Rationale and objectives: Our previous work uncovered a differential preference of maternal female rats for cues associated with pups versus cues associated with cocaine at three different postpartum time points. Our current study examines the preference for these cues in conjunction with an assessment of the capacity to express the maternal behavior at one of these time points. We examined dams at day 10 postpartum using a procedure that included two additional controls, and a complete assessment of the expression of maternal behavior and locomotor activity.
Methods: A conditioned place-preference procedure was used to determine the preference for cocaine- or pup-associated cues. The two controls were (1) a preconditioning test to verify no initial chamber preference and (2) a separate control group of postpartum day-10 dams exposed to chambers and cues but not to unconditioned stimuli. The expression of maternal behavior was determined by measurement of maternal nest building, retrieval of pups to the nest, grooming, crouching over pups, nursing, and maternal aggression. Locomotor activity was measured with an automated apparatus.
Results: Dams conditioned with cocaine or pups showed a preference for either the cocaine-associated chamber or the pup-associated chamber, confirming the existence of two similar-sized preference groups at this time point. Regardless of preference, dams had equal and robust expression of maternal behavior and similar locomotor capacity. The pre-conditioning test showed no initial chamber preferences and did not alter the conditioned preference response. The use of unconditioned stimuli in the place-preference conditioning procedure was effective and necessary for the preference response.
Conclusion: Our current study has revealed that differences in the motivational state of the maternal dam emerge even while the expression of maternal behavior is constant and substantial. The data suggest that the difference in preference is a very specific appetitive response that is not linked to expression of maternal behavior or locomotor capacity.