Rapid reacquisition of contextual fear following extinction in mice: effects of amount of extinction, acute ethanol withdrawal, and ethanol intoxication

Abstract

Rationale: Many studies have found that ethanol intoxication and withdrawal impair initial acquisition or extinction of learned behaviors. Rapid reconditioning following extinction is a form of post-extinction re-emergence of conditioned behavior that has not been studied for its interaction with ethanol intoxication or withdrawal.

Objectives: The goals of this paper were to define the parameters that allow rapid post-extinction reacquisition of fear in mice and investigate the effect of acute ethanol withdrawal and intoxication on acquisition, extinction, and post-extinction reconditioning.

Methods: We examined acquisition, extinction, and post-extinction reconditioning of contextual fear in male C57BL/6 mice. Acute ethanol withdrawal occurred 6 h following a 4 g/kg injection of 20% ethanol and acute ethanol intoxication occurred 5 min following a 1.5 g/kg injection of 20% ethanol.

Results: A weak context-shock pairing caused rapid reacquisition of conditioned freezing following moderate, but not extensive extinction. Acute ethanol intoxication impaired initial conditioning and acute ethanol withdrawal impaired rapid reacquisition after extinction, but not reconditioning or extinction itself.

Conclusions: These findings show that rapid reconditioning occurs following moderate but not extensive extinction in C57BL/6J mice. Additionally, acute ethanol withdrawal and intoxication may differentially affect different phases of conditioning. Results are discussed in terms of current ideas about post-extinction behavior and ethanol's effects on memory.

Keywords: Acute ethanol intoxication; Acute ethanol withdrawal; C57BL/6 J mice; Contextual fear conditioning; Extinction; Rapid reacquisition.

Fig. 1.. Rapid Reacquisition of Contextual Fear Following Reconditioning in C57BL/6J Mice (Moderate Extinction).

(A) Overview of the design of Experiment 1a. The times listed represent the total time of exposure to the context for a given session. A plus sign indicates a single 2-s .35 mA shock and a minus sign indicates exposure to the context without shock. (B) Freezing during each extinction session (E) by mice that received fear conditioning (RECOND) or context exposure (CTX) on Day 1 (Day 2-7). (C) Mean freezing from Test (1 day after reconditioning) for Groups CTX, COND (which received no initial conditioning or extinction), and RECOND. Significance between groups is represented by *** p < .001; ** p < .01; * p < .05. RECOND, n= 8; CTX, n=8; COND, n=8. Error bars represent standard error of the mean.

Fig. 2.. Massive Extinction before Reconditioning Prevents Rapid Reacquisition of Contextual Fear Conditioning

(A) Overview of the design of Experiment 1b. The times listed represent the total time of exposure to the context for a given session. A plus sign indicates a single .35 mA shock and a minus sign indicates exposure to the context without shock. (B) Freezing during each extinction session (E) by mice that received fear conditioning (RECOND) or context exposure (CTX) on Day 1 (Day 2-15). (C) Mean freezing from Test (1 day after reconditioning) for each group. Significance between groups is represented by *** p < .001; ** p < .01; * p < .05. RECOND, n= 8; CTX, n=8; COND, n=8. Error bars represent standard error of the mean.

Fig. 3.. AEW Does Not Affect Extinction of Contextual Fear.

(A) Overview of the design of Experiment 2. The times listed represent the total time of exposure to the context for a given session. A plus sign indicates a single .35 mA shock and a minus sign indicates exposure to the context without shock. A downward arrow indicates the administration of ethanol or saline prior to the session. (B) Mean percent freezing during the extinction session (Day 2) in which mice were 6 hr post acute ethanol injection (EXT-AEW) or saline injection (EXT-SAL). (C) Mean percent freezing during the test session (Day 3) of all groups; EXT-AEW, n = 8; EXT-SAL, n = 7; NoEXT-AEW, n = 7; NoEXT-SAL, n = 8; **, p < .01. Error bars represent standard error of the mean.

Fig. 4.. AEW Moderately Impairs Rapid Reacquisition of Contextual Fear.

(A) Overview of the design of Experiment 3. The times listed represent the total time of exposure to the context for a given session. A plus sign indicates a single .35 mA shock and a minus sign indicates exposure to the context without shock. A downward arrow indicates the administration of ethanol or saline prior to the session. (B) Mean percent freezing during extinction sessions (Days 2-7) of RECOND and CTX groups. (C) Mean percent Freezing of all groups during the 30 sec pre and post shock during Phase 3 under AEW or SAL (Day 8). (D) Mean percent freezing of all groups during the test session (Day 9) 24 hrs following reconditioning under AEW or SAL. The RECOND-SAL vs COND-SAL difference wasp =.054. CTX-AEW, n = 8; CTX-SAL, n = 7; RECOND-AEW, n = 5; RECOND-SAL, n = 7; COND-AEW, n = 8; COND-SAL, n = 8; *, p < .05 **, p < .01; ***, p < .001. Error bars represent the standard error of the mean.

Fig. 5.. AEW Does Not Affect Contextual Fear Conditioning

(A) Overview of the design of Experiment 4. The times listed represent the total time of exposure to the context for a given session. A plus sign indicates a single .35 mA shock and a minus sign indicates exposure to the context without shock. A downward arrow indicates the administration of ethanol or saline prior to the session. (B) Mean percent freezing during strong (4 Shock) or weak (1 Shock) conditioning (Day 1) in which animals were 6 hr post acute ethanol injection (AEW) or saline injection (SAL). (C) Mean percent freezing during the test session (Day 2) 24 hrs following strong conditioning. 1 Shock- AEW, n = 8; 1 Shock-SAL, n = 8; 4 Shock-AEW, n = 8; 4 Shock-SAL, n = 8. ***, p < .001. Error bars represent the standard error of the mean.

Fig. 6.. Acute Ethanol Intoxication Generally Impairs Fear Learning.

(A) Overview of the design of Experiment 5. The times listed represent the total time of exposure to the context for a given session. A plus sign indicates a single .35 mA shock and a minus sign indicates exposure to the context without shock. A downward arrow indicates the administration of ethanol or saline prior to the session. (B) Mean percent freezing during extinction sessions (Days 2-7) of RECOND and CTX groups. (C) Mean percent freezing for 30 sec pre and post shock of all groups during Phase 3 (reconditioning) under acute intoxication (INTX) or SAL (Day 8). Further significant main effects and interactions are detailed in the text. (D) Mean percent freezing of all groups during the test session (Day 9) 24 hrs following reconditioning under acute intoxication (INTX) or SAL. The RECOND-AEW vs COND-AEW difference was p = .071. CTX-AEW, n = 8; CTX-SAL, n = 8; RECOND-AEW, n = 8; RECOND-SAL, n = 8; COND-AEW, n = 8; COND-SAL, n = 8; *, p < .05 **, p < .01; ***, p < .001. Error bars represent the standard error of the mean.