Experimental Study on Morphological Changes of Proximal and Distal segment of Severed Proper Digital Nerves at Different Time Lapses, and the Influence of These Changes on Axonal Regeneration.

The purpose of this study is to investigate the morphological changes of proximal and distal segment of severed proper digital nerves at different time lapses and the influence of these changes on axonal regeneration after reconnection of severed stumps. Proper digital nerves of fingers and toes of adult Japanese monkeys were used. Every proper digital nerve on one side was divided at the base of a digit, and both stumps were ligated to prevent spontaneous reconnection, while contralateral proper digital nerve was kept intact. Exp. A-1: Morphological changes of myelinated axon of severed proximal segment of toe were investigated. Exp. A-2: Proximal segments were sutured at 3, 6, and 12 months after severance, to freshly severed distal segment of contralateral proper digital nerve. Regeneration of myelinated axons were investigated. Exp. B-1: Morphological changes of Schwann tube of severed distal segment were investigated. Exp. B-2: Distal segment of proper digital nerves of fingers was sutured at 3, and 12 months after severance, to freshly severed proximal segment of contralateral proper digital nerves. Regeneration of myelinated axon was investigated. Percent of area, density and mean diameter of myelinated axons or Schwann tubes were measured and following results were obtained. (1) Myelinated axons of severed proximal segment shrank more with prolonged time after nerve severance. (2) Capacity of sprouting and maturation of regenerating axons of proximal segment significantly decreased when nerve was kept severed for more than 3 months. This can be one of the factors of impairment of axonal regeneration when the suture of a severed nerve delays more than 3 months after its severance. (3) Schwann tubes of the distal segment of a severed nerve shrank so slowly that its influence on axonal regeneration was much less, if sutured within 1 year, than shrinkage of myelinated axons of proximal segment which was kept severed for more than 3 months