Effects of early movement restriction on sensorimotor development and motor performance in rat
Résumé
Childhood is a period of construction of the organism, during which regular physical activity favors the maturation of the neuronal networks. However, some children are hypoactive because they are bedridden (illness, accident, cerebral palsy...) or they suffer from a developmental coordination disorder. In addition to the increased risk of cardiovascular and metabolic diseases, a low level of physical activity during childhood can affect the structuring and maturation of muscle and of developing neuronal network, that may lead to cognitive and behavioral impairment. In order to better understand the emergence of neuromuscular disorders in these children, a model of sensorimotor restriction (SMR) was developed in rats. It consists in casting hindlimbs of the pups from postnatal day (PND) 1 to PND 28. These animals display a prominent motor phenotype that includes muscle weakness, locomotor disturbances and spinal hyperreflexia.
In the present study, our objective was first to characterize the effect of early SMR on sensorimotor development from PND 1 to PND 28. Our results revealed that SMR induced a delay in acquisition of the main neurodevelopmental parameters such as righting, negative geotaxis, cliff avoidance, posture, whereas ocular reflex and limb grasping remained similar to control rats. Moreover, morphological parameters were affected by SMR condition since we observed lower body weight and atrophy of postural muscle. The second objective was to examine whether, after the 28-day SMR period, a one-month recovery period without restriction could restore the sensorimotor performance.The spontaneous activity (running wheels) was progressively increased from PND 35 to PND 60, but sensorimotor tests that require a good coordination between intra- and interlimb (rotarod, locomotion) showed an enduring alteration until PND 60. In conclusion, physical activity and interactions with environment seem necessary for the harmonious maturation of organization and functions of the central nervous system.