Suzanne Van der Veldt
Dept. of Neuroscience, CHU Sainte-Justine Research Center, Université de Montréal, Canada<
Invited by Jean-Christophe Delpech and Pierre Trifilieff (NutriNeuro)
Role of theta oscillations in the dorsal and ventral hippocampus: dissociating spatial codes, memory and emotional behaviors.
While the dorsal hippocampus is known to be implicated in spatial navigation and memory, the ventral hippocampus has been proposed to act as a major modulator of anxiety. The theta oscillation, a prominent 5-10 Hz rhythm observed in the local field potential throughout the hippocampus, has been associated with spatiotemporal coding, locomotion, memory and anxiety related behaviors. Theta rhythms are modulated by several subcortical nuclei, including the medial septum and the median raphe nucleus. Using a combination of calcium imaging, optogenetics and electrophysiology in freely behaving mice, we set out to manipulate theta rhythmicity while recording from dorsal or ventral hippocampal neuronal assemblies. In the first part of the talk, I will discuss how optogenetic frequency scrambling of the medial septum completely abolishes theta, which was associated with decreased working memory retrieval while leaving encoding of place, time and distance intact. In the second part of the talk, I will discuss how optogenetic activation of the raphe-hippocampus serotonergic projection neurons leads to altered ventral hippocampal theta. Excitatory opsin ChR2-mediated optogenetic activation of these projection neurons also robustly increased anxiety levels in a sex-dependent manner, suggesting that serotonin release in the ventral hippocampus directly modulates anxiety and associated changes in oscillatory properties. Thus, the hippocampus, through inputs from both medial septum and raphe, controls memory and anxiety functions, in part through theta physiology.