SOME COMPARISONS AMONG THE CALMING AND PAIN-RELIEVING EFFECTS OF SUCROSE, GLUCOSE, FRUCTOSE AND LACTOSE IN INFANT RATS

Ultrasonic vocalizations were recorded from 10-day-old albino rats whi le they were isolated from their dam and siblings. Each rat received a 1.0% BW intra-oral infusion of sucrose, fructose, glucose or lactose at a concentration range of 0.22-0.66 M for 3 min and their vocalizati ons were determined during the infusion and for an additional 7 min. S ucrose, fructose and glucose all significantly reduced vocalizations t o about 50% of baseline levels, whereas lactose, the milk sugar, was i neffective. Moreover, the dose-response function was flat for the thre e effective sugars. In a second experiment, the effects of these sugar s on heat escape latency were measured. Sucrose, fructose and glucose each elevated the latency with which infant rats removed a paw from a 48 degrees C surface; lactose did not. These findings of lactose ineff ectiveness and the flat dose-response function for the other three sug ars exactly parallel those obtained for human newborns. Their implicat ions are discussed.