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)