Dorsal-caudal and ventral hippocampus target different cell populations in the medial frontal cortex in rodents

Abstract

Direct projections from the ventral hippocampus (vHPC) to the medial frontal cortex (MFC) play crucial roles in memory and emotional regulation. Using anterograde transsynaptic tracing and in vitro electrophysiology in mice, we document a previously unexplored pathway that parallels the established vHPC-MFC connectivity. This pathway connects the dorsal-caudal hippocampus (dcHPC) to specific subregions of the ventral MFC, in particular the dorsal peduncular cortex. Notably, this pathway exerts a strong inhibitory influence on ventral MFC by targeting a substantial proportion of inhibitory neurons. Retrograde transsynaptic tracing in rats indicated that ventral MFC subregions project disynaptically back to vHPC. These results, altogether, suggest the existence of a remarkable functional circuit connecting distinct functional areas: the cognition-related dcHPC with the emotion-related ventral MFC and vHPC. These findings further provide valuable insights in the cognitive and emotional abnormalities associated with the HPC-MFC connectivity in neurological and psychiatric disorders.