A Transient Fear Reduction by Pair-Exposure with a Non-Fearful Partner during Fear Extinction Independent from Corticosterone Level in Mice

Haruna Tomizawa,Shingo Matsuda,Daisuke Matsuzawa,Daisuke Ishii,Eiji Shimizu,Chihiro Sutoh

doi:10.4236/jbbs.2013.35043

Abstract

Social interaction is known to alter behavior and emotional responses to various events. It has been reported that when fear-conditioned animals are put in a fear extinction paradigm with non-fearful conspecifics (pair-exposure), freezing behavior decreases compared to a solitary situation. However, it remains unclear whether pair-exposure during fear extinction is persistently effective in reducing the freezing response. In this study, we examined whether the effect of pair-exposure could be persistently effective on cued and contextual fear extinction. The reduction of the fear compared to the solitary condition was transiently observed only in the cued fear extinction with no difference in the subsequent recall session. We also found that the correlation between corticosterone levels and freezing behavior during extinction was disrupted in the pair-exposure situation. These results suggest that pair-exposure reduces freezing behavior in cued fear extinction, although this fear response reduction is not persistent. The pair-exposure changed an association between corticosterone levels and freezing behavior during extinction.

Highlights

Clinical exposure therapy for anxiety disorders relies on fear extinction, which is generally believed to be a form of new learning that inhibits the expression of the already acquired fear response [1]
It has been reported that when fear-conditioned animals are put in a fear extinction paradigm with non-fearful conspecifics, freezing behavior decreases compared to a solitary situation
In the Recall, student’s t-test showed no significant difference in the two group (t (32) = −1.022) (Figure 2(a)). These findings indicated that pair-exposure during cued fear extinction reduced freezing behavior, but did not ameliorate persistent fear responses

Summary

Introduction

Clinical exposure therapy for anxiety disorders relies on fear extinction, which is generally believed to be a form of new learning that inhibits the expression of the already acquired fear response [1]. Corticosterone secretion is increased by stressful events, previous studies have reported that the pair situation attenuated the increases due to exposure to a novel environment [7], a fear-inducing animal [8] and fear conditioning [9]. These phenomena are called social buffering, which can mitigate various stress responses through signals such as odor, touch and visual stimulus from conspesifics [10,11]. We hypothesized a decrease of corticosterone secretion is a factor that leads

Methods

Results

Conclusion