Comparative survey on enzyme localization, ultrastructural arrangement and functional organization in the optic tectum of non-mammalian vertegrates.

The histochemical localization of some enzymatic activities is surveyed in the optic tectum of vertebrates from cyclostomes to birds. These data are compared with results arising from ultrastructural and experimental works in order to outline some possible connections between enzyme localization and functional organization of the optic tectum. The most interesting result derives from acetylcholinesterase which, in the majority of vertebrate species, is localized in tectal layers in which visual and other sensitive afferents discharge. Such a situation, together with some experimental and developmental results, suggests that cholinergic mechanisms play an important role in the function of the optic tectum and that these mechanisms are worthy of further and more detailed investigations.