Nitric oxide in hyperbaric oxygen-induced acute antinociception in mice.

Hyperbaric oxygen (HBO2) therapy induces analgesia in various conditions of pain in humans. In mice, HBO2 treatment evokes an acute antinociceptive response in the abdominal constriction test. To demonstrate the dependence of HBO2-induced antinociception on nitric oxide (NO), antinociceptive responsiveness to HBO2 was assessed after three different approaches that interfered with NO production. HBO2-induced antinociception was significantly attenuated by intracerebroventricular and intrathecal pretreatment with an inhibitor of NO synthase (NOS) enzyme and also by an antisense oligodeoxynucleotide directed against neuronal NOS. The antinociceptive effect was also significantly reduced in mice homozygous for a defective neuronal NOS gene. On the basis of these results, we conclude that neuronal NO is critical in the expression of the acute antinociceptive effect of HBO2.