The thalamus and its cortical projection in the brush tailed possum, Trichosurus vulpecula, and the native cat Dasyurus viverrinus, with a comparative review of thalamic organisation in marsupial and placental mammals

This thesis is presented in two parts: The first comprises a review of thalamic structure and connections in marsupial mammals, and comparison with placental species. The major groups of thalamic nuclei are treated in turn. The cytoarchitecture of each group is described and compared in different marsupials, with greatest emphasis being placed on the Virginia opossum Didelphis virginiana, the brush-tailed possum Trichosurus vulpecula, and the native cat Dasyurus viverrinus. The presently available information on afferent and efferent connections of specific regions in marsupials and placentals is then reviewed,and comparisons made within and between the two mammalian groups. Possible functional roles of each region are also briefly discussed. Among marsupials many fundamental similarities in thalamic organisation are evident, but also several important differences. Most of these differences can be seen to be related to particular groupings of animals, or to follow trends across the range of species examined. Representative Australian diprotodonts, such as Trichosurus, and to extent polyprotodonts, such as Dasyurus, number of features which distinguish them American didelphids, such as the opossum a lesser exhibit a from the Didelphis. Most of these variations in thalamic organisation show clear parallels to the morphological and serological distinctions between the three marsupial groups. Some of the distinguishing characteristics of Australian forms represent considerable progress from the relatively primitive level of development found in the didelphids, and convergence upon the more highly evolved organisational plans of advanced placental mammals. Comparisons of the connective relationship of specific thalamic regions in marsupials and placentals reveal many features which are shared by most or all species. There are occasional significant departures from what apparently constitute general mammalian plans, however most cases where important interspecies variations occur concern details in the distribution patterns of particular input and/or output connections. The most marked differences in connection patterns among both marsupials and placentals are found with the rostral ventral tier nuclei (ventroanterior-ventrolateral complexes and ventromedial nucleus or possible equivalent) and the central intralaminar group. Most other thalamic centres appear to have rather more uniform organisation. The second part of the thesis comprises published details of examinations of thalamic and cortical structure and connections in the brush-tailed possum Trichosurus vulpecula, and the native cat Dasyurus viverrinus, with short notes on somatosensory cortical organisation in the rufous wallaby Thylogale billardierii.