Citation

Trow JE, Jones AM, McDonald RJ. Physiol. Behav. 2019; 208: 112556.

Affiliation

Canadian Centre for Behavioural Neuroscience, University of Lethbridge, 4401 University Drive, Lethbridge, AB T1K 4N8, Canada. Electronic address: r.mcdonald@uleth.ca.

Copyright

(Copyright © 2019, Elsevier Publishing)

DOI

10.1016/j.physbeh.2019.05.017

PMID

31152750

Abstract

For this series of experiments, we wanted to investigate issues related to stress and learning. First, we wanted to determine if unpredictable stress might foster generalized fear responses more than predictable stress. Second, we wanted to evaluate how repeated stress might influence a rat's ability to learn what context predicts and an aversive event. Our first hypothesis was that unpredictable stress would result in generalized fear responses compared to predictable stress and these effects would worsen over repeated stress cycles. Our second hypothesis was that stress, regardless of type, would result in enhanced discriminative fear conditioning to context, a measure of fear learning. Accordingly, two groups of rats received 14-day restraint stress with one group receiving predictable while the other group received unpredictable stress. Following these experimental manipulations, both groups were given a recovery period and then an assessment of fear-based context discriminative behaviour was performed. This stress-recovery cycle was repeated, and fear conditioning was again assessed. After a single stress-recovery cycle discriminative fear conditioning to context was not impaired for either group. However, we did find that unpredictable stress facilitated behavioural expression of fear in a fearful context. Following two stress-recovery cycles the unpredictable group exhibited discriminative freezing that was elevated within the paired context, whereas, surprisingly, the predictable group did not exhibit differentiated freezing and instead spent similar amounts of time freezing in both contexts. This pattern of effects suggests that unpredictable chronic stress fostered fearful behaviour in the presence of a threatening context, whereas generalized fear is brought about by repeated predictable stress. This result is the opposite of our hypothesis that unpredictable stress would result in generalized fear. Taken together these results show that certain types of stressful experiences (unpredictable) enhance discriminative fear conditioning to context and stress over a longer period can produce generalized fear, but surprisingly in the predictable and not unpredictable condition.

Copyright © 2019. Published by Elsevier Inc.

Language: en

Keywords

Fear conditioning; Generalization; Predictable; Stress; Unpredictable