Neuronal and synaptic arrangements of the lateral geniculate nucleus in night-active primates.

The lateral geniculate nucleus (LGN) of Aotus trivirgatus and Nycticebus coucang shows two types of neurons at the ultrastructural level: a large thalamo-cortical relay neuron (TCR) and a small neuron of Golgi type II, which is considered to be an interneuron. The interneuron contains small aggregations of synaptic vesicles in the perikaryon adjacent to the cell membrane in synaptic contact to a TCR neuron. Only in the perikaryon of the interneurons can cilia have their origin. After unilateral enucleation, neurofilamentous or dark degenerations of large boutons with round vesicles (type RL) occur in the outer layers of the contralateral LGN and in the inner layers of the ipsilateral LGN. The optic terminals establish synaptic contacts in the glomerulus with dendritic spines of the TCR neurons and with presynaptic dendrites (F2) of interneurons.