Changes in progressive ratio responding for intravenous cocaine throughoutthe reproductive process in female rats

Operant responding on a progressive ratio (PR) schedule for intravenous coc aine as well as sucrose reinforcement was examined in female rats throughou t the reproductive process. Self-administration sessions began before matin g, and continued throughout pregnancy and until lactational Day 8; followin g parturition, litters were present with dams during operant sessions. Phys iological changes associated with the reproductive process dramatically alt ered PR responding for cocaine, while PR responding for sucrose was relativ ely stable throughout pregnancy and lactation. Female animals exhibited the highest number of responses/session for cocaine during estrus and the 1st trimester of pregnancy and the lowest responding near parturition, with lev els only partially recovering during lactation. Dams self-administering coc aine exhibited notably different patterns of material behavior in the opera nt chambers than dams responding for sucrose. Thus, cocaine's reinforcing e fficacy may be influenced by (a) the changing physiological profile associa ted with the reproductive process and (b) competition from the reinforcing properties of offspring during lactation. (C) 1999 John Wiley & Sons, Inc.