Postnatal development of small and large dorsal root ganglion neurons in the cat. A study on cervical levels (C5-C6) and on phrenic afferents.

During feline postnatal development, the size of phrenic afferent neurons labelled by horseradish peroxidase was evaluated in comparison to that of the bulk of counterstained neurons located in the same cervical dorsal root ganglia (DRG) (C5-C6). From age 1 week to maturity, small and large cell components were individualized from experimental size distributions using a mathematical approach. The analysis of data in adult indicated a close correspondence between small cells and unmyelinated afferents and between large cells and myelinated afferents, respectively. From age 1 week to adulthood, mean increases in cell diameter ranged between 10 microns (small cells from phrenic afferents) and 29.5 microns (large counterstained cells). In each population, the ratio of small/large cells remained constant during growth. In contrast to data in adults, at 1 week, large phrenic neurons were bigger than the counterstained ones. At 19 weeks, the cat DRG cells had not yet reached their adult size.