Gs. Hecht et al., Changes in progressive ratio responding for intravenous cocaine throughoutthe reproductive process in female rats, DEVELOP PSY, 35(2), 1999, pp. 136-145
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.