Factors influencing maternal behavior in the hubb/hubb mutant mouse

We examined the maternal behavior of hubb/hubb mutant mice and normal control (+/hubb) siblings. From previous observations we noted that mutants groom their pups less, suckle less than normal, and often cannibalize the young. To date, these observations had not been quantified. Although prolactin (PRL) is linked to maternal behavior, it was difficult to measure because of the hyperirratibility of the mutant mice. Consequently, dopamine (DA) and its metabolite, dihydroxyphenylacetic acid (DOPAC), were measured in the median eminence in brains of both normal and mutant mice. Tyrosine hydroxylase, the rate-determining step in dopamine synthesis, was localized in the brain by immunohistochemistry. Five mutant and nine normal dams were observed for pup retrieval and crouching. Mean time for pup retrieval was slower (p < 0.06) for mutants (28.09 s) than for normal dams (18.49 s). Crouching was the same for both strains. Mutant pups were cold to the touch, and not well groomed. Brains from both strains were examined at Day 11 and Day 18 of gestation and Day 2 and Day 11 of lactation. Qualitatively, tyrosine hydroxylase localization in the arcuate nucleus and median eminence was the same in both strains for the gestation samples. The decrease in staining observed from gestation to lactation in the normal mice was increased in the mutants. Dopamine was similar in both strains at all stages, but DOPAC was significantly higher at early lactation in the mutants. We do not assume an absolute inverse relationship between dopaminergic activities and prolactin, but it is likely that the increase in DOPAC in the mutant reflects a decrease in prolactin, which could contribute to the diminished maternal care in the mutants.