5-HT2C receptors in psychiatric disorders: A review

5-HT2Rs have a different genomic organization from other 5-HT2Rs. 5HT2CR undergoes post-transcriptional pre-mRNA editing generating diversity among RNA transcripts. Selective post-transcriptional editing could be involved in the pathophysiology of psychiatric disorders through impairment in G-protein interactions. Moreover, it may influence the therapeutic response to agents such as atypical antipsychotic drugs. Additionally, 5-HT2CR exhibits alternative splicing. Central serotonergic and dopaminergic systems interact to modulate normal and abnormal behaviors. Thus, 5HT2CR plays a crucial role in psychiatric disorders. 5HT2CR could be a relevant pharmacological target in the treatment of neuropsychiatric disorders. The development of drugs that specifically target 5-HT2C receptors will allow for better understanding of their involvement in the pathophysiology of psychiatric disorders including schizophrenia, anxiety, and depression. Among therapeutic means currently available, most drugs used to treat highly morbid psychiatric diseases interact at least partly with 5-HT2CRs. Pharmacologically, 5HT2CRs, have the ability to generate differentially distinct response signal transduction pathways depending on the type of 5HT2CR agonist. Although this receptor property has been clearly demonstrated, in vitro, the eventual beneficial impact of this property opens new perspectives in the development of agonists that could activate signal transduction pathways leading to better therapeutic efficiency with fewer adverse effects.

Factors triggering abolishment of benzodiazepines effects in the Four-Plate Test--retest in mice

Abolishment of anxiolytic-like effects of diazepam occurs during re-exposure to some animal tests of anxiety. We investigated the loss of anxiolytic-like effects of diazepam during Trial 2 on previously undrugged mice, namely one-trial tolerance (OTT). Swiss mice were subjected to 1) Four-Plate Test (FPT) without punishments in Trial 1 or 2) FPT without punishments in both Trials or 3) FPT with spatial modifications in Trial 1 or 4) Elevated Plus Maze (EPM), then 24 h later to FPT, with saline, diazepam (1 mg/kg) or DOI (1 mg/kg). Removing punishments in Trial 1 does not counteract the effect reduction of diazepam in Trial 2, but spatial modifications of the aversive environment. Previous exposure to EPM does not trigger a loss of efficacy of diazepam in FPT. Electric punishments do not trigger OTT to benzodiazepines; whilst knowledge of the environment seems to be responsible for this phenomenon. FPT may be useful to study OTT because punishments potentate OTT in this model of anxiety.

Dopamine dysregulation syndrome: implications for a dopamine hypothesis of bipolar disorder

OBJECTIVE

Rational therapeutic development in bipolar is hampered by a lack of pathophysiological model. However, there is a wealth of converging data on the role of dopamine in bipolar disorder. This paper therefore examines the possibility of a dopamine hypothesis for bipolar disorder.

METHOD

A literature search was conducted using standard search engines Embase, PyschLIT, PubMed and MEDLINE. In addition, papers and book chapters known to the authors were retrieved and examined for further relevant articles.

RESULTS

Collectively, in excess of 100 articles were reviewed from which approximately 75% were relevant to the focus of this paper.

CONCLUSION

Pharmacological models suggest a role of increased dopaminergic drive in mania and the converse in depression. In Parkinson's disease, administration of high-dose dopamine precursors can produce a 'maniform' picture, which switches into a depressive analogue on withdrawal. It is possible that in bipolar disorder there is a cyclical process, where increased dopaminergic transmission in mania leads to a secondary down regulation of dopaminergic receptor sensitivity over time. This may lead to a period of decreased dopaminergic transmission, corresponding with the depressive phase, and the repetition of the cycle. This model, if verified, may have implications for rational drug development.

Dopamine dysregulation syndrome: implications for a dopamine hypothesis of bipolar disorder

OBJECTIVE

Rational therapeutic development in bipolar is hampered by a lack of pathophysiological model. However, there is a wealth of converging data on the role of dopamine in bipolar disorder. This paper therefore examines the possibility of a dopamine hypothesis for bipolar disorder.

METHOD

A literature search was conducted using standard search engines Embase, PyschLIT, PubMed and MEDLINE. In addition, papers and book chapters known to the authors were retrieved and examined for further relevant articles.

RESULTS

Collectively, in excess of 100 articles were reviewed from which approximately 75% were relevant to the focus of this paper.

CONCLUSION

Pharmacological models suggest a role of increased dopaminergic drive in mania and the converse in depression. In Parkinson's disease, administration of high-dose dopamine precursors can produce a 'maniform' picture, which switches into a depressive analogue on withdrawal. It is possible that in bipolar disorder there is a cyclical process, where increased dopaminergic transmission in mania leads to a secondary down regulation of dopaminergic receptor sensitivity over time. This may lead to a period of decreased dopaminergic transmission, corresponding with the depressive phase, and the repetition of the cycle. This model, if verified, may have implications for rational drug development.

Les médicaments du sommeil et de la vigilance et leurs indications

This paper is a review of the use of drugs in sleep and wakefulness disorders. Insomnia is more often a symptom than an autonomic disorder. Good knowledge of the clinical facts is required before prescribing hypnotics. Sedative drugs are potentially hypnotics; yet, melatonin is not sedative and may be considered to resynchronise of sleep phases. Stimulant drugs are prescribed in attention disorders; methylphenidate is the more frequently used. Narcolepsy, which is characterized by daytime sleepiness and irresistible episodes of sleep, is treated by an alpha1 noradrenergic stimulant modafinil which has no amphetaminic properties.

Effect of antidepressant drugs on 6-OHDA-treated mice in the FST

There is growing evidence suggesting that dopamine could be indirectly involved in the appearance of behavioural effects of antidepressants. In this study, we induced a partial (over 70%) and non-reversible depletion of dopamine-containing neurons in mice by i.c.v. infusion of 6-OHDA. Then, we compared the antidepressant-like effect of drugs (citalopram, paroxetine, desipramine and imipramine) with or without dopamine depletion in the mice forced swimming test. Our results clearly show that lesion with 6-OHDA does not modify the response of mice to desipramine and imipramine, whereas dopamine depletion abolished the antidepressant-like effect of citalopram and paroxetine. It could then be suggested that antidepressant-like effect of selective serotonin reuptake inhibitors (paroxetine and citalopram) in the mice FST requires the activation of dopaminergic pathways to occur.

Antidepressant-like activity of selective serotonin reuptake inhibitors combined with a NK1 receptor antagonist in the mouse forced swimming test

Substance P antagonists of the neurokinin-1 receptor type (NK1) have growing interest as new antidepressant therapies. It has been postulated that these drugs exert this putative therapeutic effect without direct interactions with serotonin (5-HT) neurons. In line with this assumption, previous intracerebral in vivo microdialysis experiments provided evidence that the NK1 receptor antagonists did not change basal cortical 5-HT levels. However, we found that increases in cortical 5-HT overflow caused by systemic injection of the selective serotonin reuptake inhibitor (SSRI), paroxetine was higher in freely moving (C57BL/6x129sv) NK1-/- mutants than in wild-type NK1+/+ mice. More recently, a pharmacological study has led to a similar conclusion since GR205171, a NK1 receptor antagonist, potentiated paroxetine-induced increases in cortical 5-HT dialysate following its acute systemic or intra-raphe administration to wild-type mice . In the present study, we tested whether an acute combination of SSRI and NK1 receptor antagonist could display antidepressant-like activity using the forced swimming test in Swiss mice. We found that a single systemic dose of GR205171 (10 and 30 mg/kg, i.p.) had no effect by itself. However, it selectively potentiated the antidepressant-like activity of subactive doses of two serotonergic antidepressant drugs, citalopram and paroxetine (without psychomotor stimulant activity), but not that of noradrenaline reuptake inhibitor, desipramine. In agreement with neurochemical data, the present study confirms that co-administration of a NK1 receptor antagonist with an antidepressant drug such as a SSRI may have a therapeutic potential to improve the treatment of major depressive episodes in human compared to SSRI alone.

A typical mood stabilizers: a "typical role for atypical antipsychotics

OBJECTIVE

To assess the potential role of atypical antipsychotics as mood stabilizers.

METHOD

A MedLine, PsychLIT, PubMed, and EMBASE literature search of papers published up to December 2004 was conducted using the names of atypical antipsychotics and a number of key terms relevant to bipolar disorder. Additional articles were retrieved by scrutinizing the bibliographies of review papers and literature known to the authors. Data pertinent to the objective was reviewed according to the various phases of bipolar disorder.

RESULTS

The data is most substantive for the use of atypical antipsychotics in mania, to the extent that an argument for a class effect of significant efficacy can be made. This does not extend to bipolar depression, however, good data is now emerging for some agents and will need to be considered for each individual agent as it accumulates. As regards mixed states and rapid cycling the evidence is thus far sparse and too few maintenance studies have been conducted to make any firm assertions. However, with respect to long-term therapy the atypical antipsychotics do have clinically significant side-effects of which clinicians need to be aware.

CONCLUSION

Based on the evidence thus far it is perhaps premature to describe the atypical antipsychotics as mood stabilizers. Individual agents may eventually be able to claim this label, however, much further research is needed especially with respect to maintenance and relapse prevention.

Pharmacology of new antipsychotic drugs: are they stabilizers of schizophrenic psychosis?

Antipsychotic drugs with greater efficacy and tolerance have been sought and studied in recent years. Some of them could be used in new treatment strategies to replace the D(2) receptor antagonism induced by classic neuroleptics such as haloperidol. The development strategies in this field are not only focused on discovering specific antagonists of one subtype of dopaminergic receptor, but on the synthesis of molecules having different effects on different brain areas. Drugs with limbic and frontal cortex specificity are associated with improved tolerance, increased efficacy against negative symptoms and a higher quality of life for patients. Furthermore, some investigation is being made into the possibility of alternatives to the dopaminergic system as a target for antipsychotics. Serotonergic antagonists and alpha-adrenoceptor antagonists, for example, are also being considered as potential options in the treatment of mental diseases such as schizophrenia.

Effects of acute treatment with paroxetine, citalopram and venlafaxine in vivo on noradrenaline and serotonin outflow: a microdialysis study in Swiss mice

1. This study investigated whether a single administration of a range of doses (1, 4 and 8 mg kg-1, i.p.) of paroxetine, citalopram or venlafaxine may simultaneously increase extracellular levels of 5-HT ([5-HT]ext) and noradrenaline ([NA]ext) by using in vivo microdialysis in the frontal cortex (FCx) of awake, freely moving Swiss mice. 2. In vivo, paroxetine induced similar increases in cortical [5-HT]ext at the three doses tested, and induced a statistically significant increase in cortical [NA]ext at 4 and 8 mg x kg-1. Citalopram increased neither [5-HT]ext nor [NA]ext at the lowest dose, but increased both neurotransmitter levels at 4 and 8 mg x kg-1. At these doses, citalopram induced greater increases in cortical [5-HT]ext than in [NA]ext. Venlafaxine increased [5-HT]ext and [NA]ext to about 400 and 140% of the respective basal values at 8 mg kg-1. 3. Citalopram and paroxetine have the highest potency to increase cortical [5-HT]ext and [NA]ext, respectively. In addition, the rank of order of efficacy of these antidepressant drugs to increase [5-HT]ext in vivo in the FCx of mice was as follows: venlafaxine>citalopram>paroxetine, while the efficacy to increase cortical [NA]ext in mice of paroxetine and citalopram is similar, and greater than that of venlafaxine. 4. In conclusion, extracellular levels of cortical [NA]ext increase with the highest doses of the very selective SSRI citalopram, as well as with the very potent SSRI paroxetine. Surprisingly, the SNRI venlafaxine increased cortical [5-HT]ext to a greater extent rather than [NA]ext in the range of doses studied in mice.

Effects of chronic paroxetine treatment on dialysate serotonin in 5-HT1B receptor knockout mice

The role of serotonin (5-HT)1B receptors in the mechanism of action of selective serotonin re-uptake inhibitors (SSRI) was studied by using intracerebral in vivo microdialysis in conscious, freely moving wild-type and 5-HT1B receptor knockout (KO 5-HT1B) mice in order to compare the effects of chronic administration of paroxetine via osmotic minipumps (1 mg per kg per day for 14 days) on extracellular 5-HT levels ([5-HT]ext) in the medial prefrontal cortex and ventral hippocampus. Basal [5-HT]ext values in the medial prefrontal cortex and ventral hippocampus, approximately 20 h after removing the minipump, were not altered by chronic paroxetine treatment in both genotypes. On day 15, in the ventral hippocampus, an acute paroxetine challenge (1 mg/kg i.p.) induced a larger increase in [5-HT]ext in saline-pretreated mutant than in wild-type mice. This difference between the two genotypes in the effect of the paroxetine challenge persisted following chronic paroxetine treatment. Conversely, in the medial prefrontal cortex, the paroxetine challenge increased [5-HT]ext similarly in saline-pretreated mice of both genotypes. Such a challenge produced a further increase in cortical [5-HT]ext compared with that in saline-pretreated groups of both genotypes, but no differences were found between genotypes following chronic treatment. To avoid the interaction with raphe 5-HT1A autoreceptors, 1 micro m paroxetine was perfused locally through the dialysis probe implanted in the ventral hippocampus; similar increases in hippocampal [5-HT]ext were found in acutely or chronically treated wild-type mice. Systemic administration of the mixed 5-HT1B/1D receptor antagonist GR 127935 (4 mg/kg) in chronically treated wild-type mice potentiated the effect of a paroxetine challenge dose on [5-HT]ext in the ventral hippocampus, whereas systemic administration of the selective 5-HT1A receptor antagonist WAY 100635 did not. By using the zero net flux method of quantitative microdialysis in the medial prefrontal cortex and ventral hippocampus of wild-type and KO 5-HT1B mice, we found that basal [5-HT]ext and the extraction fraction of 5-HT were similar in the medial prefrontal cortex and ventral hippocampus of both genotypes, suggesting that no compensatory response to the constitutive deletion of the 5-HT1B receptor involving changes in 5-HT uptake capacity occurred in vivo. As steady-state brain concentrations of paroxetine at day 14 were similar in both genotypes, it is unlikely that differences in the effects of a paroxetine challenge on hippocampal [5-HT]ext are due to alterations of the drug's pharmacokinetic properties in mutants. These data suggest that there are differences between the ventral hippocampus and medial prefrontal cortex in activation of terminal 5-HT1B autoreceptors and their role in regulating dialysate 5-HT levels. These presynaptic receptors retain their capacity to limit 5-HT release mainly in the ventral hippocampus following chronic paroxetine treatment in mice.

CCK2 receptor-deficient mice have increased sensitivity of dopamine D2 receptors

The present study supports a role of CCK(2) receptors in the regulation of dopamine neurones. In pharmacological studies conducted on male CCK(2) receptor-deficient mice the changes in the activity of dopamine system were established. A low dose of dopamine agonist apomorphine (0.1 mg/kg), stimulating the pre-synaptic dopamine receptors, induced significantly stronger suppression of locomotor activity in mutant mice (-/-) compared to their wild-type littermates (+/+). The administration of amphetamine (3-6 mg/kg), a drug increasing dopamine release, caused a dose-dependent stimulation of locomotor activity in wild-type mice. In mice lacking CCK(2) receptors, a lower dose of amphetamine (3 mg/kg) tended to suppress the motor activity, whereas the higher dose (6 mg/kg) induced the significantly stronger motor stimulation in mutant mice. Moreover, in the CCK(2) receptor-deficient mice the affinity of dopamine D(2) receptors, but not 5-HT(2) receptors, was increased. Altogether, the targeted genetic suppression of CCK(2) receptors increased the sensitivity of pre- and post-synaptic dopamine D(2) receptors.

[Mechanism of action of antidepressants and therapeutic perspectives]

Depression is an incapacitating disease which needs appropriate treatment. This article reviews the pharmacology of antidepressant drugs and the future perspectives of treating mood disorders such as depression. The foremost theory for explaining the biological basis of depression has been the monoamine hypothesis. Depression is due to a deficiency in one or other biogenic monoamines (serotonin, 5-HT; noradrenaline, NA; dopamine, DA). Antidepressant drugs are therefore classified according to their ability to improve monoaminergic transmission. Since this first theory, other explanations based on abnormal function of monoamine receptors or associated with impaired signalling pathways have been suggested. Notable progress has been accomplished in the treatment of major depressive disorders with new compounds recently discovered (selective serotonin reuptake inhibitors: SSRI; serotonin noradrenaline reuptake inhibitors: SNRI). Behavioural, electrophysiological and microdialysis studies have shown that serotonin (5-HT) receptors, mainly 5-HT1A, 5-HT1B and 5-HT2C sub-types, exert a key role in modulating antidepressant activity. Indirect activation of neurotransmitter receptors by antidepressants may also lead, via increases in endogenous levels of serotonin in synapses in specific brain regions, to activation of various G proteins coupled to a receptor, signal of transduction, transcription factors and neurotrophic factors such as brain-derived neurotrophic factor (BDNF). Thus, depression may be considered as a transduction mechanism anomaly. This hypothesis needs to be clarified by molecular biology. Although antidepressants have improved the therapeutic potential compared to tricyclics (TCA) in terms of reduced side effects, a number of problems still occur with these drugs. Clinical effects are not always observed until after this time has elapsed (4-6 weeks) and a substantial proportion of depressed patients show only partial or no response to antidepressants. Knowledge of the existence of links between neurotransmitter systems and the discovery of the most specific target, 5-HT receptors, should lead to improvements in antidepressant therapy. Developing drugs using innovative mechanisms such as directly acting on 5-HT receptors (5-HT1A agonists or 5-HT2 antagonists), would appear to be useful in the treatment of depression. The use of antidepressants in anxiety disorders such as obsessional compulsive disorders and even generalised anxiety, highlights the distinction between antidepressants and classic anxiolytics such as benzodiazepines, or even buspirone.

Relationship between cerebral pharmacokinetics and anxiolytic activity of diazepam and its active metabolites after a single intra-peritoneal administration of diazepam in mice

The relationship between the cerebral pharmacokinetics of diazepam and its active metabolites (desmethyldiazepam, oxazepam) and the anxiolytic effect evaluated by the four-plates test and the light/dark test were investigated after a single intra-peritoneal injection of diazepam (1 mg/kg or 1.5 mg/kg). For up to 30 min after administration, the sedative effect interfered with the anxiolytic effect, thus the results of the anxiolytic effect were not interpretable. From 30 min to 60 min after administration, this interference disappeared, the cerebral level of benzodiazepines was stable (the brain elimination of diazepam was compensated for by the appearance of desmethyldiazepam followed by oxazepam) but the anxiolytic effect decreased dramatically in all the tests with diazepam 1 mg/kg or 1.5 mg/kg. The acute tolerance to benzodiazepines and the difference of affinity for subtypes of GABA(A) receptors between diazepam, desmethyldiazepam, oxazepam could explain this result.

[Characteristics of hypersensitivity syndrome to lamotrigine: review of one case reported in the Regional Center of Pharmacovigilance of Nantes]

Drug-induced hypersensitivity syndrome is an uncommon but potentially life-threatening idiosyncratic drug reaction. In the literature, about five cases have been reported concerning hypersensitivity syndrome with lamotrigine. Most cases concern aromatic anticonvulsants but we report a case induced by lamotrigine which is a non aromatic anticonvulsant. A 73-year-old man was treated with lamotrigine for epilepsy due to a cerebrovascular stroke for 5 weeks. After 2 weeks with a single oral dose of 50 mg lamotrigine, the patient received 100 mg. Quickly thereafter fever, erythema and edema involving the periorbital area appeared. He was then admitted to hospital and lamotrigine was immediately discontinued. He developed acute hepatic and renal failure. During his hospital stay, he was treated with systemic and topical corticosteroids. After slow improvement, he was discharged 4 weeks later. Concerning this typical case, we review the characteristics of hypersensitivity syndrome and the different etiopathogenesis. The hypersensitivity syndrome typically develops two to six weeks after a drug is first administered, later than most other serious skin reactions. This syndrome manifests as rash, fever, tender lymphadenopathy, hepatitis and eosinophilia. The mechanism of hypersensitivity syndrome is unknown. Several theories have been proposed. The reaction is secondary to circulating antibodies or concerns toxic metabolities. On the other hand, association of human herpes virus 6 infection may play a role in the development of hypersensitivity syndrome. Hypersensitivity reactions to the aromatic antiepileptic drugs appear to have an immune etiology much like lamotrigine: bioactivation, detoxification, covalent adduct formation, processing and presentation of antigen to the immune system, and consequent formation of antibody and T-cell immune effectors. Another theory involves toxic metabolites; the aromatic antiepileptic agents are metabolised by cytochrome P-450 to an arene oxide metabolite. This is normally detoxified by epoxide hydrolase. This enzyme may be lacking or mutated in persons that develop the syndrome, and this is genetically determined. Lamotrigine is mainly metabolised by hepatic glucuronidation, but hypersensitivity may involve similar processes such aromatic antiepileptic drugs, except that the toxic metabolite has not yet been found. Because of slow evolution and clinical similarity to many infectious illnesses, the diagnosis of hypersensitivity syndrome may be delayed. Prompt recognition and withdrawal of the suspected drug is essential. The goal of research is to describe a "susceptibility profile" identifying individuals at risk for these forms of drug toxicity.

[Results of a French nationwide survey of cutaneous side effects of ketoprofen gel reported between September 1996 and August 2000]

A French nation-wide pharmacovigilance survey of ketoprofen topic collated, from September 1996 to August 2000, 770 cutaneous side-effects. The frequency varies from 0.013@1000 to 0.028@1000 according to the commercial gel. Analysis concerns spontaneous notifications of French nation-wide pharmacovigilance. Sex ratio is well distributed, population is young. Treatment lasted about 12 days, the side-effects appearing after about 13 days, 25 per cent of cases are delayed to discontinuance of treatment, mainly after exposure to sunlight. Co-administered drugs are in most cases systemic or topical NSAIDs and/or fibrates and then increase the seriousness of the iatrogenic pathology. 75 per cent of cutaneous side-effects appear in summer, 50 per cent have been reported as "photosensitivity". Reactions are severe in 30 per cent of the cases. More than 80 per cent of cases present an extension beyond the site of application. The course is usually favourable and neither topical nor systemic corticosteroid treatment influence the duration of evolution. Photopatchtests testing in 23 per cent of cases show evidence of photoallergy to ketoprofen and crossed photoallergy with tiaprofenic acid, fenofibrate, oxybenzone and benzophenone. These results confirm that photoallergy is due to the common benzoylketone structure but not to their arylpropionic function. Some cases of persistent or recurrent photosensitivity must be more explored. The results lead to request a modification of marketing authorizations.

Is dopamine implicated in the antidepressant-like effects of selective serotonin reuptake inhibitors in the mouse forced swimming test?

RATIONALE

Microdialysis, binding and behavioural studies have shown that the dopaminergic system plays a role in antidepressant treatment.

OBJECTIVES

The present study determined whether the antidepressant-like effects of selective serotonin reuptake inhibitors measured in the mouse forced swimming test are mediated via dopamine receptors.

METHODS

Male Swiss mice were randomly assigned to groups of 24 animals and injected IP with citalopram, fluoxetine, fluvoxamine, sertraline, or paroxetine alone or in combination with the dopamine D(1)agonist SKF 38393, the D(1) antagonist SCH 23390, the D(2) agonist bromocriptine, the D(2) antagonist sulpiride, the D(3) agonist PD 128 907, or the D(3) antagonist nafadotride.

RESULTS

The anti-immobility effects of paroxetine, fluvoxamine and citalopram were increased by co-administration of SKF 38393 (0.5 and 2 mg/kg), SCH 23390 (0.06 mg/kg), bromocriptine (0.5 and 2 mg/kg) or PD 128 907 (1 and 2 mg/kg), and were attenuated by SCH 23390 (0.5 mg/kg). The anti-immobility effects of paroxetine and fluvoxamine were also increased with sulpiride (0.5 and 2 mg/kg). The anti-immobility effect of fluoxetine was increased by SKF 38393 (2 mg/kg) and PD 128 907(1 and 2 mg/kg) co-administration. The anti-immobility effect of sertraline (16 mg/kg) was increased by SKF 38393 (0.5 mg/kg), bromocriptine (2 mg/kg) and PD 128 907 (2 mg/kg) and the effect of sertraline (2 mg/kg) was increased by bromocriptine (2 mg/kg). The anti-immobility effect of paroxetine (4 mg/kg) was increased by nafadotride (2 mg/kg).

CONCLUSIONS

These data indicate that the antidepressant activity of various SSRIs involves different dopamine receptor subtypes and that the serotoninergic and dopaminergic systems interact with each other.

First report of mirtazapine-induced arthralgia

OBJECTIVE

The aim of our work is to describe the first two cases of arthralgia associated with the antidepressant drug mirtazapine.

METHOD

Descriptive analysis of two iatrogenic cases. The review of the literature was achieved by the traditional electronic methods. The French database of iatrogenic cases was consulted.

RESULTS

A 53-year-old man presented with gonalgia after some weeks of mirtazapine treatment. The intensity of the arthralgia was correlated with the dosage and the adverse effect rapidly disappeared after the antidepressant therapy was stopped. A 38-year-old woman received mirtazapine for 3 months and complained of arthralgia and myalgia. This clinical picture was suspended as the drug was stopped and a positive reintroduction was observed. No other cause was found in these two patients.

DISCUSSION

No similar case has been reported in the international literature, but several observations of arthralgia with mianserin are mentioned. As mirtazapine is the 6-aza derivative of the tetracyclic antidepressant mianserin, the similarities of their chemical structures begs the responsibility of mirtazapine for arthralgia.

Cholecystokinin2 receptor-deficient mice display altered function of brain dopaminergic system

RATIONALE

Cholecystokinin (CCK) has been shown to coexist and interact with dopamine in the regulation of behaviour. Two different CCK receptors (CCK1 and CCK2) have an opposite influence on the activity of dopamine neurons. Stimulation of CCK2 receptors decreases the release of dopamine and that receptor could mediate the neuroleptic-like effect of CCK.

OBJECTIVE

To investigate the activity of the dopaminergic system in pharmacological experiments on CCK2 receptor (CCK2R)-deficient mice.

METHODS

We used age- and sex-matched littermates in all our experiments. To evaluate the behavioural differences, we performed the rotarod test and measured the locomotor activity of animals using computer-connected photoelectric motility boxes. Amphetamine and apomorphine, two dopaminergic drugs with different pharmacodynamic properties, were used to influence the activity of the dopaminergic system in the brain. Neurochemical differences related to the different genotype were analysed by means of high-performance liquid chromatography and radioligand binding studies.

RESULTS

Motor co-ordination was significantly impaired in the rotarod test of CCK2R receptor-deficient mice. Moreover, the locomotor activity of heterozygous (+/-) and homozygous (-/-) CCK2R receptor-deficient mice was somewhat reduced. A low dose of apomorphine (0.1 mg/kg), an unselective agonist of dopamine receptors, suppressed locomotor activity significantly more in homozygous (-/-) and heterozygous (+/-) mutant mice than in their wild-type (+/+) littermates. Amphetamine (3-6 mg/kg), increasing release of dopamine from the presynaptic terminals, caused a dose-dependent motor stimulation in wild-type (+/+) mice. In heterozygous (+/-) and homozygous (-/-) mice, a lower dose of amphetamine (3 mg/kg) did not alter the locomotor activity, whereas the higher dose of (6 mg/kg) induced a significantly stronger increase in locomotor activity in homozygous (-/-) mice than in their heterozygous (+/-) and wild-type (+/+) littermates. Despite the changes in the action of apomorphine and amphetamine in homozygous (-/-) mice, we did not find any significant differences in the concentration of dopamine and their metabolites in the striatum or cortex. However, the density of dopamine D2 receptors was significantly increased in the striatum of homozygous (-/-) animals compared with wild-type (+/+) mice.

CONCLUSIONS

The targeted mutation of the CCK2 receptor gene induced gene dose-dependent changes in the activity of the dopaminergic system. The sensitivity of presynaptic dopamine receptors was increased in heterozygous (+/-) and homozygous (-/-) animals, whereas the increase in sensitivity of postsynaptic dopamine receptors was apparent only in homozygous (-/-) mice.

A follow-up study of a population of schizophrenic patients treated with clozapine

1. Clozapine is a dibenzodiazepine neuroleptic which presents the advantage of not having undesirable neurological side-effects. Its efficacy for the treatment of the symptoms of schizophrenia is known, but the use of clozapine is limited to treatment-resistant schizophrenic patients as it induces agranulocytosis with a higher incidence than that of other neuroleptic drugs. 2. The present study was designed in order to evaluate the benefit/risk of chronic treatment. The analysis was performed using the files of schizophrenic patients. These patients were not stabilized by a classical neuroleptic treatment and/or presented individual secondary effects. 3. Clozapine induced neutropenia and 1 case of agranulocytosis in 3 females. Analysis of leukocyte expression highlighted some premonitory symptoms in patients who presented neutropenia. The observation of 2 to 3 early successive peaks in leukocyte expression (between the third and tenth week of treatment) could be predictive of neutropenia in the 3 to 4 months of treatment. 4. The patients who presented a lower leukocyte base-line following a peak had a higher risk, of developing neutropenia. This might explain some late accidents beyond the first six months of treatment. 5. The present study confirmed the advantages of clozapine treatment and demonstrated that the risk of neutropenia may be diminished by the detection of premonitory symptoms and the early monitoring of patients at risk i.e. female patients and subjects with a lower leukocyte base-line.

Cyamemazine as an anxiolytic drug on the elevated plus maze and light/dark paradigm in mice

Several studies have demonstrated that cyamemazine, a classic antipsychotic compound, possesses anxiolytic properties in humans as well as a potent antagonistic effect on 5-HT(2C) and 5-HT(3) receptors. In this study the level of anxiety of mice was assessed in the light/dark exploration test and the elevated plus maze (EPM) following both acute and chronic administration. Spontaneous locomotor activity was measured using a photoelectric actimeter. Acute or chronic administration of cyamemazine dramatically decreases the spontaneous locomotor activity of mice at the dose of 1 mg/kg in comparison with the control group. In the light/dark exploration test, cyamemazine (0.375 mg/kg) only demonstrated anxiolytic-like activity following acute administration. In the elevated plus maze (EPM), cyamemazine did not induce any anxiolytic like effects after acute administration. However, after chronic administration, cyamemazine at doses of 0.25, 0.375, 0.5 and 1 mg/kg significantly increased the time spent in the open arms. The number of open arm entries was also increased at 0.25 and 0.5 mg/kg. Various serotonergic ligands were then used to examine the role of the various receptors in mediating the effects of cyamemazine in the EPM. Concerning the 5-HT(2) ligands DOI and mCPP antagonised the effects of cyamemazine and N-desmethyl clozapine potentiated the effects. For 2-methyl-5-HT and ondansetron, the 5-HT(3) receptor ligands did not seem to have any effect. It appears that the 5-HT(2C) receptors are more implicated in the function of mediating the anxiolytic effect of cyamemazine in the EPM. The discrepancy of results obtained in the tests, following acute or chronic administration could be the result of the combined activity of dopamine D(2) receptor antagonism with antagonism of 5-HT(2C) and 5-HT(3) receptors.

High-performance liquid chromatographic assay to determine the plasma levels of HIV-protease inhibitors (amprenavir, indinavir, nelfinavir, ritonavir and saquinavir) and the non-nucleoside reverse transcriptase inhibitor (nevirapine) after liquid-liquid extraction

A single HPLC assay was developed for therapeutic drug monitoring of 5 HIV protease inhibitors (indinavir, amprenavir, saquinavir, ritonavir, nelfinavir) and a non-nucleoside reverse transcriptase inhibitor (nevirapine) in human plasma. After liquid-liquid extraction in a mixture ethyl acetate-hexane, compounds are separated on a C18 column with a gradient elution of solvent A [acetonitrile and 0.025 M tetramethylammonium perchlorate in 0.2% aqueous trifluoroacetic acid (55:45 (v/v))] and solvent B [methanol and 0.025 M tetramethylammonium perchlorate in 0.2% aqueous trifluoroacetic acid (55:45 (v/v))]. The compounds are detected at various wavelengths: 320 nm (nevirapine), 259 nm (indinavir), 254 nm (amprenavir, nelfinavir, saquinavir) and 239 nm (ritonavir). The intra-day and inter-day precision and accuracy are lower than 15%. The limits of quantitation are 0.05 mg/l (amprenavir), 0.2 mg/l (indinavir, saquinavir, nelfinavir) and 0.4 mg/l (ritonavir, nevirapine). This method which allows to estimate simultaneously plasma levels of protease inhibitors and nevirapine can be used for therapeutic drug monitoring.

Interaction between 5-HT(1A) and 5-HT(1B) receptors: effects of 8-OH-DPAT-induced hypothermia in 5-HT(1B) receptor knockout mice

To test for adaptive compensatory changes that may have occurred in the functional activity of somatodendritic 5-HT(1A) receptors during the development of constitutive "knockout" mice lacking the 5-HT(1B) receptor subtype (5-HT(1B) -/- KO), we assayed for decrease in body temperature induced by an acute subcutaneous injection of the 5-HT(1A) receptor agonist, 8-hydroxy 2(di-n-propyl(amino)tetralin (8-OH-DPAT), either alone or in the presence of a selective 5-HT(1A) receptor antagonist, N-[4-(2-methoxyphenyl)-1-piperazinyl]-N-(2-pyridinyl) cyclo-hexanecarboxamide (WAY 100635). We compared dose-response curves, time course study, calculated ED(50) values (potency), maximal response to 8-OH-DPAT (efficacy) as well as measurements of the dose-dependent blockade of this response by WAY 100635 between wild-type controls and mutant mice. We found a higher efficacy of 8-OH-DPAT-induced hypothermia in 5-HT(1B) -/- KO compared to wild-type mice suggesting that an adaptive thermoregulatory process involving the functional activity of somatodendritic 5-HT(1A) receptors is altered in mutant mice lacking 5-HT(1B) receptors.

[5-HT1B serotonin receptors and antidepressant effects of selective serotonin reuptake inhibitors ]

We used knockout mice and receptor antagonist strategies to investigate the contribution of the serotonin (5-hydroxytryptamine, 5-HT) 5-HT1B receptor subtype in mediating the effects of selective serotonin reuptake inhibitors (SSRIs). Using in vivo intracerebral microdialysis in awake mice, we show that a single systemic administration of paroxetine (1 or 5 mg/kg, i.p.) increased extracellular serotonin levels [5-HT]ext in the ventral hippocampus and frontal cortex of wild-type and mutant mice. However, in the ventral hippocampus, paroxetine at the two doses studied induced a larger increase in [5-HT]ext in knockout than in wild-type mice. In the frontal cortex, the effect of paroxetine was larger in mutants than in wild-type mice at the 1 mg/kg dose but not at 5 mg/kg. In addition, either the absence of the 5-HT1B receptor or its blockade with the mixed 5-HT1B/1D receptor antagonist, GR 127935, potentiates the effect of a single administration of paroxetine on [5-HT]ext more in the ventral hippocampus than in the frontal cortex. Furthermore, we demonstrate that SSRIs decrease immobility in the forced swimming test; this effect is absent in 5-HT1B knockout mice and blocked by GR 127935 in wild-type suggesting therefore that activation of 5-HT1B receptors mediate the antidepressant-like effects of SSRIs. Taken together these data demonstrate that 5-HT1B autoreceptors appear to limit the effects of SSRI on dialysate 5-HT levels particularly in the hippocampus while presynaptic 5-HT1B heteroreceptors are likely to be required for the antidepressant activity of SSRIs.

Involvement of 5-HT(2C) receptors in the anti-immobility effects of antidepressants in the forced swimming test in mice

Several recent studies have demonstrated that 5-HT(1A), 5-HT(1B) and 5-HT(3) receptors were implicated in the mechanism of action of antidepressants in the mouse forced swimming test. Despite extensive evidence for a role of 5-HT(2C) receptors in depression, the precise role of these receptors in the effects of clinically established antidepressants was not directly investigated in the mouse forced swimming test. This work was aimed at exploring interactions between several doses of Ro 60-0175, a recently available, full and selective 5-HT(2C) agonist, and antidepressant drugs in the mouse forced swimming test. Spontaneous locomotor activity was measured as an index of intact sensorimotor functions and the dose-effect of Ro 60-0175 alone, as well as interactions with several antidepressants, such as tricyclic antidepressants (imipramine, desipramine and maprotiline) and selective serotonin reuptake inhibitors (paroxetine, citalopram, fluoxetine, fluvoxamine and sertraline), were studied in the mouse forced swimming test. There was no intrinsic antidepressant-like effect of Ro 60-0175, but an impairment in locomotor function was detected when using doses higher than 4 mg/kg in the mouse. There was a synergistic effect of low doses of Ro 60-0175 with sub-active doses of imipramine, paroxetine, citalopram and fluvoxamine; an antagonism between the highest dose of Ro 60-0175 and the active doses of paroxetine and fluoxetine was also detected. There is evidence that 5-HT(2C) receptors may be involved in the action of antidepressants which are able to boost the concentration of serotonin in the synapse, i.e. SSRIs and imipramine

Are there gender differences in the temperature profile of mice after acute antidepressant administration and exposure to two animal models of depression?

Numerous studies have reported gender differences in the rates of depression in humans, but few behavioural observations of antidepressant drug effects have been investigated in female mice. The forced swimming test (FST) is widely used as a predictor of antidepressant activity in rodents, as is the tail suspension test (TST), where immobility is objectively measured and in this last test, no hypothermia is induced by immersion in cold water. The present study investigated gender differences in the temperature profile of mice after acute antidepressant administration (imipramine and paroxetine) and exposure to two animal models of depression. Imipramine and paroxetine were active at 32 mg/kg in male mice in the FST, whereas they were active at 8, 16 and 32 mg/kg in female mice. In the TST, for both antidepressants immobility duration was reduced at a dose of 16 and 32 mg/kg in male mice and at 32 mg/kg in female mice. No significant difference was observed between male and female mice for immobility duration. Imipramine administration, but not paroxetine, decreased the temperature at the higher dose (32 mg/kg) in male and female mice in the FST. The body temperature was reduced in male and female mice for all treatment groups after FST challenge. Imipramine (16 and 32 mg/kg in male and 32 mg/kg in female mice), paroxetine (4, 16 and 32 mg/kg in male and 4 to 32 mg/kg in female mice) attenuated the reduction in temperature due to the FST. In the TST, imipramine tends to decrease the temperature in male and female mice, even though only imipramine at a dose of 32 mg/kg in female mice significantly decreases the temperature. Paroxetine had no effect on temperature. The TST enhanced the body temperature in male and female mice. In mice, there was no difference between the sexes after imipramine or paroxetine administration in the FST and TST. Both tests can be used to predict the activity of antidepressants as the decrease or enhancement of temperature is not correlated with a reduction in immobility duration.

Paroxetine: a review

Paroxetine is a potent and selective serotonin reuptake inhibitor (SSRI) with currently approved indications for the treatment of depression, obsessive-compulsive disorder, panic disorder and social phobia. It is also used in the treatment of generalized anxiety disorder, post traumatic stress disorder, premenstrual dysphoric disorder and chronic headache. Paroxetine, a phenylpiperidine derivative, is the most potent inhibitor of the reuptake of serotonin (5-hydroxytryptamine, 5-HT) of all the currently available antidepressants including the class of SSRIs. It is a very weak inhibitor of norepinephrine (NE) uptake but it is still more potent at this site than the other SSRIs. The selectivity of paroxetine, i.e., the ratio of inhibition of uptake of norepinephrine to serotonin (NE/5-HT) is amongst the highest of the SSRIs. Paroxetine has little affinity for catecholaminergic, dopaminergic or histaminergic systems and by comparison with tricyclic antidepressants (TCAs) has, therefore, a reduced propensity to cause central and autonomic side effects. Paroxetine exhibits some affinity for the muscarinic cholinergic receptor but much less than the TCAs. In addition, the adaptive changes of somatodendritic (5-HT(1A)) and terminal (5-HT(1B/1D)) autoreceptors observed with paroxetine are different to those observed with TCAs; it also inhibits nitric oxide synthase. It is both a substrate and an inhibitor of cytochrome isoenzyme P450 2D6. Paroxetine is well absorbed orally and undergoes extensive first pass metabolism that is partially saturable. Its metabolites are pharmacologically inactive in vivo. Steady state levels are achieved after 4-14 days and an elimination half-life of 21 h is consistent with once-daily dosing. There is wide inter-individual variation in the pharmacokinetics of paroxetine in adults as well as in the young and the elderly with higher plasma concentrations and slower elimination noted in the latter. Elimination is also reduced in severe renal and hepatic impairment. Serious adverse events are, however, extremely rare even in overdose. In summary, paroxetine is well tolerated and effective in the treatment of both depressive and anxiety disorders across the age range.

5-HT1B Autoreceptors limit the effects of selective serotonin re-uptake inhibitors in mouse hippocampus and frontal cortex

We used knockout mice and receptor antagonist strategies to investigate the contribution of the serotonin (5-hydroxytryptamine, 5-HT) 1B receptor subtype in mediating the effects of selective serotonin re-uptake inhibitors (SSRIs). Using in vivo intracerebral microdialysis in awake mice, we show that a single systemic administration of paroxetine (1 or 5 mg/kg, i.p.) increased extracellular serotonin levels [5-HT]ext in the ventral hippocampus and frontal cortex of wild-type and mutant mice. However, in the ventral hippocampus, paroxetine at the two doses studied induced a larger increase in [5-HT]ext in knockout than in wild-type mice. In the frontal cortex, the effect of paroxetine was larger in mutants than in wild-type mice at the 1 mg/kg, but not at 5 mg/kg. In addition, either the absence of the 5-HT1B receptor or its blockade with the mixed 5-HT1B/1D receptor antagonist, GR 127935, potentiated the effect of a single administration of paroxetine on extracellular 5-HT levels more in the ventral hippocampus than in the frontal cortex. These data suggest that 5-HT1B autoreceptors limit the effects of SSRIs on dialysate 5-HT levels at serotonergic nerve terminals.

Role of dopaminergic and serotonergic systems on behavioral stimulatory effects of low-dose alprazolam and lorazepam

Several recent studies have demonstrated that alprazolam and lorazepam, administered at low doses to healthy volunteers, improve cognitive functions and psychomotor performances. Paradoxical effects of low-dose benzodiazepines have been also observed in mice, in experimental pharmacology. The aim of this work was to determine, in rat, the effect of similar low-doses of benzodiazepines on spontaneous locomotor activity and performance in the elevated zero-maze, and to investigate the underlying neurobiological mechanisms. The dose-effect and the time-course of the action were studied for both compounds. Spontaneous locomotor activity was measured using a photoelectric actimeter. The level of anxiety of the animals was assessed in the elevated zero-maze. Dopamine, serotonin, and their metabolites were assayed in the extracellular striatal fluid of the awake rat, obtained by microdialysis, by HPLC--EC. Spontaneous locomotor activity observed in rats given low-dose alprazolam and lorazepam evidenced a stimulatory effect only with alprazolam. The effect was maximum 90 min after administration of 0.0050 mg/kg alprazolam. An anxiogenic-like action was evidenced with the elevated zero-maze for the two compounds. We observed a statistically significant increase in striatal dopamine concentrations only with alprazolam, during the period corresponding to the behavioral stimulatory effects. We also showed a marked trend towards increased levels of serotonin with alprazolam but this modification was not significant, in spite of statistically significant variations of 5-HIAA. In the rat, behavioral stimulatory effects of low-dose benzodiazepines is evidenced with alprazolam but not lorazepam. This effect could be explained, at least in part, by increased extracellular dopamine concentrations in the striatum. Their different structures could explain the different pattern observed for the two benzodiazepines.

Drug mechanisms in anxiety

The most common and successful therapyfor the majority of patients suffering from anxiety is treatment with benzodiazepines (BZDs). The problem of drug-induced dependency following treatment with these drugs may be avoided by developing more selective and specific BZD compounds, such as 2,3-substituted BZDs. Alternative approaches to the treatment of anxiety include the following: (i) antidepressants such as the selective serotonin reuptake inhibitors (SSRIs), which are active in treating most anxiety disorders, including GAD; (ii) metabotropic glutamate (mGluR2) receptor agonists, which negatively modulate glutamate neurotransmission, and CRF antagonists, which have been proposed to exhibit anxiolytic properties; (iii) 5-HT1A receptor agonists which have demonstrated anxiolytic effects in clinical studies, although preclinical studies have reported weak or variable effects; (iv) 5-HT moduline antagonists, as well as 5-HT2C receptor antagonists, which may have anxiolytic properties; and, finally, (v) other approaches which are under investigation, including CCK2 antagonists.

Comparison of antidepressant activity in 4- and 40-week-old male mice in the forced swimming test: involvement of 5-HT1A and 5-HT1B receptors in old mice

RATIONALE

A recent study suggested that selective serotonin reuptake inhibitors were inactive in 40-week-old male mice in the mouse forced swimming test, possibly because of alteration of 5-HT1 receptors.

OBJECTIVES

The present study was aimed at investigating the action of various antidepressant drugs in 4- and 40-week-old male mice using the mouse forced swimming test and determining the involvement of 5-HT1A and 5-HT1B receptors mediating the effects.

METHODS

Different classes of antidepressants [imipramine (tricyclic), maprotiline (noradrenline reuptake inhibitor), venlafaxine (mixed serotonin and noradrenaline reuptake inhibitors), fluvoxamine and sertraline (selective serotonin reuptake inhibitor)] were tested in the same randomised experimental session, alone and in combination with 5-HT1A and 5-HT1B receptor agonists [buspirone (partial 5-HT1A agonist), anpirtoline (5-HT1B agonist)] in the mouse forced swimming test.

RESULTS

All antidepressants were found to be active in the mouse forced swimming test in 4-week-old mice and 40-week-old mice, with the exception of fluvoxamine in the 40-week-old mice. The anti-immobility effect after antidepressant administration was higher in 4-week-old male mice than in 40-week-old male mice. Venlafaxine is the most active antidepressant drug in 40-week-old mice. Prior administration of buspirone (0.06 mg/kg, i.p.) or anpirtoline (1 mg/kg, i.p.) enhanced the antidepressant-like effects in 4-week-old mice (except in the case of sertraline, 8 mg/kg). In elderly mice, only prior administration of buspirone enhanced the antidepressant-like effects of fluvoxamine. A neurochemical study showed that significantly higher serotonin and dopamine concentrations were found in 40-week-old control mice brains than 4-week-old control mice brains but that the noradrenaline concentration is higher in 4-week-old mice.

CONCLUSION

Tricyclic, noradrenaline reuptake inhibitors and serotonin reuptake inhibitors are more active in 4-week-old mice than 40-week-old mice. Our results suggested that 5-HT1B receptors may be more altered than 5-HT1A receptors in 40-week-old mice.

The antidepressant activity of inositol in the forced swim test involves 5-HT(2) receptors

The effect of inositol as an antidepressant was previously demonstrated in both animal models of depression-like behavior and in clinical trials. Unlike most antidepressant drugs, inositol does not have a clear target in the synapse and was not demonstrated to alter monoamine levels in the brain. The present study attempted to draw a psychopharmacological profile of inositol's behavioral effects by exploring the interactions between the drug and specific receptor agonists and antagonists in the forced swim test. Rats received inositol treatment (or control) in combination with the serotonergic metabolism inhibitor PCPA or with the noradrenergic neurotoxin DSP-4. Results indicated that PCPA but not DSP-4 abolished the ability of inositol to cause a reduction in immobility time in the forced swim test. In mice, the specific 5-HT(2A)/5-HT(2C) antagonist ritanserin, but not the 5-HT(1A)/5-HT(1B)/beta adrenergic antagonist pindolol, abolished inositol's effect in the forced swim test. The 5-HT(2A)/5-HT(2C) agonist DOI and the 5-HT(1A) agonist 8-OH-DPAT did not have any significant effects on inositol's activity. The present data indicates that the antidepressant effect of inositol may involve 5-HT(2) receptors. It is thus possible that the effects of reuptake antidepressant drugs and the effects of inositol may have a common final pathway.

8-OH-DPAT, but not deramciclane, antagonizes the anxiogenic-like action of paroxetine in an elevated plus-maze

OBJECTIVE

To investigate whether a 5-hydroxytryptamine (5-HT) reuptake inhibitor (paroxetine) has an anxiogenic-like effect and what possible pharmacological mechanism underlies that action.

METHODS

We used the rat elevated plus-maze paradigm followed by measurement of locomotor activity. Some of the rats were subjected to handling and adaptation to the experimental situation, while the rest were naive to the test situation. Paroxetine was administered as a single treatment and in combination with the 5-HT1A receptor agonist (8-OH-DPAT) or 5-HT2A/2C receptor antagonist (deramciclane).

RESULTS

The administration of paroxetine induced an anxiogenic-like action in rats adapted to handling, but not in handling naive animals. Treatment with paroxetine (0.1-2 mg/kg) reduced the number of open arm visits and time spent in open arms, and the ratio between open and total arm entries in the elevated plus-maze. Paroxetine also decreased the number of line crossings and head-dips. Paroxetine caused the strongest anti-exploratory action at a dose of 0.5 mg/kg. Paroxetine did not suppress the locomotor activity of rats, showing that the described anti-exploratory effect was behaviourally specific to the plus-maze. Pretreatment with 8-OH-DPAT (0.05 mg/kg) completely reversed the anxiogenic-like action of paroxetine, whereas treatment with deramciclane (2 mg/kg) affected only the number of closed arm visits. Deramciclane (0.5-2 mg/kg) and 8-OH-DPAT (0.01-0.1 mg/kg) changed neither exploratory behaviour nor locomotor activity if given as single treatments to the habituated rats.

CONCLUSION

The 5-HT reuptake inhibitor, paroxetine, at a low dose (0.5 mg/kg) induces an anxiogenic-like action in handling adapted rats. The effectiveness of 8-OH-DPAT against paroxetine probably supports a role of both pre- and postsynaptic 5HT-ergic mechanisms in the anxiogenic-like action of paroxetine.

The mouse light-dark paradigm: a review

1. The light/dark paradigm is based on the innate aversion of rodents to brightly illuminated areas and on the spontaneous exploratory behaviour of the animals, applying mild stressors i.e. novel environment and light. The test apparatus consists of a small dark secure compartment (one third) and a large illuminated aversive compartment (two thirds). 2. The test was developed with male mice. The strain, weight and age may be crucial factors. 3. The extent to which an anxiolytic compound can facilitate the exploratory activity depends on the baseline level in the control group. Differences between the type and severity of external stressors might account for variable results reported by different laboratories. 4. In conclusion, the black and white test may be useful to predict anxiolytic-like or anxiogenic-like activity in mice. Transitions have been reported to be an index of activity-exploration because of habituation over time and the time spent in each compartment to be a reflection of aversion. Classic anxiolytics (benzodiazepines) as well as the newer anxiolytic-like compounds (e.g. serotonergic drugs) can be detected using this paradigm. It has the advantages of being quick and easy to use, without requiring the prior training of animals.

How valuable are animal models in defining antidepressant activity?

Animal models of depression have been utilised to screen novel compounds with antidepressant potential although uncertainty lingers concerning their clinical relevance. In order for a model to be considered of any value, it must possess predictive validity (does drug action in the model correspond to that in the clinic?), face validity (are there phenomenological similarities between the model and the clinic?) and construct validity (does the model possess a strong theoretical rationale?). On the one hand, there are models based on stress such as the learned helplessness model, the forced swimming test and the chronic mild stress model and, on the other hand, models based on neuronal deficits such as the olfactory bulbectomy model. To date, among models more frequently used in depression, none of them meet all these criteria. Moreover, improvements to tests are often poorly validated and estimating time of onset of action of antidepressants remains a major challenge in animal model research. Finally, reproducing the tests outside the laboratory of origin continues to be problematic and leads to variability in results. Although animal models of depression fail to be unequivocally valid, they represent the best tool to define potential antidepressant activity of drugs, to investigate their mechanism of action and, to a greater extent, explore this complex heterogeneous illness. Copyright 2001 John Wiley & Sons, Ltd.

The influence of buspirone, and its metabolite 1-PP, on the activity of paroxetine in the mouse light/dark paradigm and four plates test

Although numerous animal procedures have been employed in the study of antidepressants (ADs) in anxiety, the results following acute administration remain highly variable. The present study investigated the effect of the SSRI paroxetine (4, 8, and 16 mg/kg, IP) in two tests of anxiety in mice: the light/dark test paradigm, and the four plates test (FPT). In both tests, it was found that paroxetine resulted in an anxiolytic-like effect at doses that did not modify motor performance (at the doses of 4 and 8 mg/kg in the light/dark test and at the doses of 4, 8, and 16 mg/kg in the four plates test). In the light/dark paradigm, both doses of buspirone significantly potentiated paroxetine, while in the four plates only one dose of buspirone (a 5HT(1A) partial agonist) (0.06 mg/kg) increased the anxiolytic-like effect of paroxetine. Prior administration of 1-PP was without effect in the light/dark paradigm but antagonized the effect of paroxetine (at the dose of 0.06 and 0. 5 mg/kg) in the FPT. The results suggested that a balance between pre- and postsynaptic 5-HT(1A) receptor was implicated in the anxiolytic-like effect of paroxetine. Buspirone seemed to emphasize the role of paroxetine in 5-HT(1A) receptor modulation and exerted a biphasic influence in the two tests.

Effects of low-dose cholecystokinin on respiratory function in healthy volunteers

Injection of high doses of cholecystokinin tetrapeptide (CCK-4), a recent experimental model for panic, causes panic attacks and respiratory stimulation, a key feature of panic, in healthy volunteers. However, it has not yet been established whether respiratory stimulation is specifically linked to panic or merely an effect of arousal in general. Results of the present study show that respiratory stimulation is not merely linked to higher arousal and suggest a link between CCK-provoked panic and respiratory stimulation.

Anxiolytic-like effects of antidepressants after acute administration in a four-plate test in mice

The four-plate test (FPT) is an animal model of anxiety based on stress caused by unconditioned fear. An increase of spontaneous punished behavior was used as a measure to determine the anxiolytic effects of various antidepressants (ADs). In the present study. ADs with different mechanisms of action, including tricyclics, selective serotonin reuptake inhibitors (SSRIs), a monoamine oxidase inhibitor (MAOI), and atypicals, were studied in the FPT to evaluate their anxiolytic-like effects following acute administration. The number of punished crossings was dramatically increased by the SSRIs citalopram, fluvoxamine, and paroxetine, but not fluoxetine. The mixed 5-HT/NE reuptake inhibitors, milnacipran and venlafaxine, also demonstrated strong antipunishment effects. The specific NE reuptake inhibitors, desipramine and maprotiline, and the atypical AD trazodone, enhanced freezing behavior, suggesting anxiogenic-like behavior. It was concluded that, in the FPT, a model based on spontaneous response, where animals are exposed to an aversive environment from which they can only escape by being motionless, this kind of behavior might be related to anticipatory anxiety. In this situation, ADs acting preferentially on 5-HT transmission possessed clear anxiolytic like effects. The balance between the two transmitters, 5-HT and NE, seemed to be a crucial factor.

Cholecystokinin-induced anxiety in rats: relevance of pre-experimental stress and seasonal variations

OBJECTIVE

To examine the influence of pre-experimental stress on the anxiogenic-like action of caerulein, an agonist of cholecystokinin (CCK) receptors. Differences in the anxiety levels of rats in summer and winter, and the role of CCK in these behavioural alterations, were also examined.

DESIGN

Prospective animal study.

INTERVENTIONS

Male Wistar rats were injected with the CCK agonist caerulein, or the CCK antagonists L-365,260 or devazepide, after being exposed to pre-experimental stress (handling and isolation).

OUTCOME MEASURES

Performance in the plus-maze model of anxiety; serum levels of prolactin, thyrotropin and growth hormone; brain density and affinity of dopamine D2, serotonin 5-HT2 and CCK receptors.

RESULTS

Caerulein (5 micrograms/kg, subcutaneous injection) caused the strongest action in animals brought to the experimental room immediately before the experiment and kept in isolation after the administration of caerulein. Caerulein did not cause any reduction of exploratory activity in rats made familiar with the experimental room and kept in the home-cage after the injection of the CCK agonist. The anti-exploratory action of caerulein in stressed rats was reversed by the CCK antagonist L-365,260 (100 micrograms/kg, intraperitoneal injection), demonstrating the involvement of the CCKB receptor subtype. In addition, seasonal fluctuations occur in the exploratory activity of rats; such activity was much lower in July than in November. The rats displaying the reduced exploratory activity had an increased number of CCK receptors in the frontal cortex and hippocampus. Simultaneously, the density of serotonin 5-HT2 receptors in the frontal cortex, but not that of dopamine D2 receptors in the striatum, was elevated. The blood level of growth hormone was also higher in July.

CONCLUSIONS

The anti-exploratory action of caerulein appears to be dependent on the pre-experimental stress of rats. Moreover, the seasonal variations of exploratory behaviour of rats are evident in the plus-maze model of anxiety. The reduced exploratory activity in summer appears to be related to the elevated density of CCK and 5-HT2 receptors in the brain.