The dopamine D-2 agonist quinpirole produces environment-specific conditioned activity

The stimulant effects of various dopamine agonists can become conditioned to the particular environment with which they are repeatedly paired. The present study assessed the ability of the selective dopamine D-2 agonist quinpirole (2.5 mg/kg) to similarly show environment-specific conditioning. Rats in Paired and Unpaired groups (both n = 12) received 12 pairings of a unique environment with quinpirole or saline, respectively. Horizontal and vertical activity were automatically measured during the 60-min sessions. Home cage injections were given after each session and involved administration of saline or quinpirole to rats, whichever they did not have during the session. Intermittent tests for conditioned activity were given wherein both groups received saline prior to being placed in the chambers for 60 min. Quinpirole enhanced horizontal activity. Stimulant effects on vertical activity were also observed although they appeared after an initial suppression of the response. Conditioned activity was observed on the saline tests as the Paired group was significantly more active than the Unpaired group on each measure. The present findings suggest that enhanced stimulation of the D-2 receptor can produce environment-specific conditioned activity. Consequently, researchers using quinpirole should take this factor into consideration, particularly if utilizing chronic drug treatment.