Effect of phenol block on peripheral nerve: morphometric and histochemical study in rats

Nerve degeneration and regeneration following phenol block were investigated quantitatively by coordinated morphometry and histochemistry. Retrograde axonal transport of horseradish peroxidase was used to assess functional deficits in peripheral nerves. After one side of the rat sciatic nerve was blocked by 5 or 10% phenol, horseradish peroxidase was injected into the tibial muscular compartments bilaterally at various time intervals. The number and somatic area distribution of labeled motoneurons on the blocked side were compared to the contralateral unoperated side. After phenol block, the motoneuron number that had decreased during the first 2 weeks increased significantly at 4 weeks, and then returned to the level of the control side at 8 weeks at both phenol concentrations. No difference was found in somatic area between the blocked and control side during the process of recovery. It is concluded that phenol should not be used to cause selective and irreversible nerve block.