Operant and classically-conditioned aggressive behavior in Siamese fighting fish

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.

Translational models of adaptive and excessive fighting: an emerging role for neural circuits in pathological aggression

Aggression is a phylogenetically stable behavior, and attacks on conspecifics are observed in most animal species. In this review, we discuss translational models as they relate to pathological forms of offensive aggression and the brain mechanisms that underlie these behaviors. Quantifiable escalations in attack or the development of an atypical sequence of attacks and threats is useful for characterizing abnormal variations in aggression across species. Aggression that serves as a reinforcer can be excessive, and certain schedules of reinforcement that allow aggression rewards also allow for examining brain and behavior during the anticipation of a fight. Ethological attempts to capture and measure offensive aggression point to two prominent hypotheses for the neural basis of violence. First, pathological aggression may be due to an exaggeration of activity in subcortical circuits that mediate adaptive aggressive behaviors as they are triggered by environmental or endogenous cues at vulnerable time points. Indeed, repeated fighting experiences occur with plasticity in brain areas once considered hardwired. Alternatively, a separate "violence network" may converge on aggression circuitry that disinhibits pathological aggression (for example, via disrupted cortical inhibition). Advancing animal models that capture the motivation to commit pathological aggression remains important to fully distinguish the neural architecture of violence as it differs from adaptive competition among conspecifics.

Animal Models of (or for) Aggression Reward, Addiction, and Relapse: Behavior and Circuits

Inappropriate and pathological aggression plays a leading role in the suffering and death of millions of people, and further places an untenable strain on the caregivers and families of those afflicted. In some cases, such as addictive drugs, aggression can be highly rewarding (appetitive) and continually pursued despite short- and long-term negative consequences. Similarly, recidivism (relapse) rates for repeat violent offenders are as high as relapse rates for drug addicts. Appetitive aggression and relapse to aggression seeking can be modeled in mice studies using conditioned place preference and self-administration procedures followed by a period of abstinence and subsequent tests for relapse to aggression preference and aggression seeking. These procedures allow for the study of the mechanisms that control the appetitive versus the consummatory (attack) phases of aggressive behavior. In this review, we first discuss the behavioral procedures developed to probe appetitive aggression in mouse models, spanning from Pavlovian to operant tasks, and we also describe the recently proposed phenomenon of "aggression addiction." Next, we discuss the pharmacological and circuit mechanisms of aggression conditioned place preference and aggression self-administration, seeking, and relapse, highlighting mechanistic congruence and divergence between appetitive and consummatory phases of aggression. We conclude by discussing clinical implications of the studies reviewed.

Resurgence in Siamese fighting fish, Betta splendens

Resurgence of previously reinforced responding was investigated in male Siamese fighting fish (Betta splendens). Swimming through a ring produced 15-s mirror presentations according to, with different fish, either a fixed-ratio 1 or a variable-interval 60-s schedule of reinforcement. When responding was stable, a differential-reinforcement-of-other-behavior schedule was substituted for the mirror-presentation schedule. Following this, mirror presentations were discontinued (extinction). During this latter phase, there were transient increases in the ring-swim response relative to the frequency of such responding during the differential-reinforcement-of-other behavior schedule. Resurgence was similar for the fish exposed previously to the fixed-ratio or to the variable-interval schedule. These results extend to Siamese fighting fish a well-established behavioral phenomenon previously not observed in this species or with this response topography, and only rarely reported following the removal of a non-consumable reinforcer.

Units of analysis and kinetic structure of behavioral repertoires

It is suggested that molar streams of behavior are constructed of various arrangements of three elementary constituents (elicited, evoked, and emitted response classes). An eight-cell taxonomy is elaborated as a framework for analyzing and synthesizing complex behavioral repertoires based on these functional units. It is proposed that the local force binding functional units into a smoothly articulated kinetic sequence arises from temporally arranged relative response probability relationships. Behavioral integration is thought to reflect the joint influence of the organism's hierarchy of relative response probabilities, fluctuating biological states, and the arrangement of environmental and behavioral events in time.