U50,488 INCREASES ULTRASONIC VOCALIZATIONS IN 3-DAY-OLD, 10-DAY-OLD AND 18-DAY-OLD RAT PUPS IN ISOLATION AND THE HOME CAGE

Separation-induced calling in the young of many species can be modulat ed by the opioid system. Morphine reduces ultrasonic vocalizations (US Vs) produced by isolated rat pups, an effect blocked by naltrexone. Ce ntral administration of the mu and delta opiate receptor agonists DAMG O and DPDPE reduce USV; kappa receptor agonist U50,488 increases them. We now find that peripheral U50,488 not only boosted calling rates in isolated 3-, 10-, and 18-day-old rat pups, but also induced calling i n pups of these ages tested in the home cage with their littermates, w here USVs are seldom heard in nature. U50,488 lowered rectal temperatu re, although temperature loss and USV were not correlated within drug treatment groups. (C) 1994 John Wiley and Sons, Inc.