Increasing the incentive salience of cocaine challenges preference for pup- over cocaine-associated stimuli during early postpartum: place preference and locomotor analyses in the lactating female rat.
OBJECTIVE
Prior studies using a dual-choice conditioned place preference (CPP) procedure revealed that postpartum female rats (dams) strongly prefer chambers associated with pups over those associated with subcutaneously administered cocaine almost exclusively during early but not late postpartum (Mattson et al. 2001). The present study examines whether early postpartum dams retain strong pup-associated chamber preference when contrasted with a cocaine stimulus of greater incentive salience (intraperitoneal [IP] injections with brief conditioning sessions). Locomotor rate was measured during conditioning (stimuli-present) and test (stimulus-absent) sessions.


METHODS
A three-chambered CPP apparatus was used to compare preferences for chambers associated with IP cocaine vs age-matched pups. Unconditioned stimuli were systematically assigned to the least-preferred chamber of separate groups of dams before conditioning. Control dams verified that unconditioned stimuli were necessary for CPP and stimulus-associated locomotion.


RESULTS
Compared with most late postpartum dams (60%), only 31% of early postpartum dams preferred the cocaine-associated chamber (P < 0.05). Substantially more dams preferred the pup-associated chamber during early postpartum (27%) than late postpartum (5%; P < 0.05). Locomotor sensitization emerged across cocaine-conditioning sessions in cocaine-preferring but not pup-preferring dams (P < 0.05). Locomotor rates were consistently lower in preferred vs nonpreferred chambers during test.


CONCLUSIONS
After increasing cocaine's incentive salience, more early postpartum dams prefer the cocaine-associated chamber than previously reported (Mattson et al. 2001). However, pup-associated chamber preference was still higher in early vs late postpartum. Pup- and cocaine-preferring dams expressed differences in the induction phase of locomotor sensitization across cocaine conditioning but expressed similar motoric patterns in their preferred chambers at test.
Seip
Katharine M
KM
Center for Molecular and Behavioral Neuroscience, Rutgers University, 197 University Avenue, Newark, NJ 07102, USA. kseip@pegasus.rutgers.edu
Morrell
Joan I
JI
D000818:Animals; D000831:Animals, Newborn; D002755:Choice Behavior; D003042:Cocaine / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects*; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D005260:Female; D007274:Injections, Intraperitoneal; D007774:Lactation; D008425:Maternal Behavior; D009042:Motivation; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D049590:Postpartum Period; D051381:Rats; D017207:Rats, Sprague-Dawley; D012054:Reinforcement, Psychology; D013997:Time Factors
D018765:Dopamine Uptake Inhibitors; D003042:Cocaine