The effect of repeated daily measurements on paw withdrawal latencies in Hargreaves test.

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.