Retinopetal projections from diencephalic neurons in a primitive actinopterygian fish, the sterlet Acipenser ruthenus

Horseradish peroxidase (HRP) injections into the sterlet ( Acipenser ruthenus) retina retrogradely label neurons in the dorso-medial thalamus, bilaterally. On the contralateral side, 5–7 cells were labelled, whereas ipsilaterally, only 2–3 cells were backfilled. Such diencephalic retinopetal cells have, so far, only been found in teleosts and in tetrapods. It has, therefore, been suggested that they evolved independently in these two vertebrate groups. Our findings on a primitive actinopterygian fish, suggest a more ancient origin of diencephalic projections to the retina.