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

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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.