Program & Abstract Book - EPFL Latsis Symposium 2009

EPFL Latsis Symposium 2009: Understanding Violence
P-10
64
February 11-13 2009
th e vicious c i r c l e t o w a r D s v i o l e n c e :
fo c u s o n t h e n e g a t i v e f e e D b a c k
m e c h a n i s m s o f b r a i n s e r o t o n i n
n e u r o t r a n s m i s s i o n.
de Boer, Sietse F. 1 ; Caramaschi, Doretta 1 ; Natarajan, Deepa
1 ; Koolhaas, Jaap M. 1
1 Department of Behavioral Physiology, University of
Groningen,The Netherlands.
Individuals differ widely in their propensity for violence during social conflict.
While some individuals escalate aggression, others control their aggression
or refrain from fighting. Our research on feral (wild-derived)
rodents shows that offensive aggression is strongly related to coping with
other challenges. Highly aggressive individuals adopt a proactive coping
style, whereas low levels of aggression indicate a more passive or reactive
style of coping. These divergent stress coping styles have now been
identified in a range of species and can be considered important personality
trait-like characteristics determining the individual adaptive capacity
and hence vulnerability to stress-related pathologies, including mood
and personality disorders characterized by outbursts of intense aggression
and violence. Recent experiments show that violent characteristics
can be engendered in proactively- but not reactively- coping individuals
by permitting them repeatedly to dominate conspecifics during daily resident-intruder
contests. Clearly, these high-aggressive phenotypes develop
gradually, over the course of repeated victories, escalated (short-latency,
high-frequency and –intensity attacks), persistent (lack of attack inhibition
by defeat/submission signals from the victim), indiscriminating (attacking
female and anesthetized male intruders) and injurious (enhanced vulnerable-body
region attacks and wounding) forms of offensive aggression.
This re-developed methodological approach highlights the rewarding and
positive reinforcing nature of winning experiences that transform adaptive
aggression into a violent pathological form resembling human aggression
of clinical concern. This animal model allows us to identify the neurochemical
changes that underlie such a transformation. We focus on brain serotonin
(5-HT), as this well-conserved neurotransmitter system is the major
molecular orchestrator of aggression in many species including humans.
Based on the results of an extensive series of experiments, we provide
evidence that excessive serotonergic auto-inhibition leading to reduced
5-HT neurotransmission in several brain structures including frontal cortex
paves the way to violent aggressive outbursts.