title: In contrast to many other mammals, cetaceans have relatively small hippocampi that appear to lack adult neurogenesis.
abstract: The hippocampus is essential for the formation and retrieval of memories and is a crucial neural structure sub-serving complex cognition. Adult hippocampal neurogenesis, the birth, migration and integration of new neurons, is thought to contribute to hippocampal circuit plasticity to augment function. We evaluated hippocampal volume in relation to brain volume in 375 mammal species and examined 71 mammal species for the presence of adult hippocampal neurogenesis using immunohistochemistry for doublecortin, an endogenous marker of immature neurons that can be used as a proxy marker for the presence of adult neurogenesis. We identified that the hippocampus in cetaceans (whales, dolphins and porpoises) is both absolutely and relatively small for their overall brain size, and found that the mammalian hippocampus scaled as an exponential function in relation to brain volume. In contrast, the amygdala was found to scale as a linear function of brain volume, but again, the relative size of the amygdala in cetaceans was small. The cetacean hippocampus lacks staining for doublecortin in the dentate gyrus and thus shows no clear signs of adult hippocampal neurogenesis. This lack of evidence of adult hippocampal neurogenesis, along with the small hippocampus, questions current assumptions regarding cognitive abilities associated with hippocampal function in the cetaceans. These anatomical features of the cetacean hippocampus may be related to the lack of postnatal sleep, causing a postnatal cessation of hippocampal neurogenesis.
authors.affiliation: School of Anatomical Sciences, University of the Witwatersrand, 7 York Road, Parktown, Johannesburg, 2193, South Africa.
authors.forename: Nina
authors.initials: N
authors.lastname: Patzke
authors.forename: Muhammad A
authors.initials: MA
authors.lastname: Spocter
authors.forename: Karl Æ
authors.initials: KÆ
authors.lastname: Karlsson
authors.forename: Mads F
authors.initials: MF
authors.lastname: Bertelsen
authors.forename: Mark
authors.initials: M
authors.lastname: Haagensen
authors.forename: Richard
authors.initials: R
authors.lastname: Chawana
authors.forename: Sonja
authors.initials: S
authors.lastname: Streicher
authors.forename: Consolate
authors.initials: C
authors.lastname: Kaswera
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Gilissen
authors.forename: Abdulaziz N
authors.initials: AN
authors.lastname: Alagaili
authors.forename: Osama B
authors.initials: OB
authors.lastname: Mohammed
authors.forename: Roger L
authors.initials: RL
authors.lastname: Reep
authors.forename: Nigel C
authors.initials: NC
authors.lastname: Bennett
authors.forename: Jerry M
authors.initials: JM
authors.lastname: Siegel
authors.forename: Amadi O
authors.initials: AO
authors.lastname: Ihunwo
authors.forename: Paul R
authors.initials: PR
authors.lastname: Manger
mesh_terms: D000818:Animals; D002591:Cetacea / Q000033:anatomy & histology; D000089622:Doublecortin Domain Proteins; D006624:Hippocampus / Q000166:cytology* / Q000502:physiology*; D016014:Linear Models; D008322:Mammals / Q000033:anatomy & histology*; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D055495:Neurogenesis / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D009479:Neuropeptides / Q000378:metabolism; D013045:Species Specificity
chemical_list: D000089622:Doublecortin Domain Proteins; D008869:Microtubule-Associated Proteins; D009479:Neuropeptides