Sex differences in the acquisition and maintenance of cocaine and nicotine self-administration in rats.
RATIONALE
Consistent sex differences are observed in human drug addiction, with females often exceeding males on drug intake. However, there is still a need for animal models for some aspects of addiction such as acquisition of drug self-administration and the subsequent development of drug-seeking.


OBJECTIVES
The present study examined sex differences in the acquisition and maintenance of self-administration of two widely used stimulants, cocaine and nicotine.


METHODS
Male and female rats self-administered cocaine (0.4 mg/kg/infusion) or nicotine (0.03 mg/kg/infusion) daily under a fixed-ratio 1 (FR 1) schedule until acquisition criteria were met (maximum of 30 sessions). The self-administration criterion for cocaine was ≥20 infusions in a 2-h session and ≥5 infusions in a 1-h session for nicotine. Sex differences were assessed by examining the percentage of rats that met acquisition criteria, the number of sessions to meet criteria, and the number of infusions earned during the maintenance phase.


RESULTS
A significantly higher percentage of male rats acquired both cocaine and nicotine self-administration than females, and males met acquisition criteria in fewer sessions. However, after criteria were met, females self-administered more cocaine than males during the first 5 days of maintenance. There were no sex differences in nicotine infusions post-acquisition.


CONCLUSIONS
Differences in acquisition amongst sexes can reveal factors that are integral to initiation of drug use, an often overlooked phase of drug addiction.
['Swalve|Natashia|N|', 'Smethells|John R|JR|', 'Carroll|Marilyn E|ME|']
D000818:Animals D000697:Central Nervous System Stimulants D003042:Cocaine D005260:Female D008297:Male D009538:Nicotine D051381:Rats D012646:Self Administration D012727:Sex Characteristics D019966:Substance-Related Disorders
Sex differences Acquisition Maintenance Cocaine Nicotine Self-administration