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Neocortical neuron types in Xenarthra and Afrotheria: implications for brain evolution in mammals

Sherwood, Chet C. and Stimpson, Cheryl D. and Butti, Camilla and Bonar, Christopher J. and Newton, Alisa L. and Allman, John M. and Hof, Patrick R. (2009) Neocortical neuron types in Xenarthra and Afrotheria: implications for brain evolution in mammals. Brain Structure and Function, 213 (3). pp. 301-328. ISSN 1863-2661.

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Interpreting the evolution of neuronal types in the cerebral cortex of mammals requires information from a diversity of species. However, there is currently a paucity of data from the Xenarthra and Afrotheria, two major phylogenetic groups that diverged close to the base of the eutherian mammal adaptive radiation. In this study, we used immunohistochemistry to examine the distribution and morphology of neocortical neurons stained for nonphosphorylated neurofilament protein, calbindin, calretinin, parvalbumin, and neuropeptide Y in three xenarthran species—the giant anteater (Myrmecophaga tridactyla), the lesser anteater (Tamandua tetradactyla), and the two-toed sloth (Choloepus didactylus)—and two afrotherian species—the rock hyrax (Procavia capensis) and the black and rufous giant elephant shrew (Rhynchocyon petersi). We also studied the distribution and morphology of astrocytes using glial fibrillary acidic protein as a marker. In all of these species, nonphosphorylated neurofilament protein-immunoreactive neurons predominated in layer V. These neurons exhibited diverse morphologies with regional variation. Specifically, high proportions of atypical neurofilament-enriched neuron classes were observed, including extraverted neurons, inverted pyramidal neurons, fusiform neurons, and other multipolar types. In addition, many projection neurons in layers II–III were found to contain calbindin. Among interneurons, parvalbumin- and calbindin-expressing cells were generally denser compared to calretinin-immunoreactive cells. We traced the evolution of certain cortical architectural traits using phylogenetic analysis. Based on our reconstruction of character evolution, we found that the living xenarthrans and afrotherians show many similarities to the stem eutherian mammal, whereas other eutherian lineages display a greater number of derived traits.

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Additional Information:© Springer-Verlag 2008. Received: 5 September 2008 / Accepted: 16 October 2008 / Published online: 15 November 2008. We thank Chad Lennon and Amy Garrison for technical assistance and Dr. Mary Ann Raghanti for helpful discussion. This work was supported by the National Science Foundation (BCS-0515484, BCS-0549117, and BCS-0453005) and the James S. McDonnell Foundation (22002078).
Funding AgencyGrant Number
James S. McDonnell Foundation22002078
Subject Keywords:Brain evolution; Cerebral cortex; Interneuron; Mammal; Pyramidal cell
Issue or Number:3
Record Number:CaltechAUTHORS:SHEbsf09
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13315
Deposited By: Kristin Buxton
Deposited On:11 Feb 2009 00:50
Last Modified:09 Jun 2020 20:08

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