Mentor: Jennifer Quinn, Ph.D.

Environmental enrichment has positive influences on brain physiology and behavior, including enhanced plasticity and improved cognitive, emotional, and social performance. Conversely, stressful environments (especially when unpredictable) impair these functions. In this study, we use a 2 (sex: male, female) X 3 (housing: standard, enriched, stressful) factorial design. Enriched environments are larger than standard cages to allow for 4-6 rats per cage (social enrichment), and the addition of objects for exploration/play. The stressful environment occurs in standard caging and includes a series of mildly stressful, unpredictable, daily events. The housing manipulations occur from postnatal day 21-42. At the end of this three week period, all rats are pair-housed in standard cages for the remainder of the experiment. Behavioral assessments for anxiety, pain sensitivity, and fear are conducted during adolescence using an open field test, hot plate testing, and auditory fear conditioning/extinction. Preliminary results indicate that females demonstrate lower hot plate latencies independent of housing, suggesting increased sensitivity to pain. In the open field, enriched males spend less time in the thigmotaxic zone compared to all other males and females. This suggests that enrichment reduces anxiety in males but not females. Male rats, regardless of housing condition, demonstrate greater contextual fear conditioning. During the first tone extinction session, enriched animals trend toward greater freezing while rats from the stressful housing condition trend toward less freezing compared to standard housing. The rate of within-session extinction does not differ as a function of either sex or housing condition. When comparing freezing during the first tone on each of the four extinction days (between-session extinction), standard housing rats tend to freeze more compared to the enriched and stressful housing groups. Additional analyses are ongoing.

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