Forced Swimming Stress-Related Hypoalgesia:Nondependence on the Histaminergic Mechanisms

In experiments on mice, we examined the effects of 3-min-long forced swimming sessions on indices characterizing the state of the nociceptive system. Thirty minutes after the forced swimming episode, significantly shorter ( P < 0.05) latencies of motor reactions in the hot plate and tail flick tests were observed. At the same time, times of licking the paw within the early and late phases of the formalin test, as well as numbers of writhings in the acetic acid test, became significantly ( P < 0.05) smaller. Thus, forced swimming-induced stress results in the development of a hypoalgesia state with respect to thermoinduced pain and chemoinduced somatic (formalin test) and visceral (acetic acid test) pain. Blockers of histamine H1 (cimetidine, 10 mg/kg) and H2 (chlorpheniramine, 15 mg/kg) receptors did not influence significantly ( P > 0.05) the intensity of forced swimming-induced hypoalgesia in the tail flick and acetic acid-induced (writhing) tests. Thus, the histaminergic system is not significantly involved in the mechanisms of forced swimming-induced hypoalgesia.