Distribution and coexistence of urotensin I and urotensin II peptides in the cerebral ganglia of Aplysia californica

Abstract

Urotensin I (UI) and urotensin II (UII) were demonstrated in the cerebral ganglia of Aplysia californica by applying immunocytochemical and radioimmunoassay procedures. Sequential analysis of adjacent sections of the cerebral ganglia of Aplysia demonstrated that the UI-immunoreactive (UI-IR) neurons of the F cluster of the cerebral ganglia also contained UII immunoreactivity (UII-IR). Both UI-IR and UII-IR were also observed in a cuff-like arrangement of fibers surrounding the proximal portion of the supralabial nerve, as well as in a few fibers in the anterior tentacular nerves. The UI-IR perikarya of the cerebral ganglia appeared to project to the entire CNS of Aplysia, but the UII-IR fibers appeared only in the neuropile and commissure of the cerebral ganglia. The UI-IR staining was abolished by previous immunoabsorption of the UI antiserum with sucker ( Catastomus commersoni) UI, but not with ovine corticotropin-releasing factor (CRF), rat/human CRF, or goby ( Gillichthys mirabilis) UII. Immunostaining with UII antiserum was quenched by goby UII, but not by sucker UII-A, UII-B, UII-A(6–12), or carp ( Cyprinus carpio) UII-α and UII-γ. The UII staining was not abolished by UI or somatostatin. The F cluster was not stained when a somatostatin antiserum was applied. Radioimmunoassay of dilutions of cerebral ganglia extract, using UII antiserum, revealed a parallel displacement curve to synthetic goby UII. These results suggest: i) that both UI- and UII-like substances might exist in the cerebral ganglia of Aplysia californica; ii) that putative Aplysia UI and UII peptides are probably sharing epitopes with sucker ( C. commersoni) UI and goby ( G. mirabilis) UII, respectively; iii) that a UII-like substance coexists with UI in the same neurons of the F cluster of the cerebral ganglia of Aplysia; and iv) that the UII-like substance originating in the cells of the F cluster may have an integrated role with a still unknown action of a putative UI in the CNS of Aplysia californica.