Pre- and postnatal development of 5-hydroxytryptamine-immunoreactive cells in the superior cervical ganglion of the rat.

The pre- and postnatal development of 5-hydroxytryptamine (5-HT)-immunoreactive cells in the superior cervical ganglion of the rat was studied by indirect immunofluorescence method with an antibody to a conjugate of bovine serum albumin and 5-HT. The superior cervical ganglia from 11-day-old embryos to 90-day-old postnatal rats were examined. 5-HT-immunoreactive cells were first detected in the superior cervical ganglion on the 12th day of gestation. At this stage of development the ganglionic cells formed a condensed group, and most of them showed 5-HT-immunoreactivity. During later prenatal development the relative number of the 5-HT-immunoreactive cells in the ganglion decreased and most ganglionic cells appeared as non-reactive. 5-HT-immunoreactive cells showed some variation in size and fluorescence intensity during the whole prenatal development. In the ganglia of newborn rats a wide range of 5-HT-immunoreactive cell sizes was detected. Two types of 5-HT-immunoreactive cells were distinguished in the ganglia of 7- to 35-day-old rats: small (5-15 microns in diameter) cells and large (15-30 microns in diameter) cells, resembling in size small intensely fluorescent (SIF) cells and principal nerve (PN) cells, respectively. The relative number of the large 5-HT-immunoreactive cells gradually decreased after the first postnatal week, and these cells were not detected in the ganglia of 90-day-old rats. Small 5-HT-immunoreactive cells constantly formed clusters in the ganglia of postnatal rats. A marked, statistically significant increase in the density of 5-HT-immunoreactive cells occurred during the 4th postnatal week. The 5-HT-immunoreactive cells appeared in the prenatal superior cervical ganglion of the rat approximately at the same time as the cells showing formaldehyde-induced catecholamine fluorescence. Transient occurrence of the large 5-HT-immunoreactive cells during the first postnatal weeks of development indicates, that in the superior cervical ganglion of the rat, 5-hydroxytryptamine may be expressed in some developing PN cells early postnatally. After the 5th postnatal week, the large 5-HT-immunoreactive neuronal cells cannot be detected, and 5-HT is expressed only in the SIF cells.