High aggression in rats is associated with elevated stress, anxiety-like behavior, and altered catecholamine content in the brain

Abstract

The social defeat paradigm involves aggressive encounters between Long-Evans (LE) (resident) and Sprague-Dawley (SD) (intruder) rats. Successful application of chronic social defeat stress in SD rats is dependent upon selection of highly aggressive LE rats. Half of the LE rats screened for aggression did not meet the criterion for aggression (LE rats performing a defeat, characterized by the intruder surrendering or acquiring a supine position for at least 3 sec). The observation of the differences in the level of aggression between age and weight matched LE rats was quite compelling which led us to the present study. Herein, we measured behavioral differences between aggressor and non-aggressor LE rats. We analyzed their anxiety-like behavior using open-field and elevated plus maze tests. We also measured aggression/violence-like behavior using two tests. In one, time taken to defeat the intruder SD rat was recorded. In the second test, time taken to attack a novel object was compared between the two groups. We observed a significant increase in anxiety-like behavior in aggressor rats when compared to the non-aggressive group. Furthermore, time taken to defeat the intruder rat and to attack a novel object was significantly lower in aggressive LE rats. Biochemical data suggests that heightened anxiety-like behavior and aggression is associated with increased plasma levels of corticosterones and elevated oxidative stress. Significant alterations in dopamine (DA), norepinephrine (NE) and epinephrine (EPI) were observed within the hippocampus, amygdala and the prefrontal cortex, suggesting potential involvement of dopaminergic and noradrenergic systems in regulation of aggressive behaviors.

Relationship Between Behaviors and Catecholamine Content in Prefrontal Cortex and Hippocampus of Chronically Stressed Rats

“…Significantly decreased concentration of DA and increased concentration of NA were observed in the brain in many pathophysiological conditions. For example, significantly decreased concentration of DA and increased concentration of NA were observed in the prefrontal cortex in aggressive rats [21]. Also, the decreased concentration of DA was observed in many psychiatric and neurological disorders.…”

Mesocorticolimbic dopamine functioning in primary psychopathy: A source of within-group heterogeneity

“…In fact, Clozapine mainly works by improving the tonic stimulation of D1-receptors in the PFC (Ahlenius, 1999), which may normalize D1-to-D2 receptor activation and thereby improve cognitive stability and control of immediate tendencies in primary psychopathy. Similarly, preliminary results in rats showed that high levels of impulsive aggressiveness is associated with lower PFC DA levels (Patki et al, 2015), suggesting that increasing PFC DA levels may improve control of aggressive tendencies. In other words, when given to severely disinhibited psychopaths, Clozapine may bias their mesocortical DA profile towards a more controlled psychopathic profile.…”

Adrenergic and noradrenergic regulation of poultry behavior and production

“…In rodent models, high aggressive individuals exhibit greater anxiety-like behaviors and possess elevated NE and EP concentrations in the prefrontal cortex and amygdala as well as elevated EP in the hippocampus [33]. However, after D2 antagonism in laying hens, birds exhibited reduced aggression and tended to reduce feather pecking.…”

“…Anxiety-related behaviors, including fearful and damaging behaviors have been linked to both aggression and catecholaminergic systems [33]. In rodent models, high aggressive individuals exhibit greater anxiety-like behaviors and possess elevated NE and EP concentrations in the prefrontal cortex and amygdala as well as elevated EP in the hippocampus [33].…”