D(3) and D(2) dopamine receptor agonists differentially modulate isolation-induced social-emotional reactivity in mice

Social behavioral profiling by unsupervised deep learning reveals a stimulative effect of dopamine D3 agonists on zebrafish sociality

It has been a major challenge to systematically evaluate and compare how pharmacological perturbations influence social behavioral outcomes. Although some pharmacological agents are known to alter social behavior, precise description and quantification of such effects have proven difficult. We developed a scalable social behavioral assay for zebrafish named ZeChat based on unsupervised deep learning to characterize sociality at high resolution. High-dimensional and dynamic social behavioral phenotypes are automatically classified using this method. By screening a neuroactive compound library, we found that different classes of chemicals evoke distinct patterns of social behavioral fingerprints. By examining these patterns, we discovered that dopamine D3 agonists possess a social stimulative effect on zebrafish. The D3 agonists pramipexole, piribedil, and 7-hydroxy-DPAT-HBr rescued social deficits in a valproic-acid-induced zebrafish autism model. The ZeChat platform provides a promising approach for dissecting the pharmacology of social behavior and discovering novel social-modulatory compounds.

Cariprazine alleviates core behavioral deficits in the prenatal valproic acid exposure model of autism spectrum disorder

RATIONALE

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficits in social communication and interaction and restricted, repetitive behaviors. The unmet medical need in ASD is considerable since there is no approved pharmacotherapy for the treatment of these deficits in social communication, interaction, and behavior. Cariprazine, a dopamine D₃-preferring D₃/D₂ receptor partial agonist, is already approved for the treatment of schizophrenia and bipolar I disorder in adults; investigation in patients with ASD is warranted.

OBJECTIVES

The aim of this study was to investigate the effects of cariprazine, compared with risperidone and aripiprazole, in the rat prenatal valporic acid (VPA) exposure model on behavioral endpoints representing the core and associated symptoms of ASD.

METHODS

To induce the ASD model, time-mated Wistar rat dams were treated with VPA during pregnancy. Male offspring were assigned to groups and studied in a behavioral test battery at different ages, employing social play, open field, social approach-avoidance, and social recognition memory tests. Animals were dosed orally, once a day for 8 days, with test compounds (cariprazine, risperidone, aripiprazole) or vehicle before behavioral assessment.

RESULTS

Cariprazine showed dose-dependent efficacy on all behavioral endpoints. In the social play paradigm, only cariprazine was effective. On the remaining behavioral endpoints, including the reversal of hyperactivity, risperidone and aripiprazole displayed similar efficacy to cariprazine.

CONCLUSIONS

In the present study, cariprazine effectively reversed core behavioral deficits and hyperactivity present in juvenile and young adult autistic-like rats. These findings indicate that cariprazine may be useful in the treatment of ASD symptoms.

Neuronal Dopamine D3 Receptors: Translational Implications for Preclinical Research and CNS Disorders

Dopamine (DA), as one of the major neurotransmitters in the central nervous system (CNS) and periphery, exerts its actions through five types of receptors which belong to two major subfamilies such as D1-like (i.e., D1 and D5 receptors) and D2-like (i.e., D2, D3 and D4) receptors. Dopamine D3 receptor (D3R) was cloned 30 years ago, and its distribution in the CNS and in the periphery, molecular structure, cellular signaling mechanisms have been largely explored. Involvement of D3Rs has been recognized in several CNS functions such as movement control, cognition, learning, reward, emotional regulation and social behavior. D3Rs have become a promising target of drug research and great efforts have been made to obtain high affinity ligands (selective agonists, partial agonists and antagonists) in order to elucidate D3R functions. There has been a strong drive behind the efforts to find drug-like compounds with high affinity and selectivity and various functionality for D3Rs in the hope that they would have potential treatment options in CNS diseases such as schizophrenia, drug abuse, Parkinson’s disease, depression, and restless leg syndrome. In this review, we provide an overview and update of the major aspects of research related to D3Rs: distribution in the CNS and periphery, signaling and molecular properties, the status of ligands available for D3R research (agonists, antagonists and partial agonists), behavioral functions of D3Rs, the role in neural networks, and we provide a summary on how the D3R-related drug research has been translated to human therapy.

Cariprazine alleviates core behavioral deficits in the prenatal valproic acid exposure model of autism spectrum disorder

RATIONALE

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficits in social communication and interaction and restricted, repetitive behaviors. The unmet medical need in ASD is considerable since there is no approved pharmacotherapy for the treatment of these deficits in social communication, interaction, and behavior. Cariprazine, a dopamine D₃-preferring D₃/D₂ receptor partial agonist, is already approved for the treatment of schizophrenia and bipolar I disorder in adults; investigation in patients with ASD is warranted.

OBJECTIVES

The aim of this study was to investigate the effects of cariprazine, compared with risperidone and aripiprazole, in the rat prenatal valporic acid (VPA) exposure model on behavioral endpoints representing the core and associated symptoms of ASD.

METHODS

To induce the ASD model, time-mated Wistar rat dams were treated with VPA during pregnancy. Male offspring were assigned to groups and studied in a behavioral test battery at different ages, employing social play, open field, social approach-avoidance, and social recognition memory tests. Animals were dosed orally, once a day for 8 days, with test compounds (cariprazine, risperidone, aripiprazole) or vehicle before behavioral assessment.

RESULTS

Cariprazine showed dose-dependent efficacy on all behavioral endpoints. In the social play paradigm, only cariprazine was effective. On the remaining behavioral endpoints, including the reversal of hyperactivity, risperidone and aripiprazole displayed similar efficacy to cariprazine.

CONCLUSIONS

In the present study, cariprazine effectively reversed core behavioral deficits and hyperactivity present in juvenile and young adult autistic-like rats. These findings indicate that cariprazine may be useful in the treatment of ASD symptoms.

Role of purinergic P2X4 receptors in regulating striatal dopamine homeostasis and dependent behaviors

Purinergic P2X4 receptors (P2X4Rs) belong to the P2X superfamily of ion channels regulated by ATP. We recently demonstrated that P2X4R knockout (KO) mice exhibited deficits in sensorimotor gating, social interaction, and ethanol drinking behavior. Dopamine (DA) dysfunction may underlie these behavioral changes, but there is no direct evidence for P2X4Rs' role in DA neurotransmission. To test this hypothesis, we measured markers of DA function and dependent behaviors in P2X4R KO mice. P2X4R KO mice exhibited altered density of pre-synaptic markers including tyrosine hydroxylase, dopamine transporter; post-synaptic markers including dopamine receptors and phosphorylation of downstream targets including dopamine and cyclic-AMP regulated phosphoprotein of 32 kDa and cyclic-AMP-response element binding protein in different parts of the striatum. Ivermectin, an allosteric modulator of P2X4Rs, significantly affected dopamine and cyclic AMP regulated phosphoprotein of 32 kDa and extracellular regulated kinase1/2 phosphorylation in the striatum. Sensorimotor gating deficits in P2X4R KO mice were rescued by DA antagonists. Using the 6-hydroxydopamine model of DA depletion, P2X4R KO mice exhibited an attenuated levodopa (L-DOPA)-induced motor behavior, whereas ivermectin enhanced this behavior. Collectively, these findings identified an important role for P2X4Rs in maintaining DA homeostasis and illustrate how this association is important for CNS functions including motor control and sensorimotor gating. We propose that P2X4 receptors (P2X4Rs) regulate dopamine (DA) homeostasis and associated behaviors. Pre-synaptic and post-synaptic DA markers were significantly altered in the dorsal and ventral striatum of P2X4R KO mice, implicating altered DA neurotransmission. Sensorimotor gating deficits in P2X4R KO mice were rescued by DA antagonists. Ivermectin (IVM), a positive modulator of P2X4Rs, enhanced levodopa (L-DOPA)-induced motor behavior. These studies highlight potential interactions between P2X4Rs and DA system.

Cortical Excitability and Agressive Behavior in Post-Traumatic Stress Disorder

INTRODUCTION

Hyperarousal and alertness play an important role in the clinical presentation of Post-traumatic stress disorder (PTSD). Strenuous effort has been made to shed light on the mechanisms that cause these symptoms of patients. Based on the claim that there is a relationship between some subtypes of hyperarousal symptoms and aggression in patients with PTSD, we aimed to examine the relationship between electrophysiological measurements that was measured through transcranial magnetic stimulation (TMS) and aggression scale scores of PTSD patients in this study.

METHODS

The study included 37 patients with a diagnosis of PTSD according to DSM-IV criteria and 25 healthy volunteers. Electrophysiological measurements of participants were made with TMS. The Buss Perry Aggression Questionnaires was administered to patients and control group.

RESULTS

In the patient group, a positive correlation was found between scores of aggression and arousal symptoms. Motor excitability threshold, one of TMS measurements, which is a sign of cortical excitability, was significantly lower in the patient group than the control group. There was a negative correlation between aggression scale scores and the parameters of motor excitability threshold and cortical silent period which both shows cortical excitability of the patients.

CONCLUSION

We concluded that there was an increase in cortical excitability in PTSD patients and we suggest that this increase might be associated with hyperarousal symptoms and aggressive behavior.

A discrete dopaminergic projection from the incertohypothalamic A13 cell group to the dorsolateral periaqueductal gray in rat

Several findings have indicated an involvement of dopamine in panic and defensive behaviors. The dorsolateral column of the periaqueductal gray (dlPAG) is crucially involved in the expression of panic attacks in humans and defensive behaviors, also referred to as panic-like behaviors, in animals. Although the dlPAG is known to receive a specific innervation of dopaminergic fibers and abundantly expresses dopamine receptors, the origin of this dopaminergic input is largely unknown. This study aimed at mapping the dopaminergic projections to the dlPAG in order to provide further insight into the panic-like related behavior circuitry of the dlPAG. For this purpose, the retrograde tracer cholera toxin subunit b (CTb) was injected into the dlPAG of male Wistar rats and double immunofluorescence for CTb and tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of dopamine, was performed. Neurons labeled for both CTb and TH were counted in different dopaminergic cell groups. The findings indicate that the dopaminergic nerve terminals present in the dlPAG originate from multiple dopamine-containing cell groups in the hypothalamus and mesencephalon. Interestingly, the A13 cell group is the main source of dopaminergic afferents to the dlPAG and contains at least 45% of the total number of CTb/TH-positive neurons. Anterograde tracing with biotinylated dextran amine (BDA) combined with double immunofluorescence for BDA and TH confirmed the projections from the A13 cell group to the dlPAG. The remainder of the dopamine-positive terminals present in the dlPAG was found to originate from the extended A10 cell group and the A11 group. The A13 cell group is known to send dopaminergic efferents to several other brain regions implicated in defensive behavior, including the central amygdala and ventromedial hypothalamus. Therefore, although direct behavioral evidence is lacking, our finding that the A13 cell group is also the main source of dopaminergic input to the dlPAG suggests that dopamine might contribute to the regulation of dlPAG-mediated defensive behaviors.

The effect of SV 293, a D2 dopamine receptor-selective antagonist, on D2 receptor-mediated GIRK channel activation and adenylyl cyclase inhibition

SV 293 [1-([5-methoxy-1H-indol-3-yl]methyl)-4-(4-[methylthio]​phenyl)piperidin-4-ol] binds with 100-fold higher affinity to human D2 receptors compared to the human D3 and D4 dopamine receptor subtypes. We investigated the intrinsic efficacy of this compound at the D2 dopamine receptor subtype using both: (1) a forskolin-dependent adenylyl cyclase inhibition assay and (2) an electrophysiological assay for evaluating coupling to G-protein-coupled inwardly rectifying potassium channels. In both assays SV 293 was found to be a neutral antagonist capable of blocking the effects of the full D2-like receptor agonist quinpirole. Based upon these results we propose that SV 293 is a useful pharmacological tool that can be used for both in vitro and in vivo studies to investigate the role of D2-like dopamine receptor subtypes in neurological, neuropsychiatric and movement disorders where dopaminergic pathways have been implicated.

The role of dopamine D(3) receptors in antipsychotic activity and cognitive functions

Dopamine D(3) receptors have a pre- and postsynaptic localization in brain stem nuclei, limbic parts of the striatum, and cortex. Their widespread influence on dopamine release, on dopaminergic function, and on several other neurotransmitters makes them attractive targets for therapeutic intervention. The signaling pathways of D(3) receptors are distinct from those of other members of the D(2)-like receptor family. There is increasing evidence that D(3) receptors can form heteromers with dopamine D(1), D(2), and probably other G-protein-coupled receptors. The functional consequences remain to be characterized in more detail but might open new interesting pharmacological insight and opportunities. In terms of behavioral function, D(3) receptors are involved in cognitive, social, and motor functions, as well as in filtering and sensitization processes. Although the role of D(3) receptor blockade for alleviating positive symptoms is still unsettled, selective D(3) receptor antagonism has therapeutic features for schizophrenia and beyond as demonstrated by several animal models: improved cognitive function, emotional processing, executive function, flexibility, and social behavior. D(3) receptor antagonism seems to contribute to atypicality of clinically used antipsychotics by reducing extrapyramidal motor symptoms; has no direct influence on prolactin release; and does not cause anhedonia, weight gain, or metabolic dysfunctions. Unfortunately, clinical data with new, selective D(3) antagonists are still incomplete; their cognitive effects have only been communicated in part. In vitro, virtually all clinically used antipsychotics are not D(2)-selective but also have affinity for D(3) receptors. The exact D(3) receptor occupancies achieved in patients, particularly in cortical areas, are largely unknown, mainly because only nonselective or agonist PET tracers are currently available. It is unlikely that a degree of D(3) receptor antagonism optimal for antipsychotic and cognitive function can be achieved with existing antipsychotics. Therefore, selective D(3) antagonism represents a promising mechanism still to be fully exploited for the treatment of schizophrenia, cognitive deficits in schizophrenia, and comorbid conditions such as substance abuse.

Disruption of social approach by MK-801, amphetamine, and fluoxetine in adolescent C57BL/6J mice

Autism is a severe neurodevelopmental disorder, diagnosed on the basis of core behavioral symptoms. Although the mechanistic basis for the disorder is not yet known, genetic analyses have suggested a role for abnormal excitatory/inhibitory signaling systems in brain, including dysregulation of glutamatergic neurotransmission. In mice, the constitutive knockdown of NMDA receptors leads to social deficits, repetitive behavior, and self-injurious responses that reflect aspects of the autism clinical profile. However, social phenotypes differ with age: mice with reduced NMDA-receptor function exhibit hypersociability in adolescence, but markedly deficient sociability in adulthood. The present studies determined whether acute disruption of NMDA neurotransmission leads to exaggerated social approach, similar to that observed with constitutive disruption, in adolescent C57BL/6J mice. The effects of MK-801, an NMDA receptor antagonist, were compared with amphetamine, a dopamine agonist, and fluoxetine, a selective serotonin reuptake inhibitor, on performance in a three-chamber choice task. Results showed that acute treatment with MK-801 led to social approach deficits at doses without effects on entry numbers. Amphetamine also decreased social preference, but increased number of entries at every dose. Fluoxetine (10 mg/kg) had selective effects on social novelty preference. Withdrawal from a chronic ethanol regimen decreased activity, but did not attenuate sociability. Low doses of MK-801 and amphetamine were also evaluated in a marble-burying assay for repetitive behavior. MK-801, at a dose that did not disrupt sociability or alter entries, led to a profound reduction in marble-burying. Overall, these findings demonstrate that moderate alteration of NMDA, dopamine, or serotonin function can attenuate social preference in wild type mice.

Differential effects of dopamine receptor D1-type and D2-type antagonists and phase of the estrous cycle on social learning of food preferences, feeding, and social interactions in mice

The neurobiological bases of social learning, by which an animal can 'exploit the expertise of others' and avoid the disadvantages of individual learning, are only partially understood. We examined the involvement of the dopaminergic system in social learning by administering a dopamine D1-type receptor antagonist, SCH23390 (0.01, 0.05, and 0.1 mg/kg), or a D2-type receptor antagonist, raclopride (0.1, 0.3, and 0.6 mg/kg), to adult female mice prior to socially learning a food preference. We found that while SCH23390 dose-dependently inhibited social learning without affecting feeding behavior or the ability of mice to discriminate between differently flavored diets, raclopride had the opposite effects, inhibiting feeding but leaving social learning unaffected. We showed that food odor, alone or in a social context, was insufficient to induce a food preference, proving the specifically social nature of this paradigm. The estrous cycle also affected social learning, with mice in proestrus expressing the socially acquired food preference longer than estrous and diestrous mice. This suggests gonadal hormone involvement, which is consistent with known estrogenic regulation of female social behavior and estrogen receptor involvement in social learning. Furthermore, a detailed ethological analysis of the social interactions during which social learning occurs showed raclopride- and estrous phase-induced changes in agonistic behavior, which were not directly related to effects on social learning. Overall, these results suggest a differential involvement of the D1-type and D2-type receptors in the regulation of social learning, feeding, and agonistic behaviors that are likely mediated by different underlying states.

Evaluation of the D3 dopamine receptor selective agonist/partial agonist PG01042 on L-dopa dependent animal involuntary movements in rats

The substituted 4-phenylpiperazine D3 dopamine receptor selective antagonist PG01037 ((E)-N-(4-(4-(2,3-dichlorophenyl)piperazin-1-yl)but-2-enyl)-4-(pyridin-2-yl)benzamide) was reported to attenuate L-dopa-associated abnormal involuntary movements (AIMs) in unilaterally lesioned rats, a model of L-dopa-dependent dyskinesia in patients with Parkinson's Disease (Kumar et al., 2009a). We now report that PG01042 (N-(4-(4-(2,3-dichlorophenyl)piperazin-1-yl)butyl)-4-(pyridin-3-yl)benzamide), which is a D3 dopamine receptor selective agonist for adenylyl cyclase inhibition and a partial agonist for mitogenesis, is also capable of attenuating AIMs scores. The intrinsic activity of PG01037 and PG01042 were determined using a) a forskolin-dependent adenylyl cyclase inhibition assay and b) an assay for agonist-associated mitogenesis. It was observed that the in vivo efficacy of PG01042 increased when administered by intraperitoneal (i.p.) injection simultaneously with L-dopa/benserazide (8 mg/kg each), as compared to a 60 min or 30 min pretreatment. PG01042 was found to attenuate AIM scores in these animals in a dose dependent manner. While PG01042 did not effectively inhibit SKF 81297-dependent AIMs, it inhibited apomorphine-dependent AIM scores. Rotarod studies indicate that PG01042 at a dose of 10 mg/kg did not adversely affect motor coordination of the unilaterally lesioned rats. Evaluation of lesioned rats using a cylinder test behavioral paradigm indicated that PG01042 did not dramatically attenuate the beneficial effects of L-dopa. These studies and previously published studies suggest that both D3 dopamine receptor selective antagonists, partial agonists and agonists, as defined by an adenylyl cyclase inhibition assay and a mitogenic assay, are pharmacotherapeutic candidates for the treatment of L-dopa-associated dyskinesia in patients with Parkinson's Disease.

Synthesis and characterization of selective dopamine D2 receptor antagonists. 2. Azaindole, benzofuran, and benzothiophene analogs of L-741,626

A series of indole, 7-azaindole, benzofuran, and benzothiophene compounds have been prepared and evaluated for affinity at D2-like dopamine receptors. These compounds share structural elements with the classical D2-like dopamine receptor antagonists haloperidol, N-methylspiperone and benperidol. Two new compounds, 4-(4-iodophenyl)-1-((4-methoxy-1H-indol-3-yl)methyl)piperidin-4-ol (6) and 4-(4-iodophenyl)-1-((5-methoxy-1H-indol-3-yl)methyl)piperidin-4-ol (7), were found to have high affinity to and selectivity for D2 versus D3 receptors. Changing the aromatic ring system from an indole to other heteroaromatic ring systems reduced the D2 binding affinity and the D2 versus D3 selectivity.

Dopamine D3 receptor selective ligands with varying intrinsic efficacies at adenylyl cyclase inhibition and mitogenic signaling pathways

A panel of structurally related substituted 4-phenylpiperazines with nanomolar affinity and selectivity at D3 dopamine receptors has been synthesized. Compounds in which a heterocyclic (2-phenyl pyridyl, 3-phenyl pyridyl, benzothiophene, or benzofuran) moiety is adjacent to the amide was varied and/or a double bond (trans-butenyl) replaced the four-carbon aliphatic chain linking the arylamide with the 4-phenylpiperazine moiety were compared for (a) affinity at human D2 and D3 dopamine receptors, (b) intrinsic efficacy using an adenylyl cyclase inhibition assay, and (c) intrinsic efficacy using a mitogenic assay. All 16 compounds were (a) more efficacious for the D3 receptor cyclase inhibition assay than for the D3 receptor mitogenic assay and (b) exhibited the same or greater efficacy at D3 compared to D2 receptor (with the exception of one compound). Although the heterocyclic amide moiety appears to be the pivotal structural element determining the intrinsic efficacy of our D3 receptor selective compounds, the magnitude of the efficacy is modulated by the (a) substituent(s) on the phenyl piperazine and (b) the saturation of the four-carbon chain that links the arylamide and the phenylpiperazine. In addition, our ligands are functionally selective, because they can have differing intrinsic efficacies for the cyclase inhibition and the mitogenic activation signaling pathways. Compounds that are essentially full agonists at the cyclase assay appear to be only partial agonists in the mitogenic assay and compounds that are partial agonists in our cyclase assay are partial agonists or antagonists in the mitogenic assay.

Pharmacotherapy for aggressive behaviours in persons with intellectual disabilities: treatment or mistreatment?

BACKGROUND

Antipsychotic medications have been used extensively to treat aggressive behaviours in persons with intellectual disabilities (ID) when the main psychiatric diagnoses given to them in the past were schizophrenia, childhood psychoses and ID with behaviour problems. Today, antipsychotics are still estimated to comprise 30-50% of all the psychotropics prescribed for persons with ID, although the prevalence of psychotic disorders is only 3% in this population. The overuse of antipsychotics in persons with ID could be justified if their aggressive behaviours were associated with mostly psychotic disorders and not other psychiatric disorders or factors and if the anti-aggressive properties of the antipsychotics have been supported by basic research or reviews of clinical studies. Is that so? This article explores these questions.

METHODS

The literature on aggressive behaviours, their associations with psychiatric disorders and other contributing factors and the past and current treatment options for aggressive behaviours in persons with and without ID was reviewed. Also, the literature on basic research regarding the brain receptors implicated in aggressive behaviours and the basic research and clinical studies on the anti-aggressive properties of antipsychotics was reviewed.

RESULTS

Aggressive behaviours in persons with ID serve different functions and many factors contribute to their initiation, maintenance and exacerbations or attenuation including most of the psychiatric and personality disorders. Genetic disorders, early victimisation, non-enriched and restrictive environments during childhood or later on and traumatic brain injury, which are common in persons with ID, have been associated with aggressive behaviours and with mostly non-psychotic disorders in persons with and without ID. If the factors above and the knowledge derived from studies of domestic violence and premeditated aggression in persons without ID are considered and applied during the evaluation of the most severe aggressive behaviours in persons with ID, more appropriate and effective treatment than antipsychotics can be implemented. Basic research implicates mostly the GABA and the serotonin pre-post synaptic brain receptors influence the initiation, modulation or inhibition of aggression in animals. The anti-aggressive properties of the antipsychotics have not been supported by reviews of clinical studies and basic research is absent. Antipsychotics are the indicated treatment only for psychiatric disorders and for aggressive behaviours associated with psychotic disorders and psychotic features as activation of dopamine receptor leads to defensive aggression.

CONCLUSIONS

Most of the persons with ID and aggressive behaviours do not have a diagnosis of psychotic disorder and there is lack of strong evidence supporting the anti-aggressive properties of the antipsychotics. The overuse of antipsychotics in this population may be explained by the old, faulty notion that aggressive behaviour in persons with ID is mostly associated with psychotic disorders. Given the discrediting of this notion, the use of antipsychotics in persons with ID may, in some cases, be considered mistreatment rather than proper treatment. In order to reverse the practice of over-prescribing antipsychotics for aggressive behaviours in persons with ID, basic research information on aggression must be disseminated, the search for the 'quick fix' must be abandoned and the promotion of antipsychotics as anti-aggressive drugs must be discouraged. Matching the treatment with the variables contributing to the aggressive behaviours, seeking a long-term rather than a short-term solution and avoiding the promotion of only one type of treatment for all types of aggression might change the current practice and improve the quality of life for many persons with ID.

Differences in aggressive behavior and in the mesocorticolimbic DA system between A/J and BALB/cJ mice

The neurotransmitters DA and serotonin are known to be important modulators of aggression, but endogenous differences in these systems between aggressive and nonaggressive animals are poorly understood. To examine this issue, the mesocorticolimbic DA and serotonin systems of two mouse strains that differ in aggressive behavior, BALB/cJ and A/J, were analyzed using high performance liquid chromatography and quantitative receptor autoradiography. Significant differences in both serotonergic and dopaminergic systems were found between aggressive and nonaggressive mice. The nonaggressive A/J mice exhibited higher DA utilization in the nucleus accumbens and prefrontal cortex, higher D1 receptor expression in the rostral pole of the accumbens, and lower D2 receptor expression throughout the accumbens, as compared with aggressive BALB/cJ mice. Although correlative in nature, these data suggest that differences in mesocorticolimbic DA and serotonin systems may contribute to endogenous differences in aggression.

Detection of social approach in inbred mice

An experiment was designed to automatically assess the relative level of social interaction during encounters involving trios of inbred mice consisting of two familiar cage mate males plus an unfamiliar third male. The automation of the spatial positioning was obtained by using a video-tracking program. In addition social behaviours were manually scored. To evaluate the influence of basic motor properties on the evaluation of the level of social interaction, we analysed two strains (C57BL/6J and 129S2/Sv) that are frequently employed in transgenic research, and show very different levels of motor activity. Correlations between manual and automated parameters showed that spatial parameters correctly fitted the level of social interaction between mice. In both strains C57BL/6J and 129S2/Sv, a proximity parameter (duration of bouts during which two individuals were close to each other) defined the social approach and correctly assessed the discrimination of social novelty.

Using the MATRICS to guide development of a preclinical cognitive test battery for research in schizophrenia

Cognitive deficits in schizophrenia are among the core symptoms of the disease, correlate with functional outcome, and are not well treated with current antipsychotic therapies. In order to bring together academic, industrial, and governmental bodies to address this great 'unmet therapeutic need', the NIMH sponsored the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) initiative. Through careful factor analysis and consensus of expert opinion, MATRICS identified seven domains of cognition that are deficient in schizophrenia (attention/vigilance, working memory, reasoning and problem solving, processing speed, visual learning and memory, verbal learning and memory, and social cognition) and recommended a specific neuropsychological test battery to probe these domains. In order to move the field forward and outline an approach for translational research, there is a need for a "preclinical MATRICS" to develop a rodent test battery that is appropriate for drug development. In this review, we outline such an approach and review current rodent tasks that target these seven domains of cognition. The rodent tasks are discussed in terms of their validity for probing each cognitive domain as well as a brief overview of the pharmacology and manipulations relevant to schizophrenia for each task.

Repeated risperidone administration during puberty prevents the generation of the aggressive phenotype in a developmentally immature animal model of escalated aggression

Risperidone has been shown to be clinically effective for the treatment of aggressive behavior in children, yet until recently no information was available regarding whether risperidone exhibits aggression-specific suppression in preclinical studies employing validated developmentally immature animal models of escalated aggression. Recently, using a pharmacologic animal model of escalated offensive aggression, we reported that acute risperidone treatment selectively and dose-dependently reduces the expression of the adult aggressive phenotype, with a significant reduction in aggressive responses observed at 0.1 mg/kg, i.e., a dose within the range administered to children and adolescents in the clinical setting. This study examined whether repeated exposure to risperidone during puberty would prevent the generation of the highly escalated aggressive phenotype in this animal model. To test this hypothesis, the aggression-eliciting stimulus (i.e., cocaine hydrochloride, 0.5 mg/kg/dayx28 days) was co-administered with an aggression-suppressing dose of risperidone (i.e., 0.1 mg/kg/day) during different time frames of puberty and for varied lengths of time (i.e., 1-4 weeks), and then animals were scored for targeted measures of offensive aggression during late puberty. Risperidone administration prevented the generation of the adult aggressive phenotype, with a complete blockade of matured offensive responses (i.e., lateral attacks and flank/rump bites) seen only after prolonged periods of exposure to risperidone (i.e., 3-4 weeks). The selective prevention of these aggressive responses, while leaving other measures of aggression intact (e.g., upright offensive postures), suggest that risperidone is acting in a highly discriminatory anti-aggressive fashion, targeting neurobehavioral elements important for the mature aggressive response pattern.

Risperidone exerts potent anti-aggressive effects in a developmentally immature animal model of escalated aggression

BACKGROUND

Risperidone has been shown to be clinically effective for the treatment of aggressive behavior in children, yet no information is available regarding whether risperidone exhibits aggression-specific suppression in preclinical studies that use validated developmentally immature animal models of escalated aggression. Previously, we have shown that exposure to low doses of the psychostimulant cocaine-hydrochloride (.5 mg/kg intraperitoneally) during the majority of pubertal development (postnatal days [P]27-57) generates animals that exhibit a high level of offensive aggression. This study examined whether risperidone exerts selective aggression-suppressing effects by using this pharmacologic animal model of highly escalated offensive aggression.

METHODS

Experimental hamsters were tested for offensive aggression after the acute administration of risperidone (.05-1.0 mg/kg, intraperitoneally).

RESULTS

Risperidone dose-dependently reduced the highly aggressive phenotype, with a significant reduction observed at .1-.2 mg/kg for most aggressive responses measured. Experimental animals treated with higher doses of risperidone (.3-1.0 mg/kg) showed significant reductions in aggression and social interest toward intruders, indicating more general behavioral inhibition.

CONCLUSIONS

These studies provide evidence that risperidone exerts specific aggression-suppressing effects in a developmentally immature animal model of escalated aggression.

Prenatal cocaine alters dopamine and sigma receptor binding in nucleus accumbens and striatum in dams and adolescent offspring

Maternal cocaine abuse is a societal problem with serious impact on both mother and child. Few studies exist that study the mother/offspring dyad of neurological effects of maternal cocaine abuse. The present study was designed to study alterations in D2, D3 and sigma receptor density in nucleus accumbens and striatum of dams and male and female offspring following gestational cocaine. Long-Evans female rats were implanted with an intravenous (i.v.) access port prior to breeding and were administered saline or 3.0 mg/kg of cocaine from gestational day (GD) GD8-20 (1 injection/day-GD8-14, 2 injections/day-GD15-20). Offspring were raised by maternal dams and allowed to mature until postnatal days 31-35, at which time dams and offspring were sacrificed for assay of radioligand binding. In dams, decreased D2 (24.6%) and D3 (36.9%) binding was observed in striatum. Female offspring displayed no differences in receptor binding in either region. Male offspring displayed decreased D2 receptor binding (27.1%) in nucleus accumbens and increased D3 (75.2% and 33.5%) and sigma receptor binding (73.4% and 53.1%) in accumbens and striatum, respectively. Collectively, these data clearly demonstrate that male offspring exhibit significant alterations in D2, D3 and sigma receptor binding. These results suggest that dams and offspring display long-lasting alterations (5 weeks) in dopamine receptor binding. These alterations in dopamine and sigma receptor binding in offspring following prenatal cocaine and rearing by maternal dams are sex specific and could have profound effects on the development of behavior.

Synthesis and characterization of selective dopamine D2 receptor antagonists

A series of indole compounds have been prepared and evaluated for affinity at D2-like dopamine receptors using stably transfected HEK cells expressing human D2, D3, or D4 dopamine receptors. These compounds share structural elements with the classical D2-like dopamine receptor antagonists, haloperidol, N-methylspiperone, and benperidol. The compounds that share structural elements with N-methylspiperone and benperidol bind non-selectively to the D2 and D3 dopamine receptor subtypes. However, several of the compounds structurally similar to haloperidol were found to (a) bind to the human D2 receptor subtype with nanomolar affinity, (b) be 10- to 100-fold selective for the human D2 receptor compared to the human D3 receptor, and (c) bind with low affinity to the human D4 dopamine receptor subtype. Binding at sigma (sigma) receptor subtypes, sigma1 and sigma2, were also examined and it was found that the position of the methoxy group on the indole was pivotal in both (a) D2 versus D3 receptor selectivity and (b) affinity at sigma1 receptors. Adenylyl cyclase studies indicate that our indole compounds with the greatest D2 receptor selectivity are neutral antagonists at human D2 dopamine receptor subtypes. With stably transfected HEK cells expressing human D2 (hD2-HEK), these compounds (a) have no intrinsic activity and (b) attenuated quinpirole inhibition of adenylyl cyclase. The D2 receptor selective compounds that have been identified represent unique pharmacological tools that have potential for use in studies on the relative contribution of the D2 dopamine receptor subtypes in physiological and behavioral situations where D2-like dopaminergic receptor involvement is indicated.

S32504, a Novel Naphtoxazine Agonist at Dopamine D3/D2 Receptors: III. Actions in Models of Potential Antidepressive and Anxiolytic Activity in Comparison with Ropinirole

In forced-swim tests in mice and rats, the novel D(3)/D(2) receptor agonist S32504 [(+)-trans-3,4,4a,5,6,10b-hexahydro-9-carbamoyl-4-propyl-2H-naphth[1,2-b]-1,4-oxazine] dose-dependently (0.04-2.5 mg/kg) and stereospecifically suppressed immobility compared with its enantiomer S32601 [(-)-trans-3,4,4a,5,6,10b-hexahydro-9-carbamoyl-4-propyl-2H-naphth-[1,2-b]-1,4-oxazine]. Ropinirole was less potent than S32504 in this procedure, and it was likewise less potent than S32504 (0.04-2.5 mg/kg) in attenuating motor-suppressant properties of the alpha(2)-adrenoceptor agonist S18616 [(S)-spiro[(1-oxa-2-amino-3-azacyclopent-2-ene)-4,2'-(1',2',3',4'-tetrahydronaphthalene)]]. In a learned helplessness paradigm, S32504 (0.08-2.5 mg/kg) suppressed escape failures. Furthermore, in a chronic mild stress model of anhedonia, S32504 (0.16-2.5 mg/kg) rapidly restored the suppression of sucrose consumption. S32504 inhibited marble-burying behavior in mice (0.04-0.16 mg/kg) and aggressive behavior in isolated mice (0.04-2.5 mg/kg): only higher doses of ropinirole mimicked these actions of S32504. In tests of anxiolytic activity, S32504 was more potent (0.0025-0.16 mg/kg) than ropinirole in suppressing fear-induced ultrasonic vocalizations, and S32601 was inactive. Furthermore, in contrast to ropinirole, S32504 modestly enhanced punished responses in a Vogel conflict procedure and increased open-arm entries in a plus-maze. At doses active in the above-described procedures, S32504 did not elicit hyperlocomotion. In the forced-swim, marble-burying, and ultrasonic vocalization models, actions of S32504 were blocked by the D(2)/D(3) antagonists haloperidol and raclopride and by the D(2) antagonist L741,626 [4-(4-chlorophenyl)-1-(1H-indol-3-ylmethyl)piperidin-4-ol], but not by the D(3) receptor antagonist S33084 [(3aR,9bS)-N-[4-(8-cyano-1,3a,4,9b-tetrahydro-3H-benzopyrano[3,4-c]pyrrole-2-yl)-butyl]-(4-phenyl)benzamide. Finally, chronic administration of S32504 did not, in contrast to venlafaxine, modify corticolimbic levels of serotonin(2A) receptors or brain-derived neurotrophic factor. In conclusion, S32504 displays a broad and distinctive profile of activity in models of potential antidepressive and anxiolytic properties. Its actions are more pronounced than those of ropinirole and principally involve engagement of D(2) receptors.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

The Vogel conflict test: procedural aspects, gamma-aminobutyric acid, glutamate and monoamines

A multitude of mechanisms are involved in the control of emotion and in the response to stress. These incorporate mediators/targets as diverse as gamma-aminobutyric acid (GABA), excitatory amino acids, monoamines, hormones, neurotrophins and various neuropeptides. Behavioural models are indispensable for characterization of the neuronal substrates underlying their implication in the etiology of anxiety, and of their potential therapeutic pertinence to its management. Of considerable significance in this regard are conflict paradigms in which the influence of drugs upon conditioned (trained) behaviours is examined. For example, the Vogel conflict test, which was introduced some 30 years ago, measures the ability of drugs to release the drinking behaviour of water-deprived rats exposed to a mild aversive stimulus ("punishment"). This model, of which numerous procedural variants are discussed herein, has been widely used in the evaluation of potential anxiolytic agents. In particular, it has been exploited in the characterization of drugs interacting with GABAergic, glutamatergic and monoaminergic networks, the actions of which in the Vogel conflict test are summarized in this article. More recently, the effects of drugs acting at neuropeptide receptors have been examined with this model. It is concluded that the Vogel conflict test is of considerable utility for rapid exploration of the actions of anxiolytic (and anxiogenic) drugs. Indeed, in view of its clinical relevance, broader exploitation of the Vogel conflict test in the identification of novel classes of anxiolytic agents, and in the determination of their mechanisms of action, would prove instructive.

Influence of aging and social isolation on changes in brain monoamine turnover and biosynthesis of rats elicited by novelty stress

Aging is a risk factor of human depression. Middle-aged or older men are vulnerable to adverse life events and an absence of social contact and easily become depressed. In the present study, we investigated the influence of aging on responses to life events in socially isolated conditions. We applied isolation-rearing (4 W) to two age groups, older (18 M) and younger (11 W), of male F344 rats that had been reared in a group and then examined responses to novelty stress (20 min). Changes in brain monoamines and their metabolites such as dopamine (DA), serotonin (5-HT), dihydroxyphenylacetic acid (DOPAC), homovanilic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were measured in six regions: the prefrontal cortex, nucleus accumbens, hippocampus, amygdala, midbrain, and raphe nuclei. MANOVA was carried out for rearing condition, age, and novelty stress. Isolation significantly changed monoamines and their metabolites, except in amygdala and raphe nuclei. Aging significantly altered them in all regions, although novelty stress did not. In the amygdala and midbrain, isolation significantly changed monoamine biosynthesis, with monoamine turnover remaining unchanged. In the prefrontal cortex and nucleus accumbens, aging significantly altered turnover, while biosynthesis remained unchanged. Novelty stress significantly varied only the turnover in the prefrontal cortex. The interaction between isolation and aging indicated that aging influences changes in turnover and biosynthesis elicited by isolation primarily at the center of the mesolymbic DA system, the midbrain, and in raphe nuclei of the 5-HT system. In peripheral regions of the mesolymbic system, aging primarily affects changes in turnover induced by isolation.