Predatory threat induces huddling in adolescent rats and residual changes in early adulthood suggestive of increased resilience.

Adolescence is a critical developmental period during which chronic stress and binge alcohol consumption are often seen as environmental risk factors that confer vulnerability to later mental health problems. The current study modelled this using a 2×2 design where male Wistar rats were exposed to intermittent predatory stress (Stress condition: groups of 4 rats given 30 min of cat fur exposure in a large arena, once every 48 h) or intermittent alcohol (Alcohol condition: access to beer for 24 h every 2nd day), or both manipulations given on alternate days (Stress/Alcohol), or no manipulation (Control). The manipulations occurred over a 24 day adolescent window (postnatal day (PND) 33-57) giving a total of 12 cat fur exposures and/or 12 alternate days of beer access. Residual anxiety- and depressive-like behaviours were assessed in early adulthood (PND 58-77). Cat fur exposure was found to elicit a distinct defensive response in which groups of adolescent rats huddled together in the corner of the arena, either in "quads" (all 4 rats bunched together) or "triplets" (3 rats together and one outlier rat). Few approaches to the cat fur occurred and locomotor activity was suppressed relative to Control rats placed in the arena without fur. Huddling continued over the 12 repeated exposures to cat fur, and was temporarily exaggerated when fur from a novel cat was introduced. Interestingly, huddling and conditioned fear in the fur-associated context were most pronounced in rats receiving intermittent alcohol, suggesting that alternate day exposure to alcohol had anxiogenic effects, possibly linked to a hangover state on these days. Predatory stress did not affect overall alcohol consumption relative to rats given alcohol alone, but significantly inhibited weight gain through adolescence and into adulthood. In early adulthood, rats exposed to stress in adolescence, regardless of alcohol exposure, showed significantly reduced immobility in the forced swim test and signs of increased sociability with a novel conspecific in a social interaction paradigm. Overall, these findings suggest greater resilience in adulthood after chronic adolescent stress, indicating that coping with predators may be in some ways a form of early environmental enrichment.