Morphometric assessment of a koala brain using MR mapping methods — The Association Specialists
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Morphometric assessment of a koala brain using MR mapping methods (22214)

Kristy RQ Goh 1 , Timothy Stait-Gardner 2 , Nyoman D Kurniawan 3 , Marianne D Keller 1
  1. Sydney School of Veterinary Science, University of Sydney, Sydney, NSW, Australia
  2. Nanoscale Organisation and Dynamics Group, Western Sydney University, Sydney, NSW, Australia
  3. Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD, Australia

Australia's isolated evolution resulted in a significant divergence of brain anatomy of marsupials compared to eutherians. As brain atlases do not need to use multiple specimens; this study’s aim is to describe morphometric measurements and volumetry of a formalin-fixed brain of a naturally deceased mature female koala.1 EPA-NSW Scientific license: SL102840.

The MRI dataset was acquired on a 9.4T Bruker MR system, using a 3D multigradient echo sequence, with TR/TE = 70msec/4msec, a field of view = 3x3x4cm, single excitation, with an isotropic image resolution of 0.2mm3. For three-dimensional volume reconstruction AMIRA post-processing software was used.

The naturally lissencephalic brain of this koala had a volume of 15,549mm3. For each structure, the volume and percent-ratio to the total brain volume (tbv) were: olfactory bulbs = 418mm3 (2.85% tbv); cerebral hemispheres = 9337mm3 (60% tbv); anterior commissure, collectively ventral hippocampal commissure and fasiculans abberans were 148mm3 (1% tbv); The ventricular system = 172mm3 (1% tbv); brainstem = 1874mm3 (12.06% tbv); cerebellum = 2305mm3 (14.82% tbv).

Interhemispheric connections in marsupials are of interest, as they do not have a corpus callosum but an alternative tract, the fasciculus aberrans, which requires further investigation using tractography.

The olfactory bulb in the koala occupies a smaller proportion of the tbv compared to the quokka, which has a more variable diet.2 The caudate nucleus in the koala has been found to be larger than the putamen, which might be due to prioritisation of goal directed behaviour, over fine motor control

  1. Nowinski, W.L. Evolution of Human Brain Atlases in Terms of Content, Applications, Functionality, and Availability. Neuroinform 19, 1–22 (2021). https://doi.org/10.1007/s12021-020-09481-9
  2. Thittamranahalli Kariyappa, J., Zanoni, S., Bongers, A., Tong, L., & Ashwell, K. Magnetic resonance imaging and diffusion tensor imaging reconstruction of connectomes in a macropod, the quokka (Setonix brachyurus). Journal of Comparative Neurology, 2022;530(12), 2188–2214. https://doi.org/10.1002/cne.25328