STRESS DURING EARLY-ADOLESCENCE REDUCES RATS’ AGGRESSION AND INCREASES THEIR SEROTONIN FIBRE DENSITY IN ADULTHOOD
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Stressful experiences during youth can lead to a maladaptive behaviour profile in adulthood, including an increase in anxiety and aggression-related behaviours in humans. Rats exposed to the intermittent physical stress (IPS) paradigm in early-adolescence (PD 22 – 34) have lasting increases in anxiety-related behaviour. Greater anxiety-related behaviours have been shown to be associated with greater aggression-related behaviours. Therefore, I hypothesized that stress during early-adolescence would also lead to increases in aggression. In addition, greater anxiety and aggression have been associated with altered serotonergic function in the prefrontal cortex and ventral hippocampus. However, it is unclear whether a similar mechanism accounts for the enduring impact of stress during adolescence on those responses. In this experiment, I examined if IPS during early-adolescence increased anxiety-related behaviour in the elevated plus-maze and shock-probe burying test, as well as increased aggressive behaviour in the resident intruder test. In addition, I determined if there were changes in serotonin fibre density in the prefrontal cortex and ventral hippocampus. Male Long Evans rats (N = 24) were randomly assigned to either the early-adolescent stress or no-stress control groups. Rats were exposed to IPS stress (involving foot-shock, water immersion and elevated platform exposure) during early-adolescence and tested in the elevated plus-maze, shock-probe burying test and resident intruder test in adulthood. At the end of behavioural testing, brain tissue was examined for serotonin fibre density in the regions of interest using immunohistochemistry. Animals exposed to early-adolescent stress did not display greater levels of anxiety; however, they did display lower levels of aggression and an increase in serotonin fibre density in the prefrontal cortex. These results support that early-adolescence is a period of vulnerability of emotional development and raise the possibility that the impact of stress in adolescence on aggression in later life depends on when the stressors were experienced.
URI for this recordhttp://hdl.handle.net/1974/15853
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