Reinstatement of Pavlovian responses to alcohol cues by stress

Abstract

Rationale: Stress may contribute to relapse to alcohol use in part by enhancing reactivity to cues previously paired with alcohol. Yet, standard models of stress-induced reinstatement generally use contingent presentations of alcohol-paired cues to reinforce instrumental behaviors, making it difficult to isolate the ability of cues to invigorate alcohol-seeking.

Objective: Here we sought to test the impact of stress on behavioral responses to alcohol-paired cues, using a model of stress-induced reinstatement of Pavlovian conditioned approach, inspired by Nadia Chaudhri's work on context-induced reinstatement.

Methods: Long Evans rats were trained to associate one auditory cue with delivery of alcohol or sucrose and an alternative auditory cue with no reward. Following extinction training, rats were exposed to a stressor prior to being re-exposed to the cues under extinction conditions. We assessed the effects of yohimbine, intermittent footshock and olfactory cues paired with social defeat on responses to alcohol-paired cues and the effects of yohimbine on responses to sucrose-paired cues.

Results: The pharmacological stressor, yohimbine, enhanced alcohol seeking in a Pavlovian setting, but not in a cue-selective manner. Intermittent footshock and social defeat cues did not enhance alcohol seeking in this paradigm.

Conclusions: While yohimbine elicited reinstatement of reward-seeking in a Pavlovian setting, these effects may be unrelated to activation of stress systems or to interactions with specific cues.

Keywords: Addiction; Alcohol; Cues; Footshock; Rat; Social defeat; Stress; Yohimbine.

Figure 1.. Yohimbine reinstatement of responses to alcohol cues.

A) Port entry number during the CS+ and CS− across Pavlovian conditioning with 20% ethanol reward (n=17; 10 males and 7 females), mean +/− SEM. B) Port entry number during the CS+ and CS− across extinction training, mean +/− SEM. C) Port entry number during reinstatement tests during the CS+ and CS− after injection of yohimbine (orange) or vehicle (blue), mean +/− SEM, *, p < 0.05. D) Scatterplot showing port entry number during the CS+ and CS− from individual reinstatement sessions after injections of yohimbine (orange) or vehicle. Inset histogram shows the distribution of sessions based on the difference in the number of port entries during the CS+ and the CS−.

Figure 2.. Yohimbine reinstatement of responses to sucrose cues.

A) Port entry number during the CS+ and CS− across Pavlovian conditioning with 10% sucrose reward (n=8 males), mean +/− SEM. B) Port entry number during the CS+ and CS− across extinction training, mean +/− SEM. C) Port entry number during reinstatement tests during the CS+ and CS− after injection of yohimbine (orange) or vehicle (blue), mean +/− SEM. D) Scatterplot showing port entry number during the CS+ and CS− from individual reinstatement sessions after injections of yohimbine (orange) or vehicle. Inset histogram shows the distribution of sessions based on the difference in the number of port entries during the CS+ and the CS−.

Figure 3.. Effects of yohimbine on conditioned reinforcement by sucrose cues.

A) Number of entries into nosepoke holes that resulted in presentations of the CS+ versus CS− following injections of yohimbine (orange) versus vehicle (blue) in rats that underwent Pavlovian conditioned with 10% sucrose reward (n=8 males), mean +/− SEM, *, p < 0.05. B) Total port entries during conditioned reinforcement sessions after yohimbine (orange) versus vehicle (blue), mean +/− SEM. C) Scatterplot showing entries into the CS+-paired nosepoke versus the CS− nosepoke from individual sessions after yohimbine (orange) or vehicle (blue). Inset histogram shows the distribution of sessions based on the difference in the number of CS+ versus CS− nosepokes.

Figure 4.. Footshock reinstatement of responses to alcohol cues.

A) Port entry number during the CS+ and CS− across Pavlovian conditioning with 20% ethanol reward (n=12; 6 males and 6 females), mean +/− SEM. B) Port entry number during the CS+ and CS− across extinction training, mean +/− SEM. C) Port entry number during reinstatement tests during the CS+ and CS− after 0.4 mAmp intermittent footshock (orange), 0.8 mAmp intermittent footshock (yellow) or a 10-min control period without footshock (blue), mean +/− SEM. D) Scatterplot showing port entry number during the CS+ and CS− from individual reinstatement sessions after 0.4 mAmp intermittent footshock (orange), 0.8 mAmp intermittent footshock (yellow) or a 10-min control period without footshock (blue). Inset histogram shows the distribution of sessions based on the difference in the number of port entries during the CS+ and the CS−.

Figure 5.. Reinstatement of responses to alcohol cues by olfactory cues associated with social defeat.

A) Port entry number during the CS+ and CS− across Pavlovian conditioning with 20% ethanol reward (n=7), mean +/− SEM. B) Port entry number during the CS+ and CS− across extinction training, mean +/− SEM. C) Port entry number during reinstatement tests during the CS+ and CS− in presence of an olfactory cue previously paired with social defeat (stress odor, orange), or a control odor (blue), mean +/− SEM. D) Scatterplot showing port entry number during the CS+ and CS− from individual reinstatement sessions in presence of an olfactory cue previously paired with social defeat (stress odor, orange), or a control odor (blue). Inset histogram shows the distribution of sessions based on the difference in the number of port entries during the CS+ and the CS−.