Effects of classical and atypical antipsychotic drugs on isolation-induced aggression in male mice

A systematic review of the evidence of clozapine's anti-aggressive effects

Reducing the risk of violent and aggressive behaviour in patients with schizophrenia remains a clinical priority. There is emerging evidence to suggest that the second-generation antipsychotic, clozapine, is effective at reducing this risk in patients with schizophrenia and some evidence to suggest that it may be best in selected patients. We conducted a systematic literature search in March 2011 of all prospective and retrospective studies, which investigated clozapine's anti-aggressive effects in a variety of mental disorders. The review identified six animal studies, four randomized controlled trials, 12 prospective non-controlled studies and 22 retrospective studies, with four case studies. We found considerable evidence in support of clozapine's ability to reduce violent and aggressive behaviour. Clozapine's anti-aggressive effect was most commonly explored in patients with schizophrenia, with less evidence available for other psychiatric disorders, including borderline personality disorder, autistic spectrum disorders, post-traumatic stress disorder, bipolar disorder and learning disability. There was mixed evidence to address the question of whether or not clozapine was any more effective than other antipsychotics. In the case of schizophrenia, there was evidence to suggest that clozapine's anti-aggressive effect was more marked particularly in those with treatment-resistant illness. Its anti-aggressive effects appeared to be 'specific', being to some extent greater than both its more general antipsychotic and sedative effects. There were significant methodological inconsistencies in the studies we identified, particularly surrounding patient recruitment criteria, the definition and measurement of violence and the lack of randomized, controlled trials. Data on therapeutic monitoring were also limited. Clozapine can reduce violence and persistent aggression in patients with schizophrenia and other psychiatric disorders. It may offer an advantage over other antipsychotics, although perhaps exclusively in the case of traditionally defined 'treatment resistance' or more broadly defined 'complex cases' with co-morbidity. Larger, randomized, blinded, controlled studies with robust characterization of participants, and standardized measures of violence and aggression are, however, needed to fully understand this link and explore the possible mechanisms.

Effects of raclopride on aggression and stress in diversely selected chicken lines

Genetic selection for chickens of high (HGPS) and low (LGPS) group productivity and survivability, resulted in two distinct genetic lines characterized by differences in cannibalism, flightiness, and immunocompetence. Additionally, birds exhibited differences in behaviour and social stress coping strategy. HGPS birds have a superior stress coping strategy compared with birds of LGPS or Dekalb XL (DXL), a commercial strain. Line differences in stress response and behaviour could be due to selection-induced differences in expression of the dopaminergic system. The dopamine (D2) receptor, an integral part of the dopaminergic system, was hypothesized to be a key contributory factor of the stress response. We tested this hypothesis by injecting either a D2 antagonist (raclopride) or saline in the dominant individual in pair-housed birds for 10 days and examining stress coping ability. Results showed that dominant birds of all strains showed a reduced frequency of aggressive pecks on subordinates following raclopride injection. In contrast, subordinates paired with raclopride-injected birds increased pecking frequency. Two days after stopping injections, LGPS and DXL birds returned to pre-injection levels of aggressive threats, while HGPS birds maintained depressed frequency of threats. Strain differences in aggressive responsiveness coincided with increased epinephrine levels in raclopride treated LGPS birds relative to control LGPS birds, but not by HGPS and DXL birds. Our findings suggest a functional linkage between the genetic basis of stress coping ability and the dopamine regulation of aggressive responsiveness. The data further indicate that the sympathetic-adreno-medullary axis is directly involved in regulating both stress coping strategy and aggressiveness.

Behavioral alterations induced in rats by a pre- and postnatal exposure to 2,4-dichlorophenoxyacetic acid

The purpose of this study was to determine whether the behavioral development pattern was altered by a pre- and postnatal exposure to 2,4-Dichlorophenoxyacetic acid (2,4-D). Pregnant rats were daily orally exposed to 70 mg/kg/day of 2,4-D from gestation day (GD) 16 to postnatal day (PND) 23. After weaning, the pups were assigned to one of the two subgroups: T1 (fed with untreated diet until PND 90) and T2 (maintained with 2,4-D diet until PND 90). Effects on offsprings were evaluated with a neurotoxicological test battery. Neuromotor reflexes, spontaneous motor activity, serotonin syndrome, circling, and catalepsy were analyzed during various postnatal ages. 2,4-D neonatal exposure induced delay of the ontogeny of righting reflex and negative geotaxis accompanied by motor abnormalities, stereotypic behaviors (excessive grooming and vertical head movements), and hyperactivity in the open field. Adult rats of both sexes (T2 group) showed a diminution of ambulation and rearing, while excessive grooming responses were only observed in T2 males. Besides, these animals manifested serotonin syndrome behaviors, catalepsy, and right-turning preference. Some behaviors were reversible, but others were permanent, and some were only expressed after pharmacological challenges.

Effects of risperidone and SCH 23390 on isolation-induced aggression in male mice

In this study, the antiaggressive effects of risperidone and SCH 23390 have been explored. Using the paradigm of isolation-induced aggression, 150 albino male mice of the OF1 strain were allocated to control and experimental groups which received three doses of risperidone (0.01, 0.05 and 0.1 mg/kg) or two doses of SCH 23390 (0.05 and 0.1 mg/kg). Only the highest doses of risperidone decreased threat and attack behaviours but all doses significantly impaired motor behaviour. SCH 23390 decreased attack with the two doses used and also produced significant increases in immobility. Although both antipsychotics are antiaggressive, this action seems to be more specific in the case of risperidone. Finally, both drugs failed to affect animals with short attack latency, being antiaggressive only in subjects with long attack latency, which suggests that these two types of animals are different in their dopamine and serotonin neurotransmission.

Interaction studies of 5-HT1A receptor antagonists and selective 5-HT reuptake inhibitors in isolated aggressive mice

Recently published studies have suggested that behavioral and neurochemical changes induced by selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitors are potentiated by coadministration of a 5-HT1A receptor antagonist. The potentiating effect is hypothesized to be due to antagonism of somatodendritic 5-HT1A autoreceptors. In the present study the effects of concomitant administration of a selective 5-HT reuptake inhibitor with a 5-HT1A receptor antagonist (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl] ethyl]-N-(2-pyridinyl) cyclo-hexanecarboxamide (WAY 100635) or a beta-adrenoceptor and 5-HT1A/1B receptor antagonist (pindolol or (-)-penbutolol) were studied in isolated aggressive mice. WAY 100635 was inactive, but high doses of WAY 100635 produced a marked anti-aggressive effect when combined with a non-effective dose of citalopram or paroxetine. Low doses of pindolol, but not (-)-penbutolol, produced a minor but significant anti-aggressive effect in combination with citalopram or paroxetine. High doses of pindolol or (-)-penbutolol inhibited aggressive behavior, an effect which was reversed by citalopram or paroxetine. The beta-adrenoceptor antagonist, metoprolol, but not the alpha1-adrenoceptor antagonist, prazosin, facilitated the anti aggressive effect of citalopram. The significance of these findings is discussed relative to the above hypothesis.

The antiaggressive potency of (-)-penbutolol involves both 5-HT1A and 5-HT1B receptors and beta-adrenoceptors

The relative importance of 5-HT1A and beta-adrenergic activities in the antiaggressive effects of (-)-penbutolol was studied in male mice. (-)-Penbutolol had high affinity for 5-HT1A receptors and beta-adrenoceptors, and antagonized the 5-methoxy-N,N-dimethyltryptamine (5-MeODMT)-induced 5-HT syndrome and the 8-hydroxy-2-(di-n-propylamin)tetralin (8-OH-DPAT)-induced discriminatory stimulus in rats. (-)-Penbutolol abolished aggressive behaviour (ED50 = 56 mumol/kg), and reversed the antiaggressive effects of 8-OH-DPAT and 1-(3-trifluoromethylphenyl)piperazine (TFMPP) (ED50 = 8.1 and 2.1 mumol/kg, respectively). (N-[2-[4-(2-Methoxyphenyl)-1-piperazinyl]ethyl-N-(2-pyridinyl) cyclohexanecarboxamide (WAY 100635) reversed the antiaggressive effects of 8-OH-DPAT (ED50 = 0.012 mumol/kg), but did not affect the antiaggressive effects of TFMPP. The antiaggressive effect of a submaximal dose of 8-OH-DPAT was markedly potentiated by beta-adrenoceptor antagonists without 5-HT1A receptor affinity, whereas (-)-penbutolol was effective at only one dose (4.5 mumol/kg). In conclusion, the 5-HT1A receptor antagonistic potency of (-)-penbutolol in aggressive mice is attenuated by beta-adrenoceptor-induced facilitation of serotonergic neurotransmission.

Isolation-induced aggression in mice: effects of 5-hydroxytryptamine uptake inhibitors and involvement of postsynaptic 5-HT1A receptors

The inhibitory potencies of selective serotonin (5-hydroxytryptamine, 5-HT) uptake inhibitors on isolation-induced aggressive behaviour in male mice were studied. Furthermore, the role of postsynaptic 5-HT1A receptors in the mediation of aggressive behaviour was studied. The selective 5-HT uptake inhibitors, sertraline, floxetine, femoxetine and fluvoxamine, showed weak antiaggressive effects, and citalopram and paroxetine were ineffective. This rank of potencies corresponded with neither uptake inhibitory potencies in vitro nor potentiation of 1-5-hydroxytryptophan (1,5-HTP)-induced motor effects in vivo, as citalopram and paroxetine were among the most potent compounds in these tests. A subeffective dose of 1,5-HTP (110 mumol/kg = 25 mg/kg, s.c.) potentiated the antiaggressive effect of citalopram and paroxetine more than 110 and 1600 times, respectively. The effects of sertraline, fluvoxamine, fluoxetine and femoxetine were only potentiated 3, 36, 4 and 16 times, respectively. The 5-HT releasing compound fenfluramine inhibited the aggressive behaviour dose dependently, and depletion of 5-HT by treatment with p-chloro-phenylalanine methyl ester attenuated this effect significantly. p-Chloro-phenylalanine methyl ester was ineffective itself, but potentiated the antiaggressive effect of the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamin)tetralin (8-OH-DPAT). The beta-adrenoceptor/5-HT1A receptor antagonist, (-)-penbutolol, reversed the antiaggressive effects of 8-OHDPAT. In conclusion, selective 5-HT uptake inhibitors act in different ways on isolation-induced aggressive behaviour, and postsynaptic 5-HT1A receptors are involved in mediating the aggressive behaviour.

Prenatal exposure to cocaine: effects on aggression in Sprague-Dawley rats

Social/aggressive behavior in adult rat offspring (beginning at postnatal Day 180) prenatally exposed to saline, cocaine, or amfonelic acid (AFA) was examined. Pregnant rats received injections of 15 mg/kg of cocaine, or 0.9% saline twice daily, s.c., or on 2 consecutive days at 4-day intervals, or 1.5 mg/kg amfonelic acid daily throughout gestational Days 1-20. Frequency, duration, and latency of 11 social/aggressive behaviors were recorded for two 15-min sessions during which a smaller male intruder replaced an ovariectomized female in the resident's home cage. Subjects received a s.c. saline injection before Session 1 and 2.0 mg/kg of gepirone, a 5HT1a partial agonist, prior to Session 2. Prenatal cocaine treatment resulted in alterations of aggressive behavior. Aggressive behavior was reduced by gepirone in all groups but to a lesser extent in the AFA group.

Neurobiological mechanisms controlling aggression: preclinical developments for pharmacotherapeutic interventions

Current pharmacotherapeutic approaches to the management of violent and aggressive behavior rely mostly on agents that act as receptor agonists or antagonists at subtypes of brain dopaminergic, GABAergic, and serotonergic receptors. Ethological experimental studies in animals have shown that drugs may modulate aggression by inhibiting motor activity, by distorting aggression-provoking or -inhibiting signals, by fragmenting behavioral sequences or temporal patterning, or by increasing the rate and intensity of aggressive acts. Evidence from animal studies points to large changes in selected brain dopamine, serotonin, and GABA systems during and following aggressive and defensive behavior. However, the specificity of drugs that are currently used to control aggressive behavior through their action as agonists or antagonists at subtypes of dopamine, serotonin or GABA receptors continues to be of concern. Similar to the effects of widely used traditional neuroleptics that nonselectively antagonize dopamine receptors, the range of behaviors which is suppressed by either D1 or D2 receptor antagonists is pervasive. At present, systemic administration of dopamine receptor antagonists in animal preparations does not target aggression-specific mechanisms. The GABAA/Benzodiazepine/Chloride ionophore receptor complex is implicated in the aggression-heightening effects of alcohol and benzodiazepines. Although early reports focused on the "taming" effects of benzodiazepine anxiolytics, low doses may enhance aggression in both animals and humans. Benzodiazepine antagonists block heightened aggression after low doses of alcohol or benzodiazepines. Agonists at certain 5-HT1 receptor subtypes such as eltoprazine are potently effective in reducing aggressive behavior of males and females of various animal species under conditions that promote charging offensive-type aggression, without adversely affecting nonaggressive components of the behavioral repertoire. However, recent reports indicate that eltoprazine and related compounds may potentiate anxiety reactions in rodents, and question the behavioral specificity of these substances. Opioid receptor antagonists modulate primarily physiological and behavioral responses of defense and submission. Defeated animals show tolerance to opiate analgesia and withdrawal responses upon challenge with opioid receptor antagonists. Defensive and submissive vocalizations are potently blocked by opioid peptides. Substances that target specific receptor subtypes at serotonergic, GABAergic and opioidergic synapses are most promising for the selective modification of aggressive, defensive and submissive behavior patterns.

Changes in dopamine, serotonin and their metabolites in discrete brain areas of rat offspring after in utero exposure to cocaine or related drugs

The concentrations of dopamine (DA), serotonin (5HT) and their metabolites were quantified in 5 brain areas of rats exposed to saline, cocaine (15 mg/kg b.i.d.), amitriptyline (10 mg/kg), or amfonelic acid (AFA, 1.5 mg/kg) throughout gestation. Male pups from 3 similarly treated dams were fostered to 2 surrogate dams. The process of breeding and rearing was repeated 4 times with new dams to build the groups to 4-12, since only one pup per litter was used for any one measurement. AFA was used to mimic the dopamine (DA) uptake blockade and stimulant properties of cocaine and amitriptyline was used to mimic the other pharmacological effects of cocaine. At postnatal days (PND) 30, 60, and 180, one pup per litter was removed for HPLC analysis of monoamines. A second pup received 0.3 mg/kg haloperidol, catalepsy assessed after 1 hr, and the brain used for analysis. The cataleptic response to haloperidol was unaffected by any prenatal treatment. The striatum from PND 30 cocaine rats had decreased levels of DA without a decrease in DA metabolites. At PND 60 in cocaine exposed rats, DA and DOPAC concentrations were increased, and 5HT levels were decreased in the striatum. The amitriptyline-exposed group exhibited decreased 5HT and 5-HIAA levels in the striatum. The hypothalamus of the cocaine group had lower levels of 5-HIAA, and other brain areas had a trend for lower levels of 5HT and 5-HIAA. At PND 180, DOPAC was increased in the striatum and prefrontal cortex of the cocaine group. Haloperidol-induced altered monoamine metabolism was unaffected by any prenatal treatment at any age. These data suggest that age-related changes in the DA and 5HT neurotransmission systems occur in rats exposed prenatally to cocaine. However, the ability of the dopaminergic system to respond to a challenge by a DA receptor blocker is unaltered by these in utero treatments.

Effects of two selective dopaminergic antagonists on ethologically-assessed encounters in male mice

1. Although it is accepted that dopaminergic antagonists suppress aggressive behaviour, the drugs used have been relatively non-selective or specific to the D2 receptor. 2. The selective D1 antagonist, SCH 23390, makes it possible to evaluate the impact of this receptor on aggressive behaviour. 3. The effects of SCH 23390 and Spiperone (a D2 antagonist) on the aggressive behaviour of mice were assessed employing a "standard opponent" test. 4. Both drugs markedly decreased aggressive behaviour whilst increasing immobility. However, whilst SCH 23390 increased immobility to a small extent, Spiperone, produced a general decline in active behaviours. 5. It appears that the D1 receptor inhibition of aggression is the more specific.

The role of serotonergic mechanisms in inhibition of isolation-induced aggression in male mice

The role of serotonergic (5-HT) receptor subtypes in mediation of aggressive behaviour in isolated male mice has been studied. Increase of attack latency was used as a simple measure of antiaggressive behaviour. 5-HT1A agonists (BAY R 1531, 8-OHDPAT, flesinoxan, gepirone, 5MeO DMT, buspirone, ipsapirone, BMY 14802) completely inhibit the aggressive behaviour irrespective of their intrinsic activities. Also the putative antagonists spiroxatrine and NAN 190 as well as the non-selective 5-HT1 agonists RU 24969, TFMPP, mCPP and eltoprazine have an antiaggressive effect. The mixed 5-HT1A and beta-adrenoceptor antagonists (-)-alprenolol and pindolol are ineffective and do not inhibit the effect of 8-OHDPAT. Neither does the non-selective 5-HT antagonist metergoline. The antiaggressive effect correlates with 5-HT1A receptor affinity in vitro and with generalization to the 8-OHDPAT-induced discriminative stimulus. The selective 5-HT uptake inhibitor citalopram does not inhibit aggressive behaviour. The 5-HT2 agonist DOI has an antiaggressive effect only at high doses, whereas the 5-HT2 antagonist ritanserin and the 5-HT3 antagonist ondansetron are ineffective. Prazosin (alpha 1-adrenoceptor antagonist), clonidine (alpha 2-adrenoceptor agonist), clenbuterol (beta-adrenoceptor agonist), ketanserin (5-HT2 receptor and alpha 1-adrenoceptor antagonist), clozapine and (-)-octoclothepin (dopamine (DA), 5-HT2 receptor and alpha 1-adrenoceptor antagonist) all show an antiaggressive effect. SCH 23390 (DA D1 receptor antagonist) and emonapride (DA D2 receptor antagonist) are ineffective. In conclusion, 5-HT1A receptors are involved in mediation of isolation-induced aggressive behaviour in mice. The involvement of other 5-HT receptor subtypes needs further clarification. The adrenergic system may also be involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Clozapine: strong antiaggressive effects with minimal motor impairment

Clinical studies have shown clozapine to be effective in the treatment of schizophrenia and associated with an extremely low incidence of extrapiramidal side effects. Diverse studies indicate that clozapine is an atypical neuroleptic with a preferential activity on the mesolimbic structures and a lower affinity for striatal D2 receptors than the classical antipsychotics. The purpose of this study was to assess the behavioral properties of clozapine, especially its effects on aggressive and motor behaviors. Individually housed male mice of the OF1 strain were exposed to anosmic "standard opponents" 30 minutes after the last drug administration. One category of animals received a single IP dose of the compound (0.2, 0.5, 1 or 1.5 mg/kg). Another category received daily doses (0.5, 1 or 1.5 mg/kg) for 21 days. Encounters were videotaped and behavior evaluated using an ethologically based analysis. Clozapine, in the acute treatment condition, produced a significant decrease in "attack" and "threat" behaviors without "immobility" being significantly increased. These results suggest a rather specific antiaggressive action of the compound with little motor impairment. In the chronic administration, no significant change in aggressive behavior was observed which may be attributed to the development of some degree of tolerance.

Muscarinic antagonists attenuate the increase in accumbens and striatum dopamine metabolism produced by clozapine but not by haloperidol

1. The effect of the muscarinic antagonists, scopolamine and atropine, were examined on the increase in extracellular 3,4-dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens and the striatum induced by haloperidol and clozapine by use of in vivo differential pulse voltammetry with carbon fibre electrodes in anaesthetized rats. 2. Animals received saline (1 ml kg-1, s.c.), scopolamine (1 mg kg-1, o.p.) or atropine (20 micrograms, i.c.v.) followed 15 min later by saline (10 microliters, i.c.v.), haloperidol (1 mg kg-1, s.c.) or clozapine (30 mg kg-1, i.p.) and extracellular DOPAC was simultaneously recorded in the nucleus accumbens and the striatum every 5 min for 60 min after drug administration. 3. Scopolamine or atropine alone had no effect on the DOPAC peak height but attenuated the increase in extracellular DOPAC induced by clozapine in both brain regions. Neither scopolamine nor atropine altered the haloperidol-induced increase in accumbens or striatal extracellular DOPAC. 4. The present results demonstrate that muscarinic antagonists attenuate the increase in accumbens and striatal dopamine metabolism in vivo produced by the atypical neuroleptic clozapine but not the haloperidol-induced increase in dopamine metabolism. The results indicate that central muscarinic receptors are involved in the actions on dopaminergic function of clozapine but not haloperidol.

Effects of serotonergic agents on isolation-induced aggression

A series of serotonergic agents were assessed for their ability to antagonize isolation-induced aggression and their activity to disrupt performance in the rotorod motor coordination test. All compounds with 5-HT1A activity [buspirone, gepirone, ipsapirone, tandospirone (SM-3997), 8-OH-DPAT, Wy-48,723, BMY-7378, Wy-47,846] reduced aggression at doses below those which produced debilitation in the rotorod motor coordination test. In addition, the 5-HT3 antagonist zacopride failed to attenuate aggression or produce debilitation at any of the doses tested; however, the 5-HT2 antagonist ritanserin inhibited aggressive behavior at a high dose which was not debilitating. Benzodiazepines (chlordiazepoxide, diazepam and lorazepam), and antidepressant (desipramine) and an antipsychotic (haloperidol) reduced aggressive behavior only at debilitating doses. Activity at the 5-HT1A receptor, and possibly nonsedative anxiolytic activity, appears to be related to antagonism of isolation-induced aggression.