title: Daily morphine administration increases impulsivity in rats responding under a 5-choice serial reaction time task.
abstract: OBJECTIVE
  Repeated administration of a μ opioid receptor agonist can enhance some forms of impulsivity, such as delay discounting. However, it is unclear whether repeated administration alters motor impulsivity.
  
  
  METHODS
  We examined the effects of acute administration of morphine and amphetamine prior to and during daily morphine administration in rats responding under a five-choice serial reaction time task. Rats (n = 5) were trained to detect a brief flash of light presented randomly in one of five response holes; responding in the target hole delivered food, whereas responding in the wrong hole or responding prior to illumination of the target stimulus (premature response) initiated a timeout. Premature responding served as an index of motor impulsivity.
  
  
  RESULTS
  Administered acutely, morphine (0.1-10 mg·kg(-1) , i.p.) increased omissions and modestly, although not significantly, premature responding without affecting response accuracy; amphetamine (0.1-1.78 mg·kg(-1) , i.p.) increased premature responding without changing omissions or response accuracy. After 3 weeks of 10 mg·kg(-1) ·day(-1) morphine, tolerance developed to its effects on omissions whereas premature responding increased approximately fourfold, compared with baseline. Effects of amphetamine were not significantly affected by daily morphine administration.
  
  
  CONCLUSIONS
  These data suggest that repeated administration of morphine increased effects of morphine on motor impulsivity, although tolerance developed to other effects, such as omissions. To the extent that impulsivity is a risk factor for drug abuse, repeated administration of μ opioid receptor agonists, for recreational or therapeutic purposes, might increase impulsivity and thus the risk for drug abuse.
authors.affiliation: Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA.
authors.forename: D R
authors.initials: DR
authors.lastname: Maguire
authors.affiliation: Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA.
authors.forename: C
authors.initials: C
authors.lastname: Henson
authors.affiliation: Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA.|Department of Psychiatry, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA.
authors.forename: C P
authors.initials: CP
authors.lastname: France
mesh_terms: D000818:Animals; D002755:Choice Behavior / Q000187:drug effects*; D007175:Impulsive Behavior / Q000187:drug effects*; D007274:Injections, Intraperitoneal; D008297:Male; D009020:Morphine / Q000008:administration & dosage* / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects
chemical_list: D009020:Morphine