Long-lasting FosB/DeltaFosB 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/DeltaFosB immunohistochemistry. Rats were given 3 x60 min exposures to either a worn cat collar (repeated cat odor group) or unworn cat collar (control group). Each exposure was separated by 48h. 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 24h or 7 days after the final exposure and the brains were processed for FosB/DeltaFosB protein expression. Up-regulation of FosB/DeltaFosB was observed 24h 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/DeltaFosB 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.

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