The processing of secretogranin II in the peripheral nervous system: release of secretoneurin from porcine sympathetic nerve terminals

The distribution of secretoneurin (SN), a peptide derived from secretograni n II (SgII), in the coeliac ganglion, the splenic nerve and the spleen was examined by immunohistochemistry. In the ganglion, SN immunoreactivity (LR) was unevenly distributed. Positive nerve terminals densely surrounded some postganglionic perikarya in which also intense SN-IR was present. In the c rushed splenic nerves, intense immunoreactivities appeared proximal (but to a less extent also distal) to the crush of the nerve. Analysis by cytofluo rimetric scanning (CFS) demonstrated that SN-IR and neuropeptide Y immunore activity (NPY-IR) were predominant in the axons proximal to the crush repre senting anterogradely transported components. Using radioimmunoassay (RIA) we demonstrated that upon electrical stimulation (10 Hz, 1 min) of the sple nic nerve, significant amounts of SN-IR (64.2 +/- 2.3 fmol) were released t ogether with NA (4.1 x 10(6) +/- 0.2 fmol) and NPY (330.0 +/- 7.2 fmol) fro m the isolated perfused porcine spleen. To evaluate the processing of SgII in sympathetic neurons, boiled tissue extracts (coeliac ganglia and splenic nerve) and boiled spleen perfusate (used as a suitable source for vesicle derived peptides) were analysed by gel filtration chromatography followed b y SN-RIA. In all cases immunoreactivity was present solely as SN, indicatin g that SgII was fully processed to the free peptide. The evidence that SN i s transported to the nerve terminals and is released from the porcine splee n upon nerve stimulation, suggests that it may modulate adrenergic neurotra nsmission and may also play a role in the neuroimmune communication. (C) 19 99 Elsevier Science B.V. All rights reserved.