The role of perioral sensation in nipple attachment by weanling rat pups.

Injecting .05 ml of 1% lidocaine into each vibrissal pad, or cutting the infraorbital nerves, abolished nipple attachment in weanling Wistar rat pups. Nipple attachment recovered following infraorbital section. Injecting the local anesthetic intraperitoneally, or into the region of the masseter muscles, did not disrupt attachment, indicating that the effect of the drug on suckling was specific to the site of injection and could not be attributed to systemic toxicity or paralysis of the masseter muscles. Performance on an olfactory-guided orientation task was not disrupted by lidocaine, indicating that the drug did not render pups anosmic. Tactile sensation in the vibrissal pads, rhinarium, and upper lip was abolished after injecting the drug into the vibrissal pads. Vibrissal movement was absent following injection of lidocaine into either the vibrissal pads or the region of the masseter muscles. Shaving the vibrissae did not disrupt nipple attachment. The results are interpreted as suggesting that the nipples' textural qualities elicit attachment in weanling pups.