A repeated measures cognitive affective bias test in rats: comparison with forced swim test.

RATIONALE

There is an urgent need to identify behaviours in animals that can provide insight into the aetiology and potential treatment of depression in humans.

OBJECTIVES

This study aimed to validate a repeated measures cognitive affective bias (CAB) test in a rat model of chronic stress and compare CAB with forced swim test (FST) measures.

METHODS

Male and female Sprague Dawley rats were trained to associate large and small rewards with scent, spatial, and tactile cues, and their response to an ambiguous tactile stimulus tested. Rats underwent weekly CAB testing for 4 weeks with no intervention, or for 2 weeks of chronic restraint stress (CRS), followed by 2 weeks of fluoxetine, vehicle, or no treatment. CRS rats also underwent the FST at selected timepoints.

RESULTS

In control rats, CAB was positive and remained stable over the 4-week period. In CRS-fluoxetine and CRS-vehicle groups, CAB was initially positive, became negative during chronic restraint stress, and returned to positive by 2 weeks after treatment. However, in the CRS-no treatment group, CAB was variable at the outset and unstable over time. Behaviour in the FST was not affected by treatment, and there was no correlation between CAB and FST outcomes.

CONCLUSIONS

Instability in the CRS-no treatment group precluded interpretation of the impact of fluoxetine on CAB post-CRS. Our results suggest that behaviour in the FST does not reflect or alter affective state and support the use of CAB tests as part of the behavioural testing repertoire for preclinical animal models of affective disorders.