Introduction: The hippocampus plays a crucial role in memory formation and consolidation, which is enhanced in response to stress hormones. Given the emerging role of glial cells in memory formation and the increasing evidence of glucocorticoid responsiveness of these cells, this study aims to explore which genes are differentially regulated by fear conditioning and glucocorticoids in the different hippocampal glial cells and may therefore contribute to the enhanced memory consolidation under these conditions in mice.

Methods: We used four groups of five mice, that were either naïve or underwent fear conditioning, and had either received a single corticosterone injection, or a vehicle injection. Three hours after injection, the dentate gyri were harvested, cells were sorted using fluorescence-activated cell sorting (FACS), and single-cell RNA sequencing was performed.

Results: Many differentially regulated genes could be identified, especially for microglia and oligodendrocytes, while astrocytes were less responsive to fear conditioning or corticosterone. Corticosterone produced a marked gene downregulation in microglia and both up- and downregulation in oligodendrocytes. Whereas some genes were regulated across most hippocampal cell types, a number of genes could be identified that were uniquely regulated in microglia (including P2ry12, Bin2 and Ccr5) and oligodendrocytes (including Phactr3, Polr3e, and Nkx6-2). Fear conditioning alone did not differentially regulate many genes in any of the glial cell types, but potently affected corticosterone responses.

Conclusion: Single-cell RNA analysis reveals that corticosterone, and to a lesser extent fear conditioning, differentially regulate a large number of genes in mouse hippocampal glial cells. This suggests that enhancement of memory consolidation by glucocorticoids may be (partly) mediated by hippocampal glial cells and provides insight into the genes potentially involved in this process.