Withdrawal-like behavior in planarians is dependent on drug exposure duration.

Planarians display a concentration-related reduction in locomotor activity following their spontaneous withdrawal from opioids, cannabinoids, stimulants and benzodiazepines. This suggests that planarians display a withdrawal-like behavior that can be quantified as a reduction in locomotor activity. Because withdrawal-like behavior in previous studies has been quantified only following the cessation of a 60-min drug exposure, it is unclear whether the withdrawal response varies with drug exposure duration. Therefore, the goal of this study is to determine if the duration of drug exposure (0, 5, 15, 30, 45, 60min and 24h) to three different drugs - methamphetamine, cocaine and caffeine - affects the magnitude of withdrawal-like behavior (i.e., reduced locomotor activity) in planarians. Experiments revealed that methamphetamine (10microM) produced significant withdrawal-like behavior regardless of the exposure time (P<0.05). An exposure time of only 5min resulted in a significant reduction in locomotor activity. The peak effect, although occurring following a 24-h exposure, was only slightly greater than that caused by a 30-min exposure. For cocaine (10microM), a longer exposure time (15min) was required for the manifestation of significant withdrawal-like behavior. The peak cocaine effect was observed following a 24-h exposure. Caffeine (10microM) did not produce significant changes in locomotor activity during withdrawal or alter locomotor activity during acute exposure. The present results suggest that the magnitude of withdrawal-like behavior in planarians is dependent on both the duration and type of drug exposure, and that planarians do not display withdrawal to caffeine.