Alterations in fear conditioning and amygdalar activation following chronic wheel running in rats.
ABSTRACT 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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ABSTRACT: It is well established that physical activity can reduce the incidence and severity of anxiety disorders (see the chapter by Smits et al. in the current volume). Despite the anxiolytic effects of physical activity in humans, the underlying mechanisms remain unknown. Identification of these mechanisms could enhance our understanding of anxiety and lead to more effective therapeutic or preventative strategies. The limited understanding of the mechanisms underlying the anxiolytic effects of exercise could be due, in part, to the mixed results of animal studies on the effects of exercise on anxiety. Indeed, the effects of exercise in rodent models of anxiety is far from clear, with both anxiolytic and anxiogenic effects being reported. Despite the confusion, progress has been made toward understanding the mechanisms by which physical activity prevents anxiety. In the current chapter, we attempt to interpret the data on the behavioral effects of exercise on animal models of anxiety. We will offer a perspective on the available data that suggest specific experimental conditions under which anxiolytic effects of exercise are maximally revealed. The hope is that understanding the sometimes subtle behavioral effects of exercise in animal models will help uncover the neurobiological mechanisms underlying the effects of exercise on anxiety states. To this end, potential mechanisms will be discussed in the context of the behavioral effects of exercise on various rodent models of anxiety, including tests of learned anxiety, unlearned anxiety, and stress-induced anxiety. Learned anxiety Models of learned anxiety are based on assessing conditioned responses to stimuli previously associated with aversive events. During a typical rodent fear conditioning paradigm, a neutral, conditioned stimulus (e.g., a context or a tone) is paired with an aversive stimulus (such as a shock), so that subsequent exposure to the context or tone elicits a fear response in the absence of the aversive stimulus. The fear response in these experiments is most readily assessed using freezing or potentiation of the acoustic startle reflex. Freezing, the absence of all movement 1 2 3 4 5 6 7 8Routledge Handbook of Physical Activity and Mental Health, 1st edited by Panteleimon Ekkekakis, 01/2013: chapter Mechanisms underlying the relationship between physical activity and anxiety: Animal data: pages 130-142; routledge.
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ABSTRACT: Exercising during pregnancy has been shown to improve spatial learning and short-term memory, as well as increase brain-derived neurotrophic factor mRNA levels and hippocampal cell survival in juvenile offspring. However, it remains unknown if these effects endure into adulthood. In addition, few studies have considered how maternal exercise can impact cognitive functions that do not rely on the hippocampus. To address these issues, the present study tested the effects of maternal exercise during pregnancy on object recognition memory, which relies on the perirhinal cortex (PER), in adult offspring. Pregnant rats were given access to a running wheel throughout gestation and the adult male offspring were subsequently tested in an object recognition memory task at three different time points, each spaced 2-weeks apart, beginning at 60 days of age. At each time point, offspring from exercising mothers were able to successfully discriminate between novel and familiar objects in that they spent more time exploring the novel object than the familiar object. The offspring of non-exercising mothers were not able to successfully discriminate between objects and spent an equal amount of time with both objects. A subset of rats was euthanized 1 h after the final object recognition test to assess c-FOS expression in the PER. The offspring of exercising mothers had more c-FOS expression in the PER than the offspring of non-exercising mothers. By comparison, c-FOS levels in the adjacent auditory cortex did not differ between groups. These results indicate that maternal exercise during pregnancy can improve object recognition memory in adult male offspring and increase c-FOS expression in the PER; suggesting that exercise during the gestational period may enhance brain function of the offspring.Neuroscience 01/2014; 256:53–60. DOI:10.1016/j.neuroscience.2013.10.012 · 3.33 Impact Factor
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ABSTRACT: Three experiments used rats to examine the effect of a single bout of voluntary activity (wheel running) on the acquisition, extinction, and reconsolidation of context conditioned fear. In Experiment 1, rats provided with access to a wheel for 3 h immediately before or after a shocked exposure to a context froze more when tested in that context than rats provided with access to the wheels 6 h after the shocked exposure or rats not provided with access to the wheels. In Experiment 2, rats provided with access to the wheels immediately before or after a nonshocked exposure to the conditioned context froze less when tested in that context than rats provided with access to the wheels 6 h after the nonshocked exposure or rats not provided with access to the wheels. In Experiment 3, rats provided with access to wheels immediately after an extended nonshocked exposure to the conditioned context again froze less, whereas rats provided with access to the wheels after a brief nonshocked exposure froze more on the subsequent test than sedentary controls. These results show that a single bout of running can enhance acquisition, extinction, and reconsolidation of context conditioned fear.Learning & memory (Cold Spring Harbor, N.Y.) 01/2014; 21(2):73-81. DOI:10.1101/lm.032557.113 · 4.38 Impact Factor