1. Brain Cytoarchitecture in a Large Grazing Marsupial, Rufous Wallaby Thylogale billardieri. Cindy D. Knaff, under the direction of Dr. John I. Johnson, Radiology Supported by The Division of Integrative Biology and Neuroscience of THE NATIONAL SCIENCE FOUNDATION grants IBN 0131267, 0131028, 0131826. Poster design, adviser and printer Gearl Diggs, Radiology Dept. Michigan State University See the atlases of the brains of dolphins, sheep, humans and axolotls at http://www.brains.rad.msu.edu, http://brainmuseum.org or http://www. user/brains/atlases msu.edu A similar atlas of the brains of rufous wallabies is in preparation for these sites. turs kog REFERENCES The AUDITORY DORSAL COCHLEAR NUCLEUS shows distinct lamination in both species. This nucleus has recently been shown to have a cerebellum-like function (Oertel & Young, 2004). Clark PG, Martin KA, Rao Vm, Whitteridge D. The dorsal lateral geniculate nucleus of the sheep and its retinal connections. Q J Exp Physiol. 1988 May:73(3):295-304. Oertel D. Young ED, What’s a cerebellar circuit doing in the auditory system? Trends Neurosci. 2004 Feb:27(2):104-10. Sanderson KJ, Haight JR, Pettigrew JD. The dorsal lateral geniculate nucleus of macropodid marsupials: cytoarchitecture and retinal projections. J Comp Neurol. 1984 Mar 20:224(1):85-106. Sanderson KJ, Nelson JE, Crewther DP, Crewther SG, Hammond VE. Retinogeniculate patterns in diprotodont marsupials. Brain Behav Evol. 1987:30(1-2):22-42 DOMESTIC SHEEP Ovis aries RUFOUS WALLABY Thylogale billardieri ABOVE: Six standard views of the intact brains. ABOVE: Sagittal view of the superior and inferior colliculi. ABOVE: Coronal view of the olfactory bulb and stalk. ABOVE: Sagittal view of the lateral geniculate nucleus and optic tract. ABOVE: Horizontal view of the dorsal and ventral cochlear nuclei. ABOVE: Sagittal view of the lateral geniculate nucleus and optic tract ABOVE: Sagittal view of the superior and inferior colliculi. ABOVE: Coronal view of the olfactory bulb and stalk.. Introduction Brain evolution can be seen through comparative neurology. Wallabies, large grazing marsupials, provide opportunities to study evolutionary convergences with brains of independently evolved brains of large grazing placental mammals, from a separate branch of mammalian radiation. We have analyzed the internal structure of the brains of Rufous Wallabies Thylogale billardieri, in direct comparison with their counterpart structures in Domestic Sheep Ovis aries. Procedures Sections of brains from museum collections were examined for evidence of specializations related to herbivorous grazing behavior. These wallaby and sheep brains were dehydrated, embedded in nitrocellulose (celloidin), sectioned at 35 um intervals and were stained with thionine, a standard Nissl staining procedure, to show distributions of neuronal cell bodies.. Results Visible lamination in cell groups within the brain is one indicator of relatively well developed systems. Sections from both species show several visibly laminated brain regions subserving olfaction, vision, and audition, as well as a large extent of laminated cerebral isocortex. Conclusions These particular parallel hyperdevelopments in maximally distant related species appear to be related to environmental adaptations rather than to phylogenetic relationships. OLFACTORY SYSTEM VISUAL SYSTEM AUDITORY SYSTEM VISUAL AND AUDITORY SYSTEMS The OLFACTORY BULBS in both species are large and show a high degree of visible lamination. The VISUAL SUPERIOR COLLICULI are larger than the AUDITORY INFERIOR COLLICULI in both species, and show visible lamination. This is typical of herbivorous “prey species” who must keep a watch for predators while still far away. The VISUAL LATERAL GENICULATE NUCLEUS shows visible lamination in both species. Sheep have three distinct laminae in each lateral geniculate nucleus (Clarke, et al., 1988), while Rufous Wallabies have 7 or 8 laminae (Sanderson et al., 1984, 1987), some of which are visible here. From http://brainmuseum.org/Specimens/marsupalia/ rufwallaby/index.html Original photograph, John I. Johnson From http://brainmuseum.org/Specimens/marsupalia/rufwallaby/index.htmlFrom http://brainmuseum.org/Specimens/artiodactyla/sheep/index.html