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Inactivation of the medial prefrontal cortex interferes with the expression but not the acquisition of differential fear conditioning in rats.

Lee YK, Choi JS - Exp Neurobiol (2012)

Bottom Line: Neither the muscimol nor the aCSF infusion had any effect on differential responding.The results showed that muscimol infusion impaired differential responding: the level of freezing to CS- was indiscriminable from that to CS+.Taken together, these results suggest that the mPFC is responsible for the regulation of fear response by inhibiting inappropriate fear expressions.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Korea University, Seoul 136-701, Korea.

ABSTRACT
The medial prefrontal cortex (mPFC) has been implicated in the processing of emotionally significant stimuli, particularly the inhibition of inappropriate responses. We examined the role of the mPFC in regulation of fear responses using a differential fear conditioning procedure in which the excitatory conditioned stimulus (CS+) was paired with an aversive footshock and intermixed with the inhibitory conditioned stimulus (CS-). In the first experiment, using rats as subjects, muscimol, a gamma-amino-butyric acid type A (GABAA) receptor agonist, or artificial cerebrospinal fluid (aCSF) was infused intracranially into the mPFC across three conditioning sessions. Twenty-four hours after the last conditioning session, freezing response of the rats was tested in a drug-free state. Neither the muscimol nor the aCSF infusion had any effect on differential responding. In the second experiment, the same experimental procedure was used except that the infusion was made before the testing session rather than the conditioning sessions. The results showed that muscimol infusion impaired differential responding: the level of freezing to CS- was indiscriminable from that to CS+. Taken together, these results suggest that the mPFC is responsible for the regulation of fear response by inhibiting inappropriate fear expressions.

No MeSH data available.


Effect of muscimol infusion on differential conditioning. (A, B). Pre-conditioning drug infusion (Exp. 1). (A) No significant effect of drug infusion on discrimination ratio was found (see Results for detail). (B) Freezing levels to the CS+ and CS- during the drug-free retention test showed differential responding regardless of drug condition. (C, D) Pre-testing drug infusion (Exp 2). (C) Muscimol infusion significantly reduced discrimination ratio on the retention test. (D) Freezing levels to the CS+ and CS- during the retention test showed that inhibitory responding to CS- was impaired only in the muscimol infusion group. Data are expressed as mean ± S.E.M. Arrows indicate drug infusion (muscimol or aCSF).
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Figure 3: Effect of muscimol infusion on differential conditioning. (A, B). Pre-conditioning drug infusion (Exp. 1). (A) No significant effect of drug infusion on discrimination ratio was found (see Results for detail). (B) Freezing levels to the CS+ and CS- during the drug-free retention test showed differential responding regardless of drug condition. (C, D) Pre-testing drug infusion (Exp 2). (C) Muscimol infusion significantly reduced discrimination ratio on the retention test. (D) Freezing levels to the CS+ and CS- during the retention test showed that inhibitory responding to CS- was impaired only in the muscimol infusion group. Data are expressed as mean ± S.E.M. Arrows indicate drug infusion (muscimol or aCSF).

Mentions: Experiment 1 was conducted to examine the role of the mPFC in the acquisition of differential fear response. Total of 15 rats (aCSF, n=8; muscimol, n=7) were microinfused with muscimol or aCSF into the mPFC just before each training session. There was no significant difference between groups on the discrimination ratio throughout the conditioning sessions (Fig. 3A: F(1,8)=0.346, not significant [n.s.]), repeated measures ANOVA). In the 24-hr retention test with no drug treatment, the aCSF group and the muscimol group showed differential responding between CS+ and CS- (Fig. 3B). Both groups froze significantly more to the CS+ than to the CS- (aCSF group, t(7)=-5.685, p<.05 ; muscimol group, t(6)=-2.835, p<.05, paired t-test). The level of differential responding was also similar, such that the discrimination ratio was not different between groups (Fig. 3A: t(8)=.191, n.s., independent t-test).


Inactivation of the medial prefrontal cortex interferes with the expression but not the acquisition of differential fear conditioning in rats.

Lee YK, Choi JS - Exp Neurobiol (2012)

Effect of muscimol infusion on differential conditioning. (A, B). Pre-conditioning drug infusion (Exp. 1). (A) No significant effect of drug infusion on discrimination ratio was found (see Results for detail). (B) Freezing levels to the CS+ and CS- during the drug-free retention test showed differential responding regardless of drug condition. (C, D) Pre-testing drug infusion (Exp 2). (C) Muscimol infusion significantly reduced discrimination ratio on the retention test. (D) Freezing levels to the CS+ and CS- during the retention test showed that inhibitory responding to CS- was impaired only in the muscimol infusion group. Data are expressed as mean ± S.E.M. Arrows indicate drug infusion (muscimol or aCSF).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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Figure 3: Effect of muscimol infusion on differential conditioning. (A, B). Pre-conditioning drug infusion (Exp. 1). (A) No significant effect of drug infusion on discrimination ratio was found (see Results for detail). (B) Freezing levels to the CS+ and CS- during the drug-free retention test showed differential responding regardless of drug condition. (C, D) Pre-testing drug infusion (Exp 2). (C) Muscimol infusion significantly reduced discrimination ratio on the retention test. (D) Freezing levels to the CS+ and CS- during the retention test showed that inhibitory responding to CS- was impaired only in the muscimol infusion group. Data are expressed as mean ± S.E.M. Arrows indicate drug infusion (muscimol or aCSF).
Mentions: Experiment 1 was conducted to examine the role of the mPFC in the acquisition of differential fear response. Total of 15 rats (aCSF, n=8; muscimol, n=7) were microinfused with muscimol or aCSF into the mPFC just before each training session. There was no significant difference between groups on the discrimination ratio throughout the conditioning sessions (Fig. 3A: F(1,8)=0.346, not significant [n.s.]), repeated measures ANOVA). In the 24-hr retention test with no drug treatment, the aCSF group and the muscimol group showed differential responding between CS+ and CS- (Fig. 3B). Both groups froze significantly more to the CS+ than to the CS- (aCSF group, t(7)=-5.685, p<.05 ; muscimol group, t(6)=-2.835, p<.05, paired t-test). The level of differential responding was also similar, such that the discrimination ratio was not different between groups (Fig. 3A: t(8)=.191, n.s., independent t-test).

Bottom Line: Neither the muscimol nor the aCSF infusion had any effect on differential responding.The results showed that muscimol infusion impaired differential responding: the level of freezing to CS- was indiscriminable from that to CS+.Taken together, these results suggest that the mPFC is responsible for the regulation of fear response by inhibiting inappropriate fear expressions.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Korea University, Seoul 136-701, Korea.

ABSTRACT
The medial prefrontal cortex (mPFC) has been implicated in the processing of emotionally significant stimuli, particularly the inhibition of inappropriate responses. We examined the role of the mPFC in regulation of fear responses using a differential fear conditioning procedure in which the excitatory conditioned stimulus (CS+) was paired with an aversive footshock and intermixed with the inhibitory conditioned stimulus (CS-). In the first experiment, using rats as subjects, muscimol, a gamma-amino-butyric acid type A (GABAA) receptor agonist, or artificial cerebrospinal fluid (aCSF) was infused intracranially into the mPFC across three conditioning sessions. Twenty-four hours after the last conditioning session, freezing response of the rats was tested in a drug-free state. Neither the muscimol nor the aCSF infusion had any effect on differential responding. In the second experiment, the same experimental procedure was used except that the infusion was made before the testing session rather than the conditioning sessions. The results showed that muscimol infusion impaired differential responding: the level of freezing to CS- was indiscriminable from that to CS+. Taken together, these results suggest that the mPFC is responsible for the regulation of fear response by inhibiting inappropriate fear expressions.

No MeSH data available.