Maternal motivation of lactating rats is disrupted by low dosages of haloperidol

Motorically-active maternal behaviors of rats, such as retrieval and licking of pups, are known to be reduced or suspended following systemic injection of > or = 0.2 mg/kg haloperidol (HAL), a dopamine (DA) receptor blocker. Further, when these behaviors are thwarted by muzzling, dams persistently attempt to make snout contact with pups by pushing them with the muzzle, indicative of intense maternal motivation. To evaluate whether time spent contact-seeking by muzzle-pushing is impaired by dosages of HAL too low to reduce retrieval and licking of pups, dams were fitted with a full muzzle (FM), given 0, 0.05 or 0.10 mg/kg HAL, and reunited with their pups for 30 min after a 4-h separation. Similarly-treated dams fitted with a control muzzle, which allows perioral contact with pups, displayed essentially normal maternal behavior. In FM dams, low dosages of HAL severely and dose-dependently reduced muzzle-pushing, as well as actual contact by handling-touching and moving pups with their paws, although the latency to initiate these behaviors by responders was not impaired. A threshold level of DA is apparently necessary for efficient motor control (handling) and for maternal incentive, persistent effort to achieve contact with pups (muzzle-pushing), consistent with an arousal explanation of the action of DA.