Di-isopropylfluorophosphate induced antinociception and its interactions with opioid drugs in the rat.

The irreversible anticholinesterase, di-isopropylfluorophosphate (DFP), was shown to be antinociceptive in the paw pressure test in rats only at doses where animals exhibited marked signs of anticholinesterase poisoning. At sub-antinociceptive doses DFP potentiated the opioid drugs fentanyl and alfentanil but failed to alter morphine antinociception. These interactions differ from our previous studies using the hot plate test in mice and suggest that opioid/cholinergic interactions are species and test dependent.