PERIKARYAL MYELINATION OF CULTURED CHICK-EMBRYO STATOACOUSTIC GANGLION-CELLS - AN ELECTRON-MICROSCOPIC STUDY

Perikaryal myelin formation on cultured chick embryo statoacoustic gan glion (SAG) cells was studied using electron microscopy. SAGs were dis sected from 13-day embryos and cultured for 1 to 6 weeks. Myelinated p erikarya, which were completely encircled by two or more layers of loo se and/or compact myelin lamellae like those in vivo in the chick, wer e first observed in 3-week-cultured SAGs; myelinated axons appeared in 2-week-cultured SAGs. The perikaryal myelination progressively increa sed loose and compact lamellae and the axonal myelination increased co mpact lamellae. In 4- to 6-week-cultured SAGs, 11 to 12% of SAG cells had the myelinated perikaryon of which perikaryal myelin lamellae term inated at the axon hillock in the same manner as those in vivo in the chick. The number of layers of myelin lamellae around the myelinated p erikaryon in 5- to 6-week-cultured SAGs and around the myelinated axon in 4- to 6-week-cultured SAGs ranged between 2 and 15, and between 12 and 26, respectively. Since these numbers were consistent with those in vivo in chicks 3 days after hatching, it is suggested that the cult ure provides perikaryal myelin sheaths, which are equivalent to those in vivo in structure, in more than 10% of SAG cells, while the myelina tion process in vitro is carried our much more slowly than that in viv o.