Periodic Reporting for period 1 - CA1 layers (Contribution of distinct pyramidal cell types in hippocampal area CA1 to episodic memory formation)
Okres sprawozdawczy: 2016-06-01 do 2018-05-31
The HF is a vulnerable part of the brain and damage to its individual components is observed even in early stages of numerous neurological conditions such as stroke, epilepsy and Alzheimer's disease. Typical symptoms such as loss of memory and spatial navigation skills are likely due to such damage to the HF. The project described here provided us with more detailed information of how exactly the healthy HF functions. Understanding the exact processes of how memories are formed in the healthy brain will allow us to better understand what goes wrong in the diseased brain. This, in turn, will point us towards more directed strategies to slow down or prevent pathological memory loss and to improve memory function in patients with neurological conditions.
The formation of episodic memories does not only require the association of information about events and their places, but also that events are encoded in the correct temporal order. The temporal organization of information relies on the precise interplay between brain oscillations and the firing or individual neurons. The medial septum (MS) is a structure known to be a key generator of prominent brain oscillations referred to as the theta rhythm. How the individual cell types within the MS contribute to this function, however, remains unknown. Using patch clamp recordings and neuronal tracing techniques, the Monyer laboratory recently identified two distinct long-range-projecting GABAergic neuron (LRGN) types in the MS, which can be distinguished by their selective expression of parvalbumin (PV) and calbindin (CB) (Fuchs et al., 2016). These two cell types target specific cell types in the MEC and are ideally suited to coordinate distinct temporal computations in the MEC. We probed the function of these two LRGNs, using optogenetics and electrophysiological in vivo recordings in behaving mice. We found that the two cell types have distinct, and yet complementary functions: PV expressing LRGNs are important for the generation of the theta rhythm in the MEC, and thus for the generation of a clock-like signal for the coordination of memory components. CB expressing LRGNs, in turn, are not required to generate a clock-like signal, but instead organize the sequential firing of MEC neurons.
The results were presented at the Spring Hippocampal Research Conference 2017 in Taormina (Italy) as well as at the 11th Federation of European Neurocience Scoieties (FENS) 2018 in Berlin (Germany).