Dentate gyrus network regulation by somatostatin- and parvalbumin-expressing interneurons differentially impacts hippocampal spatial memory processing.

GABAergic interneurons regulate circuit dynamics in hippocampal structures such as CA1 that appear to be essential for memory processing. The dentate gyrus (DG) is known to play a role in pattern recognition and spatial working memory. However, the role of the DG in different stages of long-term spatial memory is poorly understood. Moreover, the roles of the predominant interneuron subtypes within the DG - somatostatin-expressing (SST+) and parvalbumin-expressing (PV+) - in different stages of memory processing are unknown. We tested how chemogenetic manipulation of DG SST+ and PV+ interneurons in mice influences the encoding, consolidation, and retrieval of hippocampus-dependent object-location memory (OLM). We find that activation of DG SST+ interneurons impairs both OLM encoding and retrieval, dramatically suppresses DG granule cell cFos expression, and (in the case of encoding) suppresses downstream CA1 network activity. Among individual mice, the degree of DG granule cell suppression is proportional to the extent of SST+ interneuron activation, and predicts the extent of OLM deficits. In striking contrast, PV+ interneuron activation selectively disrupts encoding, but not retrieval, of OLM, and minimally impacts DG or downstream hippocampal network activity. These findings demonstrate that regulation of the DG network by SST+ and PV+ interneurons differentially contributes to the various stages of spatial memory processing, and suggest that distinct network mechanisms are engaged in the hippocampus during each processing stage.