Selectivity in synaptic changes caudal to acute spinal cord transection.

The amplitude of monosynaptic EPSPs produced by the action of single semitendinosus (ST) Ia afferent fibers in ST motoneurons display little or no increase in amplitude within hours of a spinal cord transection performed at the thirteenth thoracic segment. This finding is in marked contrast to results obtained at the medial gastrocnemius (MG) Ia fiber-motoneuron synapse, where EPSPs have been shown to be enlarged, even in preparations with normal ST EPSPs. The increase in EPSP amplitude reported previously at the MG Ia-motoneurons synapse is selective and therefore is probably not a direct consequence of injury to the isolated segment of the spinal cord.