The Effects of Chronic Unpredictable Stress on the Ability to Extinguish Fear: Zinc as a Mediator
Date
2012-02-01
Authors
Knaack, Gretchen Linnea
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Abstract
Chronic stress can be deleterious to the brain and it is the unpredictability of these stressors that fails to permit habituation, the effects of which are exhibited through maladaptive behaviors such as Post Traumatic Stress Disorder (PTSD). Implementing a chronic unpredictable stress (CUS) paradigm as an animal model of PTSD may facilitate the examination of possible mechanisms relating prolonged stress to the cognitive deficits frequently observed. One factor may be zinc because it is decreased in the blood while increased in the brain during stress, and it has been previously demonstrated that excess zinc in the brain causes learning and memory deficits. To ascertain this possibility rats were raised pre- and post-natally on supplemented zinc water for four months, administered a 21 day CUS paradigm, and then underwent fear conditioning. Post stress blood samples were also analyzed. Results determined that excess zinc rats displayed learning and memory deficits on the ability to extinguish fear and recall that extinction 24 hours later. CUS decreased the level of zinc in the blood for animals that drank lab water, but increased the amount of zinc in blood for animals that were supplemented with zinc. Furthermore, there was a positive correlation between the level of zinc in the blood and the ability to extinguish fear. These data suggest that zinc may be a mediator between chronic stress and anxiety disorders.
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Keywords
Fear Extinction, Zinc, Chronic Unpredictable Stress, PTSD