Magnetic Resonance Imaging of the Brains of Three Peramelemorphian Marsupials

Abstract

Peramelemorphians (bandicoots and bilbies) are a unique and diverse group of digging Australasian marsupials, but their behavioral neurology and neuroanatomy is poorly known. Here, we have used Magnetic Resonance Imaging (MRI) to study the brains of three peramelemorphians: two bandicoots (Perameles nasuta and Isoodon obesulus) and the bilby (Macrotis lagotis), which is endangered. These brains had been stored in formaldehyde solution for more than 80 years and one of our goals was to demonstrate the feasibilty of extracting detailed comparative neuroanatomical information from the long-term preserved brains of rare, endangered, and extinct animals. High resolution anatomical and Diffusion Tensor Imaging was performed using a 9.4-T Bruker BioSpec 94/20 Avance III MRI system (Bruker, Ettlingen, Germany) located at the UNSW in Sydney. We were able to differentiate areal and laminar topography within isocortical areas (primary somatosensory – S1; and visual - V1, V2), as well as subdivisions within olfactory and limbic allocortical regions (cingulate, hippocampal). Resolution of subcortical structures was sufficient to differentiate α and β segments within the visual nucleus of the thalamus. We identified several previously unrecognized longitudinal association fiber systems as well as a rich array of sensory thalamocortical connections. Dense fiber pathways were observed to S1 and in the midbrain auditory pathways (mainly the lateral lemniscus, but also the brachium of the inferior colliculus). Our findings demonstrate the feasibility of using this sort of imaging of archived brains to analyze the neuroanatomy of rare and evolutionarily significant species and to relate these findings to the behavioral neurology of those species.