Neuronal and synaptic structure of the dorsal lateral geniculate nucleus in normal and monocularly deprived Macaca monkeys.

The dorsal lateral geniculate nucleus (dLGN) of Macaca monkeys was studied by Golgi and quantitative electron microscopic (EM) methods to determine if differences in neuronal morphology exist which might correlate with the known physiological separation of X-type cells into the parvocellular and Y-type cells into the magnocellular laminae. Monocularly lid-sutured Macaca monkeys were also studied by quantitative EM methods to compare the synaptic organization within laminae innervated by the deprived and nondeprived retinae. We have divided our sample of Golgi-impregnated neurons into three groups: Types A, B, and C. Type A neurons comprise the majority of the projections cells and are quite heterogeneous in their overall morphology. Type B neurons have long dendrites with multiple appendages; some have a locally ramifying beaded axon Type C neurons are characterized by dendrites which are mainly restricted to the interlaminar zones. We found Type A and B neurons in both the parvocellular and magnocellular laminae. The cell bodies of Type C neurons lay within the interlaminar zones or the parvocellular laminae. All three types contributed dendrites to the interlaminar zones. No significant differences in Golgi morphology other than overall size were found in parvocellular or magnocellular laminae that would explain the previously demonstrated electrophysiological differences. Terminal profiles and synapses in the parvocellular, magnocellular, and interlaminar zones were classified and counted using quantitative EM methods. RSD and F terminals were most numerous in all three zones. RLP terminals were rare in the interlaminar zones. A new type of terminal, RMD was found in the magnocellular interlaminar zones. The laminar and interlaminar zones have the same overall synaptic density, but differed in types of synaptic terminals. The only quantitative difference between any of these regions was in the magnocellular laminae where the counts showed 70% more F terminals per unit area. The same quantitative methods were applied to the laminar and interlaminar zones of dLGNs from monocularly lid-sutured monkeys. We found no qualitative or quantitative difference between the synaptology of zones receiving input from the deprived retina compared to the open eye retina, nor between any regions of the dLGN in deprived monkeys compared to normal monkeys.