Pre- and postnatal development of rat retroperitoneal paraganglia.

The prenatal and postnatal development of the rat retroperitoneal paraganglia were studied using the formaldehyde-induced catecholamine fluorescence (FIF) method. In addition, the transmitter composition of the paraganglionic cells of the newborn rat was analyzed by immunohistochemical demonstration of the catecholamine-synthesizing enzymes. The first fluorescent preaortic cells were detected in the 13.5-day-old embryos. One day later these cells constituted a distinct organ with moderately fluorescent cells, and in 15.5-day-old embryos this organ consisted cranially of moderately fluorescent and caudally of brightly fluorescent cells. The organ reached its largest size at birth and afterwards fibrous material increased between the fluorescent cells. In 4-week-old animals, only small clusters of fluorescent cells were observed in the preaortic area although many small paraganglia were situated cranially near the coeliac ganglion. In the organ of the newborn rat, many cells showed bright FIF. In addition, some cells with only slight or moderate fluorescence as well as non-fluorescent cells were detected. The analysis of immunoreactivity to the catecholamine-synthesizing enzymes showed that there was a cell population with intense reactivity to both tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH). These cells were considered as paraganglion-type cells. Some of them were also immunoreactive to phenylethanolamine N-methyltransferase (PNMT). In addition, there were cells with weak to moderate reactivity to TH and DBH but not to PNMT. Also totally negative cells were constantly seen. These findings were confirmed by using consecutive sections for the localization of different enzymes and by using the Tramu method to elute previous staining and by restaining the same sections with the other antibodies. It is concluded that the retroperitoneal paraganglia of newborn rat consist of many paraganglion-type cells containing noradrenaline, some of them containing also adrenaline, a few neuron-like cells with TH and DBH immunoreactivity, and cells containing no catecholamines.