Christina Perry, K. Drummond, M. Waring and J. H. Kim, Florey Institute of Neuroscience and Mental Health, Melbourne, Australia
For young people, friendship is often everything; and social isolation is the single biggest predictor of enduring anxiety from childhood into adolescence. Conversely physical activity during adolescence predicts low anxiety, and hence may be a protective factor against early life stress. In this study we used a preclinical model to investigate the interactive effects of social isolation and voluntary exercise on fear conditioning and extinction. Rats were housed from P21 either in isolation or in groups of three, in chambers that contained a running wheel. For half the wheel was locked to prevent running, for the remainder the wheel was available. At P42, all rats were trained to fear a tone, which was then extinguished the next day. Isolated rats showed impaired fear extinction, and this effect was rescued by exercise. Isolated rats also showed greater fear (freezing) at recall test, and freezing was reduced in rats that were allowed to run, regardless of housing conditions (isolated vs grouped). A similar pattern was observed in both male and female subjects. Cells co-expressing doublecortin and Ki-67 were counted, which revealed interesting relationships between freezing levels and hippocampal neurogenesis. These findings provide insight into environmental factors -both etiological and protective- that mediate in anxiety during adolescence. Furthermore, they show the value of lifestyle interventions to treat anxiety in vulnerable individuals.