Growth of nerve-cell body and myelinogenesis in mouse trigemnal ganglion and root: a combined cytofluorometric and morphometric study.

Postnatal growth of mouse trigeminal ganglion cells and myelinogenesis in the central and peripheral portions of the trigeminal root were studied in animals aged 0-120 days. The trigeminal ganglion cells were dispersed into single cell suspensions. The growth of individual nerve cells was quantitated by measuring total protein content with a new cytofluorometric method based on o-phthaldialdehyde binding to cells fixed in a mixture of ethanol and acetic acid. White matter from the C.N.S. protrudes from the brainstem into the trigeminal root, comes into direct contact with the P.N.S. in a transitional region. C.N.S. and P.N.S. and myelinogenesis were studied in the same population of trigeminal sensory nerve fibres. Myelinogenesis was quantitated at the ultrastuctural level by morphometric techniques. A prominent peak in nerve cell body growth occurred between 3 and 6 days. Myelinogenesis in terms of established contacts between axons and their myelinating cells started at the same time in C.N.S. and P.N.S. and the transformation from nonmyelinated to promyelinated and myelinated fibres occurred concurrently in the central and peripheral parts of the trigeminal root. The growth of the myelin sheath, that is, the addition of myelin lamellae, was faster and more intense in P.N.S. than in C.N.S. This could reflect the fact that a Schwann cell myelinates only one internode, whereas an oligodendrocyte provides myelin for several internodes in different axons. These results support the concept of a common 'signal' for myelinogenesis in C.N.S. and P.N.S.