Volume 17, Number 22,
Issue of November 15, 1997
pp. 8842-8855
Social Stress in Hamsters: Defeat Activates Specific
Neurocircuits within the Brain
Received June 11, 1997; revised Aug. 11, 1997; accepted Aug. 13, 1997.
S. Kollack-Walker,
S. J. Watson, and
H. Akil
Mental Health Research Institute, University of Michigan, 205 Zina
Pitcher Place, Ann Arbor, Michigan 48109-0720
During an agonistic encounter, subordinate male hamsters display
defensive and submissive postures and show increased secretion of
glucocorticoids, whereas dominant males do not. To determine whether
specific neuronal pathways are activated during the behavioral and
neuroendocrine responses of subordinate males, expression of
c-fos mRNA within the brains of subordinate males was
compared with the pattern in dominant males after fighting. After 1 week of handling, pairs of hamsters were either swapped between cages (handled control males), or were allowed to interact for 30 min [dominant (DOM) males and subordinate (SUB) males]. A second group of
control animals that received no handling or social stimulation (unhandled control males) were also included. After testing, all animals were killed by decapitation, their brains were removed for
c-fos in situ hybridization, and trunk blood was
collected for analysis of plasma cortisol and corticosterone levels.
Exposure of males to their partner's cage for 30 min resulted in
increased expression of c-fos mRNA in multiple brain
regions. In addition, fighting increased c-fos
expression in the medial amygdaloid nucleus of both DOM and SUB males
as well as having more selective effects. In DOM males,
c-fos expression was elevated within the supraoptic nucleus of the hypothalamus. In SUB males, c-fos
expression increased within a multitude of brain areas, including
cingulate cortex, lateral septum, bed nucleus of the stria terminalis,
medial preoptic area, several hypothalamic nuclei, central amygdaloid
nucleus, amygdalohippocampal area, dorsal periaqueductal gray, dorsal
raphe, cuneiform nucleus, and locus coeruleus. These findings are
discussed in relation to neurocircuits associated with behavioral
arousal and stress.
Key words:
c-fos;
mapping activation;
agonistic behavior;
aggression;
stress;
fear;
arousal;
defense;
hamster