Pharmacological agents and injection stress, but not social isolation, alter cognitive judgement bias in the mouse touchscreen operant chamber

Cognitive judgement bias (CJB) refers to the interpretation of ambiguous stimuli in a negative (pessimistic) or positive (optimistic) way. Negative CJB is observed in depression and anxiety, conditions that burden affected individuals and their caregivers. Pre-clinical animal research is key to understanding CJB and developing therapies for affective and anxiety disorders, so a translationally relevant CJB test would be a useful addition to the existing pre-clinical rodent touchscreen test battery. Here, a CJB task in mouse touchscreen operant chambers was adapted and validated using pharmacological agents, bupropion and tetrabenazine, known to induce positive and negative CJB, respectively. Further, negative shifts in CJB were observed following an injection procedure (handling and intraperitoneal injection with a saline solution), demonstrating the sensitivity of the task. Interestingly, whereas social isolation has been linked to changes in affective state in humans, 8 weeks of single-housing in mice did not alter CJB but did induce anxiety-like behaviour in an open field. Collectively, these results present a validated task to assess CJB in mice, which will facilitate future explorations into the underlying neurobiology and potential treatment of affective and anxiety disorders.