NEUROANATOMICAL AND FUNCTIONAL CHARACTERIZATION OF THE MOUSE INDUSIUM GRISEUM

The indusium griseum (IG) is a brain structure composed of two narrow longitudinal bilateral strips that run above the corpus callosum (CC) in its rostrocaudal length. The IG is critical during development for the formation of the CC and connects with the hippocampus, cingulate cortex and septal region. However, its function in adult mice remains unknown. We hypothesized that it might be involved in social discrimination, since it is linked with key hub regions for this type of behavior. To test this, we utilized Cre-expressing mice of both sexes to specifically target the IG. We employed anterograde and retrograde viral tracing to map its connectivity and used inhibitory DREADDs to assess the behavioral impact of silencing IG neurons in locomotion, anxiety, feeding, olfaction and social behaviors. We found that the IG receives primary inputs from the anterior cingulate, motor, piriform, entorhinal, and retrosplenial cortices, while projecting mainly to the fasciola cinerea and the septohippocampal nucleus. Behavioral assays showed that IG inhibition did not affect locomotion, anxiety, feeding, or olfaction. However, it significantly impaired the familiarization process during social novelty and repetitive presentation tests. Our preliminary results suggest that the IG acts as a functional hub, integrating cortical signals and social cues to mediate social familiarization in mice.