Anatomical changes in cat dorsal horn cells after transection of a single dorsal root

Adult cats were subjected to unilateral L6, L7, or S1 rhizotomy. After survival times of 3 to 224 days each cat's spinal cord segments L1 to S2 were serially sectioned and stained with either Golgi or Nissl stains. The Nissl-stained material was used to determine whether or not significant cell death occurred as a result of transneuronal degeneration. The Golgi material was used to determine if changes in dendritic structure occurred. Laminae IV to VI were used for these analyses. There were no statistically significant changes in cell counts when the operated side was compared with the normal side, suggesting that cell death was rare or absent. However, dendritic complexity (mean number of branches of different orders per cell) and total dendritic length decreased with time after L7 rhizotomy in segments L3 to S2. There were no significant changes in segments L1 and L2. Atrophy of dendrites was most rapid and severe in the L7 segment, decreasing as a function of distance from L7. Two hypotheses are advanced, on the basis of these data: (a) The rapidity and degree of atrophy of a dendrite is a function of severity of deafferentation of that dendrite; and (b) rapid dendritic atrophy without cell death, as is seen in L6 to S1 after L7 rhizotomy, is possible because some dendrites are totally or largely deprived of their synaptic complement, but enough of the neuron's total synaptic input is left intact to sustain the cell and prevent cell death.