CENTRAL CHANGES IN PRIMARY AFFERENT-FIBERS FOLLOWING PERIPHERAL-NERVELESIONS

Cutting or crushing rat sciatic nerve does not significantly reduce th e number of central myelinated sensory axons in the dorsal roots enter ing the fourth and fifth lumbar segments even over very extended perio ds of time. Unmyelinated axons were reduced by similar to 50%, but onl y long after sciatic nerve lesions (four to eight months), and reinner vation of the peripheral target did not rescue these axons. This indic ates that a peripheral nerve lesion sets up a slowly developing but ma jor shift towards large afferent fiber domination of primary afferent input into the spinal cord. In addition, since myelinated axons are ne ver lost, this is good evidence that the cells that give rise to these fibers are also not lost. If this is the case, this would indicate th at adult primary sensory neurons with myelinated axons do not depend o n peripheral target innervation for survival. (C) 1997 IBRO. Published by Elsevier Science Ltd.