The effect of cholinergic stimulation on rat pup ultrasonic vocalizations

As cholinergic stimulation increases vocalizations in adult rats, the present study investigated the effects of systemic oxotremorine, a cholinergic agonist, on the production of separation calls in rat pups of different ages and whether these effects are in response to central versus peripheral stimulation. The first experiment examined the dose-response effects of oxotremorine on the number of vocalizations and acoustic parameters of 10-, 15-, and 17-day-old rat pups. 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 pretreatment with atropine sulfate, which can cross the blood-brain barrier (BBB), reversed the call-reducing effect of oxotremorine whereas pretreatment with atropine methyl nitrate, which does not cross BBB, did not. Suppression of vocalizations by oxotremorine may be explained by central activation and not the peripheral effects of the drug. Dissimilar effects of cholinergic stimulation of infant and adult rat brains may be attributed to a differential role of the cholinergic system during development and maturity.