Endocannabinoid signaling and epigenetics modifications in the neurobiology of stress-related disorders.

Stress exposure is associated with psychiatric conditions, such as depression, anxiety, and post-traumatic stress disorder (PTSD). It is also a vulnerability factor to developing or reinstating substance use disorder. Stress causes several changes in the neuro-immune-endocrine axis, potentially resulting in prolonged dysfunction and diseases. Changes in several transmitters, including serotonin, dopamine, glutamate, gamma-aminobutyric acid (GABA), glucocorticoids, and cytokines, are associated with psychiatric disorders or behavioral alterations in preclinical studies. Complex and interacting mechanisms make it very difficult to understand the physiopathology of psychiatry conditions; therefore, studying regulatory mechanisms that impact these alterations is a good approach. In the last decades, the impact of stress on biology through epigenetic markers, which directly impact gene expression, is under intense investigation; these mechanisms are associated with behavioral alterations in animal models after stress or drug exposure, for example. The endocannabinoid (eCB) system modulates stress response, reward circuits, and other physiological functions, including hypothalamus-pituitary-adrenal axis activation and immune response. eCBs, for example, act retrogradely at presynaptic neurons, limiting the release of neurotransmitters, a mechanism implicated in the antidepressant and anxiolytic effects after stress. Epigenetic mechanisms can impact the expression of eCB system molecules, which in turn can regulate epigenetic mechanisms. This review will present evidence of how the eCB system and epigenetic mechanisms interact and the consequences of this interaction in modulating behavioral changes after stress exposure in preclinical studies or psychiatric conditions. Moreover, evidence that correlates the involvement of the eCB system and epigenetic mechanisms in drug abuse contexts will be discussed.

A role for the endocannabinoid enzymes monoacylglycerol and diacylglycerol lipases in cue-induced cocaine craving following prolonged abstinence.

Following exposure to drugs of abuse, long-term neuroadaptations underlie persistent risk to relapse. Endocannabinoid signaling has been associated with drug-induced neuroadaptations, but the role of lipases that mediate endocannabinoid biosynthesis and metabolism in regulating relapse behaviors following prolonged periods of drug abstinence has not been examined. Here, we investigated how pharmacological manipulation of lipases involved in regulating the expression of the endocannabinoid 2-AG in the nucleus accumbens (NAc) influence cocaine relapse via discrete neuroadaptations. At prolonged abstinence (30 days) from cocaine self-administration, there is an increase in the NAc levels of diacylglycerol lipase (DAGL), the enzyme responsible for the synthesis of the endocannabinoid 2-AG, along with decreased levels of monoacylglycerol lipase (MAGL), which hydrolyzes 2-AG. Since endocannabinoid-mediated behavioral plasticity involves phosphatase dysregulation, we examined the phosphatase calcineurin after 30 days of abstinence and found decreased expression in the NAc, which we demonstrate is regulated through the transcription factor EGR1. Intra-NAc pharmacological manipulation of DAGL and MAGL with inhibitors DO-34 and URB-602, respectively, bidirectionally regulated cue-induced cocaine seeking and altered the phosphostatus of translational initiation factor, eIF2α. Finally, we found that cocaine seeking 30 days after abstinence leads to decreased phosphorylation of eIF2α and reduced expression of its downstream target NPAS4, a protein involved in experience-dependent neuronal plasticity. Together, our findings demonstrate that lipases that regulate 2-AG expression influence transcriptional and translational changes in the NAc related to drug relapse vulnerability.

Neuroadaptations in the dorsal hippocampus underlie cocaine seeking during prolonged abstinence.

Relapse vulnerability in substance use disorder is attributed to persistent cue-induced drug seeking that intensifies (or "incubates") during drug abstinence. Incubated cocaine seeking has been observed in both humans with cocaine use disorder and in preclinical relapse models. This persistent relapse vulnerability is mediated by neuroadaptations in brain regions involved in reward and motivation. The dorsal hippocampus (DH) is involved in context-induced reinstatement of cocaine seeking but the role of the DH in cocaine seeking during prolonged abstinence has not been investigated. Here we found that transforming growth factor-ß (TGF-ß) superfamily member activin A is increased in the DH on abstinence day (AD) 30 but not AD1 following extended-access cocaine self-administration compared to saline controls. Moreover, activin A does not affect cocaine seeking on AD1 but regulates cocaine seeking on AD30 in a bidirectional manner. Next, we found that activin A regulates phosphorylation of NMDA receptor (NMDAR) subunit GluN2B and that GluN2B-containing NMDARs also regulate expression of cocaine seeking on AD30. Activin A and GluN2B-containing NMDARs have both previously been implicated in hippocampal synaptic plasticity. Therefore, we examined synaptic strength in the DH during prolonged abstinence and observed an increase in moderate long-term potentiation (LTP) in cocaine-treated rats compared to saline controls. Lastly, we examined the role of DH projections to the lateral septum (LS), a brain region implicated in cocaine seeking and found that DH projections to the LS govern cocaine seeking on AD30. Taken together, this study demonstrates a role for the DH in relapse behavior following prolonged abstinence from cocaine self-administration.

A novel role for the actin-binding protein drebrin in regulating opiate addiction.

Persistent transcriptional and morphological events in the nucleus accumbens (NAc) and other brain reward regions contribute to the long-lasting behavioral adaptations that characterize drug addiction. Opiate exposure reduces the density of dendritic spines on medium spiny neurons of the NAc; however, the underlying transcriptional and cellular events mediating this remain unknown. We show that heroin self-administration negatively regulates the actin-binding protein drebrin in the NAc. Using virus-mediated gene transfer, we show that drebrin overexpression in the NAc is sufficient to decrease drug seeking and increase dendritic spine density, whereas drebrin knockdown potentiates these effects. We demonstrate that drebrin is transcriptionally repressed by the histone modifier HDAC2, which is relieved by pharmacological inhibition of histone deacetylases. Importantly, we demonstrate that heroin-induced adaptations occur only in the D1+ subset of medium spiny neurons. These findings establish an essential role for drebrin, and upstream transcriptional regulator HDAC2, in opiate-induced plasticity in the NAc.

Opposing roles of CB1 and CB2 cannabinoid receptors in the stimulant and rewarding effects of cocaine.

BACKGROUND AND PURPOSE: The endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) bind to CB1 and CB2 cannabinoid receptors in the brain and modulate the mesolimbic dopaminergic pathway. This neurocircuitry is engaged by psychostimulant drugs, including cocaine. Although CB1 receptor antagonism and CB2 receptor activation are known to inhibit certain effects of cocaine, they have been investigated separately. Here, we tested the hypothesis that there is a reciprocal interaction between CB1 receptor blockade and CB2 receptor activation in modulating behavioural responses to cocaine. EXPERIMENTAL APPROACH: Male Swiss mice received i.p. injections of cannabinoid-related drugs followed by cocaine, and were then tested for cocaine-induced hyperlocomotion, c-Fos expression in the nucleus accumbens and conditioned place preference. Levels of endocannabinoids after cocaine injections were also analysed. KEY RESULTS: The CB1 receptor antagonist, rimonabant, and the CB2 receptor agonist, JWH133, prevented cocaine-induced hyperlocomotion. The same results were obtained by combining sub-effective doses of both compounds. The CB2 receptor antagonist, AM630, reversed the inhibitory effects of rimonabant in cocaine-induced hyperlocomotion and c-Fos expression in the nucleus accumbens. Selective inhibitors of anandamide and 2-AG hydrolysis (URB597 and JZL184, respectively) failed to modify this response. However, JZL184 prevented cocaine-induced hyperlocomotion when given after a sub-effective dose of rimonabant. Cocaine did not change brain endocannabinoid levels. Finally, CB2 receptor blockade reversed the inhibitory effect of rimonabant in the acquisition of cocaine-induced conditioned place preference. CONCLUSION AND IMPLICATIONS: The present data support the hypothesis that CB1 and CB2 receptors work in concert with opposing functions to modulate certain addiction-related effects of cocaine. LINKED ARTICLES: This article is part of a themed section on 8th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Attenuation of glutamatergic and nitrergic system contributes to the antidepressant-like effect induced by capsazepine in the forced swimming test.

The transient receptor potential vanilloid 1 (TRPV1) can modulate stress-related behaviours, thus representing an interesting target for new antidepressant drugs. TRPV1 can trigger glutamate release and nitric oxide synthesis in the brain, mechanisms also involved in the neurobiology of depression. However, it is not known if these mechanisms are involved in TRPV1-induced behavioural effects. Therefore, the aim of this study was to verify if the antidepressant-like effect induced by a TRPV1 antagonist in mice submitted to the forced swimming test (FST) would be facilitated by combined treatment with neuronal nitric oxide synthase (nNOS) inhibition and N-methyl-D-aspartate (NMDA) blockade. Male Swiss mice were given (intracerebroventricular) injections of capsazepine (CPZ) (TRPV1 antagonist - 0.05/0.1/0.3/0.6 nmol/µl), and AP7 (NMDA antagonist - 1/3/10 nmol/µl) or N-propyl-L-arginine (NPA, nNOS inhibitor - 0.001/0.01/0.1 nmol/µl), and 10 min later, submitted to an open field test, and immediately afterwards, to the FST. An additional group received coadministration of CPZ and AP7 or CPZ and NPA, in subeffective doses. The results demonstrated that CPZ (0.1 nmol/µl), AP7 (3 nmol/µl) and NPA (0.01/0.1 nmol/µl) induced antidepressant-like effects. Moreover, coadministration of subeffective doses of CPZ and AP7 or CPZ and NPA induced significant antidepressant-like effects. Altogether, the data indicate that blockade of TRPV1 receptors by CPZ induces antidepressant-like effects and that both nNOS inhibition and NMDA blockade facilitate CPZ effects in the FST.

E3 Ubiquitin-Protein Ligase SMURF1 in the Nucleus Accumbens Mediates Cocaine Seeking.

BACKGROUND: Substance use disorder is a neurobiological disease characterized by episodes of relapse despite periods of withdrawal. It is thought that neuroadaptations in discrete brain areas of the reward pathway, including the nucleus accumbens, underlie these aberrant behaviors. The ubiquitin-proteasome system degrades proteins and has been shown to be involved in cocaine-induced plasticity, but the role of E3 ubiquitin ligases, which conjugate ubiquitin to substrates, is unknown. Here, we examined E3 ubiquitin-protein ligase SMURF1 (SMURF1) in neuroadaptations and relapse behavior during withdrawal following cocaine self-administration. METHODS: SMURF1 and downstream targets ras homolog gene family, member A (RhoA), SMAD1/5, and Runt-related transcript factor 2 were examined using Western blotting (n = 9-11/group), quantitative polymerase chain reaction (n = 6-9/group), co-immunoprecipitation (n = 9-11/group), tandem ubiquitin binding entities affinity purification (n = 5-6/group), and quantitative chromatin immunoprecipitation (n = 3-6/group) (2 rats/sample). Viral-mediated gene transfer (n = 7-12/group) and intra-accumbal microinjections (n = 9-10/group) were used to examine causal roles of SMURF1 and substrate RhoA, respectively, in cue-induced cocaine seeking. RESULTS: SMURF1 protein expression was decreased, while SMURF1 substrates RhoA and SMAD1/5 were increased, in the nucleus accumbens on withdrawal day 7, but not on withdrawal day 1, following cocaine self-administration. Viral-mediated gene transfer of Smurf1 or constitutive activation of RhoA attenuated cue-induced cocaine seeking, while catalytically inactive Smurf1 enhanced cocaine seeking. Furthermore, SMURF1-regulated, SMAD1/5-associated transcription factor Runt-related transcript factor 2 displayed increased binding at promoter regions of genes previously associated with cocaine-induced plasticity. CONCLUSIONS: SMURF1 is a key mediator of neuroadaptations in the nucleus accumbens following cocaine exposure and mediates cue-induced cocaine seeking during withdrawal.

N-arachidonoyl-serotonin, a dual FAAH and TRPV1 blocker, inhibits the retrieval of contextual fear memory: Role of the cannabinoid CB1 receptor in the dorsal hippocampus.

Anandamide, an endocannabinoid, inhibits aversive responses by activating the CB1 cannabinoid receptor. At high concentrations, however, anandamide may exert pro-aversive activities mediated by the transient receptor potential vanilloid type-1 channel (TRPV1). Accordingly, N-arachidonoyl-serotonin (AA-5-HT), a dual blocker of the anandamide-hydrolysing enzyme fatty acid amide hydrolase (FAAH) and the TRPV1 channel, induces anxiolytic-like effects. Here we tested the hypothesis that AA-5-HT inhibits the expression of contextual fear conditioning by facilitating CB1 receptor signalling in the dorsal hippocampus of mice. Intraperitoneal injection of AA-5-HT (0.1, 0.3, 1 mg/kg) inhibited the retrieval of contextual fear memory (freezing response). The effect of AA-5-HT (0.3 mg/kg) was prevented by systemic injection of the CB1 receptor antagonist, AM251 (1.0 mg/kg), and mimicked by simultaneous FAAH inhibition (URB597, 0.3 mg/kg) and TRPV1 blockage (SB366791, 1 mg/kg). Injection of AA-5-HT (0.125, 0.25, 0.5 nmol) into the dorsal hippocampus also reduced freezing. Finally, the effect of systemic AA-5-HT (0.3 mg/kg) was prevented by intra-hippocampal injection of AM251 (1 nmol). In conclusion, dual FAAH and TRPV1 blockage inhibits contextual fear memory by facilitating anandamide-induced CB1 receptor activation in the dorsal hippocampus. This approach may lead to new pharmacological treatments for traumatic memories and related psychiatric disorders.

Cannabidiol, a Cannabis sativa constituent, inhibits cocaine-induced seizures in mice: Possible role of the mTOR pathway and reduction in glutamate release.

Cannabidiol (CBD), a major non-psychotomimetic constituent of Cannabis sativa, has therapeutic potential for certain psychiatric and neurological disorders. Studies in laboratory animals and limited human trials indicate that CBD has anticonvulsant and neuroprotective properties. Its effects against cocaine neurotoxicity, however, have remained unclear. Thus, the present study tested the hypothesis that CBD protects against cocaine-induced seizures and investigated the underlying mechanisms. CBD (30 mg/kg) pre-treatment increased the latency and reduced the duration of cocaine (75 mg/kg)-induced seizures in mice. The CB1 receptor antagonist, AM251 (1 and 3mg/kg), and the CB2 receptor antagonist, AM630 (2 and 4 mg/kg), failed to reverse this protective effect, suggesting that alternative mechanisms are involved. Synaptosome studies with the hippocampus of drug-treated animals revealed that cocaine increases glutamate release, whereas CBD induces the opposite effect. Finally, the protective effect of this cannabinoid against cocaine-induced seizure was reversed by rapamycin (1 and 5mg/kg), an inhibitor of the mammalian target of rapamycin (mTOR) intracellular pathway. In conclusion, CBD protects against seizures in a model of cocaine intoxication. These effects possibly occur through activation of mTOR with subsequent reduction in glutamate release. CBD should be further investigated as a strategy for alleviating psychostimulant toxicity.

Enhancement of endocannabinoid signaling protects against cocaine-induced neurotoxicity.

Cocaine is an addictive substance with a potential to cause deleterious effects in the brain. The strategies for treating its neurotoxicity, however, are limited. Evidence suggests that the endocannabinoid system exerts neuroprotective functions against various stimuli. Thus, we hypothesized that inhibition of fatty acid amide hydrolase (FAAH), the main enzyme responsible for terminating the actions of the endocannabinoid anandamide, reduces seizures and cell death in the hippocampus in a model of cocaine intoxication. Male Swiss mice received injections of endocannabinoid-related compounds followed by the lowest dose of cocaine that induces seizures, electroencephalographic activity and cell death in the hippocampus. The molecular mechanisms were studied in primary cell culture of this structure. The FAAH inhibitor, URB597, reduced cocaine-induced seizures and epileptiform electroencephalographic activity. The cannabinoid CB1 receptor selective agonist, ACEA, mimicked these effects, whereas the antagonist, AM251, prevented them. URB597 also inhibited cocaine-induced activation and death of hippocampal neurons, both in animals and in primary cell culture. Finally, we investigated if the PI3K/Akt/ERK intracellular pathway, a cell surviving mechanism coupled to CB1 receptor, mediated these neuroprotective effects. Accordingly, URB597 injection increased ERK and Akt phosphorylation in the hippocampus. Moreover, the neuroprotective effect of this compound was reversed by the PI3K inhibitor, LY294002. In conclusion, the pharmacological facilitation of the anandamide/CB1/PI3K signaling protects the brain against cocaine intoxication in experimental models. This strategy may be further explored in the development of treatments for drug-induced neurotoxicity.

Neuroinflammation as a possible link between cannabinoids and addiction.

OBJECTIVE: Substance dependence disorder is a chronically relapsing condition characterised by neurobiological changes leading to loss of control in restricting a substance intake, compulsion and withdrawal syndrome. In the past few years, (endo)cannabinoids have been raised as a possible target in the aetiology of drug addiction. On the other hand, although the exact mechanisms of the genesis of addiction remain poorly understood, it is possible that neuroinflammation might also play a role in the pathophysiology of this condition. Studies demonstrated that (endo)cannabinoids act as immunomodulators by inhibiting cytokines production and microglial cell activation. Thus, in the present review, we explore the possible role of neuroinflammation on the therapeutic effects of cannabinoids on drug addiction. METHODS: We conducted an evidence-based review of the literature in order to assess the role of cannabinoids on the neuroinflammatory hypothesis of addiction (terms: addiction, cannabinoids and inflammation). We searched PubMed and BioMedCentral databases up to April 2014 with no date restrictions. RESULTS: In all, 165 eligible articles were included in the present review. Existing evidence suggests that disruption in cannabinoid signalling during the drug addiction process leads to microglial activation and neuroinflammation. CONCLUSION: The literature showed that inflammation and changes in endocannabinod signalling occur in drug abuse; however, it remains uncertain whether these changes are causally or coincidentally associated with addiction. Additional studies, therefore, are needed to elucidate the contribution of neuroinflammation on the behavioural and neuroprotective effects of cannabinoids on drug addiction.

The antipsychotic aripiprazole selectively prevents the stimulant and rewarding effects of morphine in mice.

Aripiprazole is an antipsychotic that acts as a partial agonist at dopamine D2 receptors, with a favorable pharmacological profile. Due to its unique mechanism of action, this compound has potential application as a substitutive therapy for drug addiction. Considering that distinct neural systems subserve the addictive and analgesic actions of opioids, we tested the hypothesis that aripiprazole selectively inhibit the abuse-related, but not the antinociceptive, effects of morphine. The drugs were tested in male Swiss mice for their effects on locomotion, conditioned place preference (CPP) and nociception. Morphine (20mg/kg) increased motor activity, whereas aripiprazole (0.1, 1 and 10mg/kg) did not induce any change. This antipsychotic, however, prevented morphine-induced locomotion. In the conditioning box, aripiprazole did not induce either reward or aversion. Yet, it prevented both the acquisition and the expression of morphine-induced CPP. Finally, none of the doses of this antipsychotic interfere with morphine (5mg/kg)-induced antinociception in the tail-flick test. In conclusion, aripiprazole inhibited the abuse-related effects of morphine at doses that do not interfere with basal locomotion, reward or aversion. Also, it did not alter morphine-induced antinociceptive effects. This antipsychotic should be further investigated as a possible substitutive strategy for treating certain aspects of opioid addiction.

Inhibition of endocannabinoid neuronal uptake and hydrolysis as strategies for developing anxiolytic drugs.

The endocannabinoid system comprises the CB1 and CB2 receptors (the targets of the Cannabis sativa compound delta-9-tetrahydrocannabinol), the endogenous ligands (endocannabinoids) arachidonoyl ethanolamide (anandamide) and 2-arachidonoyl glycerol, their synthesizing machinery and membrane transport system, and the hydrolyzing enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), respectively. The endocannabinoids may act on demand to confer protection against aversive stimuli, which suggests that increasing their brain levels may represent an approach for treatment of anxiety-related disorders. Thus, this article reviews the profile of endocannabinoid reuptake and hydrolysis inhibitors in experimental tests predictive of anxiolytic activity. The FAAH inhibitors and the blockers of anandamide transport, in contrast to direct CB1 receptor agonists, induce anxiolytic effects at doses that do not interfere with motor activity. MAGL inhibitors also reduce anxiety-like behavior, although they are more likely to impair motor activity. Regarding their mechanisms, increasing anandamide levels induce responses mediated by the CB1 receptor and occluded by the transient receptor potential vanilloid type-1 channels, whereas the effects of increasing 2-arachidonoyl glycerol depend on both CB1 and CB2 receptors. Their neuroanatomical targets include various structures related to anxiety and fear responses. Understanding the pharmacological properties of FAAH and MAGL inhibitors may contribute toward the development of new anxiolytic interventions based on the endocannabinoid system.

Animal models for predicting the efficacy and side effects of antipsychotic drugs.

The use of antipsychotic drugs represents an important approach for the treatment of schizophrenia. However, their efficacy is limited to certain symptoms of this disorder, and they induce serious side effects. As a result, there is a strong demand for the development of new drugs, which depends on reliable animal models for pharmacological characterization. The present review discusses the face, construct, and predictive validity of classical animal models for studying the efficacy and side effects of compounds for the treatment of schizophrenia. These models are based on the properties of antipsychotics to impair the conditioned avoidance response and reverse certain behavioral changes induced by psychotomimetic drugs, such as stereotypies, hyperlocomotion, and deficit in prepulse inhibition of the startle response. Other tests, which are not specific to schizophrenia, may predict drug effects on negative and cognitive symptoms, such as deficits in social interaction and memory impairment. Regarding motor side effects, the catalepsy test predicts the liability of a drug to induce Parkinson-like syndrome, whereas vacuous chewing movements predict the liability to induce dyskinesia after chronic treatment. Despite certain limitations, these models may contribute to the development of more safe and efficacious antipsychotic drugs.

Effects of compounds that interfere with the endocannabinoid system on behaviors predictive of anxiolytic and panicolytic activities in the elevated T-maze.

An extensive literature has implicated the endocannabinoid system in the modulation anxiety-related responses. Nonetheless, it remains uncertain what would be the effects of endocannabinoid-related compounds against responses related to specific subtypes of anxiety disorders, particularly generalized anxiety and panic. In this context, the elevated T maze (ETM) has been developed to evaluate two distinct tasks in the same rat, inhibitory avoidance and escape response from an open arm, predictive of anxiolytic and panicolytic effects, respectively. Thus, the present study tested the hypothesis that drugs that facilitate endocannabinoid-signaling would inhibit both types of aversive responses in this model. As positive controls, diazepam attenuated only inhibitory avoidance (anxiolytic-like effect), whereas alprazolam was effective against both avoidance and escape (anxiolytic- and panicolytic like effects). The synthetic cannabinoid WIN55,212-2 (1.0 mg/kg) promoted an anxiolytic-like effect, which was prevented by pre-treatment with the CB1 receptor antagonist, AM 251 (1.0 mg/kg). At the higher dose (3.0 mg/kg), this antagonist promoted an anxiogenic-like effect. None of these drugs interfered with the escape task. The endocannabinoid (anandamide) hydrolysis inhibitor, URB 597 at doses of 0.3 and 1.0 mg/kg, induced, respectively, panicolytic- and anxiolytic-like effects, which were reversed by pretreatment with AM 251. These results suggest that drugs that act on the endocannabinoid system have different effects on the behaviors assessed in the ETM.

Modeling panic disorder in rodents.

Panic disorder (PD) is a subtype of anxiety disorder in which the core phenomenon is the spontaneous occurrence of panic attacks. Although studies with laboratory animals have been instrumental for the understanding of its neurobiology and treatment, few review articles have focused on the validity of the currently used animal models for studying this psychopathology. Therefore, the aim of the present paper is to discuss the strengths and limits of these models in terms of face, construct and predictive validity. Based on the hypothesis that panic attacks are related to defensive responses elicited by proximal threat, most animal models measure the escape responses induced by specific stimuli. Some apply electrical or chemical stimulation to brain regions proposed to modulate fear and panic responses, such as the dorsal periaqueductal grey or the medial hypothalamus. Other models focus on the behavioural consequences caused by the exposure of rodents to ultrasound or natural predators. Finally, the elevated T-maze associates a one-way escape response from an open arm with panic attacks. Despite some limitations, animal models are essential for a better understanding of the neurobiology and pharmacology of PD and for discovering more effective treatments.

Animal models for predicting the efficacy and side effects of antipsychotic drugs

The use of antipsychotic drugs represents an important approach for the treatment of schizophrenia. However, their efficacy is limited to certain symptoms of this disorder, and they induce serious side effects. As a result, there is a strong demand for the development of new drugs, which depends on reliable animal models for pharmacological characterization. The present review discusses the face, construct, and predictive validity of classical animal models for studying the efficacy and side effects of compounds for the treatment of schizophrenia. These models are based on the properties of antipsychotics to impair the conditioned avoidance response and reverse certain behavioral changes induced by psychotomimetic drugs, such as stereotypies, hyperlocomotion, and deficit in prepulse inhibition of the startle response. Other tests, which are not specific to schizophrenia, may predict drug effects on negative and cognitive symptoms, such as deficits in social interaction and memory impairment. Regarding motor side effects, the catalepsy test predicts the liability of a drug to induce Parkinson-like syndrome, whereas vacuous chewing movements predict the liability to induce dyskinesia after chronic treatment. Despite certain limitations, these models may contribute to the development of more safe and efficacious antipsychotic drugs.