Effects of repeated methylphenidate treatment in the young rat: sensitization of both locomotor activity and stereotyped sniffing.
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.
McDougall
S A
SA
Department of Psychology, California State University, San Bernardino 92407-2397, USA. smcdouga@csusb.edu
Collins
R L
RL
Karper
P E
PE
Watson
J B
JB
Crawford
C A
CA
D000375:Aging / Q000502:physiology; D000818:Animals; D003655:Decerebrate State / Q000503:physiopathology / Q000523:psychology; D018765:Dopamine Uptake Inhibitors / Q000009:adverse effects / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006614:Hindlimb / Q000502:physiology; D008297:Male; D008465:Mechanoreceptors / Q000502:physiology; D008774:Methylphenidate / Q000009:adverse effects / Q000494:pharmacology*; D009020:Morphine / Q000494:pharmacology; D009043:Motor Activity / Q000187:drug effects*; D009294:Narcotics / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000502:physiology; D013239:Stereotyped Behavior / Q000187:drug effects*; D013375:Substance Withdrawal Syndrome / Q000523:psychology
D018765:Dopamine Uptake Inhibitors; D009294:Narcotics; D008774:Methylphenidate; D009020:Morphine