The duration of chronic restraint stress protocols does not predict effect sizes in behavioural tests: a meta-analysis

Abstract Stressors are commonly used to induce models of anxiety or depression in rats. The effectiveness of these stressors is often evaluated using behavioural tests. In a previous meta-analysis of chronic variable stress (CVS) procedures, we hypothesised that the duration or intensity of CVS procedures would correlate with the magnitude of the effect sizes reported in behavioural tests. However, we did not find strong evidence for this correlation, and were concerned that variability in CVS procedure design, both the duration and the types of stressors used, may have made it challenging to determine which factors influenced effect size. To address this, we carried out a meta-analysis of studies using a simpler stress procedure – chronic restraint stress (CRS) – to study the relationship between the duration of CRS procedures and the effect sizes obtained in subsequent behavioural tests. In articles using CRS procedures with rats, we documented the duration of restraint and carried out a meta-analysis of four behavioural tests: the forced swim test (FST), the sucrose preference test (SPT), the elevated plus maze (EPM) and the open field test (OFT). We found that chronic restraint stress increased immobility in the FST, decreased sucrose preference in the SPT, decreased time spent in the open arms of the EPM but had no effect on time spent in the centre of the OFT. However, the effect sizes in all behavioural tests were not moderated by the duration of the CRS procedure, indicating that longer CRS procedures are not associated with larger effect sizes.