Neurobiology of learning and memory
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Neurobiol Learn Mem · Sep 2010
BDNF expression in perirhinal cortex is associated with exercise-induced improvement in object recognition memory.
Physical exercise induces widespread neurobiological adaptations and improves learning and memory. Most research in this field has focused on hippocampus-based spatial tasks and changes in brain-derived neurotrophic factor (BDNF) as a putative substrate underlying exercise-induced cognitive improvements. Chronic exercise can also be anxiolytic and causes adaptive changes in stress-reactivity. ⋯ There was a trend for a negative relationship between anxiety-like behavior and hippocampal BDNF. Neither the cognitive improvements nor the relationship between cognitive function and perirhinal BDNF levels persisted after 2weeks of inactivity. These are the first data demonstrating that region-specific changes in BDNF protein levels are correlated with exercise-induced improvements in non-spatial memory, mediated by structures outside the hippocampus and are consistent with the theory that, with regard to object recognition, the anxiolytic and cognitive effects of exercise may be mediated through separable mechanisms.
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Neurobiol Learn Mem · Sep 2010
Lesion of infralimbic cortex occludes stress effects on retrieval of extinction but not fear conditioning.
Chronic stress produces dendritic retraction in medial prefrontal cortex and impairs retrieval of extinction of conditioned fear, a behavior mediated by the infralimbic region (IL) of medial prefrontal cortex. To test the hypothesis that stress-induced changes in IL contribute to the stress-induced impairment in extinction retrieval, we performed an occlusion experiment in which we assessed the effects of stress alone, lesion of IL alone, and the combined effects of stress and lesion on extinction retrieval. If IL is the substrate upon which stress acts to produce deficits in extinction retrieval, then prior removal of IL should prevent the effect of stress on extinction retrieval. ⋯ However, stressed rats with IL lesions showed extinction retrieval comparable to that seen in unstressed, sham-lesioned rats. Thus, lesion of IL occluded the stress-induced impairment of extinction retrieval but failed to prevent the stress-induced facilitation of fear conditioning. This dissociation suggests that the effects of stress on these two aspects of emotion regulation are mediated at least in part by independent mechanisms, and that stress-induced changes in IL contribute to stress-induced deficits in extinction retrieval.