Effect of the subcutaneous administration of the non-steroidal anti-inflammatory drugs naproxen, ibuprofen, diclofenac and celecoxib, the corticosteroid prednisolone and the opioid morphine, on voluntary wheel running in non-inflamed mice. Data are presented as the percentage of the distance travelled, relative to their basal value, 24 h after the intraplantar (i.pl.) injection of 20 µl saline in both hindpaws. Each bar and vertical line represent the mean ± SEM of the values obtained (n=7–9 per group). There were no statistically significant differences between the values obtained in the control non-drug injected group and drug-treated groups (one-way ANOVA).