Role of the infraorbital nerve in retrieving behavior in lactating rats.

Injecting the local lidocaine into the mystacial pads of primiparous rats rendered the snout insensitive to touch and abolished the dams' ability to retrieve. Injecting the drug into the masseter muscles or intraperitoneally did not render the snout anaptic or abolish retrieval, results indicating that the effect of intramystacial lidocaine treatment could not be attributed to systemic toxicity or to the drug's spreading from the mystacial pads to affect the nearby masseter muscles. Cutting the intraorbital nerves produced a temporary retrieval impairment that was indistinguishable from that produced by intramystacial lidocaine injection. Surgical deafferentation did not affect the latency of dams to approach pups that had been displaced from the nest site, which indicates that the retrieval deficit was not due to postoperative debilitation. In addition, infraorbital section did not interfere with the ability to locate and consume a piece of cheese that had been buried in the home cage, which indicates that the operation did not produce anosmia or interfere with the muscles used to grasp pups. Cutting the facial nerves abolished vibrissal movement but did not disrupt retrieval, results indicating that the effect of infraorbital lesions could not be attributed to the loss of vibrissal cues or to nonspecific effects of nerve section. The possibility was tested that infraorbital deafferentation has a profound effect on retrieval because anaptic dams, in their initial attempts at picking up pups, elicit distress vocalizations from their offspring. Dams injected with lidocaine in the mystacial pads failed to retrieve pups that had been anesthetized with a barbiturate to abolish their distress vocalizations. Thus pup-produced vocalizations are not responsible for the retrieval impairment exhibited by anaptic mothers. It is concluded that perioral tactile sensation plays an important role in the ability of lactating rats to retrieve.