Changes in progressive ratio responding for intravenous cocaine throughout the reproductive process in female rats.

Operant responding on a progressive ratio (PR) schedule for intravenous cocaine as well as sucrose reinforcement was examined in female rats throughout the reproductive process. Self-administration sessions began before mating, and continued throughout pregnancy and until lactational Day 8; following parturition, litters were present with dams during operant sessions. Physiological changes associated with the reproductive process dramatically altered PR responding for cocaine, while PR responding for sucrose was relatively 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 levels only partially recovering during lactation. Dams self-administering cocaine exhibited notably different patterns of maternal behavior in the operant chambers than dams responding for sucrose. Thus, cocaine's reinforcing efficacy may be influenced by (a) the changing physiological profile associated with the reproductive process and (b) competition from the reinforcing properties of offspring during lactation. Copyright 1999 John Wiley & Sons, Inc.