Prior work has shown important effects of the early life environment on
development of adult stress response systems in both rats and humans. The
present thesis is based on experiments that attempt to explore: 1) adolescent stress
responding at hormonal and behavioural levels, and 2) the effects of repeated
adolescent stressor exposure on adult stress responding (hormonal and
behavioural) and levels of dopamine receptors expressed in prefrontal cortex,
using both male and female rats. Defensive behaviours exhibited during stressor
exposure and post-stress levels of circulating corticosterone were quantified as
behavioural and hormonal measures of stress responding, respectively. In the first
study, responses were compared among groups of adolescent rats exposed
repeatedly to one of two different types of cat odour stressor stimuli (J-cloth
coated in hair/dander or cat collar previously worn by a cat) or control stimuli,
and long-term outcomes were examined in adulthood. Adolescent rats showed
behavioural responses to both stressor stimuli, but behavioural inhibition was
more consistent using repeated cat collar exposure, and this treatment resulted in
long-term increases in anxiety-like behaviour in adulthood, whereas a stress-induced
adolescent corticosterone elevation was observed only in the group that
received exposure to the J-cloth stimuli. In the second study, adolescent and adult
rats were compared directly using repeated exposure to the cat collar stressor or
control stimuli. Adolescents were found to be more sensitive to the effects of the
stressor stimuli, relative to adults. Finally, in the third study, repeated exposure to
the J-cloth stressor or control stimuli was used, and stressor-exposed females
showed elevated baseline corticosterone levels prior to the final exposure.
Furthermore, stressor-exposed males and females showed lower levels of the D2
dopamine receptor in infralimbic and dorsopeduncular cortices of the prefrontal
cortex in adulthood. In addition, these studies together provide evidence that sex
differences in corticosterone levels emerge during the adolescent period. It may
be concluded that adolescence should be considered a sensitive developmental
timeframe for stress response programming.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:NSHD.ca#10222/14190 |
| Date | 22 August 2011 |
| Creators | Wright, Lisa Dawn |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
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