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

Motorically-active maternal behaviors of rats, such as retrieval and lickin g of pups, are known to be reduced or suspended following systemic injectio n of greater than or equal to 0.2 mg/kg haloperidol (HAL), a dopamine (DA) receptor blocker. Further, when these behaviors are thwarted by muzzling, d arns persistently attempt to make snout contact with pups by pushing them w ith the muzzle, indicative of intense maternal motivation. To evaluate whet her 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 thei r pups for 30 min after a 4-h separation. Similarly-treated dams fitted wit h a control muzzle, which allows perioral contact with pups, displayed esse ntially normal maternal behavior. In FM dams, low dosages of HAL severely a nd dose-dependently reduced muzzle-pushing, as well as actual contact by ha ndling-touching and moving pups with their paws, although the latency to in itiate 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. (C) 1 999 Elsevier Science B.V. All rights reserved.