Effects of repeated methylphenidate treatment in the young rat: sensitization of both locomotor activity and stereotyped sniffing

Exp Clin Psychopharmacol. 1999 Aug;7(3):208-18. doi: 10.1037//1064-1297.7.3.208.


The behavioral effects of repeated methylphenidate (MPH) treatment were assessed in young rats. In 4 experiments, rats (starting at Postnatal Day 10 or 16) were pretreated on 5 consecutive days with saline or MPH (2.5-20.0 mg/kg i.p.). Sensitization was assessed after 1 or 7 abstinence days, with rats receiving a test day challenge injection of either a low dose of MPH (2.5 mg/kg) or the same dose of MPH as given during pretreatment. Results show that a test day injection of 2.5 mg/kg MPH produced a sensitized locomotor response in rats pretreated with 2.5-20.0 mg/kg MPH. This MPH-induced locomotor sensitization was evident only after 1 abstinence day. Various pretreatment doses of MPH (5, 10, 15, or 20 mg/kg) were capable of sensitizing the stereotyped sniffing of young rats, but only rats pretreated and tested with the highest dose (20 mg/kg) of MPH showed an augmented stereotyped sniffing response that was still robust after 7 abstinence days. Results indicate that young rats are capable of exhibiting sensitization after an extended abstinence period, which contrasts with previous research suggesting that psychostimulant treatment does not produce long-term sensitization in young rats.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aging / physiology
  • Animals
  • Decerebrate State / physiopathology
  • Decerebrate State / psychology
  • Dopamine Uptake Inhibitors / adverse effects
  • Dopamine Uptake Inhibitors / pharmacology*
  • Dose-Response Relationship, Drug
  • Female
  • Hindlimb / physiology
  • Male
  • Mechanoreceptors / physiology
  • Methylphenidate / adverse effects
  • Methylphenidate / pharmacology*
  • Morphine / pharmacology
  • Motor Activity / drug effects*
  • Narcotics / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • Reaction Time / physiology
  • Stereotyped Behavior / drug effects*
  • Substance Withdrawal Syndrome / psychology


  • Dopamine Uptake Inhibitors
  • Narcotics
  • Methylphenidate
  • Morphine