Modulation of CA1 dynamics by extrahippocampal inputs during development

Abstract:
Spontaneous activity shapes neural networks during the developmental period. In the CA1 region, the different patterns of activity described in vitro provide information about the level of local connectivity. However, many studies point the role of external afferents on the development of neocortical circuits, but the role of extra-hippocampal inputs on the development of local dynamics in CA1 remains poorly understood. Recent studies suggest that activations of the entorhinal cortex (EC) and the ventral midline thalamus (VMT) are correlated with network activities in the CA1 region recorded in vivo. In my thesis, I investigated the causal link between extra-hippocampal afferents and CA1 dynamics during the first postnatal week, while revealing the involved local circuits. To do so, I performed stereotaxic injections of virus into the VMT or the EC of mice at birth, allowing opto- and chemo-genetic manipulation of these extra-hippocampal inputs during 2-photon calcium imaging and electrophysiological recordings. The results show an important role of the VMT and the EC inputs on the dynamics of CA1 neural networks at the end of the first postnatal week. They also show the integration of these afferents by the CA1 network and highlight two distinct local circuits where GABAergic neurons play a predominant role. This thesis demonstrates an essential role of extra-hippocampal inputs on the maturation of the CA1 network during development.

Jury :
Président – Frédéric Brocard, Institut de Neurosciences de la Timone – INT, Marseille
Rapportrice – Sonia Garel, Institut de Biologie de l’École Normale Supérieure – IBENS, Paris
Rapporteur – Christophe Mulle, Institut Interdisciplinaire des Neurosciences – IINS, Bordeaux
Examinatrice – Pascale Quilichini, Institut de Neurosciences des Systèmes – INS, Marseille
Examinateur – Vincent Villette, Institut de Biologie de l’École Normale Supérieure – IBENS, Paris
Invitée – Rosa Cossart, Institut de Neurobiologie de la Méditerranée – INMED, Marseille
Directrice de thèse – Agnès Baude, Institut de Neurobiologie de la Méditerranée – INMED, Marseille

Erwan Leprince – équipe : Developmental scaffolding of adult hippocampal circuits – Rossa Cossart