DISTRIBUTION OF SECRETONEURIN, A PEPTIDE DERIVED FROM SECRETOGRANIN-II, IN RAT-BRAIN - AN IMMUNOCYTOCHEMICAL AND RADIOIMMUNOLOGICAL STUDY

The distribution of secretoneurin, a peptide derived from its precurso r secretogranin II by proteolytic processing, was studied in the centr al nervous system of the rat by immunocytochemistry and radioimmunoass ay and compared to the distribution of secretogranin II messenger RNA by using in situ hybridization. With a specific antiserum a distinct s taining of fibers and to a lesser extent also of perikarya was observe d throughout the central nervous system. A high density of immunoreact ive fibers and terminals was found in several brain areas, i.e. the la teral septum, the medial parts of the amygdala, some medial thalamic n uclei, the hypothalamus, habenula, nucleus interpeduncularis, locus co eruleus, nucleus tractus solitarii, the substantiae gelatinosae of the caudal trigeminal nucleus and of the spinal cord. The quantitative di stribution as measured by a radioimmunoassay agreed well wit the varyi ng densities of immunoreactivity found by immunocytochemistry. The hig hest concentrations of this peptide were present in the hypothalamus, in particular, in the median eminence and are comparable to those of t he most highly concentrated neuropeptides. The distribution of immunop ositive perikarya corresponded well with that of secretogranin II mess enger RNA obtained by in situ hybridization. The pattern of secretoneu rin expression in rat brain was widespread and unique, partially overl apping with established chemical transmitters and neuropeptides. The f unctional significance of this new brain peptide remains to be establi shed.