Abstract
A chronic reduction in neuromuscular activity through prolonged body immobilization in human alters motor task performance through a combination of peripheral and central factors. Studies performed in a rat model of sensorimotor restriction have shown functional and biochemical changes in sensorimotor cortex. However, the underlying mechanisms are still unclear. Interest was turned towards a possible implication of Insulin-like Growth Factor 1 (IGF-1), a growth factor known to mediate neuronal excitability and synaptic plasticity by inducing phosphorylation cascades which include the PI3K–AKT pathway. In order to better understand the influence of IGF-1 in cortical plasticity in rats submitted to a sensorimotor restriction, we analyzed the effect of hindlimb unloading on IGF-1 and its main molecular pathway in structures implied in motor control (sensorimotor cortex, striatum, cerebellum). IGF-1 level was determined by ELISA, and phosphorylation of its receptor and proteins of the PI3K–AKT pathway by immunoblot. In the sensorimotor cortex, our results indicate that HU induces a decrease in IGF-1 level; this alteration is associated to a decrease in activation of PI3K-AKT pathway. The same effect was observed in the striatum, although to a lower extent. No variation was noticed in the cerebellum. These results suggest that IGF-1 might contribute to cortical and striatal plasticity induced by a chronic sensorimotor restriction.
Highlights
It is admitted since a very long time that regular physical exercise is good for health
Animal models of exercise suggest that training might enhance brain function through several mechanisms, such as neurogenesis, angiogenesis, synaptogenesis and increase in growth factors such as Brain Derived Nerve Factor (BDNF) and Insulin-like Growth Factor-1 (IGF-1) [1,5]
In the cerebellum (Fig. 3C), our results indicate no variation in phosphorylation or expression levels of the phosphoinositide 3-kinase (PI3K)-AKT pathway members
Summary
It is admitted since a very long time that regular physical exercise is good for health These last years, an increasing amount of studies has demonstrated that exercise promotes brain plasticity and has beneficial consequences on the brain, in young health population as well as during ageing [1,2,3]. Recent studies have suggested that alterations in corticospinal excitability should be taken into account to explain the degradation of posture and locomotion in human following bed-rest [9,10]. This hypothesis is sustained by data by our team which put forward the role of motor cortex in motor disabilities induced by HU in rodents [11]
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