Missaire, M. | Search bioRxiv

bioRxiv2023

Synaptic strength dynamics at cortical synaptic pathways is encoded by vigilance states duration

Interactions among brain areas are essential to most cognitive functions. Neuronal interactions between these areas depend on the modulation of synaptic strength. However, this modulation remains poorly understood. We recorded evoked synaptic responses at four hippocampal pathways in freely moving male rats across 24 hours: the Perforant Path to Dentate Gyrus (PP-DG), Fornix to Prefrontal Cortex (Fx-PFC), Fornix to Nucleus Accumbens (Fx-NAc), and the Schaffer Collaterals to CA1 (SC-CA1). We preserved the temporal dynamics of vigilance states and synaptic responses and show for the first time that synaptic strength at these four hippocampal pathways oscillates, with a very slow periodicity. We demonstrate that synaptic strength at the PP-DG, Fx-PFC, Fx-NAc pathways show a positive correlation with the duration of active wakefulness (aWK) and a negative one with the duration of most sleep states (slow wave sleep (SWS) and rapid eye movement sleep (REM)), with a positive peak correlation time-lag of 1 to 10 minutes for aWK and SWS at these 3 pathways. In contrast, no significant correlation peak is found at the SC-CA1 pathway. Finally, a model based on hypnogram data and synaptic strength at the PP-DG pathway was able to predict the evolution of synaptic strength at the PP-DG, Fx-PFC and Fx-NAc pathways, but not at the SC-CA1 pathway. These results reveal that the temporal succession of vigilance states, particularly aWK and SWS, may contribute to memory processes through rapid modulation of synaptic strength at several pathways during the sleep-wakefulness cycle, suggesting that memory processes are not only dependent on sleep amount but also on sleep architecture.

neuroscience↗

bioRxiv2020

Working and Reference Memory tasks trigger opposed long-term synaptic changes in the rat dentate gyrus

Long-term storage of information into memory is supposed to rely on long-term synaptic plasticity processes. Detection of such synaptic changes after training in long-term or reference memory (RM) tasks has yet been scarce, variable and only studied on a short time scale. On the other hand, short-term or working memory (WM) is largely known to depend on persistent neuronal activity or short-term plasticity processes. However, processing information into WM could also involve long-term synaptic changes that could be responsible for the erasure/forgetting of items previously stored in WM playing the role of proactive interference. In order to study long-term synaptic changes associated with RM or WM, we trained chronically implanted rats in three different radial maze tasks: a classical RM task and two WM tasks involving different levels of proactive interference. Synaptic responses at the perforant path to dentate gyrus synapse were recorded on a long-time scale (24h) in freely-moving rats after training in one of these three tasks. We found that consolidation of long-term information leads to a delayed synaptic potentiation, occurring 9 hours after RM training and predicting good behavioral performance on the following day. In contrast, optimal information processing into WM triggers a synaptic depression immediately observed after training and lasting 3 hours, that could act as a mechanism for interference erasure/forgetting.

animal behavior and cognition↗