Attenuating Effect of Artemin on Herpes-related Pain Responses in Mice Infected with Herpes Simplex

The influence of artemin (AR) on herpes-related pain responses was examined using mice infected with herpes simplex virus (HSV). BALB/c mice were inoculated with HSV (1×10 6 plaque-forming units) on the right hind paw, while the contralateral hind paw was without inoculation. The changes in nociceptive threshold were examined using an electric Von Fray meter. Intraperitoneal administration of AR prevented a decrease in nociceptive threshold dose-dependently in HSV-inoculated mice, which was first observed at a dose of 1.0 mg/kg and peaked at doses higher than 1.5 mg/kg. This antinociceptive effect of AR attained peaks at 120 min after administration and declined gradually to non-treated levels by 270 min. Intraperitoneal administration of AR at a dose of 1.5 mg/kg scarcely affected β-endorphin and noradrenaline levels in the central nervous system of HSV-inoculated mice. However, AR caused a significant decrease of the dynorphin levels in spinal cord. These results strongly suggest that AR exerts antinociceptive effects on herpes-related pain through changes of the dynorphin levels in the central nervous system of HSV-inoculated mice. It is also suggested that AR will be a good candidate as an antinociceptive drug for the treatment of acute herpetic pain in humans.