Development of Interlimb Coordination in the Neonatal Rat
Locomotion is a type of motor behaviour that is produced by spinal neuronal networks associated with the different limbs. The rat in which development lasts three weeks in utero and continues during the first three post-natal weeks appears to be a very attractive model for the study of interlimb coordination maturational mechanisms. An early expression of rhythmic locomotor activity is observed at birth in vitro. Neuroactive substances like excitatory amino acid or amines (5-HT...) applied on the entire brainstem/spinal cord preparation induce a unique rhythmical activity over the cervical and the lumbar generators. This strict coordination results from a mutual interaction between generators since both bursting frequencies are altered significantly after functional isolation, with a slowing down of the isolated cervical network and a significant acceleration of the lumbar burst generator. However the rat does not walk at birth due to an absence of postural regulations. During the first two weeks, the neonatal rat is able to swim or to produce “air stepping” with an ipsilateral and a contralateral alternation between the different limbs. Adult walking occurs only during the third postnatal week. At least two mechanisms are able to control this early interlimb coordination . Numerous studies showed that 5-HT has ubiquitous topic and trophic effects on the early development of neurons and synapses. Studies on “PCPA” treated and “spinal” neonatal rats demonstrated strong deficits in locomotor movements. The second mechanism concerns the sensory afferents after birth; proprioceptive peripheral loops feed the central network and adapt its activation in a coordinated manner.
Key wordsCentral Pattern Generator (CPG) gait in vitro preparation proprioceptive control serotonin (5-HT)
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