Independent Regulation of Coexisting Neuropeptides

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Contribution to Book

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American Zoology


We investigated the possible osmo? regulatory role of the caudal neurosecretory system in the trout, Oncorhynchus mykiss. Immunoreactive intensities for the caudal neuropeptides, urotensins I (UI) and II (UII), were compared sequentially following transfer of individuals to different water salinities. Two, 10 and 48h after transfer of freshwater (FW) Fish to either new FW or 100% seawater (SW) posterior spinal cords were removed, fixed, paired in blocks and double sequential immunostained. UI and UII were found to coexist in the majority of neurosecretory cells. The 2h SW neurohemal organs (NHs) had more UII and less UI intensity than FW NHs, and perikarya displayed the opposite pattern. After lOh in SW the NHs exhibited less intensities for both UI and UII, and perikarya were more intense for both relative to FW fish. By 48h we found no intensity differences. The opposite shifts in intensities of UI and UII at 2h and the reversal of intensities for just UII within lOh indicates differential regulation of the two neuropeptides. Because of their predominant coexistence, these results also suggest that the two urotensins are packag