Moderate doses of ethanol partially reverse avoidance learning deficits in high-alcohol-drinking rats

Evaluating habit formation across pairs of female and male selectively bred alcohol-preferring and non-preferring rats

Some individuals with alcohol use disorder (AUD) continue to drink because they have developed a habit where they do not consider the consequences of their actions. Genetically selected lines of alcohol-preferring and non-preferring rats allow for exploration of how specific endophenotypes, such as tendency to form habits, may be risk factors that interact with a genetic predisposition of AUD. While high alcohol drinking (HAD) and alcohol-preferring (P) rats were selectively bred to consume high amounts of freely available ethanol, they exhibit differences in alcohol-seeking behaviors as well as impulsive behaviors, and may represent different behavioral models of AUD. The goal of the current study was to compare the tendency to develop habitual behaviors across female and male HAD1, HAD2, and P rats and their respective alcohol non-preferring counterparts. Alcohol-naïve rats were trained on a variable interval schedule using a non-ethanol reinforcer and were then tested in two extinction sessions, one prior to a reinforcer devaluation (conditioned taste aversion) procedure and one after. There were no differences in total lever presses between P and alcohol non-preferring (NP) rats, but there were differences between HAD and low-alcohol drinking (LAD) rats. All six strains decreased lever pressing after reinforcer devaluation. However, P and NP females did not increase latency to first lever press after devaluation, suggesting some inclination toward habitual behavior that was not apparent in either the HAD or LAD lines. Selective breeding for alcohol preference does not seem to influence the tendency to form habits, whereas background strain and sex may have an influence on this behavior.

Alcohol-Preferring P Rats Exhibit Elevated Motor Impulsivity Concomitant with Operant Responding and Self-Administration of Alcohol

BACKGROUND

Increased levels of impulsivity are associated with increased illicit drug use and alcoholism. Previous research in our laboratory has shown that increased levels of delay discounting (a decision-making form of impulsivity) are related to appetitive processes governing alcohol self-administration as opposed to purely consummatory processes. Specifically, the high-seeking/high-drinking alcohol-preferring P rats showed increased delay discounting compared to nonselected Long Evans rats (LE) whereas the high-drinking/moderate-seeking HAD2 rats did not. The P rats also displayed a perseverative pattern of behavior such that during operant alcohol self-administration they exhibited greater resistance to extinction.

METHODS

One explanation for the previous findings is that P rats have a deficit in response inhibition. This study followed up on this possibility by utilizing a countermanding paradigm (stop signal reaction time [SSRT] task) followed by operant self-administration of alcohol across increasing fixed ratio requirements (FR; 1, 2, 5, 10, and 15 responses). In separate animals, 24-hour access 2-bottle choice (10% EtOH vs. water) drinking was assessed.

RESULTS

In the SSRT task, P rats exhibited an increased SSRT compared to both LE and HAD2 rats indicating a decrease in behavioral inhibition in the P rats. Also, P rats showed increased operant self-administration across all FRs and the greatest increase in responding with increasing FR requirements. Conversely, the HAD2 and LE had shorter SSRTs and lower levels of operant alcohol self-administration. However, for 2-bottle choice drinking HAD2s and P rats consumed more EtOH and had a greater preference for EtOH compared to LE.

CONCLUSIONS

These data extend previous findings showing the P rats to have increased delay discounting (decision-making impulsivity) and suggest that P rats also have a lack of behavioral inhibition (motor impulsivity). This supports the notion that P rats are a highly impulsive as well as "high-seeking" model of alcoholism, and that the HAD2s' elevated levels of alcohol consumption are not mediated via appetitive processes or impulsivity.

Effects of alcohol on the acquisition and expression of fear-potentiated startle in mouse lines selectively bred for high and low alcohol preference

RATIONALE

Anxiety disorders and alcohol use disorders frequently co-occur in humans perhaps because alcohol relieves anxiety. Studies in humans and rats indicate that alcohol may have greater anxiolytic effects in organisms with increased genetic propensity for high alcohol consumption.

OBJECTIVES AND METHODS

The purpose of this study was to investigate the effects of moderate doses of alcohol (0.5, 1.0, 1.5 g/kg) on the acquisition and expression of anxiety-related behavior using a fear-potentiated startle (FPS) procedure. Experiments were conducted in two replicate pairs of mouse lines selectively bred for high- (HAP1 and HAP2) and low- (LAP1 and LAP2) alcohol preference; these lines have previously shown a genetic correlation between alcohol preference and FPS (HAP > LAP; Barrenha and Chester, Alcohol Clin Exp Res 31:1081-1088, 2007). In a control experiment, the effect of diazepam (4.0 mg/kg) on the expression of FPS was tested in HAP2 and LAP2 mice.

RESULTS

The 1.5 g/kg alcohol dose moderately decreased the expression of FPS in both HAP lines but not LAP lines. Alcohol had no effect on the acquisition of FPS in any line. Diazepam reduced FPS to a similar extent in both HAP2 and LAP2 mice.

CONCLUSIONS

HAP mice may be more sensitive to the anxiolytic effects of alcohol than LAP mice when alcohol is given prior to the expression of FPS. These data collected in two pairs of HAP/LAP mouse lines suggest that the anxiolytic response to alcohol in HAP mice may be genetically correlated with their propensity toward high alcohol preference and robust FPS.

Heart rate reactivity in HAD and LAD rats during Pavlovian fear conditioning

Recently, we reported that High-Alcohol-Drinking (HAD) rats exhibited selective deficits in active avoidance learning under alcohol-naive conditions, and that administration of moderate doses of alcohol (0.5 and 1.0 g/kg) facilitated learning in these rats (Blankenship et al., 2000; Rorick et al., 2003b). We hypothesized that the deficits resulted from excessive fear in the aversive learning context and that the anxiolytic properties of alcohol may have contributed to the improved learning that was observed after alcohol administration. This hypothesis was supported by a recent study in which prolonged freezing in HAD rats was seen after a classical fear conditioning procedure (Rorick et al., 2003a). To provide additional evidence that HAD rats indeed exhibit behaviors consistent with the expression of increased fear in aversive learning contexts, we employed a Pavlovian fear conditioning task to measure heart rate in HAD and Low-Alcohol-Drinking (LAD) rats. In this study, HAD (HAD-1 and HAD-2) and LAD (LAD-1 and LAD-2) rats were assigned to one of three pre-exposure conditions: Context Only, Context/Tone, or Sequential (Context Only followed by Context/Tone) Pre-Exposure. Following pre-exposure, fear conditioning acquisition and extinction procedures were identical for all groups. Results indicated that although no baseline differences were observed between HAD and LAD rats, HAD rats receiving Context-Only pre-exposure exhibited excessive heart rate reactivity to the tone conditional stimulus during fear conditioning acquisition, compared to LAD rats receiving the same pre-exposure conditions. These findings support the hypothesis that HAD rats exhibit behaviors consistent with increased fear in aversive learning contexts, as measured by autonomic conditioning.

Fear conditioning is impaired in adult rats by ethanol doses that do not affect periadolescents

Adolescent rats and humans exhibit physiological, behavioral, and cognitive differences compared to their adult counterparts. These differences are apparent also in reactions to psychoactive drugs, such as ethanol. Recent studies have shown that though less sensitive to several behavioral indices of intoxication by ethanol, adolescent rats are more sensitive to the cognition-impairing effects of ethanol. Ethanol's effects, in the present experiment, were assessed in terms of a fear conditioning test not previously used in comparison of adult and adolescent Sprague-Dawley albino rats. Separate groups of both ages were given intraperitoneal (i.p.) ethanol before or after tone-shock conditioning. This task features a hippocampus-independent component, learned freezing to a tone, and a hippocampus-dependent component, learned freezing to context. Post-training ethanol had no effect on retention in either age, but pre-acquisition ethanol impaired adult learning more than adolescent learning, as indexed by the expression of fear at the test. Blood alcohol was equivalent in adolescents and adults at a dose that produced cognitive discrepancies. Unlike other reports, these experiments demonstrate that adolescents may not be more sensitive to ethanol's effects in all cases of learning.

High-alcohol-drinking rats exhibit persistent freezing responses to discrete cues following Pavlovian fear conditioning

We previously reported that high-alcohol-drinking (HAD) rats exhibited selective deficits in active avoidance learning and that those deficits were partially reversed by moderate doses of ethanol under certain training conditions [Pharmacol. Biochem. Behav. 75 (2003) 89]. In that study, we hypothesized that HAD deficits resulted from exaggerated fear in the conditioning context and that the anxiolytic properties of ethanol, along with prior exposure to the conditioning apparatus, were responsible for the facilitated avoidance learning that was observed in HAD rats following moderate doses of ethanol. The current study was designed to test whether HAD rats exhibit behaviors consistent with increased fear in aversive learning contexts. We used a standard Pavlovian fear conditioning paradigm to assess behavioral freezing in HAD (HAD-1 and HAD-2) and low-alcohol-drinking (LAD; LAD-1 and LAD-2) rats. No significant differences were observed between HAD-1 and HAD-2 or between LAD-1 and LAD-2 rats, indicating that the replicate lines performed similarly in this study. Both HAD and LAD rats exhibited robust fear conditioning during training. Although no differences were observed between HAD and LAD rats during fear training, HAD rats failed to extinguish freezing behavior in response to the discrete tone conditional stimulus during subsequent fear retention tests. Thus, HAD rats demonstrated prolonged cue-elicited fear that was resistant to extinction.