HALOPERIDOL INHIBITS MATERNAL RETRIEVAL AND LICKING, BUT ENHANCES NURSING BEHAVIOR AND LITTER WEIGHT GAINS IN LACTATING RATS

To determine whether the motorically-active and -inactive components of maternal behavior in rats are differentially affected by dopamine, we administered haloperidol, a dopamine receptor antagonist, to lactating rats on day 7 (+/- 1) post-partum, 3 h after dam-lifter separation and 1 h before their reunion. Compared to treatment with saline or domperidone, a peripherally-active dopamine antagonist, haloperidol treatment inhibited retrieval and licking of pups in a dose-dependent manner and hastened the onset of nursing behavior, but impaired the high crouch posture at the highest doses (8 and 10 mg/kg), Also, litters of dams treated with 0.2, 0.4, or 1.0 mg/kg haloperidol gained almost twice as much weight as litters of controls or of dams treated with 5 to 10 mg/kg haloperidol. To determine whether the milk ejection pattern accounts for differential litter weight gain after moderate and high doses of haloperidol, milk ejections were assessed by pup stretch and nipple-switching responses for 30 min after the onset of crouching following a 4 h dam-lifter separation on day 12 or 13 post-partum. The lifters of dams treated with 1 or 3 mg/kg haloperidol had substantially greater lifter weight gains than lifters of control dams or of dams treated with 5 mg/kg haloperidol. The smaller lifter weight gain of 5 mg/kg haloperidol lifters was due to a retardation of milk ejections in their dams, while the smaller gain of control litters was due, at least in part, to greater behavioral activation by their dams. Non-dopaminergic effects of large doses of haloperidol (greater-than-or-equal-to 5 mg/kg) may have reduced the display of the high crouching posture during nursing and contributed to the retardation of milk ejections. Thus, dopamine is necessary for the motorically-active components of maternal behavior, but its inhibition may be necessary for the assumption of the immobile nursing postures and for maximal lifter weight gains. We hypothesize that extra-hypothalamic as well as tuberoinfundibular dopaminergic systems are inactivated by the suckling stimulus.