Is it possible to predict the activity of a new antidepressant in animals with simple psychopharmacological tests?

An automated analysis of rat behavior in the forced swim test

The Porsolt forced swim test (FST) is a commonly used paradigm to evaluate antidepressant activity of drugs. This test is based on visual measurement of the rat's floating time (FT) in a tank filled with water. Here, we present an automated, accurate and faster method for estimating FT by the distance moved (DM) by the animal via the use of the Ethovision software in three separate experiments. Experiment 1 investigated the effect of varying delays (24-h and 7-day) between pretest and test on FT and DM. Experiment 2 aimed at examining the effects of a 2-day withdrawal period in rats sensitized to amphetamine and cocaine, on FT and DM. Finally, Experiment 3 looked at the effects of desipramine and fluoxetine on FT and DM. The results of these experiments show that increasing the delay between pretest and test reduced FT during subsequent exposure (test). In addition, rats sensitized to and then withdrawn from either amphetamine or cocaine did not differ in FT or DM compared with control rats. Finally, both desipramine and fluoxetine reduced FT and increased DM. Furthermore, DM was consistently significantly negatively correlated with FT. These results support the use of an automated method for the evaluation of rat behavior in FST.

Effects of sibutramine on the central dopaminergic system in rodents

The effects of sibutramine on central dopaminergic system in rats and mice were examined by neurochemical and behavioral pharmacological methods. Dopamine reuptake inhibition by sibutramine in brain synaptosomes was only 4-5 times stronger than those of amitriptyline and dosulepin, which do not exhibit dopamine uptake inhibition in vivo. Single treatment with sibutramine did not alter the brain content of dopamine and DOPAC. However, similar to methamphetamine and pargyline, sibutramine antagonized methyl-4-pheny-1,2,3,6-tetrahydro-pyridine (MPTP) induced dopamine depletion in mouse brain. In forced swimming tests of reserpinized mice, sibutramine shortened the immobilized time, similar to dopaminergic drugs including nomifensine, bupropion (dopamine-reuptake inhibitor), methamphetamine, SKF 38393 (dopamine D1 agonist), quinpirole (dopamine D2 agonist) and apomorphine (dopamine D1/D2 agonist). In addition, sibutramine caused rotational behavior toward the lesioned side in rats with unilateral lesions of the substantia nigra induced by 6-hydroxydopamine. These results suggest that sibutramine exhibits neurochemical and behavioral dopaminomimetic activity in vivo, which is mediated by dopamine reuptake inhibition by the active metabolites of sibutramine.

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 effect of lithium administration in animal models of depression: a short review

The aim of this short review was to collate the data involving the effects of lithium alone, or in combination, with antidepressant drugs in several animal models of depression. It has been shown that lithium administration reduced immobility in the mouse forced swimming test when given 30 min, but not 45 min, before testing. Further studies indicated that this activity was probably a result of an activity on serotonin (5-HT) 1A and 1B receptor subtypes. Lithium treatment has been shown to reverse helpless behaviour in the learned helplessness model of depression after chronic treatment (30 days), where lithium was administered in the drinking water. Further studies showed that acute (5 days) administration of lithium failed to reverse behavioural deficits. In the olfactory bulbectomised rat model of depression, several immunological and enzymatic functions have been shown to be altered and these changes are regularised by antidepressant treatment as well as lithium administration for 15 days. Hypokinesia (reduced locomotor activity) is a phenomenon observed following immobilisation stress in rats. This behavioural deficit was attenuated by lithium together with a wide range of antidepressant drugs used in the treatment of unipolar depression at non-stimulant doses. In addition, a single administration of lithium slightly inhibited midbrain raphe lesion-induced muricidal behaviour (25%); however, repeated treatment (5 days) significantly attenuated this behavioural deficit. Lithium treatment has also been shown to reverse behavioural and biochemical deficits induced by reserpine together with those induced by acute administration of single intracerebroventricular (i.c.v.) dose of the Na, K-ATPase-inhibiting compound, ouabain. Long-term studies of lithium augmentation have not been performed, so that no clear recommendations for the duration of this therapy can be made. The points raised in this short review endorse the commencement of such studies.

Psychopharmacological profile of the selective serotonin reuptake inhibitor, paroxetine: implication of noradrenergic and serotonergic mechanisms

The present study was designed to evaluate the psychopharmacological profile of the selective serotonin reuptake inhibitor paroxetine, and thus assess potential noradrenergic and/or serotonergic activity. Paroxetine dose-dependently increased mobility time in the mouse forced swimming test (8, 16, 32 and 64 mg/kg, i.p.) and reduced spontaneous locomotor activity when administered at a high dose (64 mg/kg, i.p.). Prior administration of 8-hydroxy-2-(di-n-propylamino)tetralin (1 mg/kg, i.p.), (+/-) pindolol (32 mg/kg, i.p.) or 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridyl)-1H-indole (RU 24969) (1 mg/kg, i.p.) potentiated the antidepressant-like effects of subactive doses of paroxetine (1, 2 and 4 mg/kg, i.p.) in the mouse forced swimming test. These effects were antagonized by prior administration of 1-(2-methoxyphenyl)-4-[-(2-phthalimido)butyl]piperazine) (0.5 mg/kg, i.p.). Complementary studies suggested that RU24969-induced anti-immobility effects were a result of an increase in locomotor activity; other interactions were without increase/decrease in locomotor activity. Acute administration of paroxetine (8, 16, and 32 mg/kg, i.p.) antagonized the hypothermia induced by the D2/D1 receptor agonist, apomorphine (16 mg/kg, s.c.), while repeated treatment with paroxetine (32 mg/kg) attenuated clonidine-induced (0.5 mg/kg, i.p.) hypothermia. Pre-treatment with the serotonergic neurotoxin, para-chlorophenylalanine attenuated the anti-immobility effects of low doses of paroxetine (8 and 16 mg/kg, i.p.) in the forced swimming test, whereas a higher dose of paroxetine remained active (32 mg/kg, i.p.). The results of the present study indicated that paroxetine displayed both noradrenergic-like and serotonergic-like activity in the pre-clinical psychopharmacological tests employed.

"Atypical" neuromodulatory profile of glutapyrone, a representative of a novel 'class' of amino acid-containing dipeptide-mimicking 1,4-dihydropyridine (DHP) compounds: in vitro and in vivo studies

Glutapyrone, a disodium salt of 2-(2,6-dimethyl-3,5-diethoxycarbonyl-1,4-dihydropyridine-4-carboxamido)- glutaric acid, is a representative of a novel 'class' of amino acid-containing 1,4-dihydropyridine (DHP) compounds developed at the Latvian Institute of Organic Synthesis, Riga, Latvia. Conceptually, the glutapyrone molecule can be regarded as a dipeptide-mimicking structure formed by the "free" amino acid (glutamate) moiety and "crypto" (built into the DHP cycle) amino acid ("GABA") elements. Both of these amino acids are joined by the peptide bond. This compound unlike classical DHPs lacks calcium antagonistic or agonistic properties. Our previous studies revealed a profound and long-term anticonvulsant, stress-protective and neurodeficit-preventive activities of glutapyrone. In view of structural properties the role of glutamatergic mechanisms in the mediation of central effects of glutapyrone was considered. In the present study glutapyrone at the concentration range of 1 microM(-1) mM failed to effect both NMDA ([3H]TCP) and non-NMDA ([3H]KA and [3H]AMPA) receptor ligand binding in the rat cortical membranes in vitro. The compound markedly enhanced motor hyperactivity induced by the NMDA antagonist PCP and the dopamine releasing compound D-amphetamine in the rats. Glutapyrone displayed activity in a variety of animal models relevant for affective/depressive disorders in humans i.e. reserpine-induced ptosis and hypothermia, forced swimming test and open field test. These data indicate that the unusually "broad" pharmacological spectrum of glutapyrone might involve concomitant actions on multiple neurotransmitter systems, particularly, GABA-ergic and the catecholamines. It is discussed whether these functional properties are secondary to action on intracellular events, predominantly, G protein-related since glutapyrone appears to lack direct interactions with a number of receptors including ionotropic glutamate and GABA(A)/Bzd receptors.

Effects of dopaminergic agents on reversal of reserpine-induced impairment in conditioned avoidance response in rats

Male Slc:Wistar, Std:Wistar, and Slc:F344/N rats had good acquisition of the conditioned avoidance response (CAR), while that of the male Slc:Wistar/ST, Jcl:Wistar, and Crj:Wistar rats was bad. Reserpine-induced impairment (RII) in CAR was observed 2-72 h after administration of dopaminergic (DAergic) agents in male Slc:Wistar rats. Amitriptyline (5-80 mg/kg, P.O.), imipramine, desipramine, cis-dosulepine, and trans-dosulepine at dose of 40 mg/kg, P.O. showed no antagonism against RII in CAR 20-23 h after reserpine injection (1 mg/kg, S.C.). However, the atypical antidepressive agents sibutramine (5-10 mg/kg, P.O.), bupropion (40 mg/kg, P.O.), and nomifensine (10-40 mg/kg, P.O.) exhibited antagonism against RII in CAR. The calcium channel antagonists flunarizine, nimodipine, and KP-840 at dose of 10 and 100 mg/kg, P.O., the cerebral improving agent indeloxazine (20-80 mg/kg, P.O.), the anticholinergic agent atropine (5-40 mg/kg, P.O.), 5-hydroxy-L-tryptophan (5-HTP) (40 mg/kg, I.P.), a precursor of 5-hydroxytryptamine (5-HT), and (+/-)-threo-dihydroxyphenylserine [(+/-)-threo-DOPS] (20-200 mg/kg P.O.), a norepinephrine (NE) precursor, showed no antagonism against RII in CAR. The DAergic agents methamphetamine (5 mg/kg, P.O.) and amantadine (50-250 mg/kg, P.O.), L-DOPA (200 mg/kg, P.O.), and the DAergic D1/D2 receptor agonist apomorphine (0.1-1 mg/kg, S.C.) showed marked antagonism against RII in CAR. Although the DAergic D1-receptor agonist KF-38393 (0.3-30 mg/kg, I.P.) and the DAergic D2-receptor agonist quinpirole (0.3-10 mg/kg, I.P.) induced only a weak recovery of RII in CAR when they were administered alone, in contrast to a potent synergistic recovery of RII in CAR, which was observed when SKF-38393 (1 mg/kg, I.P.) and quinpirole (1 mg/kg, I.P.) were administered together. These results suggest that the DAergic nervous system rather than the adrenergic or 5-HT nervous system is involved in RII in CAR, and that both the DAergic D1- and D2-mediated nervous systems play important roles in this process.

Effects of pretreatment with clonidine, lithium and quinine on the activities of antidepressant drugs in the mouse tail suspension test

The aim of the present study was the investigation of pretreatment effects with clonidine (0.06 mg/kg, intraperitoneal [i.p.]), lithium (1 mEq, i.p.) or quinine (0.5 mg/kg, i.p.) on the activities of various drugs acting on noradrenergic and/or serotonergic systems in the mouse tail suspension test. Drugs used in the present study included: the tricyclic antidepressants imipramine and dothiepin, the heterocyclic antidepressant trazodone, the 5-HT reuptake inhibitor (SSRI) fluoxetine, the atypical antidepressants mianserin and iprindole, the 5-HT1A receptor agonist ipsapirone, the 5-HT2A/2C receptor antagonist ritanserin, and the 5-HT3 receptor antagonist ondansetron. Clonidine, lithium and quinine differentially enhanced the effects of several psychotropic/drugs administered at sub-active doses. The activity of iprindole (32 mg/kg, i.p.) was not potentiated by pretreatment with clonidine, lithium or quinine. Our results suggest that lithium exerted additive effects via postsynaptic 5-HT1A receptor activation, quinine via potassium ion channel blockade of 5-HT3 receptors, while clonidine did so primarily via action at 5-HT2 receptors.

The characterization of oxotremorine-induced hypothermic response in the rat

Oxotremorine is a muscarinic receptor agonist that induces a variety of physiological and behavioural effects including hypothermia in mice. These effects are antagonized dose-dependently by classical anticholinergic compounds such as atropine. Although the oxotremorine-induced hypothermic response has been demonstrated in mice, few studies of the effects of this muscarinic agonist have been made in the rat. The following studies were made in male Sprague Dawley rats: 1. an investigation of the dose-response relationship between oxotremorine and hypothermia; 2. an examination of the effect of housing on the oxotremorine-induced hypothermic response, and 3, an investigation of the acute administration of various doses of atropine sulphate on the hypothermia caused by oxotremorine. The results indicate that the dose-response relationship between oxotremorine and the antagonism of hypothermia is similar in rat as it is in mice. The results also showed that this effect did not occur in group-housed animals.

A schematic representation of the psychopharmacological profile of antidepressants

1. Using simple animal tests, "behavioural" and "biochemical" aspects of depression, anxiolysis, disinhibition, psychostimulation and sedation were investigated in mice using a variety of antidepressant drugs. 2. Dothiepin and mianserin (16 and 32 mg/kg), fluoxetine (32 and 64 mg/kg), maprotiline and imipramine (16, 32 and 64 mg/kg) and viloxazine (16 mg/kg) significantly potentiated mortality following acute administration with yohimbine. 3. Dothiepin and imipramine (32 mg/kg), fluoxetine (16 and 32 mg/kg), viloxazine (8 and 16 mg/kg), maprotiline (32 mg/kg) and mianserin (32 mg/kg) reduced immobility time in the forced swimming test. 4. In the black and white box, dothiepin (32 mg/kg) significantly increased the time spent in the bright compartment: Fluoxetine (8 and 16 mg/kg) significantly increased the number of crossings between compartments, an effect indicative of desinhibition. 5. It can be concluded that dothiepin possesses both antidepressant and anxiolytic properties in these animal models. The present procedure is useful not only for the screening of compounds that may possess antidepressant properties, but is also of value in determining other properties that may contribute to the overall clinical efficacy of the drugs.

Indirect dopamine agonists effects on despair test: dissociation from hyperactivity

Both dexamphetamine and the pure dopamine reuptake inhibitor GBR 12783 elicit a stimulation of locomotion and increase swimming activity in the behavioral despair test in mice. The dopamine D1 dopamine receptor antagonist SCH 23390 dose dependently (7.5-30 micrograms/kg s.c.) antagonized the stimulant locomotor effect on both drugs but did not prevent their antiimmobility effect on the behavioral despair test. The D2 dopamine receptor antagonist haloperidol dose dependently (12.5-50 micrograms/kg i.p.) antagonized the effects of dexamphetamine on both locomotor activity and behavioral despair test. By contrast, haloperidol inhibited the effects of GBR 12783 in the forced swimming test but not on locomotion. It is concluded that indirect dopamine agonists are effective on the behavioral despair test independently of a stimulation of locomotor activity. Their effects on the despair test depend on the stimulation of D2 but not D1 dopamine receptors.

Prozac (fluoxetine, Lilly 110140), the first selective serotonin uptake inhibitor and an antidepressant drug: twenty years since its first publication

In this review, we describe the evolutionary process involved in the discovery of the selective 5-HT uptake inhibitor, fluoxetine, and summarize some of the large body of scientific research performed on fluoxetine in the 20 years since the first publication. The historical background of the proposed involvement of 5-HT in psychiatric disorders and the activity of tricyclic antidepressants in depression is reviewed. The effects of fluoxetine in various in vitro assays and in animal studies including receptor down-regulation, neurochemical and behavioral models are summarized. In addition, the clinical effectiveness of fluoxetine in depression and obsessive compulsive disorders and its potential use in other disorders are examined.

Anti-immobility activity of different antidepressant drugs using the tail suspension test in normal or reserpinized mice

The tail suspension test is a screening procedure recently used in mice to detect antidepressant activity of drugs. The ability of amine re-uptake inhibitors to decrease immobility in non-reserpinized and in reserpinized mice was studied. Reserpine (4 mg/kg ip) was injected 4 h previously. Anti-depressants were administered ip, 60 min before tail suspension. Animal activity was recorded for 6 min. Preferential serotonin re-uptake blockers (fluoxetine, fluvoxamine, clomipramine) were poorly active in non-reserpinized mice and inactive in reserpine-treated mice. Noradrenergic drugs (desipramine, demexiptiline, viloxazine) were more efficient in reserpinized than in non-reserpinized mice. The mixed serotonin-noradrenaline re-uptake inhibitor (imipramine) shows an activity which should be considered between serotonin re-uptake inhibitors and noradrenaline re-uptake inhibitors. DA re-uptake inhibitors (amineptine, GBR 12909) exhibited the highest anti-immobility effect in non reserpinized animals but were of low efficacy after reserpine treatment. Amphetamine differed from dopamine re-uptake inhibitors by its better activity in reserpinized animals. Moreover, it was the only drug showing an equal anti-immobility effect in non reserpinized and reserpinized mice because the dose of 8 mg/kg of amphetamine reduced immobility in reserpinized mice with the same intensity as the dose of 4 mg/kg in non reserpinized mice whereas no other drugs tested in this study achieved the same effect. Comparison of anti-immobility activities of putative anti-depressants in non-pre-treated and in reserpine-pre-treated mice, using the tail suspension test, may be useful to discriminate amphetamines from antidepressant drugs and to differentiate between categories of amine re-uptake blockers.

Flerobuterol: a potential antidepressant drug related to beta-adrenergic agonists. Experimental profile in mice

The potential antidepressant effect of flerobuterol (dl-(fluoro-2 phenyl)-1 t-butylamino-2 ethanol), a new drug related to beta-adrenoceptor agonists, was evaluated and compared with imipramine and salbutamol using classical psychopharmacological tests in mice. Like imipramine and salbutamol, flerobuterol (0.5-32 mg kg-1, ip) fully prevented apomorphine (16 mg kg-1, sc)- and partly reversed reserpine- and oxotremorine-induced hypothermia. At higher doses (16-32 mg kg-1), flerobuterol enhanced the toxic effects of yohimbine. Unlike imipramine, flerobuterol and salbutamol did not reduce immobility duration in the behavioural despair test. Salbutamol and flerobuterol decreased locomotor activity. Flerobuterol did not induce mydriasis, did not prevent oxotremorine-induced tremors or salivary and lacrimal gland secretion and did not reduce reserpine-induced palpebral ptosis. Propranolol (8 mg kg-1, ip) but not alpha-methyl-paratyrosine (75 mg kg-1, ip) prevented the flerobuterol-induced antagonism of apomorphine-induced hypothermia. Our results suggest that flerobuterol demonstrates potential antidepressant activity, which could be related to beta-adrenoceptor activation in mice.

Behavioral models in mice. Implication of the alpha noradrenergic system

1. The mechanism of action of drugs might change according to the test used. Several noradrenergic drugs were tested in order to understand their implication in the mobility tests. 2. It was found that clonidine, an Alpha 2 agonist, acted differently according to the test used. It provoked sedation in spontaneous activity test, and anti-immobility effects in the other tests. 3. Tail suspension test is able to show the double acting of clonidine. 4. Idazoxan might act either as an alpha 2 antagonist or as partial alpha 2 agonist. TST shown the unexpected partial alpha agonist effect of the molecule. 5. Forced swimming test is more specific for predicting antidepressant activity than tail suspension test which is close to a spontaneous activity model.