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Stressful events during gestation can have sex-specific effects on brain and behaviour, and may contribute to some of the differences observed in adult stress responding and psychopathology. We investigated the impact of a novel repeated prenatal psychological stress (prenatal predator exposure - PPS) during the last week of gestation in rats on offspring behaviours related to social interaction (play behaviour), open field test (OFT), forced swim test (FST) and sucrose preference test (SP) during the juvenile period and in adulthood. We further examined the role of postnatal environmental, using an enhanced housing condition (EHC), to prevent/rescue any changes. Some effects on anxiety, anhedonia, and stress-related coping behaviours (e.g., OFT, SP and OFT) did not emerge until adulthood. PPS increased OFT anxiety behaviours in adult males, and some OFT and SP behaviours in adult females. Contrary to this, EHC had few independent effects; most were apparent only when combined with PPS. In keeping with age-group differences, juvenile behaviours did not necessarily predict the same adult behaviours although juvenile OFT rearing and freezing, and juvenile FST immobility did predict adult FST immobility and sucrose preference, suggesting that some aspects of depressive behaviours may emerge early and predict adult vulnerability or coping behaviours. Together, these results suggest an important, though complex, role for early life psychological stressors and early life behaviours in creating an adult vulnerability to anxiety or depressive disorders and that environmental factors further modulate the effects of the prenatal stressors.

Clinical studies indicate that children who experience a traumatic brain injury (TBI) are often the victim of peer rejection, have very few mutual friends, and are at risk for long-term behavioural and social impairments. Owing to the fact that peer play is critical for healthy development, it is possible that the long-term impairments are associated not only with the TBI, but also altered play during this critical period of brain development. This study was designed to determine if social dynamics and juvenile play are altered in rats that experience a mild TBI (mTBI) early in life. Play-fighting behaviours were recorded and analyzed for young male and female Sprague Dawley rats that were given either an mTBI or a sham injury. The study found that the presence of an mTBI altered the play fighting relationship, and the nature of the alterations were dependent upon the sex of the pairing and the injury status of their peers. Sham rats were significantly less likely to initiate play with an mTBI rat, and were more likely to respond to a play initiation from an mTBI rat with an avoidant strategy. This effect was significantly more pronounced in female rats, whereby it appeared that female rats with an mTBI were particularly rejected and most often excluded from play experiences. Male rats with an mTBI learned normal play strategies from their sham peers (when housed in mixed cages), whereas female rats with an mTBI show heightened impairment in these conditions. Play therapy may need to be incorporated into treatment strategies for children with TBI.

Although attention-deficit hyperactivity disorder (ADHD) is commonly reported after moderate and severe traumatic brain injury (TBI), research is struggling to find a strong link between mild TBI or concussion and ADHD. Epidemiological studies often generate conflicting results which may be related to the difficulty identifying the lingering symptoms of mTBI, the lack of baseline knowledge and the possible exacerbation of pre-existing ADHD symptomology, and/or differential diagnostic criteria for secondary ADHD. The purpose of this study was to determine if a mild TBI/concussion in the juvenile period (postnatal day 30) could induce ADHD-like symptoms in young rodents. Using the Go/No-Go paradigm of the 5-choice serial reaction task, sustained attention, impulsivity, and response inhibition was measured. The open field was also used to measure activity levels at two time points. Animals that experienced an mTBI in the juvenile period exhibited ADHD symptomology, with sex-differences present on one of the tasks. Significant deficits were identified in sustained attention, response inhibition, and impulsivity. Immediately after the mTBI, all rats were hypoactive in the open field, and while male animals exhibited a trend toward hyperactivity in the long-term, females continued to trend toward hypoactivity for the duration of the experiment. These findings provide a unique platform upon which preventative and therapeutic strategies can be implemented and tested in an effort to improve ADHD-like symptoms following mTBI.