Light-Microscopic Analysis of Secretory Activity of Neurosecretory Cells

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In the vertebrates, the hypothalamo-neurohypophysial neurosecretory system is involved in regulation of various physiological phenomena. However, it is not yet clear how synthesis and release of neurohypophysial hormones are controlled by external and internal environmental changes. Thus, in this research project, I have attempted to study this questions by use of two dimensional light microscopic photometric techniques, Synthetic activity of neurohypophysial hormones in individual neurosecretory cells has been determined by semiquantitative immunohistochemical and oligonucleotide-mRNA in situ hybridization (ISH) techniques. The ISH method used in the present project was established and developed in our laboratory. Furthermore, the nucleotide sequences of cDNAs encoding precursors of salmonid neurohypophysial hormones were analyzed in chum salmon and masu salmon so as to examine the above questions from comparative bases.Concerning effects of environmental osmotic changes on expression … More s of neurohypophysial hormone precursor genes, we have been able to obtain following results :1) After drinking 2% NaCl solution in rats, the level of provasopressin mRNA was significantly elevated in the supraoptic nucleus, but the change in the paraventricular nucleus was not significant. While water deprivation increased the provasopressin mRNA level in both the supraoptic and paraventricular nuclei.2) Transfer of seawater-adapted rainbow trout to fresh water elevated the level of provasotocin mRNA, whereas the inverse lowered the mRNA level.3) These results indicate that expression of genes encoding vasopressin-like peptides is elevated by a hyperosmotic stimulus in the rat, whereas it is stimulated by a hypoosmotic stimulus in the salmonid fish.Application of voltage-sensitive fluorescent dyes has been tested to record discharges of individual neurosecretory cells, since secretory activity of neurohypophysial hormones is well correlated to neuronal electric activity. I have not been able to complete this part, because of a delay in preparation of computer programs used in this technique. Less