Static magnetic field-induced anti-nociceptive effect and the involvement of capsaicin-sensitive sensory nerves in this mechanism.

Data concerning the effect of static magnetic field (SMF) on nociceptive processes are contradictory in the literature probably due to differences in species, characteristics of the magnetic fields, and duration of the exposure. The aim of the present series of experiments was to elucidate the action of acute full-body exposure of mice to a special SMF developed and validated by us on acute visceral and somatic chemonociception and inflammatory mechanical hyperalgesia. SMF exposure significantly diminished the number of acetic acid- or MgSO4-induced abdominal contractions (acute visceral nociception), formalin-evoked paw lickings and liftings in both phase I (acute somatic nociception) and phase II (acute inflammatory nociception) and mechanical hyperalgesia evoked by i.pl. injection of carrageenan as well as the TRPV1 capsaicin receptor agonist resiniferatoxin. Selective inactivation of capsaicin-sensitive sensory fibres by high dose resiniferatoxin pretreatment decreased nocifensive behaviours in phase II of the formalin test to a similar extent suggesting that pro-inflammatory neuropeptides such as substance P and calcitonin gene-related peptide released from these fibres are involved in this inflammatory reaction. Significant inhibitory effects of SMF on formalin-induced nociception and carrageenan-evoked hyperalgesia were absent in resiniferatoxin-pretreated mice, which also points out that capsaicin-sensitive nerves are involved in the SMF-induced anti-nociceptive action.