Development of somatostatin-like immunoreactivity in embryonic sympathetic ganglia

Neural crest cells are the embryonic progenitors of several adult cell types, including some neurons that contain the neuroactive peptide somatostatin. To begin to understand the control of peptide expression during neuronal ontogeny, we have investigated the development of somatostatin-like immunoreactivity (SLI) in embryonic quail paravertebral sympathetic ganglia in vivo. SLI was identified by immunohistochemistry in paraformaldehyde-fixed cryostat sections from the trunk region of quail embryos. SLI was first observed in the cells of the primary sympathetic trunks at stage 18 (Zacchei, A.M. (1961) Arch. Ital. Anat. Embriol. 66:36-62), which corresponds to embryonic day 4 (E4). The primary sympathetic trunks are the sites of the initial aggregation of neural crest cells to form the sympathetic ganglia. The SLI in these cells was located in the cytoplasm and was absent from the nucleus. SLI persisted in subsequent developmental stages as formation of the definitive sympathetic ganglia occurred. At stage 23 (E7), when the lumbosacral paravertebral sympathetic ganglia have reached their definitive location, some cells in the ganglia contained SLI, and they were often located adjacent to one another. During the later stages of embryogenesis, sympathetic ganglia can be dissected from the embryo and the SLI content determined by radioimmunoassay. The amount of SLI is several-fold higher in ganglia removed at stage 23-24 (E7-8) than in ganglia removed at stage 26-27 (E9-10) or stage 31-32 (E13-14). This decline in SLI content reflects an absolute decrease per ganglion and is not solely due to the growth of tissue devoid of SLI.(ABSTRACT TRUNCATED AT 250 WORDS)