title: Sex differences in the acquisition and maintenance of cocaine and nicotine self-administration in rats.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
authors.affiliation: Department of Psychiatry, University of Minnesota, 680A Diehl Hall, 550 Essex Street SE, Minneapolis, MN, 55455, USA. nlswalve9220@gmail.com.
authors.forename: Natashia
authors.initials: N
authors.lastname: Swalve
authors.affiliation: Department of Psychiatry, University of Minnesota, 680A Diehl Hall, 550 Essex Street SE, Minneapolis, MN, 55455, USA.
authors.forename: John R
authors.initials: JR
authors.lastname: Smethells
authors.affiliation: Department of Psychiatry, University of Minnesota, 680A Diehl Hall, 550 Essex Street SE, Minneapolis, MN, 55455, USA.
authors.forename: Marilyn E
authors.initials: ME
authors.lastname: Carroll
mesh_terms: D000818:Animals; D000697:Central Nervous System Stimulants / Q000008:administration & dosage*; D003042:Cocaine / Q000008:administration & dosage*; D005260:Female; D008297:Male; D009538:Nicotine / Q000008:administration & dosage*; D051381:Rats; D012646:Self Administration; D012727:Sex Characteristics; D019966:Substance-Related Disorders
chemical_list: D000697:Central Nervous System Stimulants; D009538:Nicotine; D003042:Cocaine
keywords: Acquisition; Cocaine; Maintenance; Nicotine; Self-administration; Sex differences