Research reportCognitive and locomotor/exploratory behavior after chronic exercise in the olfactory bulbectomy animal model of depression

Despite the evidence that exercise improves cognitive behavior in animal models, little is known about these beneficial effects in animal models of pathology. We examined the effects of activity wheel (AW) running on contextual fear conditioning (CFC) and locomotor/exploratory behavior in the olfactory bulbectomy (OBX) model of depression, which is characterized by hyperactivity and changes in cognitive function. Twenty-four hours after the conditioning session of the CFC protocol, the animals were tested for the conditioned response in a conditioned and a novel context to test for the effects of both AW and OBX on CFC, but also the context specificity of the effect. OBX reduced overall AW running behavior throughout the experiment, but increased locomotor/exploratory behavior during CFC, thus demonstrating a context-dependent effect. OBX animals, however, displayed normal CFC behavior that was context-specific, indicating that aversively conditioned memory is preserved in this model. AW running increased freezing behavior during the testing session of the CFC protocol in the control animals but only in the conditioned context, supporting the hypothesis that AW running improves cognitive function in a context-specific manner that does not generalize to an animal model of pathology. Blood corticosterone levels were increased in all animals at the conclusion of the testing sessions, but levels were higher in AW compared to sedentary groups indicating an effect of exercise on neuroendocrine function. Given the differential results of AW running on behavior and neuroendocrine function after OBX, further exploration of the beneficial effects of exercise in animal models of neuropathology is warranted.

Research highlights► Chronic exercise enhanced CFC in a context-specific fashion. ► CFC behavior was preserved in the OBX model of depression. ► Locomotor/exploratory behavior in the OBX model was dependent on the context. ► Chronic exercise increased the locomotor response to an acute, aversive stressor. ► Chronic exercise influenced the function of the neuroendocrine system.