Angiotensinogen-like epitopes are present in the CNS of Aplysia california and co-localize with urotensin I- and urotensin II-like immunoreactivities in the cerebral ganglia.

Immunohistochemistry was used to demonstrate urotensin I (UI), urotensin II (UII), and angiotensinogen (Ao)-like immunoreactivities (ir) in the CNS of Aplysia californica. The fish UI is a 41 amino acid peptide that has 50% identity with mammalian corticotropin-releasing factor (CRF). Identity also exists between UI and angiotensinogen in a tetrapeptide at the N-terminus. Ao-ir neurones were found in the F cluster of the Aplysia cerebral ganglia. Beaded Ao-ir fibres were seen in the neuropile and commissure of the cerebral, pleural and pedal ganglia. Ao neurosecretory material was also seen in the perineural region of the proximal supralabial nerve. Previously we have demonstrated UI and UII immunoreactivities were present in the CNS of Aplysia. A comparison of adjacent sections of the cerebral ganglia immunostained sequentially for UI, UII and Ao revealed that all three immunoreactivities co-existed in the same cells of the F cluster of the cerebral ganglia. Liquid-phase immunoabsorption of the Ao antiserum revealed that porcine or human angiotensinogen but not UI or UII were able to quench Ao immunostaining. Conversely UI and UII staining were quenched by white sucker (Catatomus commersoni) UI and goby (Gillichtys mirabilis) UII, respectively, but they were not modified by angiotensinogen. These results suggest that UI-, UII-, and Ao-like peptides might co-exist as separate entities in the cerebral ganglia of Aplysia californica where they can act in an integrated and/or independent modulatory way.