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Early environmental insult, neuronal plasticity, and aggression
Organizer: Craig Ferris
University of Massachusetts Medical Center, Worcester, MA

The symposium will focus on the neurobiological and behavioral consequences of early environmental insult.  Data from animal studies in each of the talks support the notion that inappropriate, excessive aggressive behavior in adulthood may represent the developmental consequence of early insult.  The symposium examines the deleterious effects of physical and emotional abuse, voluntary ethanol ingestion, cocaine and anabolic steroid exposure, and lead toxicity.  Data will be presented from developmental studies comparing the aggressive behavior in siblings reared under control and stressful conditions. In each presentation, these behavioral changes are correlated with changes in endocrinology, neurochemistry and neuroanatomy that contribute to the normal regulation of agonistic behavior. 




Vasopressin/serotonin model of inappropriate aggression following adolescent abuse
Craig Ferris, R. H. Melloni Jr., and Yvon Delville
(University of Massachusetts Medical Center, Worcester, MA)
Can the stress of emotional and physical insult, i.e., threat and attack, during adolescence affect the development of the AVP and 5-HT systems and alter normal aggressive behavior in early adulthood? Adolescent male golden hamsters were weaned at postnatal day 25, and stressed for two weeks by daily, one-hour bouts of threat and attack by adult hamsters. Male littermates were run in a parallel stress study using daily one-hour trials of isolation in a novel environment.  Animals with a history of abuse show exaggerated attack behavior toward smaller males as compared to littermates with a history of isolation stress. Conversely, when confronted by males of equal size, animals with a history of abuse show diminished aggression and increased submission as compared to control littermates.  The density of AVP fibers and neurons in the hypothalamus is lower in abused animals as compared to controls. In contrast, the number of 5-HT terminals within the hypothalamus is higher in abused animals as compared to their control littermates.   (This work was supported by NIMH grant MH-52280 to C.F.F.) (back to top)

Early lead exposure alters social communication and aggression
Yvon Delville
(University of Massachusetts Medical Center, Worcester, MA)
The present experiments test the effects of early exposure to lead on aggressive behavior in golden hamsters.  Female golden hamsters were mated in the laboratory, and exposed to lead acetate through their drinking water (doses: 0, 10, 100 or 1000 ppm) from embryonic day 8 to postnatal day 25.  The pups were weaned on postnatal day 25 and were exposed to lead acetate until postnatal day 42.  Animals were tested in the resident/intruder encounters on postnatal day 45 and in the neutral arena model a week later for 4 consecutive days.  Under these conditions, animals exposed to 1000 ppm lead acetate differed from the other groups.  They were less likely to attack the intruders and more likely to retreat from them.  In contrast, a different effect was found with animals exposed to 100 ppm lead acetate.  This group contained a significantly larger proportion of aggressive animals. These results from resident/intruder tests show that, in golden hamsters, exposure to lead during development affects offensive aggression in a dose-dependent manner. (back to top)
 

Chronic cocaine exposure during adolescence increases aggressive responding in young adulthood
R. J. Harrison, D.F. Connor, and R.H. Melloni, Jr.
(University of Massachusetts Medical Center, Worcester, MA)
It was hypothesized that chronic cocaine exposure during particular phases of postnatal development predisposes animals to heightened levels of aggression, correlated with changes in AH neuropeptide expression. To test this adolescent male Syrian golden hamsters (Mesocricetus auratus) were administered cocaine hydrochloride during their adolescent development (P27-P56), and then tested for offensive aggression using the resident-intruder model. Hamsters treated with cocaine during adolescence show elevated measures of offensive aggression (i.e., increased number of bites, attacks, flank marks, and decreased latencies to bite), while total locomotor activity and sexual motivation were not significantly altered. (back to top)
 

Early anabolic steroid exposure enhances vasopressin-mediated aggression
R. H. Melloni, Jr., D.F. Connor, and R.J. Harrison
(University of Massachusetts Medical Center, Worcester, MA)
We hypothesized that chronic high dose AAS exposure during adolescence predisposes hamsters to heightened levels of aggression, correlated with changes in AH-AVP expression. To test this adolescent male hamsters were administered high doses of AAS throughout their entire adolescent development (P27-P56), and then tested for offensive aggression using the resident-intruder model. Hamsters treated with chronic high dose AAS during adolescence display heightened measures of offensive aggression (i.e., decreased latencies to bite and increased number of bites, attacks, and flank marks), and show marked increases in AH-AVP. AVP V1A antagonism markedly decreased offensive aggression. (back to top)