SUBSTANCE P-LIKE, F8FAMIDE-LIKE, AND A18FAMIDE-LIKE IMMUNOREACTIVITY IN THE NERVUS TERMINALIS AND RETINA OF THE GOLDFISH CARASSIUS-AURATUS

We re-investigated the occurrence of substance P-like immunoreactivity in the retina of the goldfish Carassius auratus using antisera to sub stance P and other tachykinins. Most antisera labelled a previously de scribed single class of mono-stratified amacrine cells arborizing in l ayer 3 of the inner plexiform layer. Preabsorption experiments showed that these amacrine cells contained at least one tachykinin-like pepti de. One antiserum (INC 353) to substance P labelled not only these ama crine cells but also fibres in layer 1 of the inner plexiform layer an d fibres in the optic nerve. These fibres were identified as retinopet al projections of the nervus terminalis, in part because of colocalize d labelling with antisera against gonadotropin-releasing hormone and F MRFamide. Preabsorption experiments showed that the substance P-immuno reactive material in the nervus terminalis was not substance P or any other typical tachykinin. Labelling of the nervus terminalis with INC 353 was blocked by preabsorption with two bovine FMRF-amide-like pepti des, F8Famide and A18Famide, which contain a substance P(4-7)-like reg ion. Antisera to F8Famide and A18Famide strongly labelled ganglia of t he nervus terminalis and retinopetal fibres. We suggest that labelling of the nervus terminalis by antisera to substance P and FMRFamide occ urs because of homologies between these antigens and a non-tachykinin, endogenous peptide that is similar to F8Famide and A18Famide.