Antiaggressive and motor effects of haloperidol show different temporal patterns in the development of tolerance

Dopamine D2 receptors act upstream of AVP in the latero-anterior hypothalamus to modulate adolescent anabolic/androgenic steroid-induced aggression in Syrian hamsters

In pubertal male Syrian hamsters, exposure to anabolic/androgenic steroids (AAS) during adolescence facilitates a high level of offensive aggression modulated by the enhanced development and activity of the vasopressin (AVP) and dopamine (DA) neural systems within the latero-anterior hypothalamus (LAH), that is, a brain region implicated in the control of aggression. The present studies provide a detailed report of the pharmacologic interactions between AVP and DA D2 receptor signaling within the LAH in the control of adolescent AAS-induced offensive aggression. Male Syrian hamsters were treated with AAS throughout adolescence and tested for aggression after local infusion of the DA D2 receptor antagonist eticlopride (ETIC) alone, or in combination with AVP in the LAH in an effort to determine the influence of DA D2 receptors relative to AVP-receptor mediated aggression mechanisms. As previously shown, ETIC infusion into the LAH suppressed adolescent AAS-induced aggressive responding; however, the AAS-induced aggressive phenotype was rescued by the coinfusion of AVP into the LAH. These behavioral data indicate that interactions between AVP and DA neural systems within the LAH modulate the control of aggression following adolescent exposure to AAS and that DA D2 receptor signaling functions upstream of AVP in the LAH to control this behavioral response.

Anterior hypothalamic dopamine D2 receptors modulate adolescent anabolic/androgenic steroid-induced offensive aggression in the Syrian hamster

In the Syrian hamster, treatment with anabolic/androgenic steroids (AAS) throughout adolescence increases dopamine and D2 receptor expression in the anterior hypothalamus (AH), a brain region implicated in the control of aggression. D2 receptor antagonists have reduced aggression in various species and animal models. However, these studies used systemic administration of drugs and reported concomitant changes in mobility. These data complicate the question of whether pharmacology targeting D2 receptors is specific to aggression or whether these drugs exert their antiaggressive effects through nonspecific mechanisms. To resolve this discrepancy, the current studies investigate whether administration of the D2 receptor antagonist eticlopride (0.01-10.0 microg in a final volume of 0.5 microl) into the AH modulates AAS-induced aggression. Antagonism of AH D2 receptors effectively suppressed AAS-induced aggression beginning at the 0.1 microg dose, with higher doses producing a floor effect, when compared with AAS-treated animals injected with saline into the AH. Importantly, these reductions in aggressive responding occurred in the absence of changes in locomotor behavior. Our findings identify a neuroanatomical locus where D2 receptor antagonism suppresses adolescent AAS-induced aggression in the absence of alterations to general mobility.

Anti-aggressive effects of GHB in OF.1 strain mice: involvement of dopamine D2 receptors

Numerous studies indicate that gamma-hydroxybutyric acid (GHB) influences the endogenous dopamine system. Both GHB and most dopaminergic D(2) receptor antagonists are effective anti-aggressive agents in animal models. The present study aimed to investigate the effects of GHB on agonistic behaviour and to implicate D(2) dopamine receptor on these behaviours. For this purpose, the effects of GHB (80, 120 and 160 mg/kg, IP) and tiapride (60 mg/kg) administered alone or in combination were examined on agonistic behaviour elicited by 'isolation' in male mice. Individually housed mice were exposed to anosmic "standard opponents" 30 min after drug administration, and the encounters were videotaped and evaluated using an ethologically based analysis. The administration of 80 and 120 mg/kg of GHB reduced threat without impairing motor activity, but the administration of 160 mg/kg of GHB or the co-administration of GHB+tiapride (a selective D(2) receptor antagonist) significantly reduced threat and attack but concomitantly increased immobility. The co-administration of GHB+tiapride had different effects to those observed by the administration of these drugs separately. It is concluded that the anti-aggressive effect of GHB appears to be mediated, at least in part, by D(2) dopamine receptors. This anti-dopaminergic activity is an indirect effect, probably induced by the activation of GHB receptors of low affinity, and in this way, this compound would reduce levels of dopamine without blockading of D(2) postsynaptic dopamine receptors.

The effects of the D1 receptor antagonist SCH-23390 on individual and aggressive behavior in male mice with different experience of aggression

The dopaminergic systems of the brain are known to be involved in the mechanisms of aggression. The present report describes studies of the effects of acute administration of the dopamine D1 receptor antagonist SCH-23390 (0.1 mg/kg, i.p., over 30 min) on the individual and aggressive behavior of male mice of the line C57BL/6J with different experience of aggression. A group of animals with no previous experience of aggression responded to administration of this agent with decreases in direct aggression (attacks), though the total time of hostile behavior, i.e., the sum of the durations of attacks, aggressive grooming, and scattering of foreign litter, showed no change. The agent had no effect on the aggressivity of animals with 20 days of experience of agonistic confrontations. The discussion addresses the possible development of pharmacological densensitization of dopamine D1 receptors in aggressive males in response to prolonged activation of the dopaminergic systems in conditions of repeated experience of aggression, as demonstrated previously.

Increase of tyrosine hydroxylase and dopamine transporter mRNA levels in ventral tegmental area of male mice under influence of repeated aggression experience

Tyrosine hydroxylase (TH) and dopamine transporter (DAT) mRNA levels in the ventral tegmental area (VTA) of midbrain were measured by multiplex RT-PCR in male mice with repeated experience of social victories (winners) and social defeats (losers) in 10 daily agonistic confrontations. Two independent experiments revealed enhanced TH and DAT mRNA levels in VTA of the winners in comparison with the losers and controls (animals after 5 days of individual housing). A positive correlation between DAT and TH mRNA levels was shown.

The decade 1989-1998 in Spanish psychology: an analysis of research in psychobiology

In this paper, we present an analysis of the research published during the 1989-1998 decade by tenured Spanish faculty members from the area of psychobiology. Database search and direct correspondence with the 110 faculty members rendered a list of 904 psychobiological papers. Classification and analysis of these papers led to the definition of at least 70 different research trends. Topics are grouped into several specific research areas: Learning and Memory; Development and Neural Plasticity; Emotion and Stress; Ethology; Neuropsychology; Sensory Processing; and Psychopharmacology. The international dissemination of this research, published in journals of high impact index, and the increasing number of papers are two noteworthy features.

Acute and subchronic effects of pimozide on isolation-induced aggression in male mice

The aim of this study was to examine the effects of pimozide (0.25-1.25 mg/kg), administered acutely or subchronically for 10 days, on agonistic behavior elicited by isolation in male mice. Individually housed mice were exposed to anosmic "standard opponents" 90 min after pimozide injections, and the encounters were videotaped and evaluated using an ethologically based analysis. 3. After acute treatment pimozide did not affect significantly aggression and immobility. However, mice treated subchronically with pimozide (0.75 and 1.25 mg/kg) showed a significant reduction in offensive behaviors (threat and attack) and an increase of immobility (1.25 mg/kg). The antiaggressive and motor actions of pimozide were more marked after subchronic treatment than after acute treatment. It might reflect an accumulation of the drug over time, an effect also described with other neuroleptics such as amisulpride.

Effects of haloperidol on communicative and aggressive behavior in male mice with different experiences of aggression

Effects of two doses of haloperidol (0.1 and 0.4 mg/kg, 30 min and 24 h, IP) on communicative and aggressive behavior in C57BL/6J male mice have been studied. Some of the mice were without prior experience of aggression ("recruits"); the others had been victorious in 20 daily aggressive confrontations ("experienced winners"). Communicative behavior was estimated as the behavioral reaction to a standard tester (loser) in the partition test. Haloperidol in either dose significantly reduced communicative behavior in the "recruits." but not in the "experienced winners." Significantly fewer attacks, less total attacking time, and total time of aggressive behavior (aggressive grooming + attacks) were demonstrated by the "experiences winners," than by the "recruits," while the latency of the first attack, the number, the total and average duration of aggressive grooming events were significantly higher. In the "recruits," haloperidol dose dependently increased the latency and decreased the number of attacks, the total attacking time, and the total time of aggressive behavior 30 min and 24 h after injection. However, haloperidol did not affect the average or total time of aggressive grooming. Neither dose significantly affected any measure of aggressive behavior in the "experienced winners." It has been concluded that repeated aggression experience reduces the pharmacological sensitivity of the dopamine receptors.

Interaction of morphine and haloperidol on agonistic and motor behaviors of male mice

To further clarify the interaction between opioid and dopaminergic systems, the effects of simultaneous administration of morphine hydrochloride (1.25 or 2.5 mg/kg) and haloperidol (0.1 mg/kg) on aggressive behavior of male mice were explored. Isolated male mice (experimental animals) were confronted in a neutral area with anosmic, group-housed consepecifics (standard opponents) 30 min after injection of both compounds, and aggression was evaluated by estimation of times allocated to 11 different behavioral categories. In the first experiment (which functioned as a pilot study), the two doses of morphine were explored. In the second one, incorporating a more complete experimental design, only the lowest morphine dose was used and the animals were preselected by a previous aggression test. In attack behavior, morphine added to haloperidol counteracted, at least partially, the antiaggressive effect of the neuroleptic. In contrast, the impairing effects of haloperidol on motor activity were increased by the addition of morphine. These results show that the behavioral effects of dopaminergic antagonists are modulated by opioid influences and that opiates and dopaminergic agents interact in a different manner on motor and on aggressive behaviors.

Acute and subchronic effects of tiapride on isolation-induced aggression in male mice

Although the antiaggressive properties of several atypical neuroleptics are known, the actions of tiapride (a selective dopaminergic D2-receptor antagonist) on agonistic behavior have not been explored and there are no studies comparing acute and subchronic effects of this compound on aggression in rodents. In this work, the effects of tiapride (20-100 mg/kg, IP), administered acutely or subchronically for 10 days, on agonistic behaviour elicited by isolation in male mice were examined. Individually housed mice were exposed to anosmic "standard opponents" 30 min after drug administration, and the encounters were videotaped and evaluated using an ethologically based analysis. Tiapride decreased time spent in offenssive behaviors significantly, without an impairment of motor activity (60 and 80 mg/kg). Moreover, no tolerance to tiapride antiaggressive activity was observed after repeated administration of the drug. On the contrary, the action on immobility showed a clear tolerance development with repeated injections (100 mg/kg). The divergence found in the temporal course of tolerance to tiapride in its antiaggressive and motor effects is discussed.

Chronic treatment with eltoprazine does not lead to tolerance in its anti-aggressive action, in contrast to haloperidol

The behavioral effects of eltoprazine and haloperidol during a 4 week treatment period were studied in the resident-intruder model of aggression in male rats. Eltoprazine, a serotonergic (5-HT1A/1B) agonist with specific anti-aggressive actions in animals, was compared to haloperidol, a neuroleptic often used to control behavioral disorders. Eltoprazine (1 or 3 mg/kg p.o.) and haloperidol (2 mg/kg p.o.) were given 60 min before a 10 min aggression test. Acutely, eltoprazine reduced aggression, without adversely affecting other behaviors. Eltoprazine (1 or 3 mg/kg p.o.) was subsequently given daily for 4 weeks and aggression tests were performed each week. The anti-aggressive effects of eltoprazine remained stable over the period of 4 weeks whereas exploration was increased. After a wash-out period of 1 week aggression had returned to baseline levels. Acutely given, haloperidol (2 mg/kg p.o.) completely reduced aggression concomitant with massive sedation. Significant tolerance developed to the sedatory actions of haloperidol over the 4 week treatment period. Aggression returned slowly, but remained below baseline values. One week after wash-out a new challenge with haloperidol (2 mg/kg p.o.) revealed significant tolerance. After 2 weeks wash-out aggression had returned to baseline. The data demonstrate persistent and specific anti-aggressive effects after eltoprazine showing no tolerance. In contrast, haloperidol showed tolerance and rebound effects for aggression. The development of tolerance after haloperidol has a different course for sedation than for the anti-aggressive action.

Behavioral profile of raclopride in agonistic encounters between male mice

Raclopride is a substituted benzamide with high selectivity as an antagonist of central dopaminergic D2 receptors and potential antipsychotic effects. In comparison with a classic DA receptor blocking agent like haloperidol, raclopride displays an atypical profile in preclinical tests for extrapyramidal side effects. Antiaggressive properties of raclopride on agonistic behavior have not yet been fully explored. In this work the effects of raclopride (0.1, 0.3, or 0.6 mg/kg) on aggressive and motor behaviors in male mice were studied. Aggression tests were performed 30 min after injections. Encounters were videotaped and behavior was evaluated, measuring the time spent in 11 broad categories of behavior. The results show a clear antiaggressive effect of raclopride, with very little motor impairment and some increase in exploratory behavior. This behavioral profile is very similar to the one observed with other atypical neuroleptics and differs somewhat from that found in the classic compounds.