Non-associative defensive responses of rats to ferret odor

Abstract

Predators and their odors offer an ethologically valid model to study learning processes. The present series of experiments assessed the ability of ferret odor to serve as an unconditioned stimulus and examined behavioral and endocrine changes in male Sprague-Dawley rats with single or repeated exposures in a defensive withdrawal paradigm or in their home cages. Rats exposed to ferret odor avoided the ferret odor stimulus more, exhibited greater risk assessment and displayed higher adrenocorticotropin hormone (ACTH) and corticosterone release compared with control odor exposed rats and these measures did not significantly habituate over repeated exposures. Ferret odor exposure did not show associative conditioning effects during extinction trials. However, rats that were pre-exposed to ferret odor only once, as compared to control and repeatedly exposed rats, displayed a sensitized ACTH and corticosterone response to an additional ferret odor exposure in small cages. These experiments suggest that ferret odor is a highly potent unconditioned stimulus that has long lasting effects on behavior and endocrine responses, and further suggests the independence of habituation and sensitization processes.

Fig. 1

Graphs showing mean (±SEM) behavior in defensive withdrawal apparatus for extinction (n=9), habituation (n=8), and control (n=9) groups for 10 min/day for 10 days. On day 1, both extinction and habituation groups were exposed to ferret odor towels. On days 2–7, only the habituation group was exposed to the ferret odor towels. And, days 8–10, habituation and control groups were exposed to control odor towels. Panel A depicts number of entries to the withdrawal chamber. Panel B depicts time spent (s) in withdrawal chamber. Panel C depicts number of visits by the rats to the towel stimulus. Panel D depicts number of head scanning movements. *Indicates a significant difference between control and habituation groups (p<0.05). ^#Indicates a significant difference between control and extinction groups (p<0.05).

Fig. 2

Graphs showing mean (±SEM) plasma levels of ACTH (Panel A) and corticosterone (Panel B) for extinction (n=8), habituation (n=8) and control (n=7) group rats exposed to ferret odor for 30 min on day 12. *Indicates a significant difference between extinction and habituation groups (p<0.05). ^#Indicates a significant difference between control and extinction groups (p<0.05).

Fig. 3

Graphs showing mean (±SEM) behavior in defensive withdrawal apparatus for control odor group (n=8) and day 1 ferret odor-exposed group (n=8) for 10 min on days 1 and 2. Panel A depicts number of entries to the withdrawal chamber. Panel B depicts time spent (sec) in withdrawal chamber. Panel C depicts number of visits to the towel stimulus. Panel D depicts number of head scanning movements. *Indicates a significant difference between groups (p<0.05).

Fig. 4

Graphs showing mean (±SEM) plasma levels of ACTH (Panel A) and corticosterone (Panel B) for control (n=8) and ferret odor exposed rats (n=8) on days 1, 4, and 9 of repeated home cage exposure to odors. *Indicates a significant difference between control and ferret odor groups (p<0.05).