Intrathecally administered pizotifen alleviates neuropathic and inflammatory pain in mice by enhancing GABAergic inhibition.

Chronic pain, such as chronic neuropathic pain and chronic inflammatory pain, is often difficult to manage and bring great trouble to patients. 5-HT plays a key role in the process of pain transmission both in centrally and peripherally. Tricyclic antidepressants (TCA) such as amitriptyline are classical 5-HT reuptake inhibitors, are recommended as the first-line treatment for chronic pain. Pizotifen, a 5-HT2 receptor antagonist, is currently used in the prevention of vascular headaches. However, the antinociceptive effect of pizotifen on non-headache pain especially chronic pain in the spinal level is still unknown. Here we find that intrathecal pizotifen attenuates neuropathic and inflammatory pain mainly due to elevated GABAergic synaptic inhibition. Neuropathic pain is induced by segmental spinal nerve ligation (SNL), and inflammatory pain is induced by intraplantar injection of complete Freund's adjuvant (CFA). Both in SNL and CFA mice, spinally administered pizotifen reduced mechanical and thermal hyperalgesia dose-dependently. Since the levels of GAD65/67 were increased, and the frequency of mIPSCs in the spinal dorsal horn was increased, together with the antinociceptive effect being reversed by both GABAAR and GAD blockade, this antinociceptive effect might be generated from strengthened GABAergic inhibition. Furthermore, high dose of pizotifen (5 µg) weakly affected motor performance and did not influence the locomotor activity in normal animals. In summary, our findings suggest that pizotifen strengthens the inhibitory synaptic transmission and exerts antinociceptive effect on both neuropathic pain and inflammatory pain in the spinal cord, and may serve as a promising remedy for chronic pain.

A zebrafish embryo screen utilizing gastrulation identifies the HTR2C inhibitor pizotifen as a suppressor of EMT-mediated metastasis.

Metastasis is responsible for approximately 90% of cancer-associated mortality but few models exist that allow for rapid and effective screening of anti-metastasis drugs. Current mouse models of metastasis are too expensive and time consuming to use for rapid and high-throughput screening. Therefore, we created a unique screening concept utilizing conserved mechanisms between zebrafish gastrulation and cancer metastasis for identification of potential anti-metastatic drugs. We hypothesized that small chemicals that interrupt zebrafish gastrulation might also suppress metastatic progression of cancer cells and developed a phenotype-based chemical screen to test the hypothesis. The screen used epiboly, the first morphogenetic movement in gastrulation, as a marker and enabled 100 chemicals to be tested in 5 hr. The screen tested 1280 FDA-approved drugs and identified pizotifen, an antagonist for serotonin receptor 2C (HTR2C) as an epiboly-interrupting drug. Pharmacological and genetic inhibition of HTR2C suppressed metastatic progression in a mouse model. Blocking HTR2C with pizotifen restored epithelial properties to metastatic cells through inhibition of Wnt signaling. In contrast, HTR2C induced epithelial-to-mesenchymal transition through activation of Wnt signaling and promoted metastatic dissemination of human cancer cells in a zebrafish xenotransplantation model. Taken together, our concept offers a novel platform for discovery of anti-metastasis drugs.

Pizotifen Inhibits the Proliferation and Migration of Colon Cancer HCT116 Cells by Down-regulating Wnt Signaling Pathway.

BACKGROUND: Pizotifen, a 5-HT2A receptor antagonist is usually considered as a preventative drug to reduce the frequency of recurrent migraine headaches in previous research. But it is not clear whether Pizotifen exerts therapeutic effect in colon cancer. The objective of this study was to investigate the effect of Pizotifen on the proliferation and migration of colon cancer HCT116 cells. METHODS: We performed cell counting kit-8 (CCK8) assay to evaluate the effects of Pizotifen on HCT116 cells proliferation, and transwell migration and invasion assays to assess cell motility. Then, flow cytometry apoptosis assay was used to evaluate the effect of Pizotifen on cell apoptosis. Finally, western blot assay was used to determine the changes of Wnt signaling pathway related proteins in HCT116 cells after Pizotifen treatment. RESULTS: The results showed that Pizotifen could significantly inhibit HCT116 cells proliferation, migration, and invasion. The results of flow cytometry apoptosis assay demonstrated that Pizotifen could promote the apoptosis of HCT116 cells. The expression of Wnt3a and ß-Catenin protein were significantly inhibited, while the expression of E-cadherin was significantly up-regulated in Pizotifen treated HCT116 cells. CONCLUSION: Pizotifen may inhibit HCT116 cells proliferation and migration by suppressing Wnt signaling pathway and it may serve as a potential candidate drug for the treatment of colon cancer in the future.

The antidepressant 5-HT2A receptor antagonists pizotifen and cyproheptadine inhibit serotonin-enhanced platelet function.

There is considerable interest in defining new agents or targets for antithrombotic purposes. The 5-HT2A receptor is a G-protein coupled receptor (GPCR) expressed on many cell types, and a known therapeutic target for many disease states. This serotonin receptor is also known to regulate platelet function. Thus, in our FDA-approved drug repurposing efforts, we investigated the antiplatelet activity of cyproheptadine and pizotifen, two antidepressant 5-HT2A Receptor antagonists. Our results revealed that cyproheptadine and pizotifen reversed serotonin-enhanced ADP-induced platelet aggregation in vitro and ex vivo. And the inhibitory effects of these two agents were found to be similar to that of EMD 281014, a 5-HT2A Receptor antagonist under development. In separate experiments, our studies revealed that these 5-HT2A receptor antagonists have the capacity to reduce serotonin-enhanced ADP-induced elevation in intracellular calcium levels and tyrosine phosphorylation. Using flow cytometry, we also observed that cyproheptadine, pizotifen, and EMD 281014 inhibited serotonin-enhanced ADP-induced phosphatidylserine (PS) exposure, P-selectin expression, and glycoprotein IIb-IIIa activation. Furthermore, using a carotid artery thrombosis model, these agents prolonged the time for thrombotic occlusion in mice in vivo. Finally, the tail-bleeding time was investigated to assess the effect of cyproheptadine and pizotifen on hemostasis. Our findings indicated prolonged bleeding time in both cyproheptadine- and pizotifen-treated mice. Notably, the increases in occlusion and bleeding times associated with these two agents were comparable to that of EMD 281014, and to clopidogrel, a commonly used antiplatelet drug, again, in a fashion comparable to clopidogrel and EMD 281014. Collectively, our data indicate that the antidepressant 5-HT2A antagonists, cyproheptadine and pizotifen do exert antiplatelet and thromboprotective effects, but similar to clopidogrel and EMD 281014, their use may interfere with normal hemostasis.

Effect of transcutaneous electrical stimulation on nociception and edema induced by peripheral serotonin.

Transcutaneous electrical nerve stimulation (TENS) is defined as the application of an electrical current to the skin through surface electrodes for pain relief. Various theories have been proposed in order to explain the analgesic mechanism of TENS. Recent studies have demonstrated that part of this analgesia is mediated through neurotransmitters acting at peripheral sites. The aim of this study was to investigate the effects of low frequency (LF: 10 HZ) TENS and high frequency (HF: 130 HZ) TENS on hyperalgesia and edema when applied before the serotonin (5-HT) administered into the rat paw. LF and HF TENS were applied to the right paw for 20 min, and 5-HT was administered immediately after TENS. The Hargreaves method was used to measure nociception, while the hydroplethysmometer (Ugo Basile®) was used to measure edema. Neither HF nor LF TENS inhibited 5-HT-induced edema. However, LF TENS, but not HF TENS, completely reduced 5-HT-induced hyperalgesia. Pre-treatment of the paw with naltrexone, prior to application of TENS, (Nx: 50 µg; I.pl.) showed a complete blockade of the analgesic effect induced by low frequency TENS. Thus, our results confirmed the lack of an anti-inflammatory effect through the use of TENS as well as the participation of peripheral endogenous opioid receptors in LF TENS analgesia in addition to its central action.

Weight gain with pizotifen therapy.

OBJECTIVE: To describe the characteristics of weight gain occurring in children treated for migranous conditions with pizotifen DESIGN: Retrospective case note review SETTING: West Suffolk Hospital between 1999 and 2003 PATIENTS: 405 clinic attendances of 121 children receiving pizotifen treatment MAIN OUTCOME MEASURES: Rates of change in weight for age z score between successive outpatient appointments were used to detect excessive weight gain. RESULTS: The mean rate of weight z score increase for 105 patients receiving a constant dosage in 181 intervals between appointments was 0.79 standard deviations per year compared with 0.11 standard deviations per year for height z score increases. The rate of weight z score increase was not correlated with pizotifen dose per kg (r = -0.08), per m(2) (r = -0.05) or initial body mass index (r = -0.04). Mean rates of z score increase were similar in patients with a satisfactory and unsatisfactory therapeutic responses. CONCLUSIONS: Excess weight gain in pizotifen therapy is not predicted by drug dosage or therapeutic response within the range of doses used in clinical practice.

Potential vascular alpha1-adrenoceptor blocking properties of an array of 5-HT receptor ligands in the rat.

This study set out to analyse the potential ability of some 5-hydroxytryptamine (5-HT) receptor ligands widely used in cardiovascular experimental models to interact with vascular alpha1-adrenoceptors in the pithed rat. These ligands included: methiothepin, methysergide and metergoline (5-HT(1)/5-HT2); WAY-100635, buspirone, ipsapirone and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (5-HT(1A)); GR127935 (5-HT(1B/1D)); ketanserin, ritanserin, spiperone and pizotifen (5-HT2); granisetron and metoclopramide (5-HT3); tropisetron (5-HT3/5-HT4); ergotamine (5-HT(1B/1D), 5-ht(5A/5B)); clozapine (5-HT6/5-HT7); as well as LY215840 and mesulergine (5-HT2/5-HT7). For this purpose, the increases in diastolic blood pressure produced by the selective alpha1-adrenoceptor agonist, phenylephrine, were analysed before and after the above antagonists or saline. The adrenoceptor antagonist properties of prazosin (alpha1) and yohimbine (alpha2) were also analysed for comparison. Thus, the phenylephrine-induced vasopressor responses were dose-dependently antagonised with the following apparent rank order of potency by: prazosin > or = methiothepin > ketanserin > clozapine > or = lisuride >> buspirone; this potency correlates with the affinity of these compounds for alpha1-adrenoceptor binding sites. In contrast, the other compounds were either devoid of any blocking effect on--or even potentiated (i.e. lisuride, methysergide, 8-OH-DPAT, granisetron and GR127935)--the responses to phenylephrine. These results show that methiothepin, ketanserin, clozapine, lisuride and buspirone can block alpha1-adrenoceptors in the rat systemic vasculature.

Pizotyline effectively attenuates the stimulus effects of N-methyl-3,4-methylenedioxyamphetamine (MDMA).

MDMA (N-methyl-3,4-methylenedioxyamphetamine) produces a discriminative stimulus (DS) effect in animals, but attempts to completely block this action with selective neurotransmitter antagonists have not been very successful. Biochemically, MDMA can increase synaptic levels of serotonin, dopamine, and norepinephrine that, conceivably, might interact with multiple populations or subpopulations of neurotransmitter receptors. The present study attempted to antagonize the DS effects of MDMA using the nonselective agents clozapine, cyproheptadine, and pizotyline. An extensive and comparative radioligand binding profile was also obtained for the latter two agents. The purported antagonists were administered in combination with the training dose of MDMA to groups of Sprague-Dawley rats trained to discriminate 1.5 mg/kg of MDMA from saline vehicle in a standard two-lever operant paradigm using a VI-15s schedule of reinforcement. Clozapine was without effect at the doses evaluated, and cyproheptadine only partially attenuated MDMA-appropriate responding. In contrast, pizotyline (AD50=2.5 mg/kg), in combination with the MDMA training dose, resulted in a dose related decrease in percent drug-appropriate responding to saline levels. In a separate group of animals trained to discriminate the structurally-related agent N-methyl-1-(4-methoxyphenyl)-2-aminopropane (PMMA) from vehicle, pretreatment with pizotyline also resulted in a substantial decrease in drug-appropriate responding. The results with cyproheptadine and pizotyline in the binding assays confirmed that these agents display high affinity for multiple subpopulations of serotonergic, dopaminergic, adrenergic, histaminergic, and cholinergic receptors. The overall results of the present investigation indicate that pizotyline, which is clinically available in some countries, might be of clinical utility in the treatment of MDMA overdose.

Serotonin2C receptor blockade and thermoregulation during exercise in the heat.

PURPOSE: The effect of serotonin (5-HT)2C receptor blockade on the thermal response and exercise performance during exercise in a warm environment was examined. METHODS: Seven endurance-trained, but not heat-acclimatized, individuals (six males and one female) performed two 40-km time trials on a static cycle ergometer in a climatic chamber maintained at a mean (SD) ambient temperature of 35.5 (0.4) degrees C. The 5-HT2C receptor antagonist, pizotifen (1.5 mg), or placebo was administered orally on the evening before and again 6 h before exercise began. RESULTS: Resting rectal temperature (Tre) was higher (P=0.03) after pizotifen than placebo administration. Tre increased over time during exercise in both trials and was higher (P<0.05) during exercise in the pizotifen trial compared with the placebo trial from 40 to 60 min of exercise. There was no difference in Tre on completion of the time trial. The median times (range) required to complete the 40-km trials were 75.4 (69.0-82.5) and 76.1 (68.0-82.1) min in the pizotifen and placebo trials, respectively. Despite a trend for speed to be slower in the later stages of exercise in the pizotifen trial, performance was not significantly influenced by administration of pizotifen (P=0.86). Resting serum prolactin (Prl) and cortisol concentrations were not different after pizotifen or placebo administration. In both trials, serum Prl and cortisol values increased over time and were increased relative to resting levels in both trials (P<0.01) but were not different between treatments. CONCLUSION: The present study suggests that 5-HT may influence body temperature via an effect on the 5-HT2C receptors, but this effect was not sufficient to influence performance.

Agomelatine(S 20098) antagonizes the penile erections induced by the stimulation of 5-HT2C receptors in Wistar rats.

Agomelatine, an antidepressant with melatonin agonist and 5-HT(2C) antagonist properties, as well as two of its main metabolites, S 21517 (N-[2-(7-hydroxy-1-naphtyl)ethyl]acetamide) and S21540 (N-[2-(3-hydroxy-7-methoxynaphtalen-1-yl)ethyl]acetamide), have been assessed in vitro on pig choroid plexus preparations to determine their affinities for 5-HT(2C) receptors and their effects on inositol phosphate production. These compounds were also tested for their ability to inhibit the penile erections induced by the 5-HT(2C) receptor agonists, m-(chlorophenyl)piperazine (mCPP, 0.75 mg/kg, SC) and Ro 60-0175 (2.5 mg/kg, SC) in Wistar rats. These in vivo effects were compared to those of melatonin and the 5-HT antagonists pizotifen and SB 206,553. Agomelatine and S 21517 had moderate affinity for 5-HT(2C) receptors and behaved in vitro as weak antagonists at this receptor subtype. S 21540 had a 10-fold lower affinity. Pizotifen and SB 206,553 antagonized mCPP- and Ro 60-0175-induced penile erections, suggesting that penile erections induced by mCPP or Ro 60-0175 resulted from the stimulation of 5-HT(2C) receptors. Whereas increasing doses (from 1.25 to 40 mg/kg, IP) of melatonin were unable to modify the penile erections induced by mCPP and Ro 60-0175, agomelatine (from 1.25 to 40 mg/kg, IP) dose-dependently decreased mCPP- as well Ro 60-0175-induced penile erections. Furthermore, increasing doses (from 1.25 to 40 mg/kg, IP) of S 21517 and S 21540, the two main metabolites of agomelatine, did not affect the penile erections induced by mCPP and Ro 60-0175. Considering the similar activity of melatonin and agomelatine at melatonin receptors, these data suggested that the reported effects were not due to the stimulation of melatonin receptors and that, contrary to melatonin, agomelatine exerted 5-HT(2C) receptor antagonist properties in addition to its agonist activity at melatonin receptors. Finally, neither S 21517 nor S 21540 seemed to participate to the observed inhibition of penile erections by agomelatine.

Hypoxic initiation of pulmonary hypertension is mediated by serotonin secretion from neuroepithelial bodies in chemodenervated dogs.

The purpose of this study was to investigate the stimulatory effect of hypoxia on the secretion of serotonin by neuroepithelial bodies (NEB) as well as to determine the relation between its level and changes in pulmonary arterial pressure (PAP) and also to determinate the effect of serotonin antagonists (pizotifen and methysergide) on the responses of pulmonary and systemic arterial pressures. The experiments were carried out in peripheral chemoreceptor-denervated dogs anesthetized with Na penthabarbital (30 mg/kg i.v.). On the breathing of normoxic and hypoxic (7% O2-93% N2) gas mixtures and on the injection of KCN (80 microg/kg i.v.), PAP, systemic arterial blood pressure (BP), tidal volume (VT), respiratory frequency (f/min), ventilation minute volume (VE) were determined. Also PAP and BP were recorded before and after the injection of pizotifen (0.5 mg/kg i.v.) and methysergide (1 mg/kg i.v.) during normoxic or hypoxic gas mixture breathing. At the end of each experimantal phase, serotonin level, PaO2, PaCO2 and pHa values in blood samples obtained from left ventricle and femoral artery were determined. On the breathing of the hypoxic gas mixture of the chemodenervated dogs, VT, VE and BP significantly decreased (P < 0.001, P < 0.001, P < 0.01). The mean value of PAP and serotonin levels (ventricular and femoral) were found significantly increased when compared with the corresponding normoxic values (P < 0.001, P < 0.05). On the other hand, injection of KCN produced no significant changes in PAP, serotonin levels, BP and respiratory parameters. After the injection of pizotifen, PAP was significantly increased in hypoxia (P < 0.01). After the injection of methysergide, the response of PAP was completely abolished during the breathing of hypoxic gas mixture. The finding of the abolition of response of PAP to hypoxia after the injection of methysergide indicates that serotonin release from NEB may be responsible for the elevation of PAP in hypoxic hypoxia.

Cortical hyperexcitability is cortical under-inhibition: evidence from a novel functional test of migraine patients.

Recent studies of the visual cortex in patients with migraine have generally concluded that migraine (particularly migraine with aura) is associated with a state of functional cortical hyperexcitability. The mechanisms giving rise to this hyperexcitability have hitherto been unclear. This paper reports two studies that used a novel investigative technique, derived from basic research in vision science, to examine specific deficits of inhibitory processing in primary visual cortex. The technique is termed the metacontrast test, and it examines visual masking under highly specified conditions. In Study 1, 12 migraine with aura patients (MA), 12 age-matched migraine without aura patients (MO) and 12 age- and sex-matched headache-free control subjects (C) were compared using the metacontrast test. MA patients were significantly less susceptible to visual masking in the metacontrast test than both MO and C groups: this result is highly consistent with a deficit in cortical inhibitory processing in MA patients. Study 2 examined MA patients taking a variety of migraine prophylactics, again using the metacontrast test. Test results normalized in those MA patients taking sodium valproate, but not in those taking other prophylactics. Sodium valproate is a GABA-A agonist that is known to cross the blood-brain barrier: GABA-ergic networks act as the primary inhibitory mechanism in visual cortex. Taken together, the results of these studies argue that cortical hyperexcitability, at least in MA patients, is likely to be a result of deficient intracortical inhibitory processes.

Antagonism of meta-chlorophenylpiperazine-induced inhibition of exploratory activity in an emergence procedure, the open field test, in rats.

The effects of meta-chlorophenylpiperazine (mCPP) were studied on exploratory behaviour in the open field test, using a procedure designed to evaluate the emergence of rats into a novel environment. mCPP reduced the exploratory activity in a dose-related manner after subcutaneous (s.c.), intraperitoneal (i.p.) and intravenous (i.v.) administration. The inhibition was manifest in all the parameters used to quantify the exploration of the open field area. Additional neuroendocrine experiments in a parallel group of rats revealed a dose-related increase in plasma prolactin and ACTH levels after i.v. mCPP, pointing to a general state of arousal in these mCPP-treated animals. A number of 5-HT antagonists were tested for their ability to prevent or reverse the behavioural inhibition induced by an i.v. injection of 1.0 g/kg mCPP given 15 min before testing in the open field. The antagonists were injected s.c. or given orally at various time intervals before mCPP, or they were injected i.v. 10 min after mCPP. The lowest active doses for the attentuation of the mCPP-induced behavioural inhibition after s.c., oral and i.v. administration, respectively, were 0.04, 40 and 10 mg/kg for pizotifen; 0.16, 0.16 and 0.16 mg/kg for mianserin; 0.63, 0.16 and 0.16 mg/kg for methysergide, and 0.16, 2.5 and 2.5 mg/kg for ritanserin. The lowest active doses of mirtazapine after s.c. and i.v. treatment were 0.01 and 0.16 mg/kg. These data indicate that mixed 5-HT1/5-HT2 receptor antagonists such as pizotifen and methysergide, and mixed 5-HT and catecholamine antagonists such as mianserin and mirtazapine are more potent antagonists of mCPP-induced behavioural inhibition in rats than the more selective 5-HT2A/5-HT2C antagonist ritanserin.

Agonist activity of antimigraine drugs at recombinant human 5-HT1A receptors: potential implications for prophylactic and acute therapy.

The actions of several serotonergic ligands in use or under development for the treatment of migraine headaches were examined at recombinant human 5-HT1A receptors stably expressed in Chinese Hamster Ovary cells. Affinities (K(i)s) at this site were determined in competition binding experiments with [3H]-8-OH-DPAT ([3H](+/-)8-hydroxy-N,N-dipropylaminotetralin), whilst agonist efficacy was measured by stimulation of [35S]-GTP gamma S (guanylyl-5'-[gamma[35S]thio]-triphosphate) binding. Of the prophylactic antimigraine drugs tested, methysergide and lisuride behaved as efficacious agonists (Emax > or = 90% relative to 5-HT) whereas pitozifen and (-)propranolol acted as a partial agonist (60%) and an antagonist, respectively. This suggests that there is no correlation between agonism at 5-HT1A receptors and prophylactic antimigraine action. In contrast, serotonin, dihydroergotamine, sumatriptan, naratriptan and alniditan, which are effective in acute interruption of migraine attacks, each displayed high efficacy (Emax = 100, 100, 92.6, 79.3, 79.1% respectively) and marked affinity (Ki = 18.7, 0.6, 127, 26.4 and 3.0 nM respectively) at 5-HT1A receptors. EC50 values for agonist stimulation of [35S]-GTP gamma S binding correlated with respective Ki values at 5-HT1A receptors (r = 0.93) and the stimulation of [35S]-GTP gamma S binding by these compounds was antagonised by the selective 5-HT1A antagonist WAY 100,635 (N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-(2-pyridinyl) cyclo-hexanecarboxamide; 100 nM). These data suggest that agonism at 5-HT1A receptors may be involved in some actions of drugs used in acute antimigraine therapy. In comparison with the above compounds, novel ligands targeted at 5-HT1B/1D receptors, such as GR125,743 (N-[4-methoxy-3-(4-methyl-piperazin-1-yl)phenyl] -3-methyl-4-(4-pyridyl)benzamide) and GR 127,935 (N-[4-methoxy-3-(4-methylpiperazin-1-yl)-phenyl]-2'-methyl-4'-(5-m ethyl-1, 2,4-oxadiazol-3-yl)-biphenyl-4-carboxamide), only weakly activated [35S]-GTP gamma S binding (32.4 and 32.1% efficacy) and displayed moderate affinity at 5-HT1A receptors (Kis 53.1 and 49.8 nM) suggesting that they constitute useful tools to differentiate 5-HT1A and 5-HT1B/1D receptor-mediated actions. In conclusion, the present data indicates that several antimigraine agents exhibit marked 5-HT1A receptor activity and that although this is unlikely to be important for prophylactic action it may be relevant to the ancilliary properties of drugs used for acute migraine treatment.

The antiserotonin agent pizotifen does not increase endurance performance in humans.

This study investigated the effect of the serotonin receptor antagonist pizotifen on endurance performance during treadmill exercise in humans. Eight healthy men exercised to exhaustion on a treadmill at an intensity corresponding to 70% of their maximal oxygen uptake (VO2max). Pizotifen was administered orally in a 1-mg dose 5 h before the start of exercise. The study was double blind, using a randomized, placebo-controlled crossover design. Oxygen uptake, heart rate, and ratings of perceived exertion were measured and blood samples taken for determination of concentrations of lactate, glucose, amino acids, ammonia, and haematocrit. Measurements were made at intervals of 30 min during the run and at exhaustion. There was no significant difference between the placebo and the pizotifen trials for any of the variables except for the plasma free-tryptophane: branched chain amino acid ratio which was somewhat lower after pizotifen at postexercise. Pizotifen did not increase exercise time to exhaustion, which was even shorter after pizotifen than after placebo in seven out of the eight subjects; the difference between pizotifen and placebo did not reach the level of statistical significance [109.4 (SD 6.7) min after pizotifen versus 119.8 (SD 12.5) min after placebo]. The results do not support the hypothesis that there is a central component to fatigue which is mediated by the serotoninergic neurones.

Further evidence that prolactin secretion in adult female rats is differently modified after neonatal estrogenization or androgenization: responses to methysergide, quipazine, and pizotifen.

The role of the serotoninergic system in the control of prolactin secretion was investigated in adult female rats treated on the first day of life with estradiol benzoate (EB) (100 micrograms), testosterone propionate (TP) (25 or 100 micrograms), or olive oil. Blood of rats was obtained through a chronic intraatrial cannula at 0, 30, 60, 90, and 120 min after the IP administration of the serotoninergic blockers methysergide (0.75, 2.5, and 7.5 mg/kg) or pizotifen (2 mg/kg), the agonist quipazine (3 or 30 mg/kg), or saline. We have found that 1) the anovulatory syndrome induced by EB or 100 micrograms injection of TP was associated with hyperprolactinaemia, whereas normal prolactin concentrations in plasma were observed in females injected with 25 micrograms of TP; 2) methysergide administration increased plasma prolactin concentrations in control and androgenized females but not in the estrogenized ones. This different response may be related to the antidopaminergic action of methysergide, because both estrogenized and androgenized females responded similarly after pizotifen injection; 3) after quipazine injection, an initial stimulation was observed in females injected with estradiol or 100 micrograms of TP, but not in other groups, whereas a delayed inhibition occurred in androgenized females. These results suggest that the effects of estrogenization and androgenization on both the dopaminergic and serotoninergic control of prolactin secretion are qualitatively different.

Stimulus effects of ibogaine in rats trained with yohimbine, DOM, or LSD.

The stimulus effects of ibogaine were compared with those of yohimbine, an alpha 2-adrenoceptor antagonist, 2,5-dimethoxy-4-methylamphetamine (DOM), a 5-hydroxytryptamine2 (5-HT2) agonist, and lysergic acid diethylamide (LSD), a nonspecific 5-HT agonist. Rats were trained with either yohimbine (6 mg/kg), DOM (0.6 mg/kg), or LSD (0.1 mg/kg) vs. no treatment in a two-lever discrimination task. Tests of generalization were then conducted with ibogaine. In yohimbine-trained animals, 39.7% of responses following ibogaine (15 mg/kg) were on the drug-appropriate lever, but this response level was not significantly different from no treatment-appropriate responding. A response distribution that was significantly different from responding under both drug and no treatment training conditions was observed in DOM-trained rats after administration of 15 mg/kg ibogaine. Pizotyline (BC-105) blocked all DOM-appropriate responding produced by ibogaine. In LSD-trained animals, 20 mg/kg ibogaine mimicked LSD. Pizotyline blocked LSD-appropriate responding produced by ibogaine in five of six animals. The present data suggest the involvement of 5-HT2 receptor activity, and the possibility of a 5-HT1A contribution, in the stimulus properties of ibogaine.

[Serotonin agonists and antagonists in migraine]. / Agonistes et antagonistes de la sérotonine et migraine.

Serotonin agonists (for the acute treatment of attacks) and antagonists (for prophylactic treatment) are the most widely used drugs to treat migraine. However, their effectiveness is not complete and their use is limited by side effects. The activity and presumptive mode of action of these drugs provide support for the role of serotonin in the pathophysiology of migraine and suggest that the trigeminal-vascular system is at the center of the attack; however, other factors and mechanisms may also be involved.

Affinity profiles of pizotifen, ketotifen and other tricyclic antimuscarinics at muscarinic receptor subtypes M1, M2 and M3.

The affinity of pizotifen, ketotifen and other tricyclic antimuscarinic drugs for different muscarinic receptor subtypes was investigated in vitro in functional experiments with field-stimulated vas deferens of the rabbit (M1 and M2 receptors) and with ileum and trachea of the guinea-pig (M3 receptors). All compounds were competitive antagonists in the three tissues. Like the close analogue cyproheptadine (pA2 = 7.99-8.08), pizotifen (pA2 = 7.23-7.81) and ketotifen (pA2 = 6.34-6.99) were devoid of selectivity for the receptor subtypes studied. Thiazinamium, although exhibiting high affinity for muscarinic receptors (pA2 = 7.83-8.51), was found to be non-selective. In contrast, the novel pirenzepine analogue nuvenzepine was selective for M1 receptors (pA2 = 6.63-7.74). The lack of selectivity of cyproheptadine, pizotifen and ketotifen is reflected in the chemical structures of these drugs. All three antagonists are composed of a very similar tricyclic ring system linked to a 1-methyl-4-piperidylene ring. The finding that thiazinamium, pizotifen and cyproheptadine were potent muscarinic antagonists and possessed non-selective affinity characteristics may have therapeutic implications.