Ferret odor as a processive stress model in rats: neurochemical, behavioral, and endocrine evidence

Abstract

Predator odors have been shown to elicit stress responses in rats. The present studies assessed the use of domestic ferret odor as a processive stress model. Plasma corticosterone and adrenocorticotropin hormone levels were higher after 30 min of exposure to ferret odor (fur/skin) but not control odors, ferret feces, urine, or anal gland secretions. Behavioral differences were also found between ferret and the control odors as tested in a defensive withdrawal paradigm. In addition, c-fos messenger RNA expression in several brain areas previously associated with processive stress was significantly higher in ferret odor-exposed rat brains than in control odor-exposed brains. These results suggest that ferret odor produces a reliable unconditioned stress response and may be useful as a processive stress model.

Figure 1

A: Mean plasma levels of corticosterone (CORT; ± SEM) for rats exposed to ferret odor (n = 12) and control odor (n = 8) for 30 min. B: Mean plasma levels of adrenocorticotropin hormone (ACTH; ± SEM) for rats exposed to ferret odor (n = 12) and control clean towel odor (n = 8) for 30 min. Asterisks indicate a significant difference from control odor (p < .05).

Figure 2

Representative photomicrographs depicting c-fos expression in the brain after ferret odor or control odor exposure for 30 min. Note the high c-fos induction in cortex, lateral septum (LS), the oval and fusiform nuclei of the bed nucleus of stria terminalis (BSTov and BSTfu), paraventricular nucleus of the hypothalamus (PVN), basolateral nucleus of the amygdala (BlA), and nucleus of tractus solitarius (NTS). CeA = central nucleus of amygdala; MeA = medial nucleus of the amygdala.

Figure 3

A: Mean plasma levels of corticosterone (CORT; ± SEM) for rats exposed to ferret odor (n = 8), strawberry odor (n = 8), and clean odor (n = 8) for 30 min during the dark phase of the light– dark circadian cycle. B: Mean plasma levels of adrenocorticotropin hormone (ACTH; ± SEM) for rats exposed to ferret odor (n = 8), strawberry odor (n = 8), and clean odor (n = 8) for 30 min during the dark phase of the light– dark circadian cycle. Asterisks indicate a significant difference from ferret odor (p < .05).

Figure 4

Graphs showing mean (± SEM) behavior in defensive withdrawal apparatus during exposure to ferret odor (n = 9), strawberry odor (n = 8), or clean towel odor (n = 8) for 10 min. A: Number of visits by the rats to the area where the towel stimulus was. B: Number of chewing bouts on the towel stimulus. C: Time (in seconds) spent in the area with the towel stimulus. Asterisks indicate a significant difference from ferret odor (p < .05).

Figure 5

Graph showing mean (± SEM) plasma levels of corticosterone (CORT) for rats exposed to ferret fur (n = 8) or control odor (n = 8) for 30 min. Asterisk indicates a significant difference from control odor (p < .05).