Ethopharmacology of aggression: impact on autonomic and mesocorticolimbic activity

To fight or not to fight: activation of the mPFC during decision to engage in aggressive behavior after ethanol consumption in a novel murine model

RATIONALE

Alcohol consumption is a common antecedent of aggressive behavior. The effects of alcohol on the decision to engage in aggression in preference over pro-social interaction are hypothesized to arise from augmented function within the medial prefrontal cortex (mPFC).

OBJECTIVE

In a newly developed procedure, we studied social decision-making in male C57BL/6 J mice based on preferentially seeking access to either sociosexual interactions with a female partner or the opportunity to attack an intruder male. While deciding to engage in aggressive vs. sociosexual behavior, corresponding neural activation was assessed via c-Fos immunoreactivity in cortical, amygdaloid and tegmental regions of interest. A further objective was to investigate how self-administered alcohol impacted social choice.

METHODS

During repeated confrontations with an intruder male in their home cage, experimental mice engaged in species-specific sequence of pursuit, threat, and attack behavior within < 2 min. Mice were then conditioned to respond at one of two separate illuminated operanda in an experimental chamber (octagon) attached to their home cage; completion of 10 responses (fixed ratio 10; FR10) was reinforced by access to either a female or a male intruder which were presented in the resident's home cage. Brains were harvested following choice between the concurrently available aggressive and sociosexual options and processed for c-Fos immunoreactivity across 10 brain regions. In two separate groups, mice were trained to rapidly self-administer ethanol prior to a social choice trial in order to examine the effects of alcohol on social choice, sociosexual, aggressive acts and postures, and concurrent c-Fos activity in the mPFC and limbic regions.

RESULTS AND DISCUSSION

Eight out of 65 mice consistently chose to engage in aggressive behavior in preference to sociosexual contact with a female when each outcome was concurrently available. Self-administered alcohol (experiment 1: 1.2 ± 0.02 g/kg; experiment 2: 0, 1.0, 1.5, and 1.8 g/kg) increased responding for the aggressive option in mice that previously opted predominantly for access to sociosexual interactions with the female. When choosing the aggressive, but not the sociosexual option, the prelimbic area of the mPFC revealed increased c-Fos activity, guiding future detailed inquiry into the neural mechanisms for aggressive choice.

Children’s Vocal Properties as Mobilizers of Stress-Related Physiological Responses in Adults

We measured the ways that women with varying degrees of perceived power respond physiologically to children’s elevated vocal pitch (F0 : fundamental frequency), a social dependence/immaturity cue. Listeners believed either that they would provide instructions or make judgments about the children they heard. As predicted, women with low perceived power in caregiving relationships (i.e., who attributed greater power to children than to self) were highly reactive to children’s pitch properties—in particular, when they anticipated providing instructions. When expecting to provide instructions to children with higher F0 voices, women with low perceived power showed elevations in cortisol levels and heart rate (consistent with defensive mobilization for threat). In all other pairings of women and children, cortisol and heart rate levels held relatively constant or declined. In addition, women with low perceived power showed better recall of messages from children with higher F0 voices than lower F0 voices. Implications are drawn for interaction patterns that foster caregiving stress and conflict.

D1-like dopamine receptor density in nuclei involved in social behavior correlates with song in a context-dependent fashion in male European starlings

Research in songbirds shows that singing behavior is regulated by both brain areas involved in vocal behavior as well as those involved in social behavior. Interestingly, the precise role of these regions in song can vary as a function of the social, environmental and breeding context. To date, little is known about the neurotransmitters underlying such context-dependent regulation of song. Dopamine (DA) modulates highly motivated, goal-directed behaviors (including sexually motivated song) and emerging data implicate DA in the context-dependent regulation of singing behavior. This study was performed to begin to examine whether differences in DA receptors may underlie, in part, context-dependent differences in song production. We used autoradiographic procedures to label D1-like and D2-like DA receptors to examine the relationship between DA receptor density and singing behavior in multiple contexts in male European starlings (Sturnus vulgaris). Within a breeding context (when testosterone (T) was high), D1-like receptor density in the medial preoptic nucleus (POM) and midbrain central gray (GCt) negatively correlated with song used to attract a female. Additionally in this context, D1-like receptor density in POM, GCt, medial bed nucleus of the stria terminalis (BSTm), and lateral septum (LS) negatively correlated with song likely used to defend a nest box. In contrast, in a non-breeding context (when T was low), D1-like receptor density in POM and LS positively correlated with song used to maintain social flocks. No relationships were identified between song in any context and D2-like receptor densities. Differences in the brain regions and directional relationships between D1-like receptor binding and song suggest that dopaminergic systems play a region and context-specific role in song. These data also suggest that individual variation in singing behavior may, in part, be explained by individual differences in D1-like receptor density in brain regions implicated in social behavior.

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.

Effect of environmental stressors on opiate and psychostimulant reinforcement, reinstatement and discrimination in rats: a review

Studies in humans suggest that exposure to life stressors is correlated with compulsive drug abuse and relapse to drugs during periods of abstinence. The behavioral and neurobiological mechanisms involved in the effect of stress on drug abuse, however, are not known. Here, we review data from studies using preclinical models in rats on the effect of environmental stressors on opiate and psychostimulant reinforcement, as measured by the intravenous drug self-administration and conditioned place preference procedures, on relapse to these drugs, as measured by the reinstatement procedure, and on the subjective effects of these drugs, as measured by the drug discrimination procedure. The results of the studies reviewed here suggest that while stressors are important modulators of the behavioral effects of opiate and psychostimulant drugs, the effect of stress on behavior in these animal models is stressor-specific, and to some degree, procedure- and drug-class-specific. The review of studies on the neurobiological mechanisms underlying stress-drug interactions in these animal models indicate that central noradrenaline and extrahypothalamic corticotropin-releasing factor mediate the effect of one form of stress (intermittent footshock) on reinstatement of opiate and psychostimulant seeking after prolonged drug-free periods. At present, however, little is known about the neuronal events that mediate the effect of environmental stressors on opiate and psychostimulant reinforcement or discrimination. The broader implications of the data reviewed here for future research and for the treatment of opiate and psychostimulant addiction are briefly discussed.

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.

Ethanol modulates evoked dopamine release in mouse nucleus accumbens: dependence on social stress and dose

Ethanol may modulate the activity of presynaptic terminals to increase extracellular dopamine release in the nucleus accumbens though conflicting results have been published. It has been suggested that the stress of social defeat might be a factor influencing the effects of ethanol. We investigated the effects of ethanol on the evoked dopamine overflow in the nucleus accumbens in anaesthetised mice by in vivo voltammetry. Dominant animals, subordinates which had been defeated following eight intruder-resident encounters, and subordinate nondefeated mice were used. The overflow was evoked by electrical stimulation of the median forebrain bundle (100 pulses) at low (20 Hz) and high (50 Hz) frequencies of stimulation. Ethanol at 0.1 and 2 g/kg had no effects on evoked dopamine overflow in aggressive and nondefeated mice. Ethanol increased dopamine release at 0.1 g/kg and decreased release at 2 g/kg following high frequency stimulation in defeated mice. These data suggest that the stress of social defeat may have sensitised the machinery involved in dopamine release to ethanol, a process that may increase the reinforcing properties of this compound.

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.

Recurrent aggressive episodes entrain ultradian heart rate and core temperature rhythms

The present study was designed to investigate the effects of recurrent aggressive episodes on the synchrony of autonomic circadian and ultradian rhythms. Eight aggressive male rats were entrained to a reverse 12 h:12 h light-dark cycle and then implanted with telemetry senders to continuously monitor heart rate (HR) and core temperature (Tc). The amplitude and the time of the peak (acrophase) for each of the circadian and ultradian oscillations were quantified by nonlinear, least-squares, multioscillator cosinor analysis that included the first four harmonics of the circadian rhythm. After recovery from surgery, the 3- and 5-cycle/day ultradian rhythms of HR and Tc were the prominent ultradian components that were synchronized to the light-dark cycle. First, the resident males confronted a male intruder daily at lights-off (0800 hours) for a period of 3 weeks. Second, after a 3-week recovery period, 15 daily aggressive confrontations were scheduled, with the intruders being introduced at 1200 hours. During the course of the confrontations the amplitude of 3- and 5-cycle/day oscillations in HR and Tc decreased, whereas the hemicircadian (2 cycles/day) rhythm amplitude doubled with minor changes of the circadian amplitude. The hemicircadian acrophase coincided with the time of the confrontation most clearly, and this alignment lasted for more than 1 week after the last social confrontation, even in the absence of a reminder. We interpret the synchronization of the hemicircadian acrophases to the time point of social confrontations as anticipating the physiological demands of the aggressive encounters.