SECRETONEURIN - A MARKER IN RAT HIPPOCAMPAL PATHWAYS

Secretoneurin is a 33-amino acid peptide, generated in brain by proteo lytic processing of secretogranin II. The distribution of secretoneuri n-like immunoreactivity and secretogranin II mRNA was investigated in the hippocampus of the rat. Secretogranin II mRNA was found in high co ncentrations throughout the granule cell and pyramidal cell layers and in many local neurons, notably in the hilus of the dentate gyrus. The general distributional pattern of secretoneurin-like immunoreactivity was characterized by a prominent staining in the area of the terminal field of messy fibers with an obvious staining in the infrapyramidal area of CA3 and a strongly immunopositive band in the inner third of t he molecular layer of the dentate gyrus. Lesions of the granule cells by local injection of colchicine significantly reduced secretoneurin-l ike immunoreactivity in the terminal, field of messy fibers, but not i n the inner molecular layer of the dentate gyrus. On the other hand, d estruction of interneurons of the dentate gyrus (messy cells and certa in gamma-aminobutyricacid-ergic interneurons) by kainic acid-induced s eizures was associated with a reduction of secretoneurin-like immunore activity in the inner molecular layer of the dentate gyrus. However, 3 0 days after kainic acid-induced seizures, a strongly secretoneurin-im munoreactive band reappeared in this area, which at this late time poi nt is due to sprouting of messy fibers collaterals. Our experiments su ggest a widespread distribution of secretoneurin-like immunoreactivity in neurons of the hippocampal formation with a preferential localizat ion in excitatory pathways including associational/commissural fibers originating from secretoneurin-containing messy cells. (C) 1997 Wiley- Liss, Inc.