Abstract
Recent evidence has revealed the impact of exercise in alleviating anxiety and mood disorders; however, the exercise protocol that exerts such benefit is far from known. The current study was aimed to assess the effects of long-term moderate exercise on behavioural coping strategies (active vs. passive) and Hypothalamic-Pituitary-Adrenal response in rats. Sprague-Dawley male and female rats were exposed to 32-weeks of treadmill exercise and then tested for two-way active avoidance learning (shuttle-box). Two groups were used as controls: a non-handled sedentary group, receiving no manipulation, and a control group exposed to a stationary treadmill. Female rats displayed shorter escape responses and higher number of avoidance responses, reaching criterion for performance earlier than male rats. In both sexes, exercise shortened escape latencies, increased the total number of avoidances and diminished the number of trials needed to reach criterion for performance. Those effects were greater during acquisition in female rats, but remained over the shuttle-box sessions in treadmill trained male rats. In females, exercise did not change ACTH and corticosterone levels after shuttle-box acquisition. Collectively, treadmill exercise improved active coping strategies in a sex-dependent manner. In a broader context, moderate exercise could serve as a therapeutic intervention for anxiety and mood disorders.
Highlights
Using animal models, there are two main categories for measuring anxiety: unconditioned response tests and conditioned response tests[10,11]
Other studies have reported that treadmill exercise protocols of similar intensity or middle-intensity (14 m/min, 60 min/day) but longer duration (24, 64 weeks) led to a reduction of anxiety-like behaviour in the elevated plus-maze and the open field tests[13,14], and counteracted the impairments produced by postnatal-maternal deprivation on fear memories[15]
We showed sex differences on shuttle-box performance, female rats acquiring active avoidance behaviour faster and earlier than did male rats
Summary
There are two main categories for measuring anxiety: unconditioned response tests (which require no training and usually have eco/ethological validity) and conditioned response tests (which often require training and involve learned/punished responses)[10,11] Unconditioned tests, such as the elevated plus-maze and open field tests, evaluate coping strategies under novel threatening conditions (i.e. environments) that approximate to the natural open or unprotected spaces, shown to elicit anxiety[10]. We aimed to investigate the impact of long-term moderate-intensity treadmill exercise on coping strategies in a conditioned conflict test involving anxiety To test this hypothesis, we used the two-way (shuttle-box) active avoidance paradigm, which involves a fear-mediated conflict between a tendency to freeze against a tendency to actively escape The main advantages of our model over other models of exercise are that a) using a treadmill model, the duration and intensity of exercise can be adjusted by the experimenter, and control for the heterogeneity described with other models (e.g. voluntary exercise training31); and b) including two control groups: a sedentary male (M) and female (F) group, receiving no manipulation (M-SED and F-SED, respectively), and a control male and female group (M-CON and F-CON, respectively) exposed to a stationary treadmill under the same conditions as for the treadmill (TM) group can serve to detect the influence of other variables, such as daily handling and mere exposure to the treadmill apparatus[32]
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