Abstract
The hippocampal output structure, the subiculum, expresses two major memory relevant network rhythms, sharp wave ripple and gamma frequency oscillations. To this date, it remains unclear how the two distinct types of subicular principal cells, intrinsically bursting and regular spiking neurons, participate in these two network rhythms. Using concomitant local field potential and intracellular recordings in an in vitro mouse model that allows the investigation of both network rhythms, we found a cell type-specific segregation of principal neurons into participating intrinsically bursting and non-participating regular spiking cells. However, if regular spiking cells were kept at a more depolarized level, they did participate in a specific manner, suggesting a potential bimodal working model dependent on the level of excitation. Furthermore, intrinsically bursting and regular spiking cells exhibited divergent intrinsic membrane and synaptic properties in the active network. Thus, our results suggest a cell-type-specific segregation of principal cells into two separate groups during network activities, supporting the idea of two parallel streams of information processing within the subiculum.
Highlights
The subiculum constitutes the major output structure of the hippocampal formation [1]
Using simultaneous local field potential (LFP) and sharp microelectrode recordings in an in vitro acute hippocampal slice preparation that permits the reproduction of the two prominent network rhythms, sharp waves (SPW) and gamma frequency oscillations, we investigated the intrinsic and synaptic properties of subicular principal cells (PCs) as well as their functional involvement in both network rhythms
We suggest a bimodal working model that depends on the functional state of the subicular PC types: a low or moderate activity level seems to result in an active participation of the intrinsically bursting (IB) cell type whereas a high state of excitation appears to be necessary to sufficiently arouse the regular spiking (RS) cell type
Summary
The subiculum constitutes the major output structure of the hippocampal formation [1]. Using simultaneous local field potential (LFP) and sharp microelectrode recordings in an in vitro acute hippocampal slice preparation that permits the reproduction of the two prominent network rhythms, SPW and gamma frequency oscillations, we investigated the intrinsic and synaptic properties of subicular PCs as well as their functional involvement in both network rhythms. Our results indicate two separate ways of information processing represented by the two distinct subicular PC classes In this context, we suggest a bimodal working model that depends on the functional state of the subicular PC types: a low or moderate activity level seems to result in an active participation of the IB cell type whereas a high state of excitation appears to be necessary to sufficiently arouse the RS cell type. Together with divergent synaptic properties during the network activities, our results support the idea of two independent streams of information flow within the hippocampal output structure
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