Methadone produces conditioned place preference in the rat.

The appetitive properties of methadone were investigated using the conditioned place preference paradigm. Male Sprague-Dawley rats received conditioned place preference training for a 6-day period. The apparatus consisted of two chambers with distinctive visual and tactile cues, separated by removable doors. Rats received intraperitoneal (IP) injections of methadone (1.0, 2.0, 4.0, 6.0, 8.0, and 10.0 mg/kg methadone HCl) paired with one chamber and saline paired with the other chamber on alternating days. On the seventh day, rats were allowed free run of the entire apparatus and time spent in either chamber was computer recorded. Methadone produced a place preference for the side previously paired with drug in a dose-dependent manner. Place preference for methadone peaked at 4.0 mg/kg and aversion was produced at 10.0 mg/kg. These results indicate that at intermediate doses, methadone does have appetitive properties and is capable of producing a conditioned place preference.