Characteristics of spinal dorsal horn neurons after partial chronic deafferentation by dorsal root transection

Unilateral transections of 1-3 lumbar dorsal roots were performed in 13 adult cats to investigate the effect of partial deafferentation on dorsal horn neurons. Eleven to 45 days after deafferentation various parameters of spontaneous and evoked activity of 169 neurons were measured and compared to the data of 168 neurons from previous experiments recorded under identical experimental conditions except that these animals had not been deafferented. Eighty-six of the units encountered were located in the segment of transected dorsal root(s) and 82 in the caudally adjacent segment. No significant differences could be observed in the functional properties of these two samples of units. Most parameters measured indicate that either no change at all in responsiveness or signs of decreased excitability occurred in the partially deafferented neurons compared to units recorded in control animals. Discharges evoked by noxious skin heating indicate a linear relationship between discharge frequency and skin temperature. This kind of encoding curve could also be measured during a reversible cold block of the spinal cord at segment L1. The mean encoding curves before and during spinal blockade were not different in deafferented compared to corresponding curves measured in control animals. The only finding that could be interpreted as an indication for increased excitability of partially deafferented neurons was that the mean frequency of spontaneous discharges of a subsample of heat-sensitive neurons was higher in deafferented compared to control animals. Possible mechanisms are discussed.