Changes in hippocampal CA1 region activity during early postnatal development     

Robin DARD

Cossart Lab “Developmental scaffolding of adult hippocamal circuits”

Abstract

This thesis work first described the activity patterns observed in vivo in the CA1 region of the hippocampus in mice during the first two weeks of postnatal life in mice. We then sought to understand the neural circuits supporting these activities. Finally, we were interested in understanding how the activity contributes to the anatomical and functional development of CA1.

Our results highlight the already established link between sensory feedback related to mouse sleep twitches and activation in the CA1 region of the hippocampus during the first week of life. Using a chemogenetic approach we could study the influence of other regions projecting to CA1 during the first week of life. Thus, we could show that, as suggested by Valeeva and colleagues, sensory information is relayed to the hippocampus via the entorhinal cortex. In vitro results show that the reuniens nucleus could also modulate CA1 dynamics. In addition, in vivo results show that this nucleus would be involved in the modulation of the activity of pyramidal cells but not in their synchronization. We have shown a rapid inversion of the relationship between movement and activity around postnatal day nine (P9). Indeed, whereas movement was followed by activation in CA1 before P9, it leads to a strong reduction of activity at later stages. This transition in CA1 dynamics in response to sensory feedback coincides with the age at which we observed a rapid development of inhibitory perisomatic innervation onto CA1 pyramidal cells. This transition is also marked by the emergence of activity outside the periods of movement, which reflects the disengagement of the hippocampus from sensory inputs. Finally, we could show that the development of perisomatic innervation from parvalbumin expressing interneurons depends at least in part on the activity of hippocampal somatostatin interneurons.

Jury

Michel Picardo,  Thesis Co-Director de thèse – INMED, Marseille
Rosa Cossart, Thesis Director – INMED, Marseille
Christophe Porcher,  Jury President – INMED, Marseille
Lisa Roux, Rapportrice – IINS, Bordeaux
Vincent Villette, Reporting – IBENS, Paris
Claire Wyart, Reviewer – ICM, Paris
David Dupret, Reviewer – MRC Brain Network Dyamics Unit, Oxford (UK)
Franck Debarbieux, Reviewer – INT, Marseille

Inmed meeting room – Monday, October 24th at 2 am