Pup-Associated Conditioned Place Preference Reaction and Maternal Care in Depressive WAG/Rij Rats

Abstract

The acquisition of a conditioned place preference reaction (CPPR) associated with own pups and foster pups was compared in female WAG/Rij and Wistar rats, along with maternal behavior in a “place preference” chamber from day 2 to day 8 after birth. In addition, females’ behavior was assessed in the open field, elevated plus maze, and forced swimming tests before pregnancy and after birth of pups. Female WAG/Rij rats acquired the CPPR associated with their own pups (WAG/Rij) and foster pups (Wistar) less well. Thus, the number of females with increases in the time spent in the initial non-preferred sector after it was combined with pups and the number of females achieving the CPPR acquisition criterion were smaller in WAG/Rij rats than Wistar rats. Female WAG/Rij rats, as compared with female Wistar rats, showed lower levels of maternal care in the place preference chamber in relation to both their own pups and foster pups: the numbers of approaches to the pups were smaller, as were the numbers of retrievals, and the non-feeding-related times spent in contact with pups were shorter. The durations of immobility in the forced swimming test were greater in WAG/Rij females than Wistar females both before pregnancy and after delivery of pups, which is evidence for a stable depression-like state. Before pregnancy, there were no statistically significant interstrain differences in anxiety levels. After birth of pups, anxiety levels in WAG/Rij females decreased, while those in Wistar females showed no significant change. These results provide evidence that the worse acquisition of the CPPR and the decreased maternal care in depressed WAG/Rij females were not associated with the features of their own pups but were related to their depressive state. In other words, pups provided weaker reinforcement for depressed mothers than for “normal” (nondepressed) mothers.