Effect of nerve crush on perikaryal number and volume of neurons in adult rat dorsal root ganglion

Assumption‐free stereological methods were applied to assess the effect of nerve crush on perikaryal number and mean volume of neuronal subpopulations in adult rat dorsal root ganglion (DRG). The L5 spinal nerve of 20 Wistar rats was crushed approximately 7 mm distal to the DRG, and the contralateral spinal nerve and DRG were left intact and used as controls. After four, 15, 45, and 120 days, the rats were killed, and the tissue was fixed and processed for subsequent preparation of 30‐μm‐thick sections. Estimates of neuron number were obtained with the optical fractionator technique and estimates of the mean perikaryal volume with the vertical planar rotator principle. Perikaryal loss was progressive during the early study period but stabilized 45 days after nerve injury. The mean number (n) of all neurons in intact L5 DRG was 16,400 (S.D. = 2,000). The loss of perikarya was 16% (P < 0.05) after four days, 15% (P < 0.05) after 15 days, 30% (P = 0.059) after 45 days, and 34% (P < 0.05) after 120 days. B cells were lost at an earlier time than were A cells, and the B cell loss was more pronounced (39% vs. 22%, respectively, after 120 days). For A cells, the mean perikaryal volume was initially reduced but was normalized at the end of the study. Distributions of perikaryal volume showed that the curves of both A and B cells were uniformly displaced toward smaller values 15 and 45 days after injury. Neuronal loss caused by crush seems similar to that seen in rats exposed to permanent axotomy (Vestergaard et al. [1997] J Comp Neurol 388:307–312) at the same location, indicating that survival of perikarya is not dependent on possibility for fiber growth. J. Comp. Neurol. 412:186–192, 1999. © 1999 Wiley‐Liss, Inc.