Electron microscopic identification of axon terminals of retinopretectal fibers in the cat by a combined horseradish peroxidase and tritiated amino acids tracing method.

The terminal nucleus of the optic tract in the pretectum was observed electron microscopically in the cat after intravitreous injection of a mixture of HRP and tritriated amino acids. Autoradiographic silver grains, and often also HRP granules, were seen in large axon terminals containing round synaptic vesicles and pale mitochondria. These terminals occasionally made synaptic contracts with the presynaptic dendrites and were involved in the formation of the synaptic triad.