The effects of strain and estrous cycle on heroin- and sugar-maintained responding in female rats

Behav Brain Res. 2021 Jul 9;409:113329. doi: 10.1016/j.bbr.2021.113329. Epub 2021 Apr 29.


Heroin intake decreases during the proestrus phase of the estrous cycle in female, Long-Evans rats. The purpose of this study was to (1) determine if proestrus-associated decreases in heroin intake extend across rat strains and (2) determine if proestrus-associated decreases in responding extend to a nondrug reinforcer. Female rats were implanted with intravenous catheters and trained to self-administer heroin. Estrous cycle was tracked daily for the duration of the study. During testing, Lewis, Sprague Dawley, and Long-Evans rats self-administered low (0.0025 mg/kg) and high (0.0075 mg /kg) doses of heroin and then self-administered sugar on fixed ratio (FR1) schedules of reinforcement. Heroin intake decreased significantly during proestrus in all three rat strains under at least one dose condition; however, sugar intake did not decrease during proestrus in any strain. These data suggest that responding maintained by heroin, but not a nondrug reinforcer, significantly decreases during proestrus in female rats and that these effects are consistent across rat strain.

Keywords: Opioid; Proestrus; Reinforcement; Self-administration.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Behavior, Animal / physiology*
  • Dietary Sugars / administration & dosage*
  • Estrous Cycle / metabolism
  • Estrous Cycle / physiology*
  • Female
  • Heroin / administration & dosage*
  • Narcotics / administration & dosage*
  • Rats
  • Rats, Inbred Lew
  • Rats, Long-Evans
  • Rats, Sprague-Dawley
  • Reinforcement Schedule
  • Self Administration
  • Sugars


  • Dietary Sugars
  • Narcotics
  • Sugars
  • Heroin