An anatomical study of some somesthetic afferents to the intercollicular terminal zone of the midbrain of the opossum

Abstract

Following lesions of the dorsal column nuclei, spinal cord and sensorimotor cortex, anterograde degeneration was traced to a common target in the central midbrain; the intercollicular terminal zone. Although not all the midbrain projections of the three pathways are contained within this zone, it receives overlapping projections from each of the three body-related somesthetic pathways studied. The intercollicular terminal zone covers the entirety of the external nucleus of the inferior colliculus and the intercollicular nucleus of Mehler, spilling over into adjacent parts of the central gray and deep layers of the superior colliculus. Little evidence of somatotopy in the somesthetic projections was disclosed, and bilateral input was found in each experimental case, regardless of the type of lesion. Golgi-stained material was examined to explore the basis of the extensiveness of the terminal zone. These materials showed that the dendritic spread of neurons in the external nucleus of the inferior colliculus and the intercollicular nucleus, taken together, covers the entirety of the intercollicular terminal zone. That is, the dendrites invade the same portions of the central gray and deep layers of the superior colliculus which are covered by the terminal field. We conclude that a tripartite division of the sensory midbrain may be justified: with the somesthetic modality being represented anatomically in a fashion at least roughly analogous to that of vision and audition.

Systematic mapping of the monkey inferior colliculus reveals enhanced low frequency sound representation

“…The RP is a small area that receives input from the auditory brainstem but differs from the ICC in that it sends its output primarily to the SC rather than the MGB (Harting and Van Lieshout 2000;Osen 1972). The intercollicular tegmentum is part of the mesencephalic reticular formation, and receives inputs from a variety of auditory, visual, and somatosensory sources (Lopez et al 1999;Robards 1979;RoBards et al 1976). …”

Reptilian Somatosensory Midbrain: Identification Based on Input from the Spinal Cord and Dorsal Column Nucleus

“…Spinal projections to the midbrain, exclusive of terminations in the superior colliculus have been in vestigated in hedgehogs Schroeder and Jane, 1976], tree shrews Jane, 1971, 1976], opossums [Mehler, 1969;Hazlett et al, 1972;RoBards et al, 1976], rats [Mehler, 1969;Zemlan et al, 1978], cats [Mehler 1969;Bjorkeland and Boivie, 1984a;Wiberg and Blomqvist, 1984a], slow loris [Schroeder and Jane, 1976], Ma caque monkeys [Mehler et al, 1960;Mehler, 1969;Wiberg et al, 1987] and chimpanzees [Mehler, 1969]. All of these studies emphasize a projection to 'nucleus intercollicularis', bearing in mind differences in the description of this area.…”

“…All of these studies emphasize a projection to 'nucleus intercollicularis', bearing in mind differences in the description of this area. When terminations to the external nucleus of the inferior colliculus have been described, they are considered to be less dense than those to the intercollicular nucleus: hedgehogs, tree shrews, slow loris [Schroeder and Jane, 1976]; opos sums [RoBards et ah, 1976] and cats [Bjbrkeland and Boivie, 1984a], Projections of the dorsal column nucleus to the mesencephalon, exclusive of terminations in the supe rior colliculus, have also been analyzed in hedgehogs Schroeder and Jane, 1976], tree shrews [Schroeder and Jane, 1976], mar mosets [Schroeder and Jane, 1976], African green monkeys [Schroeder and Jane, 1976], opossums [Hazlett et al, 1972;RoBards et al, 1976;RoBards, 1979], rats [Feldman and Kruger, 1980], cats [Berkely and Hand, 1978;Bjorkeland and Boivie, 1984b;Wiberg and Blomqvist, 1984b], and Macaque monkeys [Wi berg et al, 1987], In all these species, projections to the external nucleus of the inferior colliculus or to the lateral region of the central nucleus of the inferior coliculus have been documented. In some animals, addi tional connections with the intercollicular nucleus have been described: oppossums [RoBards et al, 1976]; cats [Bjorkeland and Boivie, 1984b;Wiberg and Blomqvist, 1984b]; rats [Feldman and Kruger, 1980] and monkeys [Wiberg et al, 1987].…”

The Auditory Brain Stem of a Marsupial

“…In Golgi material, dendritic orientation is displayed clearly by elements in ICC of both species [Morest, 1964;Rocket and Jones, 1973], but the lateral and rostral areas of the auditory midbrain appear not to be organized in this way. Neurons in ICX of Didelphis have large radiate dendritic fields and do not form stratified ensembles [RoBards et al, 1976].…”