Effects of ethanol on encoding, consolidation, and expression of extinction following contextual fear conditioning

Abstract

Studies of contextual fear conditioning have found that ethanol administered prior to a conditioning session impairs the conditioned freezing response during a test session the next day. The present experiments examined the effects of ethanol on extinction, the loss of conditioned responding that occurs as the animal learns that a previously conditioned context no longer signals shock. Ethanol (1.5 g/kg) administered prior to single (Experiment 1) or multiple (Experiment 2) extinction sessions impaired extinction. Ethanol administered prior to a test session disrupted the expression of freezing after extinction (Experiments 3-5). There was some evidence that ethanol served as an internal stimulus signaling the operation of conditioning or extinction contingencies (Experiments 4-5). In Experiment 6, postsession injections of 1.5 g/kg ethanol had no effect on extinction with brief (3 min) or long (24 min) exposures to the context, but injections of 3 g/kg after long exposures impaired extinction. Together, these results indicate that ethanol affects extinction by acting on multiple learning and performance processes, including attention, memory encoding, and memory expression.

Figure 1.

Dose effects of ethanol on extinction of contextual fear. Mean percent freezing is shown for the final 12 min of the 24-min acquisition (Acq) session, which was preceded by saline injections in all mice. Extinction and test session freezing is shown in 3-min time blocks. Mice received injections of saline (0.0), 0.5, 1.0, or 1.5 g/kg (20% v/v) of ethanol prior to extinction and injections of saline prior to acquisition and testing. Bars represent SEMs.

Figure 2.

Effects of ethanol on multiple sessions of extinction in the shocked (Ctx S) or novel (Ctx N) context. Mean percent freezing is shown for the final 12 min of the 24-min acquisition (Acq) session, which was preceded by saline injections in all mice. Freezing is shown in blocks of 3 min for each of the three 12-min extinction sessions in Context S (the shocked context) or N (the novel context) and for the single test session in Context S. Bars represent SEMs.

Figure 3.

Effects of ethanol during extinction and testing. Mean percent freezing is shown for the final 12 min of the 24-min acquisition (Acq) session, which was preceded by saline injections in all mice. Freezing is shown in blocks of 3 min for extinction sessions preceded by ethanol or saline and for the test session, also preceded by ethanol or saline. Test labels in parentheses represent injections during acquisition, extinction, and testing (S or E; e.g., SES represents saline during acquisition, ethanol during extinction, and saline during testing). Bars represent SEMs.

Figure 4.

Effects of ethanol during acquisition, extinction, and testing. (a) Mean percent freezing is shown in blocks of 3 min for the 24-min acquisition session and the three 12-min extinction sessions. Mice received saline (open squares) or ethanol (closed squares) prior to acquisition. Groups were subdivided and received saline (Groups SS and ES) or ethanol (Groups SE and EE) prior to extinction. (b) Mean percent freezing is shown for the first 6 min of the test session, as a function of test injection (saline or ethanol). Labels above the bar denote the injection prior to acquisition, extinction, and testing (S or E). Bars represent SEMs.

Figure 5.

Effects of ethanol on extinction and on freezing in a separately conditioned context. Freezing is shown in blocks of 3 min for the three extinction sessions in Context B preceded by ethanol or saline and for the test session in Context A, also preceded by ethanol or saline. Bars represent SEMs.

Figure 6.

Effects of post-session injections of ethanol on short or long extinction sessions. (a) Mean percent freezing is shown for each of four 3-min extinction sessions. (b) Mean percent freezing is shown for each of four 24-min extinction sessions. Each tick mark represents one 3-min block. Bars represent SEMs.