Oral methylphenidate establishes a conditioned place preference in rats

Area of Science:

• Neuroscience
• Pharmacology
• Behavioral Science

Background:

• Illicit methylphenidate abuse is a growing concern.
• While intranasal abuse is common, oral (per os; p.o.) methylphenidate also presents abuse potential.

Purpose of the Study:

• To compare the abuse potential of oral (p.o.) versus intraperitoneal (i.p.) methylphenidate in a rat model.
• To investigate the effect of administration timing on methylphenidate's rewarding effects.

Main Methods:

• Rats received p.o. or i.p. methylphenidate (3 or 10 mg/kg) or saline immediately or 30 minutes before conditioning trials.
• Conditioned place preference (CPP) was used to assess the rewarding effects of methylphenidate.
• Preference was measured in a drug-free session after repeated pairings of the drug with a specific compartment.

Main Results:

• Both 3 and 10 mg/kg i.p. methylphenidate produced significant CPP when administered immediately before conditioning.
• Only 10 mg/kg p.o. methylphenidate produced significant CPP under immediate preconditioning.
• No CPP was observed for any dose of i.p. or p.o. methylphenidate when administered 30 minutes prior to conditioning.

Conclusions:

• Oral methylphenidate demonstrates rewarding effects, but at higher doses than i.p. administration.
• Conditioning appears to require ascending, not descending, drug levels, potentially explaining the reduced abuse liability of oral methylphenidate.
• Findings align with clinical observations of lower abuse potential for orally administered methylphenidate compared to other routes.