Myelination of rat sciatic nerve: comparison of undernutrition and cholesterol biosynthesis inhibition.

Abstract

The effects of partial feeding and subsequent free feeding on myelination of rat sciatic nerve were investigated and compared with the effects of daily i.p. administration of AY9944 (trans-1, 4-bis-(2-chlorobenzylaminomethyl)-cyclohexane dihydrochloride), a cholesterol biosynthesis inhibitor. The frequency distributions of myelin sheath thicknesses in electron micrographs of sciatic nerves of experimental and control littermates were compared together with the relationships of axon circumference to myelin sheath thickness. Undernutrition and administration of a hypocholesteremic drug (AY9944) had dissimilar effects on myelinating rat sciatic nerve. Myelination of rat sciatic nerve was retarded more than the circumferential growth of the axon by undernutrition from 4 to 12, 4 to 18, and 12 to 26 days of age. The retardation of myelination caused by undernutrition from 4–12 days of age was still evident at 26 days of age but not at 34 days of age, whereas retardation of myelination after undernutrition from 4 to 18 days of age was still present at 46 days of age. AY9944 had no effect on the frequency distributions of myelin sheath thickness although 22% of Schwann cells in the 11 day old rats injected daily from 2 days of age contained crystalline and lamellar inclusions; and the AY9944 treated rats gained weight less quickly than their littermates. Undernutrition during a critical period in the development of rat peripheral nerve can cause deficits in myelin accumulation not fully accounted for by generalized growth retardation.