The hypothesis that repeated measurements during 4 subsequent days affect withdrawal latencies in Hargreaves test
was investigated. Paw withdrawal latencies to radiant heat were determined in the control, tramadol or saline group of
male Wistar rats. The control group (N=10) had no treatment. Tramadol group (N=7) and saline group (N=7) received
one daily intraperitoneal injection of tramadol (15 mg/kg) or saline (0.9% NaCl), respectively. A significant decline in
withdrawal latencies was observed in the control group on the day 2 to day 4, when compared to day 1 (p<0.05 Bonferroni
test). In the saline and tramadol groups, latencies remained stable from day 1 to day 4. During the entire testing
period withdrawal latencies were 27–50% longer in tramadol group (p<0.05 ANOVA) compared with the saline group.
When compared to the control group, the effect of tramadol, was noted from the second to forth day (p<0.01 Bonferroni
test), but not on the first day. Finally, a tendency to decrement in withdrawal latencies existed on day 1 in the saline
group compared with control group, but this difference does not reach significance. We conclude that one day of training
affect withdrawal latencies in the Hargreaves test
