Antagonism of stress-induced analgesia by quaternary naloxone.

Both naloxone hydrochloride and the quaternary compound, naloxone methylbromide, significantly reduced antinociception elicited by 90 s of continuous footshock. Peripheral specificity of quaternary naloxone was demonstrated by its lack of antagonism of morphine analgesia. These results suggest that a significant portion of the antinociception elicited by these parameters of footshock and assessed by tail-flick procedures in rats is due to the activation of peripheral endorphins.