Sex differences in the acquisition of IV methamphetamine self-administration and subsequent maintenance under a progressive ratio schedule in rats.
BACKGROUND
Previous work indicates that female rats initiate cocaine use sooner than male rats and reach significantly higher break points (BPs) for a single injection of cocaine under a progressive ratio (PR) schedule compared to male rats.


OBJECTIVE
The present study extends previous work examining sex differences to the acquisition of methamphetamine (METH) (0.02 mg/kg) and maintenance of METH-maintained responding under a PR schedule.


METHODS
An automated priming procedure that has previously been shown to be sensitive to sex differences was used for the acquisition of drug self-administration. A PR schedule that has been shown to be sensitive in detecting sex differences in maintenance levels of cocaine-reinforced responding was used for the maintenance phase of the experiment.


RESULTS
A greater percentage of female rats met the acquisition criterion for METH (0.02 mg/kg) self-administration compared to male rats (55.6% versus 11.1%, respectively), and they did so at a significantly faster rate. Under stable fixed-ratio 1 (FR1) conditions (after acquisition and 5 days before the PR schedule) female rats responded for significantly more METH (0.02 mg/kg) infusions compared to males. Dose-response curves obtained under the PR schedule during maintenance indicated that female rats self-administered significantly more METH infusions compared to male rats.


CONCLUSIONS
These data suggest that female rats are more vulnerable to the acquisition of METH self-administration, and they are more motivated to self-administer METH compared to male rats under a PR schedule during the maintenance phase.
Roth
Megan E
ME
Department of Psychiatry, University of Minnesota Medical School, Mayo Box 392, Minneapolis, MN 55455-0392, USA. roth0180@umn.edu
Carroll
Marilyn E
ME
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005260:Female; D007275:Injections, Intravenous; D008297:Male; D008694:Methamphetamine / Q000008:administration & dosage*; D009042:Motivation; D051381:Rats; D017208:Rats, Wistar; D012646:Self Administration / Q000523:psychology; D012737:Sex Factors
D000697:Central Nervous System Stimulants; D008694:Methamphetamine