Nociceptive circling and naloxone.

Under suitable conditions, mice exhibit rotatory behaviour, with a direction preference. Noxious electric stimulation to the feet of mice was found to increase significantly the rate of turning, as well as the ratio between circling in the preferred and in the opposite direction (the latter change was not significant statistically). Naloxone injected prior to the stimulation period tended to reverse the effects of the stimulation. These facts may imply that enkephalins are released during this stimulation and influence rotatory behaviour.