Effects of naltrexone on spontaneous itch-associated responses in NC mice with chronic dermatitis.

The effects of the opioid antagonist naltrexone on spontaneous itch-associated behaviors and cutaneous nerve activities were examined to determine whether it inhibits pruritus through peripheral action in NC mice with chronic dermatitis. Their rostral-back scratching and caudal-back biting were 19 and 3.4 times more, respectively, than those of control mice. The activities of cutaneous nerves innervating the rostral and caudal back were 9.5 and 5.4 times more, respectively, in affected mice than in control mice. Subcutaneous injections of naltrexone significantly inhibited the scratching and biting, without effects on the nerve activities. The results suggest that the peripheral action does not play a central role in inhibiting chronic itch-associated behaviors.