Retinal projections in the red belly squirrel (Callosciurus erythraeus Roberti): an autoradiographic study

Tritiated labeled materials, [3H]proline and [3H]fucose, were used as tracers of the visual pathway by injection into the right eve of the red belly squirrel, After a designated survival period, the animals were sacrificed, and the brains were removed and processed using standard autoradiographic procedures. Sections were then examined under a microscope and some subcortical nuclei including the suprachiasmatic nucleus (SCN), dorsal and ventral lateral geniculate nuclei(dLGN and vLGN), three optic accessory nuclei (i.e., the medial, lateral and dorsal terminal nuclei - MTN, LTN and DTN), the nuclei of the pretectal area(PTN) and the superior colliculus(SC) in the subcortical regions were marked by labeled isotopes. Radioactive materials were found in the pulvinar nucleus(Pul), parabigeminal nucleus(PB) and dorsal lateral pontine gray(DLP). Some nuclei among the targets of retinal projection in the red belly squirrel received their projection bilaterally while others only did contralaterally. In addition, layered structures of the SC and LGN were clearly demonstrated in the brain of the red belly squirrel. Some differences in the optic system between the red belly squirrel and its near relative, the grey squirrel of North American, and other mammals are discussed.