Impulsive choice and environmental enrichment: Effects of d-amphetamine and methylphenidate

• Published in: Behavioural brain research 2008-11, Vol.193 (1), p.48-54
• Main Authors: Perry, Jennifer L., Stairs, Dustin J., Bardo, Michael T.
• Format: Article
• Language: English
• Subjects: Amphetamine; Amphetamine - administration & dosage; Amphetamine - pharmacology; Animals; Behavior, Animal - drug effects; Behavior, Animal - physiology; Behavioral psychophysiology; Biological and medical sciences; Central Nervous System Stimulants - administration & dosage; Central Nervous System Stimulants - pharmacology; Choice Behavior - drug effects; Choice Behavior - physiology; Conditioning, Operant - drug effects; Conditioning, Operant - physiology; Delay discounting; Dopamine Agents - administration & dosage; Dopamine Agents - pharmacology; Environment; Environmental enrichment; Fundamental and applied biological sciences. Psychology; Impulsive Behavior - psychology; Impulsive choice; Individual differences; Injections, Subcutaneous; Male; Medical sciences; Methylphenidate; Methylphenidate - administration & dosage; Methylphenidate - pharmacology; Motor Activity - drug effects; Motor Activity - physiology; Neuropharmacology; Pharmacology. Drug treatments; Psychoanaleptics: cns stimulant, antidepressant agent, nootropic agent, mood stabilizer; Psychoanaleptics: cns stimulant, antidepressant agent, nootropic agent, mood stabilizer..., (alzheimer disease); Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Psychopharmacology; Rats; Rats, Sprague-Dawley; Reinforcement Schedule; Reinforcement, Psychology; Reward; Substance-Related Disorders - physiopathology
• ISSN: 0166-4328; 1872-7549
• DOI: 10.1016/j.bbr.2008.04.019

Individual differences in impulsive choice and rearing in differential environments are factors that predict vulnerability to drug abuse. The present study determined if rearing influences impulsive choice, and if d-amphetamine or methylphenidate alters impulsive choice in differentially reared rats. Male Sprague-Dawley rats were raised from 21 days of age in either an enriched condition (EC) or an isolated condition (IC) and were tested as young adults on an adjusting delay task. In this task, two levers were available and a response on one lever yielded one 45 mg food pellet immediately, whereas a response on the other yielded three pellets after an adjusting delay. The delay was initially set at 6 s, and it decreased or increased by 1 s following responses on the immediate or delayed levers, respectively. A mean adjusted delay (MAD) was calculated upon completion of each daily session, and it served as the quantitative measure of impulsivity. Once MADs stabilized, rats were injected with saline, d-amphetamine (0.5, 1.0, or 2.0 mg/kg, s.c.), or methylphenidate (2.5, 5.0, or 10.0 mg/kg, s.c.) 15 min prior to adjusting delay sessions. EC rats had higher baseline MADs (were less impulsive) than IC rats. Additionally, administration of d-amphetamine, but not methylphenidate, dose-dependently increased impulsive choice (decreased MADs) in EC rats. In IC rats, d-amphetamine and methylphenidate dose-dependently decreased impulsivity (increased MADs). These results indicate that rearing environment influences impulsive choice and moderates the effect of psychostimulants on impulsive choice. Specifically, psychostimulants may decrease environment-dependent impulsive choice in individuals with high levels of impulsivity (e.g., those with ADHD), whereas they may increase impulsive choice in individuals with low levels of impulsivity.