelium, smooth muscle and plasma, using the rat tail artery as a model. 2. While by itself agmatine (10 nM-1 mM) was without effect on isolated arterial rings, at the highest concentration used (1 mM) it slightly increased EC50 values for contractions elicited respectively by the alpha 1- and alpha 2- adrenoceptor agonists methoxamine and clonidine. 3. Agmatine (0.03-1 mM) produced a concentration-dependent transient inhibition of the contractions induced by transmural nerve stimulation (TNS; 200 mA, 0.2 ms, 1 Hz, 10 s). This effect was abolished by the alpha 2-adrenoceptor antagonists, rawolscine and idazoxan. 4. In the presence of rawolscine or idazoxan, agmatine produced a concentration-dependent delayed facilitation of TNS-induced contractions, which was prevented by cocaine. 5. Neither inhibitory nor potentiating actions were produced by agmatine on contractions induced by noradrenaline (NA) administration. 6. Agmatine did not directly affect [3H]-NA uptake in bovine cultured chromaffin cells. 7. Agmatine can regulate vascular function by two opposing actions at sympathetic nerve terminals, with different latencies: a transient inhibition of NA release mediated by prejunctional alpha 2-adrenoceptors and a cocaine-sensitive delayed facilitation the mechanism of which is undetermined at present. 8. The results reveal the existence of a novel endogenous amine modulating NA release in the perivascular sympathetic terminals.     

D-Cycloserine, a positive modulator of NMDA receptors, inhibits serotonergic function

The administration of the N-methyl-D-aspartate (NMDA)-associated glycine recognition site agonist D-cycloserine (DCS) to rats inhibited the head shakes and the forepaw treading induced by the serotonin (5HT) precursor, L-5-hydroxy-tryptophan [(-)5HTP], as well as the forepaw treading and motility elicited by the selective 5HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). The head shakes typically induced by the 5HT2 receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI), were unaffected by DCS pretreatment. The results are consistent with reduced serotonergic transmission produced by NMDA activation, as suggested by other authors. Due to the important role played in the pathogenesis of schizophrenia by glutamate deficiency/serotonin activation, the results support the view that positive modulators of NMDA receptors, activating glutamate receptors and reducing serotonergic tone, might be useful in the alleviation of psychotic symptoms. However, because of its partial agonist properties at the glycine recognition site, D-cycloserine shows some effects that might make it unsuitable for clinical use.     

Effects of the co-administration of mirtazapine and paroxetine on serotonergic neurotransmission in the rat brain.

The alpha(2)-adrenoreceptor antagonist mirtazapine, which is also a 5-HT(2), 5-HT(3) and H(1) receptors antagonist and the selective serotonin (5-HT) reuptake inhibitor paroxetine are effective antidepressant drugs which enhance 5-HT neurotransmission via different mechanisms. The present studies were undertaken to determine whether the mirtazapine-paroxetine combination could induce an earlier and/or a greater effect on the 5-HT system than either drug alone. Using in vivo electrophysiological paradigms, the firing activity of dorsal raphe 5-HT neurons was decreased by 70% in rats treated with paroxetine (10 mg/kg/day, s.c.) for 2 days and was back to normal after 21 days. In contrast, a 2-day treatment with mirtazapine (5 mg/kg/day, s.c.) did not alter the firing of 5-HT neurons whereas it was increased by 60% after 21 days of treatment. A low dose of mirtazapine (5 mg/kg/day, s.c.x2 days) failed to offset the decremental effect of paroxetine on the 5-HT neuron firing activity, but a higher dose (10 mg/kg/day, s.c.x2 days) did attenuate the decremental effect of paroxetine. In the dorsal hippocampus, neither mirtazapine (5 mg/kg/day, s.c.) nor a paroxetine (10 mg/kg/day, s.c.) treatment altered the responsiveness of 5-HT(1A) receptors to microiontophoretically-applied 5-HT. Both in controls and in rats treated for 2 days with paroxetine alone, the administration of the 5-HT(1A) antagonist WAY 100635 (25-100 microg/kg, i.v.) did not change the firing activity of dorsal hippocampus CA(3) pyramidal neurons. However, WAY 100635 increased significantly the firing activity of these neurons in rats treated with mirtazapine alone but to a greater extent with both mirtazapine and paroxetine for 2 days. After 21 days of treatment, WAY 100635 increased to a greater degree the firing rate of CA(3) pyramidal neurons in rats which received the combination over rats given either drug alone. It is concluded that the mirtazapine-paroxetine combination shortened the delay in enhancing the tonic activation of postsynaptic 5-HT(1A) receptors and produced a greater activation of the postsynaptic 5-HT(1A) receptors than either drug given alone. The present results suggested that mirtazapine may have a faster onset of action than a SSRI, and that the co-administration of mirtazapine and paroxetine may accelerate the antidepressant response and as well as being more effective than either drug alone.     

Pituitary adenylate cyclase activating polypeptide is a potent vasodilator and oedema potentiator in rabbit skin in vivo.

1. The effects of pituitary adenylate cyclase activating polypeptide (PACAP) on microvascular blood flow and plasma protein leakage were investigated in rabbit skin in vivo. 2. Intradermal injection of PACAP38, the 38 amino acid form of the peptide, caused a dose-dependent increase in blood flow measured by a 133Xe clearance technique. An equivalent increase in blood flow was induced by 10(-12) mol per site of PACAP38, 10(-12) mol per site of human alpha-calcitonin gene-related peptide (CGRP) and 10(-10) mol per site of vasoactive intestinal polypeptide (VIP). 3. The vasodilator activity of PACAP38 was not significantly different from that of the 27 amino acid form of the peptide, PACAP27, when measured with a laser Doppler flow meter, causing a 104 +/- 14% compared with 110 +/- 18% increase above basal blood flow at 10(-12) mol per site respectively. 4. At 10(-12) mol per site the effect of PACAP38 was longer lasting than that of CGRP. Blood flow remained significantly increased above control at 2 h with PACAP38 (P less than 0.05) whereas blood flow after intradermal CGRP had returned to control values by this time. 5. PACAP38 injected alone had no significant effect on microvascular leakage of 125I-labelled albumin. However, PACAP38 significantly potentiated bradykinin-induced oedema where it was approximately 100 fold more potent than VIP. 6. Oedema potentiation induced by PACAP38 was not inhibited by indomethacin at a dose which did inhibit potentiation of bradykinin-induced oedema by arachidonic acid.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of bulbar serotonergic neurotransmission in the initiation of swallowing in the rat

In rats anaesthetized with urethane and subjected to pharyngolaryngeal deafferentation, activation of central serotonin receptors was shown to evoke repetitive swallowing. Dose-response relationships were examined for the deglutitory effects of l-tryptophan, l-5-hydroxytryptophan (l-5-HTP), quipazine (QPZ), chloro-piperazinyl-pyrazine (CPP), 5-methoxydimethyltryptamine (5-MeODMT) and tryptamine. Agonists could be grouped according to their efficacy in increasing either repetitive swallowing rate or buccopharyngeal deglutitory pressure. With respect to the former, the efficacy increased in the following order: 5-MeODMT, l-tryptophan < tryptamine, l-5-HTP < QPZ < CPP; with respect to the latter, it decreased in the order: 5-MeODMT, QPZ >l-5-HTP, l-tryptophan > tryptamine, CPP. The stimulatory effects on the swallowing rate were inhibited by methysergide, metergoline and d-lysergic acid diethylamide (LSD). The persistence of these effects after decerebration and their elicitation, upon close-arterial and topical drug administration to the fourth ventricle, implicate the rhombencephalon as the major locus of action. Serotonin agonists enhanced reflex deglutition elicited by electrical stimulation of the superior laryngeal nerve or the solitary tract. Antagonists blocked the facilitation of reflex swallowing at the same dose levels at which they abolished agonist-evoked swallowing; however, they failed to diminish maximal reflex responses. The data support the hypothesis that the neural substrate of serotonergically-evoked, “automatic” swallowing is organized within the rhombencephalon and operates to set a facilitatory bias for deglutitory internuncial neurones as well as effector motoneurones.     

Is long-term heavy alcohol consumption toxic for brain serotonergic neurons? Relationship between years of excessive alcohol consumption and serotonergic neurotransmission.

The relationship between years of excessive alcohol consumption and central serotonergic neurotransmission, as assessed by the prolactin (PRL) response to D-fenfluramine, was investigated in 22 male alcohol-dependent subjects. A negative correlation was obtained, that is, the longer duration of excessive alcohol consumption the lower PRL response to D-fenfluramine. It is therefore suggested that long duration of excessive alcohol consumption in alcohol-dependent subjects causes a reduction in central serotonergic neurotransmission, possibly by a toxic effect of alcohol on serotonin neurons. The relationship between depressive and anxiety symptoms during on-going drinking and the PRL response to D-fenfluramine was also investigated. No such correlations were obtained, suggesting that reduction in central serotonergic neurotransmission does not pre-dispose to the development of depressive and anxiety symptoms, at least in relation to on-going drinking in alcohol-dependent subjects.     

d-Propoxyphene is a potent inhibitor of debrisoquine, but not S-mephenytoin 4-hydroxylation in vivo

The debrisoquine and S-mephenytoin 4-hydroxylation phenotyping tests were performed in 14 healthy subjects. All were extensive metabolizers of both drugs. After at least 4 weeks, they received a 150 mg tablet of d-propoxyphene and 5 h later the debrisoquine-mephenytoin test was repeated. This single dose of d-propoxyphene caused no change in mephenytoin S/R ratio, but increased the debrisoquine metabolic ratio (MR) in each subject (p less than 0.025). The four subjects with a relatively high MR (5.1-8.3) in the first test had an MR of debrisoquine in the second test ranging between 22 and 40, falsely classifying them as "poor metabolizers" of debrisoquine. This shows that d-propoxyphene is a potent inhibitor of debrisoquine, but not of S-mephenytoin 4-hydroxylase in vivo. A previous in vitro study has shown that d-propoxyphene inhibits the hydroxylation of desipramine, which is a substrate of the debrisoquine hydroxylase.     

Endogenous nitric oxide as a modulator of rabbit skeletal muscle microcirculation in vivo.

1. Intravital microscopy of rabbit tenuissimus muscle microvasculature was used for in vivo studies of the role of endogenous nitric oxide (NO) in local vascular control. Derivatives of arginine were applied topically in order to modulate the formation of NO from L-arginine. 2. L-NG-monomethylarginine (L-NMMA) (10-100 microM), but not D-NG-monomethylarginine (D-NMMA), dose-dependently reduced microvascular diameters. The vasoconstriction induced by L-NMMA (100 microM) was prevented by pretreatment with L-arginine (1 mM) but not with D-arginine (1 mM). Intravenous infusions of L-arginine (300 mg kg-1) reversed the effect of L-NMMA (100 microM). L-Arginine or D-arginine applied topically at 1 mM per se had no effect on microvascular diameters. 3. Vasodilatation by acetylcholine (0.03-3 microM) was significantly inhibited by L-NMMA (100 microM), whereas vasodilatation by adenosine (0.1-100 microM) or sodium nitroprusside (100 nM) was not affected. 4. The hyperaemic response after tenuissimus muscle contractions induced by motor nerve stimulation was unaffected by the presence of L-NMMA (100 microM). 5. Aggregates of platelets and white blood cells were seen in venules during superfusion with L-NMMA (100 microM), but not with D-NMMA (100 microM). 6. Our results suggest that endogenous NO formed from L-arginine is a modulator of microvascular tone and platelet and white cell-vessel wall interaction in vivo. Nitric oxide does not, however, appear to play a role in the mediation of functional hyperaemia in this tissue.     

Dimethyl sulfoxide is a potent modulator of estrogen receptor isoforms and xenoestrogen biomarker responses in primary culture of salmon hepatocytes

Dimethyl sulfoxide (DMSO) has been frequently used as carrier solvent in toxicological experiments where the most compelling DMSO attributes are its exceptionally low toxicity and environmental impact. We were inspired by recent and consistent observations that ethanol and DMSO modulate endocrine-disruptor biomarker responses in both in vitro and in vivo studies in our laboratory, to take a critical evaluation of these effects. Quantitative (real-time) polymerase chain reaction (PCR) method with specific primer pairs was used in this study to measure DMSO-induced time-dependent modulation of estrogen receptor (ER) isoforms, vitellogenin (Vtg) and zona radiata-protein (Zr-protein) gene expression patterns in primary culture of salmon hepatocytes. In addition, immunochemical analysis, using indirect enzyme linked immunosorbent assay (ELISA) with monoclonal (Vtg) and polyclonal (Zr-proteins) antibodies was used to detect and measure Vtg and Zr-proteins secreted in culture media. Salmon hepatocytes were isolated by a two-step collagenase perfusion method and exposed to 0.1% or 10 microL/L of DMSO after 48 h pre-culture. Cells were harvested at 12, 24, 48 and 72 h after exposure and analysed for ERalpha, ERbeta, Vtg and Zr-protein gene expression using real-time PCR method. Media samples were collected at similar time-intervals for protein analysis. Our data show that DMSO-induced significant increase in ERalpha, ERbeta, Vtg and Zr-protein genes in a time-dependent manner. Indirect ELISA analysis showed a time-specific effect of DMSO. The use of DMSO as carrier solvent in fish endocrine disruption studies should be re-evaluated. We recommend more investigation, using other endocrine-disruptor biomarkers in order to validate the suitability of common carrier solvents used in toxicology with the aim of setting new maximum allowable concentrations. In particular, given the high sensitivity of genomic approaches in toxicology, these results may have serious consequences for the interpretation of biomarker responses.