Guy Griebel

Anxiolytic- and antidepressant-like effects of the non-peptide vasopressin V1b receptor antagonist, SSR149415, suggest an innovative approach for the treatment of stress-related disorders

The limbic localization of the arginine vasopressin V1b receptor has prompted speculation as to a potential role of this receptor in the control of emotional processes. To investigate this possibility, we have studied the behavioral effects of SSR149415, the first selective and orally active non-peptide antagonist of vasopressin V1b receptors, in a variety of classical (punished drinking, elevated plus-maze, and light/dark tests) and atypical (fear/anxiety defense test battery and social defeat-induced anxiety) rodent models of anxiety, and in two models of depression [forced swimming and chronic mild stress (CMS)]. When tested in classical tests of anxiety, SSR149415 produced anxiolytic-like activity at doses that ranged from 1 to 30 mg/kg (i.p. or p.o.), but the magnitude of these effects was overall less than that of the benzodiazepine anxiolytic diazepam, which was used as a positive control. In contrast, SSR149415 produced clear-cut anxiolytic-like activity in models involving traumatic stress exposure, such as the social defeat paradigm and the defense test battery (1–30 mg/kg, p.o.). In the forced swimming test, SSR149415 (10–30 mg/kg, p.o.) produced antidepressant-like effects in both normal and hypophysectomized rats. Moreover, in the CMS model in mice, repeated administration of SSR149415 (10 and 30 mg/kg, i.p.) for 39 days improved the degradation of the physical state, anxiety, despair, and the loss of coping behavior produced by stress. These findings point to a role for vasopressin in the modulation of emotional processes via the V1b receptor, and suggest that its blockade may represent a novel avenue for the treatment of affective disorders.

Differences in anxiety-related behaviours and in sensitivity to diazepam in inbred and outbred strains of mice

Abstract Rationale: Natural strain differences exist in mice for behavioural traits such as emotional reactivity. Objective: The present experiments compared the behavioural profiles of nine strains of mice (BALB/c, C57BL/6, C3H, CBA, DBA/2, NMRI, NZB, SJL, Swiss) in two models of anxiety after the administration of the benzodiazepine diazepam. Methods: The tests used were the light/dark choice task and the elevated plus-maze, two well-validated anxiolytic screening tests. Results: In vehicle-treated animals, differences on variables designed to measure anxiety-related behaviours were observed in both tests. In the light/dark test, the strains could be divided into three distinct groups: two non-reactive strains (NZB and SJL), an intermediate-reactive group (C3H, CBA, DBA/2, NMRI, C57BL/6 and Swiss), and one highly reactive strain (BALB/c). In the elevated plus-maze, SJL, NMRI, CBA and, to a lesser extent, C3H strains of mice, consistently showed low levels of anxiety-related behaviours. Intermediate levels were seen in the Swiss and BALB/c strains, and high levels of emotional reactivity were seen in C57BL/6, DBA/2 and NZB. The strain distribution between the light/dark and the elevated plus-maze tests shows similarities and differences, suggesting that each of these experimental procedures represents a different set of behaviours. Marked differences between a number of strains of mice in their sensitivity to the anxiolytic-like action of diazepam were observed in both the light/dark and the elevated plus-maze tests. Mice of the BALB/c, Swiss and, to a lesser extent, CBA and C3H strains were responsive to diazepam in both tests, although in the case of CBA mice, effects may have been contaminated by behavioural suppression. SJL mice were largely unresponsive to the action of the benzodiazepine in both tests, whereas in C57, DBA/2, NMRI and NZB mice, diazepam produced positive effects only in the elevated plus-maze. Conclusion: The finding of differential strain distributions both with and without diazepam treatment in the light/dark and the elevated plus-maze tests, indicates that not all strains of mice are suitable for investigating the effects of GABA/BZ receptor ligands. This study may thus provide a useful guide for choosing the best strain of mice for studying the pharmacology of fear-related behaviours.

Nicotine-associated cues maintain nicotine-seeking behavior in rats several weeks after nicotine withdrawal: reversal by the cannabinoid (CB1) receptor antagonist, rimonabant (SR141716).

Conditioned stimuli are important for nicotine dependence and may trigger craving and relapse after prolonged nicotine abstinence. However, little is known about the pharmacology of this process. Among the systems that have been shown to play a role in drug-seeking behavior is the endocannabinoid transmission. Therefore, the present study examined the resistance to extinction of drug-seeking behavior elicited by nicotine-associated environmental stimuli and the effects of the selective CB1 cannabinoid antagonist rimonabant (SR141716) on the reinforcing effects of nicotine-related stimuli. Rats were trained to self-administer nicotine (0.03 mg/kg/injection, i.v.) under conditions in which responding was reinforced jointly by response-contingent nicotine injections and stimuli (light and tone). After self-administration acquisition, nicotine was withdrawn and lever pressing was only reinforced by contingent presentation of the audiovisual stimuli. Under such a condition, responding persisted for 3 months, following which nonpresentation of the cues produced a progressive extinction of responding. As expected, rats trained to lever-press for saline injections paired with the audiovisual stimuli did not acquire the self-administration. These findings indicate that the cues required learned association with nicotine to acquire reinforcing properties and to function as conditioned reinforcers. When administered 1 month following nicotine withdrawal, rimonabant (1 mg/kg, i.p.) decreased conditioned behavior. These results showing the persistence of a nicotine-conditioned behavior are congruent with the role of nicotine-related environmental stimuli in nicotine craving in abstinent smokers. Rimonabant, which has been shown previously to reduce nicotine self-administration, may be effective not only as an aid for smoking cessation but also in the maintenance of abstinence.

SSR180711, a Novel Selective |[alpha]|7 Nicotinic Receptor Partial Agonist: (II) Efficacy in Experimental Models Predictive of Activity Against Cognitive Symptoms of Schizophrenia

SSR180711 (4-bromophenyl 1,4diazabicyclo(3.2.2) nonane-4-carboxylate, monohydrochloride) is a selective α7 nicotinic receptor (n-AChR) partial agonist. Based on the purported implication of this receptor in cognitive deficits associated with schizophrenia, the present study assessed efficacy of SSR180711 (i.p. and p.o.) in different types of learning and memory involved in this pathology. SSR180711 enhanced episodic memory in the object recognition task in rats and mice (MED: 0.3 mg/kg), an effect mediated by the α7 n-AChR, as it was no longer seen in mice lacking this receptor. Efficacy was retained after repeated treatment (eight administrations over 5 days, 1 mg/kg), indicating lack of tachyphylaxia. SSR180711 also reversed (MED: 0.3 mg/kg) MK-801-induced deficits in retention of episodic memory in rats (object recognition). The drug reversed (MED: 0.3 mg/kg) selective attention impaired by neonatal phencyclidine (PCP) treatment and restored MK-801- or PCP-induced memory deficits in the Morris or linear maze (MED: 1–3 mg/kg). In neurochemical and electrophysiological correlates of antipsychotic drug action, SSR180711 increased extracellular levels of dopamine in the prefrontal cortex (MED: 1 mg/kg) and enhanced (3 mg/kg) spontaneous firing of retrosplenial cortex neurons in rats. Selectivity of SSR180711 was confirmed as these effects were abolished by methyllycaconitine (3 mg/kg, i.p. and 1 mg/kg, i.v., respectively), a selective α7 n-AChR antagonist. Additional antidepressant-like properties of SSR180711 were demonstrated in the forced-swimming test in rats (MED: 1 mg/kg), the maternal separation-induced ultrasonic vocalization paradigm in rat pups (MED: 3 mg/kg) and the chronic mild stress procedure in mice (10 mg/kg o.d. for 3 weeks). Taken together, these findings characterize SSR180711 as a promising new agent for the treatment of cognitive symptoms of schizophrenia. The antidepressant-like properties of SSR180711 are of added interest, considering the high prevalence of depressive symptoms in schizophrenic patients.

Effects of the cannabinoid CB1 receptor antagonist rimonabant in models of emotional reactivity in rodents

BACKGROUND The endocannabinoid system has been implicated in the modulation of emotional processes. METHODS These experiments aimed to investigate the effects of the cannabinoid CB1 receptor antagonist rimonabant (SR141716) in animal models measuring aspects of emotional reactivity and depression. RESULTS Rimonabant had weak anxiolytic-like activity in the elevated plus-maze and failed to affect flight and risk assessment activities in the mouse defense test battery (MDTB). It produced clear anxiolytic-like effects in the Vogel conflict test (.3-3 mg/kg intraperitoneal [i.p.]) and on defensive aggression in the MDTB (1 and 10 mg/kg, i.p.). The effects of rimonabant in the MDTB paralleled those observed with CB1 receptor knockout mice in this procedure. In the forced-swimming test in rats and the tonic immobility paradigm in gerbils, rimonabant (3 and 10 mg/kg per os [p.o.]) produced antidepressant-like effects that were comparable to those observed with the reference antidepressant, fluoxetine. In the chronic mild stress model in mice, repeated administration of rimonabant (10 mg/kg, p.o.) for 5 weeks improved the deleterious effects produced by stress. CONCLUSIONS These findings point further to a role for the endocannabinoid system in the modulation of emotional processes and suggest that it may be primarily involved in the adaptive responses to unavoidable stressful stimuli.

The free-exploratory paradigm: an effective method for measuring neophobic behaviour in mice and testing potential neophobia-reducing drugs.

When given the opportunity to choose between a novel and a familiar compartment (free-exploratory paradigm), BALB/c mice exhibited a preference for familiar places and a marked number of attempts at entry into the novel compartment followed by avoidance responses. In contrast, C57BL/6 mice showed a preference for novel places and very few avoidance responses towards novelty. When novelty was reduced by two familiar odours, fresh sawdust or urine of conspecifics, the neophobia of the BALB/c mice was reversed and the animals clearly showed a preference for the novel compartment. This experimental paradigm can be proposed as an effective animal model for investigating drugs potentially able to reduce neophobia in BALB/c mice. The effects of anxiolytics, effective in the usual animal models of “state” anxiety, were investigated in the free-exploratory paradigm which may model another type of anxiety termed by Lister (1990) “trait” anxiety. Thus, the behavioural effects of two benzodiazepine full agonists, chlordiazepoxide and diazepam, two non-benzodiazepine partial agonists at benzodiazepine receptors, Ro 19–8022 and alpidem, the 5-HT1A receptor agonist, 8-OH-DPAT, and the 5-HT, receptor antagonist, zacopride, were assessed in BALB/c and C57BL/6 mice. Chlordiazepoxide, diazepam and Ro 19–8022 completely reversed the preference of BALB/c mice for the familiar compartment, treated animals exhibiting a significant preference for novel places. In contrast, alpidem, 8-OH-DPAT and zacopride did not significantly modify their behaviour. Moreover, the same drugs did not modify the specific responses of C57BL/6 mice toward novelty. These results demonstrate that drugs which bind in a non-selective manner to heterogeneous benzodiazepine recognition sites were very effective in reducing neophobia in BALB/c mice, whereas 5-HT-interacting drugs were unable to counteract their neophobic behaviour. Thus, the free-exploratory paradigm can be proposed as an effective method for testing potential neophobia- (“trait” anxiety) reducing drugs.

Neurochemical, electrophysiological and pharmacological profiles of the selective inhibitor of the glycine transporter-1 SSR504734, a potential new type of antipsychotic.

Noncompetitive N-methyl-D-aspartate (NMDA) blockers induce schizophrenic-like symptoms in humans, presumably by impairing glutamatergic transmission. Therefore, a compound potentiating this neurotransmission, by increasing extracellular levels of glycine (a requisite co-agonist of glutamate), could possess antipsychotic activity. Blocking the glycine transporter-1 (GlyT1) should, by increasing extracellular glycine levels, potentiate glutamatergic neurotransmission. SSR504734, a selective and reversible inhibitor of human, rat, and mouse GlyT1 (IC50=18, 15, and 38 nM, respectively), blocked reversibly the ex vivo uptake of glycine (mouse cortical homogenates: ID50: 5 mg/kg i.p.), rapidly and for a long duration. In vivo, it increased (minimal efficacious dose (MED): 3 mg/kg i.p.) extracellular levels of glycine in the rat prefrontal cortex (PFC). This resulted in an enhanced glutamatergic neurotransmission, as SSR504734 potentiated NMDA-mediated excitatory postsynaptic currents (EPSCs) in rat hippocampal slices (minimal efficacious concentration (MEC): 0.5 μM) and intrastriatal glycine-induced rotations in mice (MED: 1 mg/kg i.p.). It normalized activity in rat models of hippocampal and PFC hypofunctioning (through activation of presynaptic CB1 receptors): it reversed the decrease in electrically evoked [3H]acetylcholine release in hippocampal slices (MEC: 10 nM) and the reduction of PFC neurons firing (MED: 0.3 mg/kg i.v.). SSR504734 prevented ketamine-induced metabolic activation in mice limbic areas and reversed MK-801-induced hyperactivity and increase in EEG spectral energy in mice and rats, respectively (MED: 10–30 mg/kg i.p.). In schizophrenia models, it normalized a spontaneous prepulse inhibition deficit in DBA/2 mice (MED: 15 mg/kg i.p.), and reversed hypersensitivity to locomotor effects of d-amphetamine and selective attention deficits (MED: 1–3 mg/kg i.p.) in adult rats treated neonatally with phencyclidine. Finally, it increased extracellular dopamine in rat PFC (MED: 10 mg/kg i.p.). The compound showed additional activity in depression/anxiety models, such as the chronic mild stress in mice (10 mg/kg i.p.), ultrasonic distress calls in rat pups separated from their mother (MED: 1 mg/kg s.c.), and the increased latency of paradoxical sleep in rats (MED: 30 mg/kg i.p.). In conclusion, SSR504734 is a potent and selective GlyT1 inhibitor, exhibiting activity in schizophrenia, anxiety and depression models. By targeting one of the primary causes of schizophrenia (hypoglutamatergy), it is expected to be efficacious not only against positive but also negative symptoms, cognitive deficits, and comorbid depression/anxiety states.

The Mouse Defense Test Battery: pharmacological and behavioral assays for anxiety and panic

The Mouse Defense Test Battery was developed from tests of defensive behaviors in rats, reflecting earlier studies of both acute and chronic responses of laboratory and wild rodents to threatening stimuli and situations. It measures flight, freezing, defensive threat and attack, and risk assessment in response to an unconditioned predator stimulus, as well as pretest activity and postthreat (conditioned) defensiveness to the test context. Factor analyses of these indicate four factors relating to cognitive and emotional aspects of defense, flight, and defensiveness to the test context. In the Mouse Defense Test Battery, GABA(A)-benzodiazepine anxiolytics produce consistent reductions in defensive threat/attack and risk assessment, while panicolytic and panicogenic drugs selectively reduce and enhance, respectively, flight. Effects of GABA(A)-benzodiazepine, serotonin, and neuropeptide ligands in the Mouse Defense Test Battery are reviewed. This review suggests that the Mouse Defense Test Battery is a sensitive and appropriate tool for preclinical evaluation of drugs potentially effective against defense-related disorders such as anxiety and panic.

SSR180711, a Novel Selective α 7 Nicotinic Receptor Partial Agonist: (1) Binding and Functional Profile

In this paper, we report on the pharmacological and functional profile of SSR180711 (1,4-Diazabicyclo[3.2.2]nonane-4-carboxylic acid, 4-bromophenyl ester), a new selective α7 acetylcholine nicotinic receptor (n-AChRs) partial agonist. SSR180711 displays high affinity for rat and human α7 n-AChRs (Ki of 22±4 and 14±1 nM, respectively). Ex vivo 3[H]α-bungarotoxin binding experiments demonstrate that SSR180711 rapidly penetrates into the brain (ID50=8 mg/kg p.o.). In functional studies performed with human α7 n-AChRs expressed in Xenopus oocytes or GH4C1 cells, the compound shows partial agonist effects (intrinsic activity=51 and 36%, EC50=4.4 and 0.9 μM, respectively). In rat cultured hippocampal neurons, SSR180711 induced large GABA-mediated inhibitory postsynaptic currents and small α-bungarotoxin sensitive currents through the activation of presynaptic and somato-dendritic α7 n-AChRs, respectively. In mouse hippocampal slices, the compound increased the amplitude of both glutamatergic (EPSCs) and GABAergic (IPSCs) postsynaptic currents evoked in CA1 pyramidal cells. In rat and mouse hippocampal slices, a concentration of 0.3 μM of SSR180711 increased long-term potentiation (LTP) in the CA1 field. Null mutation of the α7 n-AChR gene totally abolished SSR180711-induced modulation of EPSCs, IPSCs and LTP in mice. Intravenous administration of SSR180711 strongly increased the firing rate of single ventral pallidum neurons, extracellularly recorded in anesthetized rats. In microdialysis experiments, administration of the compound (3–10 mg/kg i.p.) dose-dependently increased extracellular acetylcholine (ACh) levels in the hippocampus and prefrontal cortex of freely moving rats. Together, these results demonstrate that SSR180711 is a selective and partial agonist at human, rat and mouse α7 n-AChRs, increasing glutamatergic neurotransmission, ACh release and LTP in the hippocampus.

Effects of the selective nonpeptide corticotropin-releasing factor receptor 1 antagonist antalarmin in the chronic mild stress model of depression in mice

Several recent studies on corticotropin-releasing factor (CRF) have suggested that this neuropeptide may play a role in depression. Consequently, CRF receptor antagonists have been proposed as potential new agents for the treatment of this condition. This study investigated the effects of a 4-week treatment with the well-known CRF(1) receptor antagonist, antalarmin, and the prototypical selective serotonin reuptake inhibitor (SSRI), fluoxetine, in the chronic mild stress (CMS) model in BALB/c mice. Animals were exposed to 9 weeks of CMS which rapidly (within 2 weeks) produced decrease of physical state (PS), body weight gain and blunted emotional response in the light/dark test. Chronic treatment with antalarmin (10 mg/kg ip) and fluoxetine (10 mg/kg ip) led to an improvement of CMS-induced modifications. These results suggest that CRF(1) receptor antagonists may represent potential antidepressants.