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International audience; This work was carried out to evaluate the potential in vivo toxicity of 3,4‐dihydroxyphenylacetaldehyde (DOPAL), an aldehyde formed from dopamine by monoamine oxidase (MAO) that is oxidised mainly to 3,4‐dihydroxyphenylacetic acid (DOPAC) by brain aldehyde dehydrogenases (ALDH). In this study, male Sprague‐Dawley rats were treated with levodopa (L‐dopa)‐benserazide, which increases DOPAL production by MAO, and disulfiram, an irreversible inhibitor of ALDH, which reduces the formation of DOPAC from DOPAL. An acute systemic intraperitoneal (i.p.) injection of 100 mg/kg disulfiram and L‐dopa‐benserazide (100 mg/kg + 25 mg/kg, 24 hr later) significantly increased DOPAL striatal level. A 30‐day treatment with disulfiram (100 mg/kg i.p., once every 2 days) and L‐dopa‐benserazide (100 mg/kg + 25 mg/kg, two times/day) did not affect either indexes used to assess integrity of the nigrostriatal dopaminergic neurones (i.e., the striatal content in dopamine and binding to the vesicular monoamine transporter on striatal membranes). These results do not evidence any deleterious effect of DOPAL and argue against toxicity of L‐dopa therapy

The role of the adenosine A(2A) receptor in the hypnotic effects of ethanol was assessed in mice. The duration of the loss of righting reflex following acute ethanol administration was shorter for A(2A) receptor-deficient mice (A(2A)R KO) than for wild-type mice (A(2A)R WT), whereas the fall in body temperature was not different between the two phenotypes. In contrast, the duration of the loss of righting reflex was increased in A(2A)R KO mice versus controls after administration of pentobarbital. Dipyridamole, an inhibitor of adenosine uptake, increased the sleep time observed following administration of ethanol in CD1 mice and in A(2A)R WT but not in A(2A)R KO mice. SCH 58261, a selective A(2A) receptor antagonist, unlike DPCPX, a selective A(1) receptor antagonist, shortened the duration of the loss of righting reflex induced by ethanol, thus mimicking the lack of receptor in deficient mice. Finally, the non-selective adenosine receptor antagonist caffeine (25 mg/kg) reduced ethanol-induced hypnotic effects. These results indicate that the activation of A(2A) receptors that follows an increase in extracellular adenosine levels caused by the administration of high doses of ethanol plays a role in its hypnotic effects. Thus, A(2A) receptor antagonists may be useful therapeutic agents for alleviating ethylic coma.

A2A receptor knockout (A2AR-/-) mice are more anxious and aggressive, and exhibit reduced exploratory activity than their wild-type littermates (A2AR+/+). Because alpha-melanocyte-stimulating hormone (alpha-MSH) influences anxiety, aggressiveness and motor activity, we investigated the effect of A2AR gene disruption on alpha-MSH content in discrete brain regions and pro-opiomelanocortin (POMC) expression in the hypothalamus and pituitary. No modification in alpha-MSH content was observed in the hypothalamus and medulla oblongata where POMC-expressing perikarya are located. In the arcuate nucleus of the hypothalamus, POMC mRNA levels were not affected by A2AR disruption. Conversely, in A2AR-/- mice, a significant increase in alpha-MSH content was observed in the amygdala and cerebral cortex, two regions that are innervated by POMC terminals. In the pars intermedia of the pituitary, A2AR disruption provoked a significant reduction of POMC mRNA expression associated with a decrease in alpha-MSH content. By contrast, in the anterior lobe of the pituitary, a substantial increase in POMC mRNA and adrenocorticotropin hormone concentrations was observed, and plasma corticosterone concentration was significantly higher in A2AR-/- mice, revealing hyperactivity of their pituitary-adrenocortical axis. Together, these results suggest that adenosine, acting through A2A receptors, may modulate the release of alpha-MSH in the cerebral cortex and amygdala. The data also indicate that A2A receptors are involved in the control of POMC gene expression and biosynthesis of POMC-derived peptides in pituitary melanotrophs and corticotrophs.

Rationale: The elevated plus-maze and the light/dark box are two established anxiety tests in rodents, which are useful to screen putative anxiogenic effects of drugs. Objective: Caffeine is well known to promote anxious behaviour in humans and animal models, but the precise site of action of the drug is still a matter of debate. The present study investigated whether the anxiogenic effects of caffeine observed in mice depend on the blockade of A2A receptor. First, the effects induced by the non-selective drug caffeine were compared with those elicited by two selective A2A receptor antagonists over a wide range of doses in the same experimental conditions. The effects of A2A or A1 adenosine receptor agonists and of a selective A1 adenosine receptor antagonist were also investigated. Second, wild-type and A2A receptor knockout mice offered another approach to delineate the role played by A2A receptor in caffeine’s anxiogenic effects. Methods: Mice were exposed to the elevated plus-maze or to the light/dark box for 5 min after acute or chronic administration of tested drugs. Results: Caffeine acutely administered (50 or 100 mg/kg IP) induced anxiety-like effects in both procedures. Its chronic administration (50 mg/kg IP twice daily) for 1 week or consumption in the drinking water (0.3 g/l) for 8 days or 2 months were also anxiogenic in the plus-maze test. The A2A receptor antagonists ZM241385 (up to 60 mg/kg IP) and SCH58261 (up to 10 mg/kg IP) were devoid of acute effects in both tests. One week administration of ZM241385 (30 mg/kg IP) or SCH58261 (3 mg/kg IP) had no effects in the plus-maze test. An antagonist (DPCPX) and an agonist (CPA) at A1 receptors had no acute effects on anxiety-related indices, whereas an A2A receptor agonist (CGS 21680) displayed non-specific motor effects in the plus-maze test. Acute administration of caffeine (50 mg/kg IP) induced no clear-cut anxiety-like effects in the plus-maze test in A2A receptor knockout mice that exhibited higher basal anxiety levels than wild-type mice. Chronic administration (50 mg/kg IP twice daily) for 1 week elicited less anxiety-like behaviour in A2A receptor knockout than in wild-type mice. Conclusions: Adaptative mechanisms following mutation in A2A receptors or their long-term blockade after chronic ingestion of caffeine may be responsible for increase proneness to anxiety. However, the short-term anxiety-like effect of caffeine in mice might not be related solely to the blockade of adenosine A2A receptors, since it is not shared by A2A selective antagonists.

In mice, low doses (1-2-4 mg/kg s.c.) of dexamphetamine stimulated locomotor activity in a dose-dependent manner. Over the same range of doses the drug dose dependently inhibited the in vivo striatal binding of the dopamine uptake inhibitor, [ 3 H]GBR 12783. At 3 mg/kg dexamphetamine, the stimulant effect and the inhibition of the striatal binding of [ 3 H]GBR 12783 displayed a similar time course. Pretreatments that either increased (L-DOPA 200 mg/kg, benserazide 50 mg/kg i.p.) or decreased (reserpine 5 mg/kg s.c., α-methyl-p-tyrosine 200 mg/kg) striatal dopamine levels did not modify the inhibition by dexamphetamine of [ 3 H]GBR 12783 binding in vivo. This suggests that the inhibition is due to a direct effect of dexamphetamine, not mediated by endogenous dopamine, and further that a unique site is responsible for the neuronal uptake of dexamphetamine and for the binding of pure dopamine uptake inhibitors.

International audience; In depressed patients, sleep undergoes marked alterations, especially sleep onset insomnia, sleep fragmentation, and disturbances of the Rapid Eye Movement (REM) sleep. Abnormalities of rest-activity rhythms and of hypothalamic-pituitary-adrenocortical function have also been described in these patients. In the present study, we examined the presence of such abnormalities in a recently developed line of mice (Helpless mice-H) that exhibit depression-like behaviors in validated tests, compared to the nonhelpless (NH) line derived from the same colony. Experiments were essentially carried out in females for which previous studies showed marked differences between H and NH lines. Compared to NH mice, the H line exhibited (i) lower basal locomotor activity, (ii) sleep fragmentation, shift towards lighter sleep stages, and facilitation of REM sleep reflected by increased amounts and decreased latency, (iii) larger response to the REM sleep promoting effect of muscarinic receptor stimulation (by arecoline). In contrast, H and NH mice were equally responsive to the REM sleep inhibitory effect of 5-HT1A receptor stimulation (by 8-OH-DPAT). In addition, a deficiency in delta power enhancement after sleep deprivation was observed in the H group, and acute immobilization stress in this group failed to elicit a REM sleep rebound and was associated with a long-lasting raise in serum corticosterone levels. These results further validate H mice as a depression model and suggest they might be of particular interest for investigating the neurobiological mechanisms and possibly genetic substrates underlying sleep alterations associated with depression.

Depression is a multifactorial illness and genetic factors play a role in its etiology. The understanding of its physiopathology relies on the availability of experimental models potentially mimicking the disease. Here we describe a model built up by selective breeding of mice with strikingly different responses in the tail suspension test, a stress paradigm aimed at screening potential antidepressants. Indeed, “helpless” mice are essentially immobile in the tail suspension test, as well as the Porsolt forced-swim test, and they show reduced consumption of a palatable 2% sucrose solution. In addition, helpless mice exhibit sleep–wakefulness alterations resembling those classically observed in depressed patients, notably a lighter and more fragmented sleep, with an increased pressure of rapid eye movement sleep. Compared with “nonhelpless” mice, they display higher basal seric corticosterone levels and lower serotonin metabolism index in the hippocampus. Remarkably, serotonin 1A autoreceptor stimulation induces larger hypothermia and inhibition of serotoninergic neuronal firing in the nucleus raphe dorsalis in helpless than in nonhelpless mice. Thus, helpless mice exhibit a decrease in serotoninergic tone, which evokes that associated with endogenous depression in humans. Finally, both the behavioral impairments and the serotoninergic dysfunction can be improved by chronic treatment with the antidepressant fluoxetine. The helpless line of mice may provide an opportunity to approach genes influencing susceptibility to depression and to investigate neurophysiological and neurochemical substrates underlying antidepressant effects.

The selective A2A receptor antagonist [3H]SCH 58261 was injected intravenously in mice and the radioactivity accumulating in various brain regions was determined by tissue sampling. Radioactivity levels in regions of interest such as the striatum were highest 15 min after injection and quickly declined thereafter (30 min and 1 h postinjection) in a time-dependent manner. The amount of labelling was ranked as follows striatum (4.6 +/- 0.3 fmol/mg protein) > cortex > hippocampus > pons = hypothalamus > cerebellum (0.5 +/- 0.05 fmol/mg protein). Specific labelling of the A2A receptor occurred in striatum and cortex because significantly less radioactivity accumulated in these areas from adenosine A2A receptor knockout mice as compared to wild-type littermates. In control outbred CD1 mice, a striatum-to-cerebellum ratio of 7.6 +/- 0.6 was found. At 30 min postinjection, the nonselective adenosine receptor antagonist caffeine reduced the radioactivity due to [3H]SCH 58261 in the striatum by 32% at 1 mg/kg i.p. and by 66% at the stimulant dose of 6.25 mg/kg i.p. Radioactivity in the striatum was lowered, respectively, by 66 and 86% 30 min after injection of 3 or 10 mg/kg i.p. doses of unlabelled SCH 58261. The present results indicate that [3H]SCH 58261 directly labels striatal A2A receptors in vivo. Thus [3H]SCH 58261 is an excellent tool for studying brain distribution and A2A receptor occupancy of various compounds ranging from xanthines, such as caffeine, to other A2A antagonists.

Considering the existing interactions between ethanol and adenosine, the influence of the genetic impairment of the adenosine A(2A) receptor has been examined upon the seizures occurring at the cessation of chronic ethanol intake or 'ethanol withdrawal' in male mice. Acute clearance of ethanol did not differ between adenosine A(2A) receptor knockout and wild-type mice. Mice were exposed for 10 days to a diet consisting of a milky chocolate drink that contained increasing concentrations (1.8, 3.6 and 6.3% v/v) of ethanol. Adenosine A(2A) receptor knockout mice ingested similar amounts of the fluid, either containing alcohol or not, as did the controls. The severity of handling-induced convulsions during withdrawal was significantly reduced in the adenosine A(2A) receptor knockout mice as compared with their wild-type controls. The selective adenosine A(2A) receptor antagonist ZM 241385 (20 mg/kg) also significantly attenuated the intensity of withdrawal-induced seizures occurring in wild-type male mice when intraperitoneally administered twice daily during the last 5 days of the forced alcohol intake. These results suggest that selective adenosine A(2A) receptor antagonists may be useful in the treatment of alcohol withdrawal.

Catalepsy assessed using the bar test was measured in both adenosine A2A receptor knockout (A2AR KO) and wild-type (A2AR WT) mice submitted to acute administration of the dopamine D2 receptor antagonist haloperidol (0.5, 2, 4, 6 mg/kg i.p.), the dopamine D1 antagonist SCH 23390 (0.3-3 mg/kg, s.c.), the vesicular monoamine transporter blocker reserpine (3-5 mg/kg, s.c.) or the acetylcholine muscarinic receptor agonist pilocarpine (25-50 mg/kg, i.p.). Except for reserpine, catalepsy scores were significantly lower in A2AR KO mice than in A2AR WT mice following low doses of these cataleptogenic agents. These results suggest that adenosine A2A receptors influence not only dopamine D2 and D1 receptor-mediated neurotransmission but also acetylcholine muscarinic receptor-mediated neurotransmission.

1. Adenosine, an ubiquitous neuromodulator, and its analogues have been shown to produce 'depressant' effects in animal models believed to be relevant to depressive disorders, while adenosine receptor antagonists have been found to reverse adenosine-mediated 'depressant' effect. 2. We have designed studies to assess whether adenosine A2A receptor antagonists, or genetic inactivation of the receptor would be effective in established screening procedures, such as tail suspension and forced swim tests, which are predictive of clinical antidepressant activity. 3. Adenosine A2A receptor knockout mice were found to be less sensitive to 'depressant' challenges than their wildtype littermates. Consistently, the adenosine A2A receptor blockers SCH 58261 (1 - 10 mg kg(-1), i.p.) and KW 6002 (0.1 - 10 mg kg(-1), p.o.) reduced the total immobility time in the tail suspension test. 4. The efficacy of adenosine A2A receptor antagonists in reducing immobility time in the tail suspension test was confirmed and extended in two groups of mice. Specifically, SCH 58261 (1 - 10 mg kg(-1)) and ZM 241385 (15 - 60 mg kg(-1)) were effective in mice previously screened for having high immobility time, while SCH 58261 at 10 mg kg(-1) reduced immobility of mice that were selectively bred for their spontaneous 'helplessness' in this assay. 5. Additional experiments were carried out using the forced swim test. SCH 58261 at 10 mg kg(-1) reduced the immobility time by 61%, while KW 6002 decreased the total immobility time at the doses of 1 and 10 mg kg(-1) by 75 and 79%, respectively. 6. Administration of the dopamine D2 receptor antagonist haloperidol (50 - 200 microg kg(-1) i.p.) prevented the antidepressant-like effects elicited by SCH 58261 (10 mg kg(-1) i.p.) in forced swim test whereas it left unaltered its stimulant motor effects. 7. In conclusion, these data support the hypothesis that A2A receptor antagonists prolong escape-directed behaviour in two screening tests for antidepressants. Altogether the results support the hypothesis that blockade of the adenosine A2A receptor might be an interesting target for the development of effective antidepressant agents.

The acute motor effects elicited by drugs acting upon adenosine A(2A) receptors, namely the highly selective agonist CGS 21680 or the antagonists SCH 58261 and ZM 241385, were investigated in mice. CGS 21680 dose-dependently (0.1-2.5 mg/kg i.p.) decreased horizontal and vertical motor activities. The depressant effect of CGS 21680 (0. 5 mg/kg i.p.) was maintained in mice pretreated by the adenosine receptor antagonist 8-(p-sulfophenyl)-theophylline (10-30 mg/kg i.p. ), which poorly penetrates the blood-brain barrier, but was completely lost in adenosine A(2A) receptor knockout mice. Thus, the adenosine A(2A) receptor is critically involved in motor activity. SCH 58261 (1-10 mg/kg i.p.) increased locomotion and rearing with a quick onset, but for a shorter period in mice habituated to the environment than in mice unfamiliar to it. ZM 241385 (7.5-60 mg/kg i. p.) stimulated horizontal and vertical activities with a slow onset at the two highest tested doses, similarly in naive and in habituated mice. The increase in locomotion elicited by ZM 241385 (15-30 mg/kg i.p. and 10-20 nM i.c.v.) was retained in mice treated by CGS 21680 (0.5 mg/kg i.p.) but that elicited by SCH 58261 (1-3-10 mg/kg i.p. and 10-20 nM i.c.v.) partially subsided. In conclusion, both 'striatal-like'/'SCH 58261-sensitive' adenosine A(2A) receptors and 'ZM 241385-sensitive'/'atypical' CGS 21680 binding sites may mediate CGS 21680-induced motor effects. Moreover, our results suggest that 'atypical' CGS 21680 binding sites could be adenosine A(2A) receptors with a peculiar pharmacological profile.

1. The locomotor stimulatory effects induced by caffeine (1,3, 7-trimethylxanthine) in rodents have been attributed to antagonism of adenosine A(1) and A(2A) receptors. Little is known about its locomotor depressant effects seen when acutely administered at high doses. The roles of adenosine A(1) and A(2A) receptors in these activities were investigated using a Digiscan actimeter in experiments carried out in mice. Besides caffeine, the A(2A) antagonist SCH 58261 (5-amino-7-(beta-phenylethyl)-2-(8-furyl)pyrazolo[4,3-e]-1,2, 4-triazolo[1,5-c]pyrimidine), the A(1) antagonist DPCPX (8-cyclopentyl-1,3-dipropylxanthine), the A(1) agonist CPA (N(6)-cyclopentyladenosine) and A(2A) receptor knockout mice were used. 2. Caffeine had a biphasic effect on locomotion of wild-type mice not habituated to the open field, stimulating locomotion at 6.25 - 25 mg kg(-1) i.p. doses, while depressing it at 100 mg kg(-1). In sharp contrast, caffeine dose-dependently decreased locomotion in A(2A) receptor knockout mice over the whole range of tested doses. 3. The depressant effects induced by high doses of caffeine were lost in control CD1 mice habituated to the open field. 4. The A(1) agonist CPA depressed locomotion at 0.3 - 1 mg kg(-1) i.p. doses. 5. The A(1) antagonist DPCPX decreased locomotion of A(2A) receptor knockouts and CD1 mice at 5 mg kg(-1) i.p. and 25 mg kg(-1) i.p. respectively. 6. DPCPX (0.2 - 1 mg kg(-1) i.p.) left unaltered or even reduced the stimulant effect of SCH 58261 (1 - 3 mg kg(-1) i.p.) on CD1 mice. 7. These results suggest therefore that the stimulant effect of low doses of caffeine is mediated by A(2A) receptor blockade while the depressant effect seen at higher doses under some conditions is explained by A(1) receptor blockade.

The antimicrobial agent oxolinic acid, injected i.p. in mice, induced a dose dependent increase in locomotor activity. This stimulation culminated at the 32 mg/kg dose and became smaller for higher doses (64-128 mg/kg). When opposed to increasing doses (50-100-200 microg/kg i.p.) of haloperidol (D2 dopamine receptor antagonist), the stimulant locomotor effect of 32 mg/kg oxolinic acid was not significantly reversed. On the contrary increasing doses (7.5-15-30 microg/kg s.c.) of SCH 23390 (D1 dopamine receptor antagonist) inhibited the stimulant locomotor effect. In mice made completely akinetic by a pretreatment with reserpine (4 mg/kg s.c., 18 h before testing), dexamphetamine (2 mg/kg s.c.) reversed this akinesia and even displayed a stimulant activity, similar to that observed in mice not treated by reserpine. On the contrary, oxolinic acid (32 mg/kg) did not reverse the reserpine induced akinesia and even opposed the reversion induced by dexamphetamine. In a synaptosomal fraction prepared from striatum of rats, oxolinic acid inhibited the 3H dopamine uptake with an IC50 = 4.3+/-0.6 x 10(-6) M. Finally, in mice injected i.v. with a tracer dose of 3H WIN 35428 (1 microCi) (a dopamine uptake blocker), 32 mg/kg oxolinic acid, i.p. administered, reduced by about 50% the specific binding of the radioligand to striatal dopamine carriers. It is concluded that the stimulant locomotor effect of oxolinic acid depends on the blockade of the neuronal dopamine uptake complex.

We investigated whether the antidepressant tianeptine shares the dopamine uptake inhibitory properties of the chemically related antidepressant amineptine. Tianeptine dose dependently (5, 10, 20, 40 mg/kg IP) increased locomotor activity in mice. This stimulant effect (20 mg/kg IP) was dose dependently prevented not only by the D 1 dopamine receptor antagonist SCH 23390 (7.5, 15, 30 μg/kg SC), but also by the D 2 dopamine receptor antagonist haloperidol (50, 100, 200 μg/kg IP), in contrast to that elicited by dopamine uptake inhibitors. Where the latter prevent dexamphetamine-induced (3 mg/kg SC) reversion of akinesia in mice pretreated with reserpine (4 mg/kg SC, 5 h before test), tianeptine (20 mg/kg IP, 30 min before test) did not. Tested up to a concentration of 10−4 M, tianeptine did neither inhibit the [ 3 H]dopamine uptake into mouse striatal synaptosomes nor compete in vitro with the specific binding of [ 3 H]WIN 35,428 at dopamine transporters from striatal membranes. Finally, in mice injected IV with a tracer dose of [ 3 H]WIN 35,428 (1 μCi), the highest tested dose of tianeptine (40 mg/kg IP) did not reduce the specific binding of the radioligand to striatal dopamine transporters. It is concluded that the antidepressant effect of tianeptine does not depend upon a blockade of the neuronal dopamine transporter.

International audience; Intracerebroventricular injection of the octadecaneuropeptide ODN in mouse, at doses of 12.5-1000 ng, reduced the percentage of convulsing animals and increased the latency of convulsions elicited by pentylenetetrazol (50 mg/kg, intraperitoneal [i.p.]). ODN also reduced the percentage of mortality induced by pentylenetetrazol (100 mg/kg, i.p.). The COOH-terminal octapeptide fragment of ODN was approximately equally effective but acted more rapidly than ODN to reverse the convulsant effect of pentylenetetrazol. ODN (100 ng, intracerebroventricular [i.c.v.]) increased the convulsion latency and reduced the percentage of animals that convulsed after the administration of the inverse agonist of benzodiazepine receptors DMCM (13 mg/kg, i.p.), whereas the benzodiazepine receptor antagonist flumazenil (1 mg/kg, subcutaneously) abrogated the protective effect of ODN (100 ng, i.c.v.) on pentylenetetrazol-induced convulsions. ODN (100 ng, i.c.v.) also reduced the percentage of DBA/2J mice displaying audiogenic convulsions. In contrast, ODN did not reduce the percentage of mice displaying tonic or clonic convulsions when electrical interauricular stimulations were applied. It is concluded that ODN, or more likely a proteolytic fragment derived from ODN, reduces pentylenetetrazol-induced convulsions through activation of central-type benzodiazepine receptors.

International audience; High concentrations of diazepam-binding inhibitor (DBI) have been detected in brain areas containing dopaminergic cell bodies and nerve terminals. In the present study, we have investigated the effect of a proteolytic fragment of DBI, the octadecaneuropeptide ODN, on apomorphine-induced yawning in Sprague-Dawley rats. Injection of graded doses of ODN (12.5 to 100 ng i.c.v.) caused a dose-dependent inhibition of apomorphine-induced yawning and penile erections. At a dose of 100 ng, intracerebroventricularly administered ODN was able to inhibit, during more than 3 h, the apomorphine-evoked yawning. ODN also inhibited pilocarpine-induced yawning. Apomorphine induces a bell-shaped dose-dependent effect on yawning with a maximum response at the dose of 100 microg/kg and a much lower effect at a dose of 200 microg/kg. Injection (i.c.v.) of 100 ng ODN markedly attenuated the number of yawns induced by 100 microg/kg apomorphine but partially restored the yawning behavior in rats treated with a 200 microg/kg dose of apomorphine. At doses of 0.5 or 5 mg/kg s.c., diazepam did not modify the inhibitory effect of ODN on the apomorphine-induced yawning. Taken together, the present data suggest that ODN inhibits yawning downstream dopaminergic as well as cholinergic synapses involved in yawning. In addition, the effect of ODN cannot be ascribed to an inverse agonistic activity on central-type benzodiazepine receptors.

International audience; The octadecaneuropeptide ODN has been originally characterized as an endogenous ligand of central-type benzodiazepine receptors, on its ability to displace the anxiogenic compound beta-[3H]carboline-3-carboxylate methyl ester from its binding sites. The aim of the present study was to investigate the anxiogenic effects of intracerebroventricular administration of ODN in mice and rats. At doses ranging from 10 to 100 ng, ODN increased in mice the latency to explore a white compartment when the animals were placed in a black one. ODN also reduced the first stay duration in the white compartment. These effects were antagonized by diazepam (0.075 mg/kg, s.c.) as well as flumazenil (1 mg/kg, s.c.), indicating that ODN acts as an inverse agonist on central-type benzodiazepine receptors. In rats, ODN reduced the latency to enter a black compartment when the animals were placed in the white one. In the plus-maze elevated test, ODN reduced, in both mice and rats, the number of entries and the time spent in the open arm. In mice, ODN (100 ng) increased the thigmotaxis index, i.e. the distance traveled in the peripheral zone of the open field. Time-course studies revealed that a significant effect of ODN (100 ng) in the black/white compartment test was only observed 40 min after the injection and lasted between 3 and 6 h. The effect of a 1000-ng dose of ODN appeared more tardily than that of a 10-ng dose. In addition, a 1000-ng dose of ODN occluded the early effect of a 100-ng dose on the white compartment first stay duration. The COOH-terminal octapeptide of ODN was more rapidly effective than ODN in the black/white compartment test, suggesting that the anxiogenic effect of the peptide requires the formation of biologically active proteolytic fragment.

Antidepressants are used since 40 years. All presently used antidepressants have a slow onset of action and do not improve all patients; thus, there is an absolute need for new antidepressants. A variety of animal models, often based upon the monoaminergic theory of depressive disorders, has been used to screen the current antidepressants. In fact, the main focus of most of these animal models has been to predict the antidepressant potential i.e. to establish predictive validity. However, the evaluation of such animal models should also consider face validity, i.e. how closely the model resembles the human condition, and this should help to identify innovating medicines. Antidepressants, when taken by a healthy person, induce nothing more than side effects, unrelated to an action on mood, whereas they alleviate depressive symptomatology in depressed patients. We have speculated that genetically selected animal models would be closer to the human clinical situation than models based on standard laboratory strains. We have depicted here that marked differences exist between strains of mice in the amount of immobility i.e. "spontaneous helplessness" observed in the tail suspension test, a method used to screen potential antidepressants. We have studied the behavioural characteristics of mice selectively bred for spontaneous high or low immobility scores in the tail suspension test. Hopefully, these selectively bred lines will provide a novel approach to investigate behavioural, neurochemical and neuroendocrine correlates of antidepressant action.

Adenosine is released from metabolically active cells by facilitated diffusion, and is generated extracellularly by degradation of released ATP. It is a potent biological mediator that modulates the activity of numerous cell types, including various neuronal populations, platelets, neutrophils and mast cells, and smooth muscle cells in bronchi and vasculature. Most of these effects help to protect cells and tissues during stress conditions such as ischaemia. Adenosine mediates its effects through four receptor subtypes: the A1, A2a, A2b and A3 receptors. The A2a receptor (A2aR) is abundant in basal ganglia, vasculature and platelets, and stimulates adenylyl cyclase. It is a major target of caffeine, the most widely used psychoactive drug. Here we investigate the role of the A2a receptor by disrupting the gene in mice. We found that A2aR-knockout (A2aR-/-) mice were viable and bred normally. Their exploratory activity was reduced, whereas caffeine, which normally stimulates exploratory behaviour, became a depressant of exploratory activity. Knockout animals scored higher in anxiety tests, and male mice were much more aggressive towards intruders. The response of A2aR-/- mice to acute pain stimuli was slower. Blood pressure and heart rate were increased, as well as platelet aggregation. The specific A2a agonist CGS 21680 lost its biological activity in all systems tested.

The tail suspension test is a behavioural primary screen for detecting potential antidepressant drugs. In this test, a reduction of duration of immobility after treatment with imipramine is obtained in mice of the NMRI strain but not of the CD1 strain. The present experiments evidence important differences between individuals of the latter strain in both the amount of immobility observed in naive mice and the effects of three antidepressants. The reproducibility of the tail suspension-induced behavioural despair was high in individual CD1 male mice and allowed a preselection of spontaneous high and low immobility scorers. Only the high immobility scorers were responsive to imipramine (30 mg/kg), desipramine (30 mg/kg) and paroxetine (10 mg/kg). The percentage of spontaneous high immobility scorers was higher in NMRI (50%) than in CD1 (20%) mice, justifying the use of the former strain for screening potential antidepressants. However, controlling for individual differences in the spontaneous performance in this animal model of depression may provide a useful tool to study behavioural, neurochemical and neuroendocrine correlates of antidepressant action.

Lines of mice were selectively bred to diverge in their spontaneous helplessness in the tail suspension test. By the second generation of selection, only mice of the helpless line were sensitive to the antidepressant imipramine. Genetic factors substantially contribute to the susceptibility to helplessness in this mouse model. These selectively bred lines may represent potentially useful animal models to investigate behavioural, neurochemical and neuroendocrine correlates of antidepressant action.

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.

The in vivo striatal binding of [3H]SCH 23390, an antagonist of the D1 dopamine receptors, was investigated in mice submitted to pretreatment to either decrease (gammabutyrolactone 750 mg/kg, i.p.) or, increase (3,4-dihydroxyphenylalanine (L-DOPA) 200 mg/kg i.p. plus dexamphetamine 4 mg/kg, s.c.) dopaminergic transmission. Such conditions failed to modify [3H]SCH 23390 binding. However, we observed that dopamine (at concentrations > or = 1 microM), reduced the in vitro binding of [3H]SCH 23390 in membrane fractions. These results suggest that modifications in dopamine neurotransmission do not alter the in vivo quantification of D1 receptors with [3H]SCH 23390, for example, in studies that use positron emission tomography.

We compared the ability of various dopamine (DA) uptake inhibitors to displace the in vivo striatal [ 3 H]GBR 12783 (1-[2(diphenylmethoxy) ethyl)-4-(3-phenyl-1[ 3 H]-2-propenyl)-piperazine) binding with their stimulant effect on locomotor activity on mice. GBR 12783 (8 mg/kg), GBR 13069 (10 mg/kg), cocaine (20 mg/kg), mazindol (3 mg/kg) or pyrovalerone (2 mg/kg) stimulated locomotion as long as they occupied the DA uptake complex. In contrast, nomifensine (3 mg/kg) did not stimulate locomotion although it completed with [ 3 ]GBR 12783 for the occupancy of the DA uptake complex at a significant level (> 50%). Administered at their ED 50 doses, GBR 12783, BTCP (N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine, GBR 13069, amineptine and dexamphetamine significantly increased locomotor activity whereas the other inhibitors tested did not. The locomotor response elicited by GBR 12783 (10 mg/kg) was not decreased by desipramine (20 mg/kg) nor by oxaprotiline (10 mg/kg). The increase in locomotion elicited by GBR 12783 was positively correlated with the basal locomotor activity of the mice. The stimulant effect of GBR 12783 was potentiated by SKF 525A and by budipine. Additional pharmacological properties might conceal the relationship between the effects of some DA uptake inhibitors on locomotion, and on in vivo occupancy of DA uptake sites.

Various characteristics of the in vivo striatal binding of [3H]GBR 12783 (1-[2-(diphenylmethoxy)-ethyl]-4-(3-phenyl-1[3H]-2-propenyl)pipera zine), a specific ligand of the neuronal dopamine uptake complex, were determined in mice. Increasing doses of the ligand revealed the saturability of the binding at a single site with half-maximal saturation at a dose of approximately 7 mumol/kg and an apparent maximal number of binding sites (Bmax) of 12.8 pmol/mg protein in striatum. Specific binding was prevented by various dopamine uptake blockers, pyrovalerone, GBR 13069, GBR 12783, N-[1-2-benzo(b)thiophenyl)cyclohexyl] piperidine, cocaine, methylphenidate and was inhibited in a stereoselective manner by the enantiomers of nomifensine. Other drugs which are not dopamine uptake blockers either did not modify [3H]GBR 12783 binding (the diphenylbutylpiperazine derivative flupenthixol) or increased it (the diphenylpiperazine derivative flunarizine or the chemically unrelated compounds fenfluramine and SKF 525A). A close correlation was found between occupancy of the striatal [3H]GBR 12783 binding site and the stimulant locomotor effect of the drug. A similar specific striatal binding of [3H]GBR 12783 was evidenced in both NMRI and CD1 strains. It was concluded that [3H]GBR 12783 administered in vivo provides a measure of the density of dopamine uptake sites in mouse striatum.

At 0 degrees C, when Na+ was the only cation present in the incubation medium, increasing the Na+ concentration from 3 to 10 mM enhanced the affinity of [3H]1-[2-(++di-phenylmethoxy)ethyl]-4-(3-phenyl-2-propenyl)piperaz ine [( 3H]GBR 12783) for the specific binding site present in rat striatal membranes without affecting the Bmax. For higher Na+ concentrations, specific binding values plateaued and then slightly decreased at 130 mM Na+. In a 10 mM Na+ medium, the KD and the Bmax were, respectively, 0.23 nM and 12.9 pmol/mg of protein. In the presence of 0.4 nM [3H]GBR 12783, the half-maximal specific binding occurred at 5 mM Na+. A similar Na+ dependence was observed at 20 degrees C. Scatchard plots indicated that K+, Ca2+, Mg2+, and Tris+ acted like competitive inhibitors of the specific binding of [3H]GBR 12783. The inhibitory potency of various cations (K+, Ca2+, Mg2+, Tris+, Li+, and choline) was enhanced when the Na+ concentration was decreased from 130 to 10 mM. In a 10 mM Na+ medium, the rank order of inhibitory potency was Ca2+ (0.13 mM) greater than Mg2+ greater than Tris+ greater than K+ (15 mM). The requirement for Na+ was rather specific, because none of the other cations acted as a substitute for Na+. No anionic requirement was found: Cl-, Br-, and F- were equipotent. These results suggest that low Na+ concentrations are required for maximal binding; higher Na+ concentrations protect the specific binding site against the inhibitory effect of other cations.