The ability to recognize dangerous situations and environments is crucial for survival, but overestimating risk can lead to pathological avoidance of normal activities, potentially leading to anxiety disorders. Many studies over the past several decades have begun to identify the brain regions underlying threat detection and anxiety behavior. In particular, the ventral hippocampus has emerged as a critical structure for emotional behaviors, including innate anxiety. Recent work from our lab and others has shown that ventral CA1 pyramidal neurons encode information about anxiety, and these CA1 neurons preferentially target downstream structures such as hypothalamus and medial prefrontal cortex. However, the neural representation of anxiogenic environments in the initial stage of the trisynaptic circuit— the dentate gyrus— is unknown. Here, I use Dock10-Cre and Drd2-Cre mouse lines to gain optical access to granule cells and mossy cells, respectively, in the ventral dentate gyrus. Calcium activity was recorded during free exploration of the elevated plus maze (EPM) and open field test (OFT).

Single cell activity and population coding were analyzed for mossy cells, granule cells, and CA1 pyramidal neurons. I found that anxiety-related activity was present in granule cells and vCA1, however mossy cells encoded novelty and spatial position. Furthermore, chemogenetic inhibition of mossy cells did not disrupt behavior in the EPM or OFT, but did disrupt acquisition of a contextual fear memory. These findings support the notion that different features of an anxiogenic environment are encoded by different cell types, and that anxiety information is present at the earliest stage of the trisynaptic circuit.