Synaptic patterns in the superficial layers of the superior colliculus of the monkey,Macaca mulatta

Summary While the synaptic patterns studied with the electron microscope in the upper layers of the superior colliculus of the monkey are basically similar to those described for the rat, there are notable differences in the terminal patterns of the afferent pathways.The retinotectal pathway in monkeys terminates sparsely near the surface in the caudal part of the colliculus. Most of the terminals undergo an electron dense reaction in degeneration and are rapidly removed from their postsynaptic sites.The corticotectal pathway terminates heavily throughout superficial layers making both axodendritic and serial synaptic connections. The terminals undergo neurofilamentous and dense degenerative reactions.It is suggested from a comparison of the retinotectal and retinogeniculate pathways that terminals which undergo the neurofilamentous degenerative reaction belong to a different population of axons from those undergoing only the dense reaction.