Ventral midline thalamus is necessary for hippocampal place field stability and cell firing modulation

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Cholvin, Thibault | Hok, V. | Giorgi, Lisa | Chaillan, Franck, A | Poucet, Bruno

Edité par CCSD ; Society for Neuroscience -

International audience. The reuniens (Re) and rhomboid (Rh) nuclei of the ventral midline thalamus are reciprocally connected with the hippocampus (Hip) andthe medial prefrontal cortex (mPFC). Growing evidence suggests that these nuclei might play a crucial role in cognitive processesrequiring Hip–mPFC interactions, including spatial navigation. Here, we tested the effect of ReRh lesions on the firing properties andspatial activity of dorsal hippocampal CA1 place cells as male rats explored a familiar or a novel environment. We found no change in thespatial characteristics of CA1 place cells in the familiar environment following ReRh lesions. Contrariwise, spatial coherence was decreasedduring the first session in a novel environment. We then investigated field stability of place cells recorded across 5 d both in thefamiliar and in a novel environment presented in a predefined sequence. While the remapping capacity of the place cells was not affectedby the lesion, our results clearly demonstrated a disruption of the CA1 cellular representation of both environments in ReRh rats. Morespecifically, we found ReRh lesions to produce (1) a pronounced and long-lasting decrease of place field stability and (2) a strongalteration of overdispersion (i.e., firing variability). Thus, in ReRh rats, exploration of a novel environment appears to interfere with therepresentation of the familiar one, leading to decreased field stability in both environments. The present study shows the involvement ofReRh nuclei in the long-term spatial stability of CA1 place fields.

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