Transsynaptic labeling of neurons in the optic tectum of xenopus after intraocular [3H]proline injection

Quantitative assays of labeling patterns in the optic tectum of the from Xenopus after intraocular [3H]proline injection have been made by light and electron microscopy. Peaks in grain density were seen in layers 9, 8 and 6 of the optic tectum contralateral to the injected eye. This label persisted with little diminution for up to 50 days after eye injection. Electron microscopic autoradiography showed that silver grains in layers 9 and 8 were mainly located on optic nerve terminals and their postsynaptic structures. A considerable number of neuron somata in layer 6 were labelled. Label in layer 7 was concentrated over vertically oriented dendrites of neurons in layer 6 and deeper layers. It is concluded that radioactive labeled material was transported transsynaptically from optic nerve terminals synapsing on dendrites in layers 8 and 9 and that labeled material was transported in those dendrites to their cell bodies mainly located in layer 6. (Auth.)