title: On the organization of the retino-tecto-thalamo-telencephalic pathways in a Chilean rodent; the Octodon degus.
abstract: After performing eye enucleations or restricted lesions in the superior colliculus or the pulvinar nucleus, the degeneration patterns provoked by these procedures were analyzed by means of the Nissl and the Fink-Heimer methods in 30 specimens of Octodon degus. The pulvinar or lateroposterior nucleus can be subdivided into 3 regions (rostrolateral, rostromedial and caudal), on the basis of cytoarchitecture, tectofugal afferent and efferent connections to the cerebral cortex. In addition, this nucleus projects to the ipsilateral tail of the caudate nucleus and the nucleus lateralis dorsalis of the thalamus, which has been shown to project over the cingulate cortex in this animal 43. These findings support the possibility that the pulvinar may have an important role visuo-limbic interactions, by way of its connections with the nucleus lateralis dorsalis. Another highly interesting finding from the phylogenetic point of view is that the organization of the pulvinar in the Octodon degus is remarkably similar to that of the inferior pulvinar described for the owl monkey 46. Furthermore, the fact that the organization of the retino-tecto-thalamo-cortical pathways described in the grey squirrel 54 and in the tree shrew 33 is strikingly similar to those found in the Octodon degus, a semi-fossorial South American rodent that has evolved in isolation from the two former species for about 40 million years, makes it impossible to explain the organization of this pathway by advocating convergent evolution, due to environmental pressures determined by arboreal life, as postulated by kaas et al 39.
mesh_terms: D000818:Animals; D001479:Basal Ganglia / Q000033:anatomy & histology; D002421:Caudate Nucleus / Q000033:anatomy & histology; D004292:Dominance, Cerebral / Q000502:physiology; D005829:Geniculate Bodies / Q000033:anatomy & histology; D008032:Limbic System / Q000033:anatomy & histology; D009410:Nerve Degeneration; D009900:Optic Nerve / Q000033:anatomy & histology; D012160:Retina / Q000033:anatomy & histology*; D012377:Rodentia / Q000033:anatomy & histology*; D013477:Superior Colliculi / Q000033:anatomy & histology*; D013569:Synapses / Q000648:ultrastructure; D013687:Telencephalon / Q000033:anatomy & histology*; D013702:Temporal Lobe / Q000033:anatomy & histology; D013787:Thalamic Nuclei / Q000033:anatomy & histology*; D014793:Visual Cortex / Q000033:anatomy & histology; D014795:Visual Pathways / Q000033:anatomy & histology