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Neuronal morphology in the African elephant (Loxodonta africana) neocortex

Abstract

Virtually nothing is known about the morphology of cortical neurons in the elephant. To this end, the current study provides the first documentation of neuronal morphology in frontal and occipital regions of the African elephant (Loxodonta africana). Cortical tissue from the perfusion-fixed brains of two free-ranging African elephants was stained with a modified Golgi technique. Neurons of different types (N = 75), with a focus on superficial (i.e., layers II–III) pyramidal neurons, were quantified on a computer-assisted microscopy system using Neurolucida software. Qualitatively, elephant neocortex exhibited large, complex spiny neurons, many of which differed in morphology/orientation from typical primate and rodent pyramidal neurons. Elephant cortex exhibited a V-shaped arrangement of bifurcating apical dendritic bundles. Quantitatively, the dendrites of superficial pyramidal neurons in elephant frontal cortex were more complex than in occipital cortex. In comparison to human supragranular pyramidal neurons, elephant superficial pyramidal neurons exhibited similar overall basilar dendritic length, but the dendritic segments tended to be longer in the elephant with less intricate branching. Finally, elephant aspiny interneurons appeared to be morphologically consistent with other eutherian mammals. The current results thus elaborate on the evolutionary roots of Afrotherian brain organization and highlight unique aspects of neural architecture in elephants.

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Acknowledgments

Partial support for this work was provided by the Thomas M. McKee Professorship in the Natural Sciences (B.J.), The Colorado College’s divisional research funds (B.J.), the James S. McDonnell Foundation (grant 22002078, to C.C.S., P.R.H.), and the South African National Research Foundation (P.R.M.; FA2005033100004). We would also like to thank Dr. Hilary Madzikanda of the Zimbabwe Parks and Wildlife Management Authority, and Dr. Bruce Fivaz and the team at the Malilangwe Trust, Zimbabwe.

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Correspondence to Bob Jacobs.

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Jacobs, B., Lubs, J., Hannan, M. et al. Neuronal morphology in the African elephant (Loxodonta africana) neocortex. Brain Struct Funct 215, 273–298 (2011). https://doi.org/10.1007/s00429-010-0288-3

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Keywords

  • Dendrite
  • Morphometry
  • Dendritic spine
  • Golgi method
  • Brain evolution