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 Neuroscienceof THE NATIONAL SCIENCE FOUNDATION

grants IBN 0131267, 0131028, 0131826.

Poster design, adviser and printerGearl 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.

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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: 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..

ResultsVisible 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.html From http://brainmuseum.org/Specimens/artiodactyla/sheep/index.html