Maturation of oligodendroglia and myelinogenesis in rat optic nerve: A quantitative histochemical study

Microchemical techniques correlated with histologic observations were used to study rat optic nerve at 5, 10, 15, 20, 30, 40 and 50 days of postnatal development. Cell enumeration was accomplished by combining DNA as says with previously reported differential cell counts in electron microscopic montages (Vaughn, '69). At 5 days of age, the optic nerve contained unmyelinated axons, and its volume and total number of glia (DNA) were less than 40% of 50‐day‐old values. The cell population was composed of equal numbers of fibrous astrocytes and glial stem cells but contained only 7% oligodendrocytes. Between 5 and 20 postnatal days, mitotic proliferation of these stem cells resulted in a 3‐fold increase of DNA, while numbers of oligodendroglia increased 10‐fold. The cell population of the nerve at 20 postnatal days was similar to that found in the adult, with oligodendrocytes constituting 60% of the total cell population. Although these cells continuously formed myelin throughout postnatal development, their maximal rate of myelin lipid deposition (cerebrosides and cholesterol) occurred between 5 and 20 postnatal days. Hence, the most rapid rate of myelinogenesis in rat optic nerve occurred during the first three weeks of postnatal life and was synchronous with the mitotic proliferation and cellular differentiation of interfascicular oligodendroglia.