Alterations in fear conditioning and amygdalar activation following chronic wheel running

Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, Columbia, SC 29208, USA.
Pharmacology Biochemistry and Behavior (Impact Factor: 2.78). 07/2006; 84(2):306-12. DOI: 10.1016/j.pbb.2006.05.015
Source: PubMed


Several convergent lines of evidence point to the amygdala as a key site of plasticity underlying most forms of fear conditioning. Studies have shown that chronic physical activity, such as wheel running, can alter learning in a variety of contexts, including aversive conditioning. The ability of chronic wheel running (WR) to alter both behavioral correlates of fear conditioning and indices of amygdalar activation, however, has not been simultaneously assessed. Here, rats were given constant access to either free-turning or--as a control--locked (LC) running wheels in their home cages. After 8 weeks of housing under these conditions, animals were exposed to a series of shocks in a separate testing chamber. Twenty-four hours later, the animals were returned to the shock chamber and freezing behavior was measured as an indicator of contextual fear conditioning. The animals were then sacrificed and their brains processed for immunohistochemical detection of Fos to assess patterns of putative neuronal activation. WR rats spent significantly more time freezing than their LC counterparts upon return to the shock-paired context. The enhanced conditioned freezing response was most pronounced in animals showing high levels of nightly wheel running activity. WR animals also had significantly higher levels of neuronal activation, as indicated by Fos expression in the central nucleus of the amygdala, but less activation in the basolateral nucleus, compared to sedentary controls. These data demonstrate the ability of chronic physical activity to alter contextual fear conditioning and implicate the amygdala as a potential site of plasticity underlying this phenomenon.

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    • "In human, exercise can decreases cognitive impairment associated with aging [31] and reduces the risk for several neurological diseases [32] [33]. In laboratory animals, exercise improves the cognitive function at different ages [34] [35] and in several tasks such as the Morris water maze [23,36–40], the inhibitory avoidance [24] [25] [41] [42] and context fear conditioning [43] [44]. Within this context, it is well accepted that both omega-3 supplementation and physical exercise may affect several cognitive parameters and brain plasticity [34] [35] [40] [45]. "
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    ABSTRACT: Both fish oil supplementation and physical exercise are able to induce benefits to mental health by providing an improvement in cognitive performance and enhancing neuroplasticity and protection against neurological lesions. The aim of the present study was to investigate the cognitive effects in rats of the: (1) a diary and prolonged fish oil supplementation (85mg/kg/day) initiated from prenatal period to the midlife (300 day/old); (2) moderate physical exercise in treadmill initiated from adolescent period to midlife and (3) association of fish oil supplementation and moderate physical exercise protocol during the same period. Animals were submitted to the habituation in the open-field, object recognition and to the plus-maze discriminative avoidance tasks. Our results demonstrated that a diary and prolonged fish oil supplementation can facilitate the persistence of the long-term habituation and recognition memories without, however, affecting the discriminative avoidance memory. Conversely, although the program of physical exercise exerted no effects on habituation or objects recognition, it was able to potentiate the persistence of the discriminative avoidance memory. Such promnestic effects (induced by both fish oil supplementation and physical exercise) were not accompanied by alterations in emotionality or locomotor activity. Our findings suggest that fish oil supplementation, initiated from prenatal period to midlife, and physical exercise program applied throughout the life induced distinctly a better cognitive performance.
    Full-text · Article · Oct 2012 · Behavioural brain research
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    • "Consistent with these results, changes in activation patterns in the amygdala, a limbic region involved in fear and anxiety, are found between sedentary and wheel-running groups following contextual fear conditioning . In this case, eight weeks of wheel running altered c-Fos levels in the amygdala following contextual fear conditioning (Burghardt et al., 2006b). Access to a running wheel also alters depression-like behavior or coping strategies in rodents (Table 3). "
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    ABSTRACT: Running wheels are commonly employed to measure rodent physical activity in a variety of contexts, including studies of energy balance and obesity. There is no consensus on the nature of wheel-running activity or its underlying causes, however. Here, we will begin by systematically reviewing how running wheel availability affects physical activity and other aspects of energy balance in laboratory rodents. While wheel running and physical activity in the absence of a wheel commonly correlate in a general sense, in many specific aspects the two do not correspond. In fact, the presence of running wheels alters several aspects of energy balance, including body weight and composition, food intake, and energy expenditure of activity. We contend that wheel-running activity should be considered a behavior in and of itself, reflecting several underlying behavioral processes in addition to a rodent's general, spontaneous activity. These behavioral processes include defensive behavior, predatory aggression, and depression- and anxiety-like behaviors. As it relates to energy balance, wheel running engages several brain systems-including those related to the stress response, mood, and reward, and those responsive to growth factors-that influence energy balance indirectly. We contend that wheel-running behavior represents factors in addition to rodents' tendency to be physically active, engaging additional neural and physiological mechanisms which can then independently alter energy balance and behavior. Given the impact of wheel-running behavior on numerous overlapping systems that influence behavior and physiology, this review outlines the need for careful design and interpretation of studies that utilize running wheels as a means for exercise or as a measurement of general physical activity.
    Full-text · Article · Mar 2012 · Neuroscience & Biobehavioral Reviews
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    • "In order to control for non-memory aspects of the behavioural task, such as locomotor activity or context arousal [23], additional SC and EC mice were exposed to the same behavioural procedure, except the electric foot shock during the acquisition session . These control groups are mostly used in addressing brain activation studies with aversive tasks using electric foot shock as stimulus [18] [24] [25]. The same ISI were used for these control groups: 24 h ISI (n = 6 per housing condition) or 8 weeks ISI (n = 6 per housing condition). "
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    ABSTRACT: Environmental enrichment is known to improve learning and memory in adult rodents. Whereas the morphological changes underlying these beneficial effects are well documented, few studies have addressed the influence of this housing condition on the neuronal networks underlying memory processes. We assessed the effects of environmental enrichment on behavioural performances and brain metabolic activation during a memory task in mice. Adult mice were housed in standard (SC) or enriched (EC) conditions for 3 weeks. Then, recent and remote memory performances were measured in the passive avoidance test. After testing, brain metabolic activation was assessed through cytochrome oxidase (CO) activity. EC improved recent memory, in association with an increased metabolic activation in the frontal and prefrontal cortices and a decreased activation in the baso-lateral amygdala and the hippocampus. EC did not improve remote memory, and globally decreased CO activity. Our findings suggest the involvement of regions of pivotal importance during recent memory, such as the frontal cortex, in the beneficial effects of EC.
    Full-text · Article · Nov 2011 · Behavioural brain research
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