title: Exercise decreases speedball self-administration.
abstract: OBJECTIVE
  Epidemiological studies report that individuals who exercise are less likely to abuse drugs. Preclinical studies report that exercise, in the form of treadmill or wheel running, reliably decreases the self-administration of psychomotor stimulants and opioids. To date, preclinical studies have only examined the effects of exercise on responding maintained by individual drugs and not by combinations of multiple drugs. This limits the translational appeal of these studies because polydrug abuse is common among substance abusing populations. The purpose of this study was to examine the effects of exercise on the self-administration of speedball, a combination of cocaine and heroin that is frequently encountered in intravenous drug abusing populations.
  
  
  METHODS
  Female rats were obtained at weaning and assigned to sedentary or exercising conditions. Sedentary rats were housed in standard cages that permitted no exercise beyond normal cage ambulation; exercising rats were housed in similar cages with an activity wheel. After 6weeks, rats were implanted with intravenous catheters and trained to self-administer cocaine, heroin, and dose combinations of cocaine and heroin (i.e., speedball) on a progressive ratio schedule of reinforcement.
  
  
  RESULTS
  Doses of speedball maintained greater levels of responding than corresponding doses of cocaine and heroin alone. Importantly, responding maintained by cocaine, heroin, and speedball was lower in exercising rats than sedentary rats.
  
  
  CONCLUSIONS
  These data indicate that exercise decreases the self-administration of speedball and suggest that exercise may reduce the abuse of drug combinations that have traditionally been resistant to treatment.
authors.affiliation: Department of Psychology, Davidson College, USA.
authors.forename: Ryan T
authors.initials: RT
authors.lastname: Lacy
authors.affiliation: Department of Psychology, Davidson College, USA.
authors.forename: Justin C
authors.initials: JC
authors.lastname: Strickland
authors.affiliation: Department of Psychology, Davidson College, USA.
authors.forename: Mary K
authors.initials: MK
authors.lastname: Brophy
authors.affiliation: Department of Psychology, Davidson College, USA.
authors.forename: Maryam A
authors.initials: MA
authors.lastname: Witte
authors.affiliation: Department of Psychology, Davidson College, USA; Program in Neuroscience, Davidson College, USA. Electronic address: masmith@davidson.edu.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Smith
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D003042:Cocaine / Q000008:administration & dosage*; D005081:Exercise Therapy / Q000379:methods; D005260:Female; D003932:Heroin / Q000008:administration & dosage*; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D012651:Self Medication / Q000523:psychology*; D019966:Substance-Related Disorders / Q000628:therapy*
chemical_list: D003932:Heroin; D003042:Cocaine
keywords: Cocaine; Exercise; Heroin; Progressive ratio; Rat; Self-administration; Speedball