抄録
In the previous study, we showed that the corticospinal (CS) synapses and terminals are distributed in the whole spinal cord at P7 and then eliminated from the ventrolateral side until P10. In this study, we further investigated the development of CS synapses subsequent to the elimination electrophysiologically and morphologically. Field EPSPs of CS synapses were evoked by stimulation of the medullary pyramid and recorded from the lower cervical cord (C7). For anterograde labeling of the CS terminals at C7, biotin dextran amine (BDA) was injected to the sensorimotor cortex. The spinal cord were fixed and sectioned several days after the injection. At the beginning of morphological study we determined the area of sensorimotor cortex projecting to C7. The amplitude of the largest negative peak of the field EPSPs continuously increased until 4 or 5 postnatal week. On the other hand, the spatial pattern of the distribution of the potentials was nearly constant after P10. The terminal distribution was analyzed by counting the number of axons within ventrolateral and dorsomedial area. After a relatively stable period of P10 and P11 following the elimination, the number of the terminals increased again in the ventrolateral area, which was the case with the dorsomedial area. The continuous amplitude increase of largest negative field EPSPs may be an electrophysiological counterpart of CS terminals re-innervation. Thus development of the CS innervation seems to consist of at least two steps. [J Physiol Sci. 2006;56 Suppl:S172]
