RETINOPETAL PROJECTIONS FROM DIENCEPHALIC NEURONS IN A PRIMITIVE ACTINOPTERYGIAN FISH, THE STERLET ACIPENSER-RUTHENUS

Horseradish peroxidase (HRP) injections into the sterlet (Acipenser ru thenus) retina retrogradely label neurons in the dorso-medial thalamus , bilaterally. On the contralateral side, 5-7 cells were labelled, whe reas ipsilaterally, only 2-3 cells were backfilled. Such diencephalic retinopetal cells have, so far, only been found in teleosts and in tet rapods. It has, therefore, been suggested that they evolved independen tly in these two vertebrate groups. Our findings on a primitive actino pterygian fish, suggest a more ancient origin of diencephalic projecti ons to the retina.