Organization and chemical neuroanatomy of the African elephant (Loxodonta africana) hippocampus
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Elephants are thought to possess excellent long-term spatial–temporal and social memory, both memory types being at least in part hippocampus dependent. Although the hippocampus has been extensively studied in common laboratory mammalian species and humans, much less is known about comparative hippocampal neuroanatomy, and specifically that of the elephant. Moreover, the data available regarding hippocampal size of the elephant are inconsistent. The aim of the current study was to re-examine hippocampal size and provide a detailed neuroanatomical description of the hippocampus in the African elephant. In order to examine the hippocampal size the perfusion-fixed brains of three wild-caught adult male African elephants, aged 20–30 years, underwent MRI scanning. For the neuroanatomical description brain sections containing the hippocampus were stained for Nissl, myelin, calbindin, calretinin, parvalbumin and doublecortin. This study demonstrates that the elephant hippocampus is not unduly enlarged, nor specifically unusual in its internal morphology. The elephant hippocampus has a volume of 10.84 ± 0.33 cm³ and is slightly larger than the human hippocampus (10.23 cm3). Histological analysis revealed the typical trilaminated architecture of the dentate gyrus (DG) and the cornu ammonis (CA), although the molecular layer of the dentate gyrus appears to have supernumerary sublaminae compared to other mammals. The three main architectonic fields of the cornu ammonis (CA1, CA2, and CA3) could be clearly distinguished. Doublecortin immunostaining revealed the presence of adult neurogenesis in the elephant hippocampus. Thus, the elephant exhibits, for the most part, what might be considered a typically mammalian hippocampus in terms of both size and architecture.
KeywordsAdult hippocampal neurogenesis Calcium-binding proteins Hippocampus Doublecortin Memory Proboscidean
This study was supported by a grant from the South African National Research Foundation to PRM (Grant number: FA2005033100004), the Swiss-South African Joint Research Programme to AOI and PRM, a fellowship within the Postdoc-Programme of the German Academic Exchange Service, DAAD (NP), and the James S. McDonnell Foundation (Grant 22002078 to PRH). We would 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.
Conflict of interest
The authors have no conflict of interest.
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