INVOLVEMENT OF OPIOID RECEPTORS IN SHAKING BEHAVIOR INDUCED BY PARAQUAT IN RATS

Paraquat (30-70 mg/kg intraperitoneally) caused typical shaking behavi our in rats in a dose-dependent manner. Myoclonus also appeared after the shaking behaviour in several rats treated with the highest dose of paraquat. Morphine (5 mg/kg intraperitoneally, 30 min. before paraqua t) significantly reduced the frequency of shaking behaviour. The allev iation by morphine disappeared when naloxone (1.5 mg/kg intraperitonea lly 15 min. after morphine) was coadministered. Although there was no histological change in brain slices of paraquat-treated rats (70 mg/kg intraperitoneally), the fluorescein uptake into brain was increased b y the treatment. Morphine prevented the increase of fluorescein uptake , but naloxone failed to antagonize this effect. On the other hand, in tracerebroventricularly administered paraquat (25.7 mug/rat) caused tr emor in all rats, but not shaking behaviour nor myoclonus. These findi ngs suggest that paraquat administered systemically as well as central ly may be toxic to the brain. Although the actions of paraquat on the brain seem to be complicated, opioid receptors may play a role in the actions.