Litoxetine: a selective 5-HT uptake inhibitor with concomitant 5-HT3 receptor antagonist and antiemetic properties

The Implication of 5-HT Receptor Family Members in Aggression, Depression and Suicide: Similarity and Difference

Being different multifactorial forms of psychopathology, aggression, depression and suicidal behavior, which is considered to be violent aggression directed against the self, have principal neurobiological links: preclinical and clinical evidence associates depression, aggression and suicidal behavior with dysregulation in central serotonergic (5-HT) neurotransmission. The implication of different types of 5-HT receptors in the genetic and epigenetic mechanisms of aggression, depression and suicidality has been well recognized. In this review, we consider and compare the orchestra of 5-HT receptors involved in these severe psychopathologies. Specifically, it concentrates on the role of 5-HT_1A, 5-HT_1B, 5-HT_2A, 5-HT_2B, 5-HT_2C, 5-HT₃ and 5-HT₇ receptors in the mechanisms underlying the predisposition to aggression, depression and suicidal behavior. The review provides converging lines of evidence that: (1) depression-related 5-HT receptors include those receptors with pro-depressive properties (5-HT_2A, 5-HT₃ and 5-HT₇) as well as those providing an antidepressant effect (5-HT_1A, 5-HT_1B, 5-HT_2C subtypes). (2) Aggression-related 5-HT receptors are identical to depression-related 5-HT receptors with the exception of 5-HT₇ receptors. Activation of 5-HT_1A, 5-HT_1B, 5-HT_2A, 5-HT_2C receptors attenuate aggressiveness, whereas agonists of 5-HT₃ intensify aggressive behavior.

5-HT Receptors and the Development of New Antidepressants

Serotonin modulates several physiological and cognitive pathways throughout the human body that affect emotions, memory, sleep, and thermal regulation. The complex nature of the serotonergic system and interactions with other neurochemical systems indicate that the development of depression may be mediated by various pathomechanisms, the common denominator of which is undoubtedly the disturbed transmission in central 5-HT synapses. Therefore, the deliberate pharmacological modulation of serotonergic transmission in the brain seems to be one of the most appropriate strategies for the search for new antidepressants. As discussed in this review, the serotonergic system offers great potential for the development of new antidepressant therapies based on the combination of SERT inhibition with different pharmacological activity towards the 5-HT system. The aim of this article is to summarize the search for new antidepressants in recent years, focusing primarily on the possibility of benefiting from interactions with various 5-HT receptors in the pharmacotherapy of depression.

Dysfunction in Serotonergic and Noradrenergic Systems and Somatic Symptoms in Psychiatric Disorders

Somatic symptoms include a range of physical experiences, such as pain, muscle tension, body shaking, difficulty in breathing, heart palpitation, blushing, fatigue, and sweating. Somatic symptoms are common in major depressive disorder (MDD), anxiety disorders, and some other psychiatric disorders. However, the etiology of somatic symptoms remains unclear. Somatic symptoms could be a response to emotional distress in patients with those psychiatric conditions. Increasing evidence supports the role of aberrant serotoninergic and noradrenergic neurotransmission in somatic symptoms. The physiological alterations underlying diminished serotonin (5-HT) and norepinephrine (NE) signaling may contribute to impaired signal transduction, reduced 5-HT, or NE release from terminals of presynaptic neurons, and result in alternations in function and/or number of receptors and changes in intracellular signal processing. Multiple resources of data support each of these mechanisms. Animal models have shown physiological responses, similar to somatic symptoms seen in psychiatric patients, after manipulations of 5-HT and NE neurotransmission. Human genetic studies have identified many single-nucleotide polymorphisms risk loci associated with somatic symptoms. Several neuroimaging findings support that somatic symptoms are possibly associated with a state of reduced receptor binding. This narrative literature review aimed to discuss the involvement of serotonergic and noradrenergic systems in the pathophysiology of somatic symptoms. Future research combining neuroimaging techniques and genetic analysis to further elucidate the biological mechanisms of somatic symptoms and to develop novel treatment strategies is needed.

Looking beyond 5-HT(3) receptors: a review of the wider role of serotonin in the pharmacology of nausea and vomiting

The concept that 5-hydroxytryptamine (5-HT; serotonin) is involved in the emetic reflex was revealed using drugs that interfere with its synthesis, storage, release and metabolism ahead of the discovery of selective tools to modulate specific subtypes of receptors. This review comprehensively examines the fundamental role of serotonin in emesis control and highlights data indicating association of 5-HT1-4 receptors in the emetic reflex, whilst leaving open the possibility that 5-HT5-7 receptors may also be involved. The fact that each receptor subtype may mediate both emetic and anti-emetic effects is discussed in detail for the first time. These discussions are made in light of known species differences in emesis control, which has sometimes affected the perception of the translational value of data in regard to the development of novel anti-emetic for use in man.

Discovery of 1-[2-(2,4-dimethylphenylsulfanyl)phenyl]piperazine (Lu AA21004): a novel multimodal compound for the treatment of major depressive disorder

The synthesis and structure-activity relationship of a novel series of compounds with combined effects on 5-HT(3A) and 5-HT(1A) receptors and on the serotonin (5-HT) transporter (SERT) are described. Compound 5m (Lu AA21004) was the lead compound, displaying high affinity for recombinant human 5-HT(1A) (K(i) = 15 nM), 5-HT(1B) (K(i) = 33 nM), 5-HT(3A) (K(i) = 3.7 nM), 5-HT(7) (K(i) = 19 nM), and noradrenergic β(1) (K(i) = 46 nM) receptors, and SERT (K(i) = 1.6 nM). Compound 5m displayed antagonistic properties at 5-HT(3A) and 5-HT(7) receptors, partial agonist properties at 5-HT(1B) receptors, agonistic properties at 5-HT(1A) receptors, and potent inhibition of SERT. In conscious rats, 5m significantly increased extracellular 5-HT levels in the brain after acute and 3 days of treatment. Following the 3-day treatment (5 or 10 (mg/kg)/day) SERT occupancies were only 43% and 57%, respectively. These characteristics indicate that 5m is a novel multimodal serotonergic compound, and 5m is currently in clinical development for major depressive disorder.

Cisplatin-induced emesis: systematic review and meta-analysis of the ferret model and the effects of 5-HT₃ receptor antagonists

Purpose

The ferret cisplatin emesis model has been used for ~30 years and enabled identification of clinically used anti-emetics. We provide an objective assessment of this model including efficacy of 5-HT₃ receptor antagonists to assess its translational validity.

Methods

A systematic review identified available evidence and was used to perform meta-analyses.

Results

Of 182 potentially relevant publications, 115 reported cisplatin-induced emesis in ferrets and 68 were included in the analysis. The majority (n = 53) used a 10 mg kg⁻¹ dose to induce acute emesis, which peaked after 2 h. More recent studies (n = 11) also used 5 mg kg⁻¹, which induced a biphasic response peaking at 12 h and 48 h. Overall, 5-HT₃ receptor antagonists reduced cisplatin (5 mg kg⁻¹) emesis by 68% (45–91%) during the acute phase (day 1) and by 67% (48–86%) and 53% (38–68%, all P < 0.001), during the delayed phase (days 2, 3). In an analysis focused on the acute phase, the efficacy of ondansetron was dependent on the dosage and observation period but not on the dose of cisplatin.

Conclusion

Our analysis enabled novel findings to be extracted from the literature including factors which may impact on the applicability of preclinical results to humans. It reveals that the efficacy of ondansetron is similar against low and high doses of cisplatin. Additionally, we showed that 5-HT₃ receptor antagonists have a similar efficacy during acute and delayed emesis, which provides a novel insight into the pharmacology of delayed emesis in the ferret.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Possible involvement of peripheral serotonin 5-HT3 receptors in fluvoxamine-induced emesis in Suncus murinus

Selective serotonin reuptake inhibitors fluvoxamine and fluoxetine, as well as serotonin (5-HT), induced vomiting in Suncus murinus (a house musk shrew). Fluvoxamine- and fluoxetine-induced vomiting gradually decreased with their repeated administration. Vomiting induced by serotonin also decreased with repeated treatment with serotonin. In these shrews, fluvoxamine-induced vomiting was partially inhibited. Fluvoxamine might induce vomiting, at least partially, by indirectly activating peripheral 5-HT(3) receptors, since serotonin has been reported to induce vomiting by activating peripheral 5-HT(3) receptors and granisetron, a 5-HT(3) antagonist, partially suppressed fluvoxamine-induced vomiting in our previous finding. In addition, fluvoxamine-induced vomiting was impaired more effectively using a step-wise dose-up schedule of fluvoxamine than a fixed high-dose schedule. Therefore, a careful dosing strategy starting with a low dose might be effective for avoiding emesis associated with the clinical use of fluvoxamine.

Serotonin, dopamine and norepinephrine transporters in the central nervous system and their inhibitors

An overview is presented on progress made in the research on neuronal transporters of serotonin, dopamine and norepinephrine in the central nervous system. Tools developed by molecular biology, such as expression of cloned transporters, their mutants and chimera in non-neuronal cells offered the opportunity to study the putative domains for binding of substrates and uptake inhibitors and discover factors in the regulation of the transporter function. The study of the distribution of monoamine transporters in human brain became possible by the development of selective radiolabelled transport inhibitors. The relationships between the chemical structure of the uptake inhibitors and the affinity for the monoamine transporters is reported, and the (potential) therapeutic applications of the compounds are discussed.

Influence of fluoxetine and litoxetine on 5-HT4 receptor-mediated relaxation in the rat isolated oesophagus

The influence of two selective serotonin reuptake inhibitors (SSRIs), litoxetine and fluoxetine, has been studied on 5-HT4 receptor-mediated relaxation in the rat isolated oesophageal muscularis mucosae. In carbachol-precontracted oesophageal tissues, 5-hydroxytryptamine (5-HT) (0.1 nM-1 microM) induced concentration-dependent relaxations. Concentration-response curves were monophasic and reproducible. Litoxetine at concentrations without antimuscarinic properties (10 nM-1 microM) caused concentration-dependent relaxations, which reduced carbachol tone up to 37%. Higher litoxetine concentrations (3 microM-300 microM) were associated with marked relaxation up to the abolition of carbachol tone. The overall curve profile of litoxetine was biphasic in nature with a high (10 nM-1 microM) and a low (3 microM-300 microM) potency phase. Unlike 5-HT, the second curve of litoxetine was not reproducible, with a reduction involving mainly the low potency phase. Compared to litoxetine, fluoxetine caused minimal relaxation (less than 10% at 1 microM). Treatment of rats with parachlorophenylalanine (pCPA: 375 mg kg-1 per day, for two days), to deplete endogenous 5-HT stores, did not modify the relaxant effect of 5-HT, while it significantly reduced the high potency phase of litoxetine. In tissues from untreated rats, this phase was reduced by the 5-HT4 receptor antagonist GR 125487 (10 nM) to an extent similar (P = 0.20: ANOVA for continuous-by-class effects) to that induced by pCPA treatment. However, in tissues from pCPA treated animals GR 125487 (10 nM) exerted a slight but significant antagonism of litoxetine response (P = 0.037: ANOVA for continuous-by-class effects) mainly involving the high potency phase. In tissues from untreated rats, litoxetine (1 microM) increased the relaxant effects of 5-HT, while in tissues from pCPA treated animals it exerted a small but significant depression of the maximal response to 5-HT, without changing its potency value. Fluoxetine (1 microM) slightly, but significantly, antagonized the relaxant effect of 5-HT in an unsurmountable manner. In conclusion, litoxetine up to 1 microM relaxed the rat isolated oesophageal muscularis mucosae through a mechanism involving release of endogenous 5-HT, which in turn activates 5-HT4 receptors. However, based on results with GR 125487 in tissues from pCPA treated rats, a small component of litoxetine-induced relaxation may involve a direct activation of 5-HT4 receptors. It is unlikely that blockade of 5-HT reuptake can participate in the action of litoxetine, since fluoxetine, a 5-HT reuptake inhibitor equipotent to litoxetine, was ineffective in the same range of concentrations. The antimuscarinic activity of litoxetine, previously demonstrated in the isolated guinea-pig intestine, played a role at concentrations greater than 1 microM. The 5-HT-releasing action of litoxetine could account for the potentation by litoxetine of 5-HT-induced relaxation in tissues from untreated rats, which was reversed by pCPA treatment. Under these conditions, litoxetine depressed relaxations to high 5-HT concentrations only. In tissues from untreated rats, fluoxetine slightly but unsurmountably antagonized 5-HT-induced relaxations, thus confirming previous observations in the guinea-pig small intestine.

The 5-HT3 receptor agonist attenuates the action of antidepressants in the forced swim test in rats

Involvement of 5-hydroxytryptamine (5-HT)3 receptors in action of antidepressants was examined in the forced swim test in rats. Rats were forced to swim in a cylinder for 15 min on day 1 and for 5 min on day 2. Imipramine, desipramine and mianserin, administered after the 15-min swim session on day 1 and before the 5-min swim test on day 2, dose-dependently decreased the duration of immobility in the swim test on day 2. 1-(m-Chlorophenyl)-biguanide (mCPBG) attenuated the decreased duration of immobility induced by imipramine, desipramine and mianserin, although mCPBG did not affect the duration of immobility when it was given alone. ICS205-930 dose-dependently decreased the duration of immobility in the swim test on day 2, and the effect of ICS205-930 was attenuated by mCPBG. These results suggest that the suppression of 5-HT3 receptor activity may contribute to the action of antidepressants.

Characterisation of a postjunctional 5-ht7-like and a prejunctional 5-HT3 receptor mediating contraction of rat isolated jejunum

The 5-HT (5-hydroxytryptamine)-induced contractile biphasic concentration-effect curve in rat isolated jejunum was investigated. The pEC50 values for the first and second phases were 8.0 and 6.1, respectively. The responses were insensitive to atropine (0.1 microM), ketanserin (2 microM), (-)-pindolol (5 microM), yohimbine (0.1 microM) and GR 113808 ({1-[2-(methyl-sulphonylamino)ethyl]-4-piperidinyl}methyl 1-methyl-1 H-indole-3-carboxylate, 1 microM) but susceptible to cocaine (10 microM). The low affinity phase was blocked by tetrodotoxin (1 microM), ondansetron (1 microM) and SR48968 (S)-N-methyl-N-[4-(4-acetylamino-4-phenyl piperidino)-2-(3,4-dichlorophenyl)butyl]benzamide, 0.1 microM). The high affinity phase was antagonised non-surmountably by fluoxetine (1 microM) methysergide (0.1 microM), spiperone (0.1 microM) and methiothepin (0.1 microM). Ritanserin (0.01-0.1 microM) and mesulergine (0.01-0.1 microM) acted as surmountable, competitive antagonists with pA2 values of 8.0 and 8.1, respectively. Clozapine (0.1 microM) was a surmountable antagonist with an apparent pA2 value of 8.0. The rank potency order of the 5-HT receptor agonists was 5-CT (5-carboxyamidotryptamine) > or = 5-HT = 5-methoxytryptamine > or = alpha-methyl-5-HT > > 8-OH-DPAT ((+/-)-2-dipropyl-amino-8-hydroxy-1,2,3, 4-tetrahydronaphthalene) > dipropyl-5-CT > renzapride = sumatriptan. The responses to 5-HT and 5-CT were not potentiated by pargyline (10 and 100 microM). It is suggested that rat jejunum contains a neuronal 5-HT3 receptor facilitating neurokinin release and a contractile smooth muscle 5-HT receptor with a pharmacological operational profile similar to the cloned 5-ht7 receptor.

Role of 5-hydroxytryptamine3 (5-HT3) antagonists in the prevention of emesis caused by anticancer therapy

Most anticancer drugs are cytotoxic and produce various side-effects, among which nausea and vomiting are almost ubiquitous and usually extremely distressing to the patient. Cancer chemotherapy elicits two main phases of vomiting: an intense, acute phase of vomiting that occurs almost immediately following anti-cancer therapy and a milder, delayed phase of nausea and vomiting of longer duration. The mechanisms underlying the induction of nausea and vomiting after cancer chemotherapy are poorly understood but may be mediated by serotonin (5-hydroxytryptamine or 5-HT), particularly in the acute phase. Serotonin activates 5-HT3 receptors, which function as ligand-gated ion channels located either in the periphery and/or in the central nervous system to produce emesis, among other effects. The peripheral 5-HT3 receptors may be pharmacologically distinct from the central 5-HT3 receptors and may exhibit some association with GTP-binding proteins. In addition, different populations may exist as distinct subtypes of the same receptor. The 5-HT3 receptor antagonist ondansetron (GR 38032F) is effective in preventing the emesis induced by cytotoxic agents currently used in the treatment of many forms of cancer. Ondansetron has, comparatively, a much higher efficacy in the treatment of acute emesis following cancer chemotherapy than it does in the delayed phase, suggesting that the late phase of emesis may be mediated by other distinct mechanisms.

Prophylactic effect of serotonin uptake inhibitors against motion sickness in Suncus murinus

The prophylactic effect of serotonin uptake inhibitors, imipramine and fluoxetine, against motion sickness was investigated in Suncus murinus. Imipramine (s.c.) and fluoxetine (i.p.) inhibited motion-induced emesis dose dependently with ID50 values of 1.7 and 26 mg/kg, respectively. The results suggest that increasing the concentration of serotonin in the synaptic cleft can prevent motion-induced emesis and that serotonin uptake inhibitors are effective as anti-motion sickness drugs.

The psychomotor and cognitive effects of litoxetine in young and middle aged volunteers

1. The effects of a range of doses of litoxetine (twice daily for 4 days), a novel specific serotonin re-uptake inhibitor, were evaluated in young and middle aged volunteers. 2. Psychometric testing was carried out at various time points on days 1 and 4 of each treatment period. The test battery consisted of critical flicker fusion (CFF), choice reaction time (CRT), compensatory tracking (CTT), Stroop and Sternberg memory scanning tests. Subjective feelings of sleep and sedation were measured by the Leeds Sleep Evaluation Questionnaire (LSEQ) and line analogue rating scales (LARS). 3. Pharmacokinetic profiles were determined from analyses of blood samples taken after the final dose on day 5. 4. Overall, there were few changes in any of the psychometric tests and although the higher doses of litoxetine improved CFF, these effects were weak in that differences could only be detected when the results were pooled against time. 5. The pharmacokinetic profile of litoxetine was very similar in both the young and middle aged subjects, and there was no difference regarding tolerability. 6. There is little evidence from this study to suggest that litoxetine has any intrinsic sedative activity which is likely to interfere with the performance of activities of everyday life.

Ifenprodil inhibition of the 5-hydroxytryptamine3 receptor

The anti-hypertensive drug ifenprodil is known to interact potently with the alpha 1-adrenergic receptor as well as a number of other second messenger-linked receptors. In addition to these properties, ifenprodil has been shown to prevent glutamate-mediated excitotoxicity via non-competitive antagonism of NMDA receptors [Legendre and Westbrook (1991) Molec. Pharmac. 40: 289-298; Shalaby et al. (1992) J. Pharmac. Exp. Ther. 260: 925-932]. With these things in mind, we have begun to examine the specificity of ifenprodil for various ligand-gated ion channels using electrophysiological methods. While ifenprodil effectively inhibits NMDA-mediated currents in cortical neurons in culture, it does not interact with either kainate or GABA receptors. Surprisingly, ifenprodil also acts as a relatively potent antagonist of the 5-hydroxytryptamine3 (5-HT3) receptor in the NG108-15 neuroblastoma x glioma cell line. Furthermore, several aspects of ifenprodil action on the 5-HT3 receptor resemble its interaction with the NMDA receptor. Namely, inhibition of 5-HT3-mediated cation currents is readily reversible, has relatively slow onset, is non-competitive, and is not voltage dependent. Since most of the known 5-HT3 antagonists are competitive, it is possible that ifenprodil may define a unique modulatory site(s) on this neurotransmitter receptor.

The interaction of antidepressant drugs with central and peripheral (enteric) 5-HT3 and 5-HT4 receptors

1. A combined study of receptor binding in central neuronal cell membranes and functional responses in isolated segments of guinea-pig small intestine allowed characterization of the interaction of four antidepressant drugs with central and peripheral 5-HT3 and 5-HT4 receptors. 2. Clomipramine, paroxetine and fluoxetine inhibited [3H]-DAU 6215 binding to 5-HT3 recognition sites in NG 108-15 cells with IC50 values in the range 1.3-4 microM. Litoxetine had an IC50 of 0.3 microM. The specific binding of [3H]-GR 113808 to 5-HT4 recognition sites in pig striatal membranes was inhibited by all four antidepressants with negligible potency (IC50 values > or = 20 microM). 3. In whole ileal segments, concentration-response curves to 5-HT were biphasic, with the high- and low-potency phases involving 5-HT4 and 5-HT3 receptors, respectively. Curves to 2-methyl-5-hydroxytryptamine (2-methyl-5-HT: a 5-HT3 receptor agonist) and 5-methoxytryptamine (5-MeOT: a 5-HT4 receptor agonist) were monophasic. All antidepressants were used at concentrations lacking anticholinoceptor properties, as demonstrated in both electrically stimulated longitudinal muscle-myenteric plexus preparations (LMMPs) and in unstimulated LMMPs following addition of acetylcholine (100 nM). 4. Fluoxetine (0.1-1 microM) and litoxetine (0.3-3 microM) antagonized both the high- and low-potency phases of the 5-HT curve. Schild analysis for the low-potency phase yielded pA2 estimates of 6.6 +/- 0.3 (Schild slope of 1.1) and of 6.6 +/- 0.1 (Schild slope of 1.1), respectively. At higher concentrations (3 microM), fluoxetine markedly inhibited the 5-HT response maximum. Clomipramine (10-300 nM) inhibited, by a mechanism independent of concentration, both phases of the 5-HT curve with a reduction of the maximum response. Paroxetine (1 microM) was ineffective on the high-potency phase, but caused a rightward shift of the low-potency phase (pKB: 6.1 +/- 0.01). 5. Responses to 2-methyl-5-HT were inhibited by 1 microM fluoxetine (pKB: 5.4 +/- 0.02). Like clomipramine(30 and 100 nM), litoxetine (1 and 3 microM) produced rightward displacements of 2-methyl-5-HT-induced contractions, which were virtually independent of antidepressant concentration (pKB values: 6.0 +/- 0.02 and 5.5 +/- 0.01, respectively). At higher concentrations, fluoxetine (3 microM) and clomipramine (300 nM)markedly reduced the 2-methyl-5-HT response maximum. Paroxetine (1 micro M) was ineffective.6. Responses to 5-MeOT were shifted to the right by fluoxetine (0.1-1 micro M) and litoxetine (1 and 3 microM)in a concentration-dependent manner. At higher concentrations, fluoxetine (3 microM) markedly reduced the 5-MeOT response maximum, an effect also observed with 100 and 300 nM clomipramine. Paroxetine(1 microM) was ineffective.7. In unstimulated LMMPs, the excitatory effects evoked by 5-HT, 2-methyl-5-HT and 5-MeOT and the antagonism produced by 300 nM clomipramine were comparable to those obtained in whole ileal segments. This suggests that 5-HT contained in the mucosa of whole preparations does not interfere with agonist-induced contractile responses and with the inhibitory effect of antidepressant drugs.8. In conclusion, our results show that clomipramine, fluoxetine, paroxetine and litoxetine possess low to moderate potency/affinity at both central and peripheral (enteric) 5-HT3 receptors. In contrast, all four antidepressants are virtually ineffective at central 5-HT4 receptors. Inhibition of 5-HT4 receptor mediated ileal contractions by fluoxetine, litoxetine and clomipramine may result from allostericant agonism or, more likely, from post-receptor blockade of second messenger generation. The interaction of antidepressants with central and peripheral 5-HT3 and 5-HT4 receptors may be relevant for both potential therapeutic action and adverse effects at gastrointestinal level.

Drugs affecting serotonin receptors

A greater understanding of the various serotonin receptor subtypes has led to a clearer appreciation of the role of serotonin in gastrointestinal motility, sensation and secretion. Serotonin is definitely involved in the aetiopathogenesis of cisplatin-induced emesis and carcinoid diarrhoea. The application of serotonergic drugs in clinical therapeutics for gut disturbances is presently dominated by the use of 5-HT3 antagonists for acute chemotherapy-induced nausea and vomiting, and the use of substituted benzamides which are 5-HT4 agonists stimulating gut motor function through 5-HT4 neuronal receptors. The best-studied 5-HT4 agonist is cisapride, which has been shown to stimulate motility at several levels of the gut. Cisapride is approved for healing and maintenance treatment of reflux oesophagitis and is used in several countries for the alleviation of symptoms consistent with regional stasis, from dyspepsia to constipation. Carcinoid diarrhoea is a prototypic disease associated with deranged serotonin metabolism, and a rationale for using 5-HT3 or 5-HT4 antagonists is based on the recent appreciation of the important role of impaired gut motor function in carcinoid diarrhoea. In the future, greater understanding of the serotonin receptor subtypes and their role in gut disorders may lead to novel approaches to alleviate increased visceral perception of functional gastrointestinal disorders, to correct changes in colonic capacitance, or to alter gastrointestinal motility that contributes to diarrhoea or constipation. However, at the present time, it must be stressed that these uses are still at an experimental stage and that careful validation and proper controlled studies are still required.

EEG profile of litoxetine after single and repeated administration in healthy volunteers

1. Litoxetine is a selective serotonin reuptake inhibitor with antidepressant activity in animal models and in depressed patients. 2. This double-blind, cross-over, placebo-controlled study was carried out in 12 healthy young male volunteers. The aim was to assess the EEG profile of litoxetine in parallel with its pharmacokinetics after a single dose or multiple administrations for 4 days (6 doses) of two dosages (10 mg and 25 mg). Spectral analysis of four EEG leads (F4-T4, F3-T3, T4-02 and T3-01) was done up to 12 h post-dose. 3. In single or multiple doses, litoxetine induced EEG changes characterised by a dose-related increase in fast beta energies, mainly beta 2, without any changes in slow waves (delta and theta). A slight reduction in alpha activity occurred only after repeated doses. 4. EEG changes occurred after a single oral administration and lasted at least 12 h with litoxetine blood concentrations ranging from 4 to 10 ng ml-1. With repeated administrations, the pharmacodynamic steady-state was achieved as the increase in beta 2 energies was the same before and 12 h post-dose. These effects occurred with litoxetine blood concentrations ranging from 3 to 7 ng ml-1 with the 10 mg dosage and from 8 to 18 ng ml-1 with the 25 mg dosage. The EEG profile did not change after 4 days of repeated administration, indicating that tolerance did not develop. 5. Cmax and AUC showed proportionality between the administered dosages of 10 and 25 mg.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioural pharmacology of 5-HT3 receptor antagonists: a critical update on therapeutic potential

There has been tremendous interest in 5-HT3 receptor antagonists since their discovery and the subsequent identification of 5-HT3 receptors in the CNS. Based on the results of early behavioural tests with these compounds, there has been substantial interest in their potential use for the treatment of various CNS disorders. In this review, Andrew Greenshaw attempts to clarify the status of the therapeutic potential of these drugs, discussing inconsistencies in preclinical findings and identifying areas in need of clarification through future research. 5-HT3 receptor antagonists are claimed to be potentially useful in the treatment of nausea, inflammatory pain (migraine and irritable bowel syndrome), anxiety, depression, schizophrenia, dementia and drug abuse!