Continuous naloxone administration via osmotic minipump decreases autotomy but has no effect on nociceptive threshold in the rat

Abstract

Rats with unilaterally sectioned sciatic nerves were continuously administered naloxone HCl (80 or 800 .mu.g/h) or equivalent volumes of saline (1 or 10 .mu.l/h) s.c. via osmotic minipumps over a 2 or 5 wk period. Rats receiving 80 .mu.g/h naloxone for 5 wk exhibited significantly less self-mutilation (autotomy) of the denervated foot than saline controls or rats receiving 80 .mu.g/h naloxone for 2 wk. The nociceptive threshold of intact rats infused with the same dose of naloxone was tested on a hot plate. In these animals there was no influence on the nociceptive threshold during naloxone administration for 1 wk. Autotomy was also reduced in rats infused with 800 .mu.g/h naloxone. The nociceptive threshold of intact rats infused with this dose of naloxone or an equivalent volume of saline (10 .mu.g/h) was increased, suggesting that the presence of the larger osmotic pump caused analgesia.