Pre- and postnatal development of the small intensely fluorescent cells in the rat superior cervical ganglion

A fluorescence microscopical study has been performed in the pre- and postnatal development of the sympathetic superior cervical ganglion of Sprague-Dawley rat. Ganglia from 10.5- to 21.5-day-old embryos and newborn to 90-day-old postnatal rats were freeze-dried and the catecholamine-containing cells were demonstrated by formaldehyde-induced fluorescence. The first catecholamine-containing cells appeared on day 11.5 of gestation. The ganglia of 11.5- to 12.5-day-old embryos contained a continuous range of cells showing weak to bright fluorescence intensities. In the ganglia of 13.5- to 14.5-day-old embryos few solitary cells or small groups of cells showing bright fluorescence were discernible among weakly fluorescent developing principal nerve cells. The cell numbers of both types markedly increased during the prenatal period while the mean diameter of the brightly fluorescent cells significantly decreased. In the late prenatal ganglia clusters were observed in which a large brightly fluorescent cell was surrounded by other intensely fluorescent cells of various sizes. There were about 300 small intensely fluorescent (SIF) cells in the ganglia of newborn rats. This number decreased by about 50% during postnatal week 1 and again increased during postnatal week 4 reaching the adult value of about 500 cells/ganglion. During the postnatal development the SIF cells formed clusters, the largest of which contained several hundred cells. Occurrence of large intensely fluorescent cells during a limited period suggests that this cell type represents a transitional form. It is possible that in the rat the primitive sympathetic cells continue their development along two lines: some cells remain weakly fluorescent and give rise to the principal nerve cells, and others accumulate catecholamine(s) and are transformed, possibly after mitotic divisions, into smaller brightly fluorescent cells which mature into SIF cells late postnatally.