EFFECT OF HYPOTHYROIDISM ON RAT PERIPHERAL NERVOUS-SYSTEM

THE function and structure of the peripheral nervous system of Sprague -Dawley rats, 3 months after the induction of hypothyroidism by admini stration of N-propylthiouracil in drinking water, has been studied. Th e motor action potential amplitude of the caudal nerve showed a signif icant reduction (p < 0.001) when compared with an age-matched control group of animals. Computer-assisted morphometric analysis of sciatic n erves of hypothyroid rats showed normal distribution and density of my elinated fibers, and a normal axon/myelin ratio. Electron microscopy r evealed only minor alterations in axons of myelinated fibers character ized by a dissolution of neurotubules. After two months of substitutio n therapy these effects were reversed. The present data suggest that e arly impairment of nerves induced by hypothyroidism is rare and could be related to metabolic alterations rather than to structural changes and is reversible with hormone treatment.