Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com Original Paper Brain Behav Evol 2007;70:71–89 DOI: 10.1159/000102970 Cyto- and Chemoarchitecture of the Cerebellum of the Short-Beaked Echidna (Tachyglossus aculeatus) K.W.S. Ashwell a G. Paxinos b C.R.R. Watson c a Department of Anatomy, School of Medical Sciences, b Prince of Wales Medical Research Institute, The University of New South Wales, Sydney, c Division of Health Sciences, Curtin University of Technology, Perth, Australia ebellar white matter or terminating on Lugaro cells. Calbin- din immunoreactivity was also present in inferior olivary complex neurons. Calretinin immunoreactivity was found in pontocerebellar fibers and small cells in the deep granule cell layer of the ansiform lobule. We found that, although the deep cerebellar nuclei were much less clearly demar- cated than in the rodent cerebellum, it was possible to dis- tinguish medial, interposed and lateral nuclear components in the echidna. As far as we can determine from our tech- niques, the cerebellum of the echidna shows all the gross and cytological features familiar from the cerebellum of therian mammals. Copyright © 2007 S. Karger AG, Basel Introduction The monotremes are a unique group of non-therian mammals confined to Australasia and currently repre- sented by several species of echidna (long- and short- beaked) and the platypus [Griffiths, 1978; Musser, 2003]. Monotremes are of great biological interest because they demonstrate a mosaic of mammalian and reptilian fea- tures in their skeleton and reproductive physiology. The Key Words Deep cerebellar nuclei  Purkinje cells  Parvalbumin  Calbindin  Calretinin Abstract The monotremes (echidnas and platypus) have been claimed by some authors to show ‘avian’ or ‘reptilian’ fea- tures in the gross morphology and microscopic anatomy of the cerebellum. We have used Nissl staining in conjunction with enzyme histochemistry to acetylcholinesterase and cytochrome oxidase and immunohistochemistry to non- phosphorylated neurofilament protein (SMI-32 antibody), calcium binding proteins (parvalbumin, calbindin and cal- retinin) and tyrosine hydroxylase to examine the cyto- and chemoarchitecture of the cerebellar cortex and deep cere- bellar nuclei in the short-beaked echidna. Immunoreactivi- ty for non-phosphorylated neurofilament (SMI-32 antibody) was found in the deep cerebellar nuclei and in Purkinje cells of most regions except the nodule. Purkinje cells identified with SMI-32 immunoreactivity were clearly mammalian in morphology. Parvalbumin and calbindin immunoreactivity was found in Purkinje cells with some regional variation in staining intensity and in Purkinje cell axons traversing cer- Received: September 7, 2006 Returned for revision: October 20, 2006 Accepted after revision: October 26, 2006 Published online: May 18, 2007 A/Prof. Ken Ashwell Department of Anatomy, School of Medical Sciences The University of New South Wales Sydney, NSW 2052 (Australia) Tel. +61 2 9385 2482, Fax +61 2 9385 8016, E-Mail k.ashwell@unsw.edu.au © 2007 S. Karger AG, Basel 0006–8977/07/0702–0071$23.50/0 Accessible online at: www.karger.com/bbe