Effects of sex and the estrous cycle on regulation of intravenously self-administered cocaine in rats.
BACKGROUND
Previous research with both humans and animals suggests that there are sex differences in cocaine self-administration; in rodents, ovarian hormones may underlie these differences.


OBJECTIVE
A two-lever drug self-administration procedure was used to compare regulation of intravenously self-administered cocaine in male and female rats and among females in different phases of the estrous cycle.


METHODS
Eleven female and seven male age-matched Wistar rats were trained to self-administer nine doses of cocaine (0.0-2.4 mg/kg) during daily 5-h sessions. Experimental test chambers were equipped with two levers and associated stimulus lights. A response on the lever with stimuli signaling an increase in cocaine dose increased the infusion duration by 3 s, and a response on the other lever decreased the infusion duration by 3 s.


RESULTS
After responding for cocaine stabilized, regulation was disrupted more in females than in males (r2=78.9, r2=92.6, respectively) with the greatest disruption observed in females during the estrus phase (r2=48.5). Mean dose size varied considerably for males and for females in the metestrus/diestrus and proestrus phases; however, estrus females responded almost exclusively on the lever associated with an increase in cocaine dose.


CONCLUSIONS
These findings indicate sex differences in the regulation of cocaine self-administration, and they suggest that ovarian hormones may be responsible for the observed sex differences.
Lynch
W J
WJ
Department of Psychiatry, University of Minnesota, Minneapolis 55455, USA.
Arizzi
M N
MN
Carroll
M E
ME
D000818:Animals; D003042:Cocaine / Q000008:administration & dosage*; D004971:Estrus; D005260:Female; D007262:Infusions, Intravenous; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012646:Self Administration; D012737:Sex Factors
D003042:Cocaine