Aggression and aspects of impulsivity in wild‐type rats

Abstract

Aggression is closely related to impulsive behavior both in humans and in animals. To avoid potential negative consequences, aggressive behavior is kept in control by strong inhibitory mechanisms. Failure of these inhibitory mechanisms results in violent behavior. In the present experiments, we investigated whether aggressive behavior is related to impulsive behavior. Furthermore, we investigated if violent behavior can be distinguished from "normal" aggressive behavior in terms of impulsivity levels. We used rats of the wild-type Groningen strain, rats of this strain differ widely in their level of offensive aggression expressed toward an unfamiliar intruder male, ranging from no aggression at all to very high levels of intense and sometimes violent behavior. Violent behavior was displayed by some of the animals that were given repeated winning experience. We used behavioral performance in an unpredictable operant conditioning paradigm for food reinforcement (variable interval 15) and performance in a differential-reinforcement of low rate (DRL-60s) responding as determinants for impulsivity. We predicted that offensive aggression is correlated with behavioral flexibility measured by the VI-15 procedure and that aggressive behavior is characterized by low behavioral inhibition on the DRL task. In addition we expected that violent animals would be characterized by extremely low levels of behavioral inhibition on the DRL task. We showed that the level of offensive aggression indeed positively correlated with VI-15 performance. In addition, we showed that behavioral performance on the DRL procedure is similar in low and high aggressive rats. However, violent animals can be dissociated by a lower efficiency of lever pressing on a DRL-60s schedule of reinforcement.

Adolescent social defeat disturbs adult aggression-related impulsivity in wild-type rats

“…The experience of social defeat during adolescence neither affected the average level of adult aggressive behavior, nor did it change operant conditioning performance on the VI-15 schedule of reinforcement. However, the correlation between adult offensive behavior and VI-15 performance observed in the control group and that is repeatedly found in other experiments (Coppens et al, 2014) was not present in defeated animals.…”

“…However, the highly significant correlation between offensive aggression and VI-15 performance suggests that this indeed reflects aspects of impulsivity, which is consistent with the coping style model. In general, high levels of impulsivity and aggressive behavior are components of a proactive coping style (Cervantes and Delville, 2007;Coppens et al, 2014;David et al, 2004;Koolhaas et al, 1999). Performance in the VI-15 schedule of reinforcement seems to reflect behavioral flexibility as well.…”

“…Rats of the WTG strain show a broad variation in the level of offensive aggressive behavior toward an unfamiliar intruder, ranging from no aggression at all to very high levels of aggressive behavior (De Boer et al, 2003). Furthermore, high-aggressive animals are inefficient in an unpredictable operant conditioning paradigm (variable-interval 15 s) for food reinforcement compared to low-aggressive animals (Coppens et al, 2014). Since the capacity to learn an operant conditioning paradigm is largely independent of age, the performance in a variable interval schedule can be used as an early indicator of individual variation in juveniles and a predictor of adult coping style.…”

“…Coping styles are defined as suits of correlated behaviors that are consistent over time and across situations (Koolhaas et al, 1999). High levels of aggressive behavior and impulsivity are characteristics of a proactive coping style (Coppens et al, 2014). Delville and colleagues suggested that individual differences in aggressive and impulsive behavior may be related to individual variation in prefrontal cortex functioning (Cervantes and Delville, 2007).…”

Putting the “Biology” Back into “Neurobiology”: The Strength of Diversity in Animal Model Systems for Neuroscience Research

“…In a rational approach to increase biological markers through animal models, consider that most rodent models are based on highly inbred rats and mice. These inbred strains do not reflect the full range of behavioral responses of natural populations and therefore almost certainly do not demonstrate the full range of physiological or molecular responses of wild animals (Sgoifo et al, 1996; de Boer et al, 2003; Coppens et al, 2014). It is likely that one reason that models derived from laboratory-raised animals are not well translated into clinical successes is that the human condition is far closer to that of wild animals than to those of inbred rodents that are bred, raised and held under conditions that can only be described as highly deprived with respect to sensory input and behavioral opportunities (Van de Weerd et al, 1997; Kavelaars et al, 1999; van den Berg et al, 1999; de Boer et al, 2003; Meeusen, 2005; Korte et al, 2007; Balcombe, 2010; Blanchard, 2010; MacGillivray et al, 2012; König et al, 2015; Smith et al, 2016).…”