Long-lasting FosB/ΔFosB immunoreactivity in the rat brain after repeated cat odor exposure

Cat odor elicits defensive responses in rats that are modified by repeated exposure to the odor. We explored the neural correlates of this adaptation using FosB/ΔFosB immunohistochemistry. Rats were given 3 × 60 min exposures to either a worn cat collar (repeated cat odor group) or unworn cat collar (control group). Each exposure was separated by 48 h. Rats exposed to cat odor initially showed strong defensive responses (decreased contact, increased retreat, and increased fecal pellets), however these responses had habituated by the final exposure. Rats were perfused 24 h or 7 days after the final exposure and the brains were processed for FosB/ΔFosB protein expression. Up-regulation of FosB/ΔFosB was observed 24 h after repeated cat odor exposure in the nucleus accumbens core, caudate putamen, ventrolateral periaqueductal gray, and four hypothalamic regions: lateral hypothalamus, ventromedial hypothalamus, anterior hypothalamic nucleus, and dorsal premammillary nucleus. FosB/ΔFosB expression remained elevated 7 days after repeated cat odor exposure in the nucleus accumbens core, caudate putamen and anterior hypothalamic nucleus. These findings provide initial evidence that behavioral changes occurring as a result of repeated predatory stress are associated with long-lasting regionally specific neuroadaptations in the brain.