[The subnucleus gelatinosus of the nucleus tractus solitarii is a catecholaminergic nucleus--immunohistochemical and ultrastructural studies in human fetuses].

The subnucleus gelatinosus of the nucleus tractus solitarii (SG) has been described in man by Olszewski and Baxter (1954). It is located in the dorsolateral corner of the nucleus tractus solitarii at the level of the area postrema and appears as the small, round area characterized by a peculiar gelatinous appearance of the ground substance. In this communication, we describe the existence of many catecholamine neurons in this particular area of human fetuses. We examined the lower medulla oblongata of five human fetuses (CRL: 155-275 mm, GA: 17-27 wks). The brains were obtained within 1-3 hours after death following therapeutic or spontaneous abortions. They were immediately fixed with 4% paraformaldehyde in 0.1 M phosphate buffer, pH 7.4, dehydrated graded alcohol, and embedded in paraffin. Serial 6 micron-sections containing the SG were cut from the lower medulla oblongata of each fetus. These sections were stained by peroxidase-antiperoxidase (PAP) technique using rabbit anti-bovine TH sera. The preparation and the specificity of the antisera used were described elsewhere (Nakashima et al, 1983 & 1984). In addition, ultrastructural examination was made on the unilateral SG of one fetus (CRL: 215 mm, GA: 23 wks). Immunohistochemically, many TH-positive neurons were observed in the SG of all cases. They were fairly uniform in size, 10-15 microns in diameter, showing round to oval cell somata and unipolar or bipolar processes. In the neuropil, numerous TH-positive fibers were found oriented randomly. Some of TH-positive fibers were seen extending toward the area postrema in the dorsomedial region of this subnucleus. A small number of TH-negative neurons were also noted. Ultrastructurally, the neurons observed were small in size and possessed in general a scanty cytoplasmic rim around the round nucleus. In the neuropil, unmyelinated nerve fibers, axon terminals with synaptic vesicles, dendrites and glial cell processes were observed. Synaptic structures encountered were axo-dendritic and axo-somatic. However, axo-axonic synapses could not be found. It was of interest that large dense-cored vesicles were frequently seen together with clear vesicles in the axon terminals. There have been so far many reports with regard to the distribution of the catecholamine neurons in the central nervous system of various mammals including man. In the medulla oblongata, the dorsomedial catecholamine neurons have been well known as the A2 group since the first description in rats by Dahlström and Fuxe (1964).(ABSTRACT TRUNCATED AT 400 WORDS)