Gender differences in the reinforcing properties of morphine.
The purpose of the present studies was to examine whether gender differences could be observed in an important aspect of morphine's pharmacology: its reinforcing properties. Our results showed that morphine served as a positive reinforcing agent in both male and female rats in a place conditioning paradigm, but that the dose-response curves displayed marked sex-related differences. At doses from 0.2 up to 10.0 mg/kg, morphine induced an equally strong preference for the drug-associated chamber in males and females. However, as the dose was increased from 10-17.5 mg/kg, morphine ceased to act as a positive reinforcer in males. In contrast, a very strong preference for the morphine-associated chamber was still observed in females at doses up to 30 mg/kg. No gender differences in the blood and brain levels of morphine were observed subsequent to morphine administration during the conditioning phase, suggesting that pharmacokinetic factors were not involved in the sex-related differences observed. Consequently, these results suggest that there are intrinsic sex-linked differences in the doses of morphine that can induce a preference for the drug-associated chamber in a place-conditioning paradigm that are most likely related to differences in the sensitivity of the central nervous system to morphine's reinforcing properties in males and females.
Cicero
T J
TJ
Washington University School of Medicine, Department of Psychiatry, St. Louis, MO 63110, USA.
Ennis
T
T
Ogden
J
J
Meyer
E R
ER
D000818:Animals; D001921:Brain / Q000378:metabolism; D003213:Conditioning, Psychological / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D008297:Male; D009020:Morphine / Q000493:pharmacokinetics / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012054:Reinforcement, Psychology; D012727:Sex Characteristics
D009020:Morphine