The fine structure of the lateral geniculate complex in the frog Rana esculenta

The lateral geniculate complex of the frog is composed of two neuropil areas, the neuropil of Bellonci and the corpus geniculatum thalamicum that receive axons of retinal origin. The nucleus of Bellonci, and some other cell groups project dendrites into the neuropil. In normal animals three types of axon terminals (A1, A2, A3), light and dark dendrites, dendritic appendages and presynaptic dendrites were distinguished as components of the lateral geniculate circuitry. Using horseradish peroxidase labelling of the optic nerve and eye removal, type A1 profiles were identified as the terminals of retinal afferents. Type A2 profiles may belong to intrinsic fibrus, and type A3 profiles may be the terminals of tectal afferents. Presynaptic dendrites are usually engaged in serial synapses. The fine structure of the lateral geniculate complex is very similar to that of the 9th layer of the optic tectum.