Perikaryal myelination of cultured chick embryo statoacoustic ganglion cells: an electron microscopic study.

Perikaryal myelin formation on cultured chick embryo statoacoustic ganglion (SAG) cells was studied using electron microscopy. SAGs were dissected from 13-day embryos and cultured for 1 to 6 weeks. Myelinated perikarya, which were completely encircled by two or more layers of loose and/or compact myelin lamellae like those in vivo in the chick, were first observed in 3-week-cultured SAGs; myelinated axons appeared in 2-week-cultured SAGs. The perikaryal myelination progressively increased loose and compact lamellae and the axonal myelination increased compact lamellae. In 4- to 6-week-cultured SAGs, 11 to 12% of SAG cells had the myelinated perikaryon of which perikaryal myelin lamellae terminated 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 perikaryon 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 culture provides perikaryal myelin sheaths, which are equivalent to those in vivo in structure, in more than 10% of SAG cells, while the myelination process in vitro is carried out much more slowly than that in vivo.