Comparative Contemplations on the Hippocampus

Kleven, Heidi; Flatmoen, Asgeir Kobro

doi:10.1159/000475703

Cited by 23 publications

(24 citation statements)

References 72 publications

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“…Such a projection from LCd to MC of lizards was considered comparable to part of the perforant pathway of mammals (the other part being the projection from DC2, which as discussed above is comparable to mammalian medial entorhinal cortex or MEC) (López‐García et al, ; also discussed by Medina et al, ). In mammals, the projections from LEC to DG originate from superficial layer II cells (reviewed by Witter, ; Witter & Amaral, ; Witter et al, ), which express reelin at least in some mammals as the ferret (Ramos‐Moreno, Galazo, Porrero, Martínez‐Cerdeño, & Clascá, ) and the mouse (Allen Developing Mouse Brain Atlas). The presence of such reelin‐containing cells densely grouped in layer II is characteristic of the entorhinal cortex in mammals, as they are not observed in other neighboring cortical areas (containing dispersed reelin cells mostly related to interneurons; the neocortex also contains reelin‐positive projection neurons but located in layer 5), with the exception of the piriform/olfactory cortex (Ramos‐Moreno et al, ; Allen Developing Mouse Brain Atlas).…”

Section: Discussionmentioning

confidence: 99%

“…As noted above, the avian APHcl/CDL and its lateral extension (an olfactory bulb‐recipient area, which also keeps strong Lhx9 expression) were suggested to be comparable to the medial entorhinal cortex of mouse (Abellán et al, ; see also Redies et al, ; Suárez, Dávila, Real, Guirado, & Medina, ). The lizard DC2 has also been proposed to be comparable to the medial entorhinal cortex (Medina et al, ) based on its projections to the MC (dentate gyrus homologue), which resemble part of the perforant pathway of mammals (López‐García et al, ), that is, the projection from the entorhinal cortex to the dentate gyrus (Canto, Wouterlood, & Witter, ; van Strien et al, ; Witter, ; Witter & Amaral, ; Witter, Kleven, & Flatmoen, ). In birds, the APHcl/CDL also projects to the dentate gyrus homologue (including the V‐shaped area; Atoji & Wild, ; the dentate gyrus homology is based on topological position and expression of the transcription factor Prox1: Abellán et al, ; Atoji, Sarkar, & Wild, ; Medina et al, ).…”

Section: Discussionmentioning

confidence: 99%

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Expression of regulatory genes in the embryonic brain of a lizard and implications for understanding pallial organization and evolution

Desfilis

Abellán

Sentandreu

et al. 2017

J of Comparative Neurology

179

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The comparison of gene expression patterns in the embryonic brain of mouse and chicken is being essential for understanding pallial organization. However, the scarcity of gene expression data in reptiles, crucial for understanding evolution, makes it difficult to identify homologues of pallial divisions in different amniotes. We cloned and analyzed the expression of the genes Emx1, Lhx2, Lhx9, and Tbr1 in the embryonic telencephalon of the lacertid lizard Psammodromus algirus. The comparative expression patterns of these genes, critical for pallial development, are better understood when using a recently proposed six‐part model of pallial divisions. The lizard medial pallium, expressing all genes, includes the medial and dorsomedial cortices, and the majority of the dorsal cortex, except the region of the lateral cortical superposition. The latter is rich in Lhx9 expression, being excluded as a candidate of dorsal or lateral pallia, and may belong to a distinct dorsolateral pallium, which extends from rostral to caudal levels. Thus, the neocortex homolog cannot be found in the classical reptilian dorsal cortex, but perhaps in a small Emx1‐expressing/Lhx9‐negative area at the front of the telencephalon, resembling the avian hyperpallium. The ventral pallium, expressing Lhx9, but not Emx1, gives rise to the dorsal ventricular ridge and appears comparable to the avian nidopallium. We also identified a distinct ventrocaudal pallial sector comparable to the avian arcopallium and to part of the mammalian pallial amygdala. These data open new venues for understanding the organization and evolution of the pallium.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Expression of regulatory genes in the embryonic brain of a lizard and implications for understanding pallial organization and evolution

Desfilis

Abellán

Sentandreu

et al. 2017

J of Comparative Neurology

179

View full text Add to dashboard Cite

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“…The cytoarchitecture, connectivity, and other features of the amniote hippocampus have recently been reviewed in depth [Striedter, 2016;Reiter et al, 2017;Witter et al, 2017]. All amniotes share some features, such as the presence of double pyramidal cells (neurons with dendritic trees that extend both superficially and deep to the cell body layer), while some features are shared among some but not all amniotes, and some, possibly including the presence or at least elaboration of a distinct dentate gyrus, may be unique to only one clade -mammals in the case of the dentate gyrus [Striedter, 2016;Bingman and Muzio, 2017].…”

Section: Comparison Of Hippocampal Formation Morphology Across Amniotesmentioning

confidence: 99%

Of Horse-Caterpillars and Homologies: Evolution of the Hippocampus and Its Name

Butler

2017

Brain Behav Evol

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The hippocampus was first named in mammals based on the appearance of its gross morphological features, one end of it being fancied to resemble the head of a horse and the rest of it a silkworm, or caterpillar. A hippocampus, occupying the most medial part of the telencephalic pallium, has subsequently been identified in diverse nonmammalian taxa, but in which the “horse-caterpillar” morphology is lacking. While some strikingly similar functional similarities have been identified, questions of its homology (“sameness”) across these taxa and about the very fundamental relationship of structure to function in central nervous system structures remain open. The hippocampal formation of amniotes participates in allocentric (external landmark) spatial navigation, memory, and attention to novel stimuli, and these functions generally are shared across amniotes despite variation in its morphological features. Substantially greater deviation in its morphology occurs in anamniotes, including amphibians and ray-finned fishes (actinopterygians), but its functions of allocentric spatial navigation and/or memory have been found to be preserved by studies in these taxa. Its shared functional roles cannot be used as evidence of structural homology, but given that other criteria indicate homology of the medial pallial derivative across these clades, the similar functions themselves may be regarded as homologous functions if they are based on the same cellular mechanisms and connections. The question arises as to whether the similar functions are performed by as yet undiscovered, shared morphological features or by different features that accomplish the same results via different mechanisms of neural function.

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“…In rodents and many other mammals the ventral extension is of small size, but in primates) the ventral portion is very large (Insausti, ). From a functional point of view the dorsal hippocampus has been shown to be associated with navigation and memory processes, whereas the ventral hippocampus was associated with emotional, anxiety or stress related behaviours (Moser, Moser, & Andersen, ; Witter, Kleven, & Flatmoen, ). Both dorsal and ventral parts of the hippocampus have a complex internal structure, the most recognizable parts of the which are the cornu ammonis (CA) (Ammon's horn) and dentate gyrus (DG) regions (Figure ).…”

Section: Introductionmentioning

confidence: 99%

Elongation of the CA1 field of the septal hippocampus in ungulates

Watson

Binks

2018

J of Comparative Neurology

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It is widely assumed that the hippocampal formation seen in laboratory rodents and in primates is typical of that seen in other mammals. We have tested this assumption by examining sections of brains of 56 mammals from 20 mammalian orders from images on the http://brainmuseum.org website. We found wide variation in the form of the hippocampal formation, the most extreme examples of which are seen in ungulates, which possess an unusual elongation of the distal CA1 of the septal hippocampus. This phenomenon has not previously been reported. In individual coronal sections of the brains of seven artiodactyl ungulates, the pyramidal layer of CA1 is four times as long as CA2 + CA3. In a perissodactyl ungulate (Burchell's zebra) the distal end of CA1 is so large that it forms a number of folds. A similar but less pronounced CA1 elongation was seen in the brains of 14 carnivores. A modest elongation of CA1 is also present in some other placental mammals, notably the elephant shrew, hyrax, capybara, beaver, and rabbit. The elongation was not present in brains of primates, marsupials, or monotremes. The distal part of CA1 has been shown to play a role in object integration into the spatial map. We hypothesize that the distal CA1 enlargement could serve to enhance the ability to integrate objects into spatial navigation, which would be an advantage for migrating herds of ungulates. We suggest that the remarkable elongation of Q5 CA1 represents a major evolutionary specialization in the ungulates.

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Comparative Contemplations on the Hippocampus

Cited by 23 publications

References 72 publications

Expression of regulatory genes in the embryonic brain of a lizard and implications for understanding pallial organization and evolution

Expression of regulatory genes in the embryonic brain of a lizard and implications for understanding pallial organization and evolution

Of Horse-Caterpillars and Homologies: Evolution of the Hippocampus and Its Name

Elongation of the CA1 field of the septal hippocampus in ungulates

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