Distinct patterns of Fos immunoreactivity in striatum and hippocampus induced by different kinds of novelty in mice

In this study the immediate-early gene Fos was used to investigate the response to different novel stimuli in a wide array of brain regions including the hippocampus, the rhinal cortex, the frontal cortex and different components of the striatal complex. Independent groups of CD-1 mice were exposed to three different novelty conditions: (1) novel environment (empty open field); (2) complex novel environment (i.e. open field containing objects); and (3) identity-based detection of novel objects. We observed that a complex novel environment and a knowledge-based novelty modulated Fos levels in both the dorsal and the ventral components of the striatum, while Fos immunoreactivity in the medial temporal lobe was only increased after exposure to novel environments, regardless of their complexity. Finally, we observed a strong increase of Fos levels in the prefrontal cortex in all the three novel conditions examined, indicating a major involvement of this structure in novelty assessment. Overall the present study demonstrates that distinct brain regions are recruited in different kinds of novelty and emphasizes the role of the striatal complex in processing complex novel information.