Scopolamine effects on ultrasonic vocalization emission and behavior in the neonatal mouse

Developmental alterations of the cholinergic system can lead to short- and long-term detrimental consequences for brain function. In order to study the cholinergic modulation of behavior in the neonatal mouse, we characterized ultrasonic vocalizations and spontaneous behavior of 5- and 8-day old CD-1 Swiss mice after i.p. administration of the muscarinic antagonist scopolamine (doses, 0.8 and 2 mg/kg) during both a first isolation of 30 min and a re-isolation of 5 min, occurring immediately after a brief reunion with the mother. As concerns the first isolation, on PND 5, only scopolamine 0.8m g/kg increased the number of ultrasonic vocalizations and, on PND 8, both doses increased it in a dose-dependent fashion. Scopolamine effects on spontaneous behavior were very limited on PND 5, but markedly evident on PND 8, the high dose increasing activity profile. Independently from treatment, the brief reunion with the mother had no effects on mouse ultrasound emission during re-isolation. The present results show that the cholinergic system plays a role in inhibiting rodent pup USV emission and spontaneous behavior and suggest that the analysis of spontaneous behavior and, in particular, of the number of ultrasonic vocalizations represents a valuable tool to detect precocious developmental alterations of the cholinergic function in the mouse, the most used animal species to model human health disorders.