DEVELOPMENT OF LOCOMOTION IN THE RAT - THE SIGNIFICANCE OF EARLY MOVEMENTS

The development of the nervous system is determined by an interaction between genetic and epigenetic factors. We investigated the possible r ole of proprioceptive afferent input in the development of locomotion in the rat. Kinematic analysis of locomotion in normal rats reveals a marked transition from immature overground locomotion into the adult p attern around the 15th postnatal day. Around this age, the timing of E MG activity in the tibialis anterior and the gastrocnemius muscle in t he hindpaw gains accuracy and the intensity of the EMG increases. In t he soleus muscle we observbed an increased regularity in the shape of individual motor unit potentials. Neuroanatomical research revealed th e occurrence of dendrite bundles in the motoneuronal pool of the soleu s muscle pool from the ]6th day as the result of a reorganisation. Imm obilisation of one hindlimb in an extended position by casts around th e leg from the first till the 20th postnatal day does not interfere wi th the development of dendrite bundles in the soleus motoneuronal pool . Howeverm, we demonstrated long lasting abnormalities in the timing o f the EMG activation patterns in the gastrocnemius and the tibialis an terior muscles. It is conceivable that the experimental interference w ith afferent feed back is the causative factor of these functional abn ormalities.