Pair housing does not alter incubation of craving, extinction, and reinstatement after heroin self-administration in female and male rats

Rationale Evidence suggests that single housing in rats acts as a chronic stressor, raising the possibilities that it contributes to measures of heroin craving and that pair housing ameliorates such measures. Objectives This study aimed to determine whether pair housing after heroin self-administration reduces the incubation of craving, extinction, and reinstatement of heroin seeking. Methods Single-housed female and male Sprague-Dawley rats underwent daily 6-h heroin self-administration, wherein active lever presses produced a heroin infusion paired with light/tone cues. One d after self-administration, rats underwent a baseline cued-seeking test wherein active lever presses only produced light/tone cues. Immediately following this cued-seeking test, rats were either pair-housed with a weight- and sex-matched naïve rat or remained single-housed for the rest of the study. For 14 d, rats remained in their homecages, after which they underwent a cued-seeking test to assess the incubation of craving compared to their baseline test. Rats then underwent extinction sessions followed by cue-induced and heroin-primed reinstatements. Results The findings reveal that pair-housed rats did not differ from single-housed rats in terms of the incubation of craving, extinction, or reinstatement of heroin seeking. Additionally, the results did not reveal any evidence of sex-based differences in the study. Conclusions The present work indicates that pair housing during the forced abstinence period does not alter measures of heroin craving/seeking. These findings suggest that the chronic stress of single housing specifically during forced abstinence does not contribute to the degree of such measures. ### Competing Interest Statement The authors have declared no competing interest.