3,4-Methylenedioxymethamphetamine and naloxone in rat rotational behaviour and open field

It has recently been shown that 3,4-Methylenedioxymethamphetamine (MDMA) has an anti-parkinsonian effect in rodent models of Parkinson's disease. The mechanism of this anti-parkinsonian action is unknown. Opioids have been suggested to play a role in MDMA-induced behaviour. We therefore investigated MDMA and naloxone in the rat rotational behavioural model. Male Sprague-Dawley rats were lesioned unilaterally with 6-hydroxydopamine at the medial forebrain bundle. Administration of R/S-MDMA (5 mg/kg, s.c.) produced ipsilateral rotations. Naloxone (2, 5, 10 mg/kg, s.c.) did not produce rotations on its own but reduced the number of MDMA-induced ipsilateral rotations. This effect was not dose-dependent. In contrast to reports on mice, in unlesioned animals, naloxone (10 mg/kg, s.c.) did not block MDMA (5 mg/kg, s.c.)-induced hyperactivity in an open field in our experiment. It is concluded that endogenous opioids play a role in MDMA's action in the rat rotational behavioural model.