Weekday-only chronic oral methylphenidate self-administration in male rats: Reversibility of the behavioral and physiological effects.

Methylphenidate (MP) is a commonly prescribed psychostimulant for Attention Deficit Hyperactivity Disorder (ADHD). We recently reported behavioral and developmental effects of chronic MP use in healthy rats. The current study investigated how interrupting chronic MP treatment with weekend abstinence altered the behavioral and physiological consequences of chronic MP treatment, and if prolonged abstinence would reverse the observed effects. Male Sprague Dawley rats were assigned to one of three treatment groups: water (W); low dose (LD) MP; and high dose (HD) MP. For 13 weeks, rats had access to drink from a bottle containing 4 mg/kg MP (LD), 30 mg/kg MP (HD) or water (W) for 1 h, and 10 mg/kg MP (LD), 60 mg/kg MP (HD) or water (W) for the next 7 h, each week day. During weekends, all animals received only water as well as throughout the 5-week-long abstinence phase, which immediately followed the treatment phase. Throughout the treatment phase, regardless of weekend abstinence, chronic MP resulted in significant decreased food and fluid intake and body weight. Also, HD MP exposure resulted in the following behavioral effects: increased open field and circadian locomotor activity; increased latency to immobility and decreased time spent immobile in the forced swim test; increased center activity in the open field and percent of time spent in an open arm of the elevated-plus-maze; and increased social affiliation and memory in the Crawley's three chamber sociability test. During the prolonged (5-week) abstinence phase, all these effects were reversed while HD treated rats increased their fluid intake. These results indicated that intermittent brief abstinence periods (weekend's off-treatment) produced the same behavioral and developmental effects as those previously reported with chronic (7 days/week) MP treatment, but were reversible following a prolonged abstinence period (5 weeks).