The effect of cholinergic stimulation on rat pup ultrasonic vocalizations

As cholinergic stimulation increases vocalizations in adult rats, the prese nt study investigated the effects of systemic oxotremorine, a cholinergic a gonist, on the production of separation calls in rat pups of different ages and whether these effects are in response to central versus peripheral sti mulation. The first experiment examined the dose-response effects of oxotre -morine on the number of vocalizations and acoustic parameters of 10-, 15-, and 17-day-old rat pumps. In contrast to other studies on adult rats, pup vocalizations were decreased while marginally changing acoustic parameters. The second experiment, using muscarinic antagonists, showed that pretreatm ent with atropine sulfate, which can cross the blood-brain barrier (BBB), r eversed the call-reducing effect of oxotremorine whereas pretreatment with atropine methyl nitrate, which does nor cross BBB, did not. Suppression of vocalizations by oxotremorine may be explained by central activation and no t the peripheral effects of the drug. Dissimilar effects of cholinergic sti mulation of infant and adult mt brains may be attributed to a differential role of the cholinergic system during development and maturity. (C) 2001 Jo hn Wiley & Sons, Inc.