c-Fos expression correlates with performance on novel object and novel place recognition tests.

In rodents, many studies have been carried out using novelty-preference paradigms. The results show that the perirhinal cortex and the hippocampus are involved in the recognition of a novel object, "what", and its new position, "where", respectively. We employed these two variants of a novelty-preference paradigm to assess whether the expression of the immediate-early gene c-fos in the dorsal hippocampus and perirhinal cortex correlates with the performance discrimination ratio (d2), on the respective versions of the novelty preference tests. A control group (CO) was added to explore c-fos activation not specific to recognition. The results showed different patterns of c-Fos protein expression in the hippocampus and perirhinal cortex. The Where Group presented more c-Fos positive nuclei than the What and CO groups in the CA1 and CA3 regions, whereas in the perirhinal cortex, the What Group showed more c-Fos positive nuclei than the Where and CO groups. The correlation results indicate that levels of c-Fos in the CA1 area and perirhinal cortex correlate with effective exploration, d2, on the respective versions of the novelty preference tests, novel place and novel object recognition. These data suggest that the hippocampal CA1 and perirhinal cortex are specifically related to the level of recognition of place and objects, respectively.