Neuronal circuits within the homing pigeon hippocampal formation. Issue 7 (18th February 2023)

• Record Type: Journal Article
• Authors: Rook, Noemi; Stacho, Martin; Schwarz, Ariane; Bingman, Verner P.; Güntürkün, Onur
• Is Part Of: Journal of comparative neurology. Volume 531:Issue 7(2023)
• Page Start: 790
• Page End: 813
• Publication Date: 2023-02-18
• Subjects: avian hippocampus -- calbindin -- CaMKIIα -- doublecortin -- GFAP -- intrahippocampal circuitry -- topography -- tracing; Comparative neurobiology -- Periodicals; Neurology -- Periodicals; 616
• DOI: 10.1002/cne.25462
• Languages: English
• ISSNs: 0021-9967

Abstract

Abstract: The current study aimed to reveal in detail patterns of intrahippocampal connectivity in homing pigeons ( Columba livia ). In light of recent physiological evidence suggesting differences between dorsomedial and ventrolateral hippocampal regions and a hitherto unknown laminar organization along the transverse axis, we also aimed to gain a higher‐resolution understanding of the proposed pathway segregation. Both in vivo and high‐resolution in vitro tracing techniques were employed and revealed a complex connectivity pattern along the subdivisions of the avian hippocampus. We uncovered connectivity pathways along the transverse axis that started in the dorsolateral hippocampus and continued to the dorsomedial subdivision, from where information was relayed to the triangular region either directly or indirectly via the V‐shaped layers. The often‐reciprocal connectivity along these subdivisions displayed an intriguing topographical arrangement such that two parallel pathways could be discerned along the ventrolateral (deep) and dorsomedial (superficial) aspects of the avian hippocampus. The segregation along the transverse axis was further supported by expression patterns of the glial fibrillary acidic protein and calbindin. Moreover, we found strong expression of Ca 2+ /calmodulin‐dependent kinase IIα and doublecortin in the lateral but not medial V‐shape layer, indicating a difference between the two V‐shaped layers. Overall, our findings provide an unprecedented, detailed description of avian intrahippocampal pathway connectivity, and confirm the recently proposed segregation of the avian hippocampus along the transverse axis. We also provide further support for the hypothesized homology of the lateral V‐shape layer and the dorsomedial hippocampus with the dentate gyrus and Ammon's horn of mammals, respectively. Abstract : In this study, we investigated the intrinsic connectivity of the pigeon hippocampal formation (HF) using in vivo and in vitro tracings. Moreover, pigeon hippocampal brain sections were immunohistochemically stained against CaMKIIα, calbindin, GFAP and DCX to further differentiate between potential hippocampal subdivisions. Using these techniques, we found that the pigeon HF can be segregated along its transverse axis into a dorsomedial (superficial) and ventrolateral (deep) pathway.