The dependence of optic tectal development, especially differentiation of the stratum griseum periventriculare, on optic innervation is analysed in teleost fish in a comparative anatomical and experimental embryological study.
Tectal development of the blind cave fish, Astyanax hubbsi, lacking optic nerves hence having non-innervated tecta, is compared to its river relative, the normal-eyed A. mexicanus. In the embryonic tectum of cave fish there is less white and grey matter, with smaller sized nuclei in the subventricular zone; in the cave adult the tectum is hypoplastic with poorly differentiated neurons in the stratum griseum periventriculare.
Extirpation of eye Anlage in river fish embryos produced changes in the tectum comparable to the differences between embryonic tecta of cave and river fish.
One-eyed catfish, Ictalurus nebulosus, with a relatively fibre-poor optic nerve from an underdeveloped retina on the eyed side, showed better differentiated cells in the periventricular layer of the innervated side than in the non-innervated side. Periventricular neurons in the tecta of normal catfish were still better differentiated, demonstrating that differentiation of these cells is ‘dosage-dependent’ upon the amount of optic innervation.
Embryo zebrafish, Brachydanio rerio, subjected to extirpation of eye Anlage before optic nerve outgrowth, showed the dependence of differentiation of tectal subventricular cells on optic nerve ingrowth as early as the third day of development.
Zebrafish raised in the dark compared to those raised in light showed no discernible tectal differences under light microscopy.
Lack of differentiation of the neurons in the stratum griseum periventriculare in cave fish, and in eye-extirpated fish, has not been previously emphasized. Differentiation of these neurons appears largely dependent upon interaction with ingrowing optic axons, independent of visual function.
Study of the digestive tract of a rare species of Iranian blind cave fish (Iranocypris typhlops)
