PSA‐NCAM expression in the teleost optic tectum is related to ecological niche and use of vision in finding food

In this study, tangential migration and neuronal connectivity organization were analysed in the optic tectum of seven different teleosts through the expression of polysialylated neural cell adhesion molecule (PSA‐NCAM) in response to ecological niche and use of vision. Reduced PSA‐NCAM expression in rainbow trout Oncorhynchus mykiss optic tectum occurred in efferent layers, while in pike Esox lucius and zebrafish Danio rerio it occurred in afferent and efferent layers. Zander Sander lucioperca and European eel Anguilla anguilla had very low PSA‐NCAM expression in all tectal layers except in the stratum marginale. Common carp Cyprinus carpio and wels catfish Silurus glanis had the same intensity of PSA‐NCAM expression in all tectal layers. The optic tectum of all studied fishes was also a site of tangential migration with sustained PSA‐NCAM and c‐series ganglioside expression. Anti‐c‐series ganglioside immunoreactivity was observed in all tectal layers of all analysed fishes, even in layers where PSA‐NCAM expression was reduced. Since the optic tectum is indispensable for visually guided prey capture, stabilization of synaptic contact and decrease of neurogenesis and tangential migration in the visual map are an expected adjustment to ecological niche. The authors hypothesize that this stabilization would probably be achieved by down‐regulation of PSA‐NCAM rather than c‐series of ganglioside.