Properties of synaptic linkage from long ranging afferents onto dorsal horn neurones in normal and deafferented cats.

1. In intact cats, dorsal horn cells sometimes respond to afferents entering the cord three or four segments more rostral. If dorsal roots near a segment have been cut for at least 4 weeks, many more cells respond to these long ranging afferents. Using extra- and intracellular recording, we examined the change in the nature of the connectivity of the long ranging afferents from dorsal roots L3 and L4 onto cells in L7. 2. In intact animals 33% of all cells in L7 recorded extracellularly and 48% of those recorded intracellularly exhibited responses to electrical stimulation of skin whose afferents entered the spinal cord over dorsal roots L3 and L4. Most of these responses had a long latency and followed high frequency stimulation poorly. 3. Thirty-eight to fifty-one days after cutting dorsal roots L5-S2, 76% of cells recorded intracellularly in L7 responded to long ranging afferents, in contrast to 48% in the intact cord. In these preparations 48% of all cells responded in less than 5 msec versus 12% in intact cats. Furthermore, 21% of the cells had natural receptive fields in the distant dermatome versus 1% in intact animals. 4. Chronic deafferentation of a segment increased the number of cells responding to afferents arriving over distal dorsal roots and increased the speed and power of the responses.