Quantitative ultrastructural stereology of synapses in nucleus dorsalis after a peripheral nerve injury at birth.

Utilizing recent techniques in quantitative stereology, this investigation studied the synaptology of nucleus dorsalis (Clarke's column) in 12-week-old rats whose sciatic nerves were crushed in the 1st postnatal day. Four morphometric variables were analyzed at the levels of L1 and L3 spinal cord segments: total surface area of synaptic contact zones per unit volume (SV), total length of synaptic contact zones per unit area (LA), average length of synaptic membrane (L), and numerical density of synapses per unit volume (NV). The original raw data were corrected for Holmes's effect. The results indicated that peripheral nerve crush at birth induced a transganglionic change in central sensory terminals with a loss of numerous synapses. A significant loss (P less than 0.001) of about 32% in the SV and LA and a significant loss (P less than 0.001) of about 36% in the NV were observed on the experimental side. There was no preferential loss of synapses in either segment. The mean synaptic membrane length showed no significant difference between the control and experimental sides. The control values of the four morphometric variables calculated for L3 were lower than those calculated for L1. The loss of synapses after a peripheral nerve lesion was probably due to the loss of sensory neurons and their central processes, but there were other possibilities.