Developmental predictors of an impulsive-aggressive phenotype

The Serotonergic Control of Play Fighting in Male Juvenile Hamsters: Opposite Effects of 5-HT1A and 5-HT3 Receptor Manipulations

In male hamsters, puberty is associated with increased serotonin innervation and unusual responses to fluoxetine, such as enhanced play-fighting activity against intruders but also an acceleration of its maturation from attacks focused on the face (frontal attacks) to the lower belly and rump, suggesting a role for serotonin (5-HT). We tested the role of 5-HT1A and 5-HT3 receptor subtypes on play-fighting behavior observed during resident intruder tests through peripheral treatment with receptor agonists and antagonists. Contrary to observations in adult hamsters, we did not observe any overarching effects of treatment on measures of play-fighting activity, nor its maturation from frontal attacks. However, secondary analyses highlighted variability within the datasets. A subgroup of animals presented inhibited play-fighting activity in response to treatment with DPAT, a 5-HT1A receptor agonist, but these animals also showed enhanced locomotor activity and reduced interest in engaging their opponents. In addition, early juvenile agonistic behavior was predictive of responsiveness to other treatments. The 5-HT1A receptor antagonist, WAY, caused a reduction in play-fighting activity in high attackers and an increase in low attackers. Though high attackers under pretest conditions were equally inhibited by CBG, a 5-HT3 receptor agonist, they performed a higher proportion of frontal attacks. Finally, the density of 5-HT1A and 5-HT3 receptor immunoreactivity was compared among subjects sampled at postnatal Day 35 (early puberty) or postnatal Day 70 (adulthood) within areas mediating the control of social behavior in adults. Adult males showed a higher density of immunolabeling for 5-HT1A receptors in the anterior hypothalamus and medial amygdala, as well as 5-HT3 receptors in the lateral septum. The data suggest that the development of 5-HT receptor expression participates in the control of play-fighting activity and its maturation during puberty in male hamsters.

Nuance and behavioral cogency: How the Visible Burrow System inspired the Stress-Alternatives Model and conceptualization of the continuum of anxiety

By creating the Visible Burrow System (VBS) Bob Blanchard found a way to study the interaction of genetics, physiology, environment, and adaptive significance in a model with broad validity. The VBS changed the way we think about anxiety and affective disorders by allowing the mechanisms which control them to be observed in a dynamic setting. Critically, Blanchard used the VBS and other models to show how behavioral systems like defense are dependent upon context and behavioral elements unique to the individual. Inspired by the VBS, we developed a Stress Alternatives Model (SAM) to further explore the multifaceted dynamics of the stress response with a dichotomous choice condition. Like the VBS, the SAM is a naturalistic model built upon risk assessment and defensive behavior, but with a choice of response: escape or submission to a large conspecific aggressor. The anxiety of novelty during the first escape must be weighed against fear of the aggressor, and a decision must be made. Both outcomes are adaptively significant, evidenced by a 50/50 split in outcome across several study systems. By manipulating the variables of the SAM, we show that a gradient of anxiety exists that spans the contextual settings of escaping an open field, escaping from aggression, and submitting to aggression. These findings correspond with increasing levels of corticosterone and increasing levels of NPS and BDNF in the central amygdala as the context changes.Whereas some anxiolytics were able to reduce the latency to escape for some animals, only with the potent anxiolytic drug antalarmin (CRF1R-blocker) and the anxiogenic drug yohimbine (α2 antagonist) were we able to reverse the outcome for a substantial proportion of individuals. Our findings promote a novel method for modeling anxiety, offering a distinction between low-and-high levels, and accounting for individual variability. The translational value of the VBS is immeasurable, and it guided us and many other researchers to seek potential clinical solutions through a deeper understanding of regional neurochemistry and gene expression in concert with an ecological behavioral model.