Electromyographic patterns associated with nonnutritive sucking in 11–13-day-old rat pups.

Abstract

Experiments (3) describe an electromyographic (EMG) recording technique designed to measure the frequency, duration and intensity of nonnutritive sucking (NNS) in rat pups. Rat pups, 11- to 13-days old, were separated from their mothers for 2-6 or 20-24 h and then allowed to suckle an anesthetized dam for up to 3 h without receiving any milk. Jaw-muscle EMG and nipple detachments were recorded. Different EMG patterns representing 2 discrete modes of sucking were reliably discerned from polygraph records, as were changes in the overall intensity of EMG. In addition, 20-24 h separated pups engaged in more frequent NNS bouts and bouts of longer duration than 2-6 h separated pups. Pups separated by 20-24 h engaged in a mode of NNS not seen in 2-6 h separated pups. Overall EMG intensity was higher and frequency of nipple detachments was lower in animals separated for 20-24 h. In both groups of pups, but particularly the 20-24 h pups, frequency of some NNS patterns decreased as the length of the dry suckling test increased. The EMG intensity decreased over time in both groups, and frequency of nipple detachments increased in 2-6 h separated pups. Some aspects of NNS may be highly labile and respond to variations of both deprivation from the mother (separation) and nutritive deprivation (dry suckling).