Behavioural Brain Research 151 (2004) 9–16 Research report Scopolamine effects on ultrasonic vocalization emission and behavior in the neonatal mouse Igor Branchi a,∗ , Patrizia Campolongo a,b , Enrico Alleva a a Section of Behavioral Pathophysiology, Laboratorio Fisiopatologia di Organo e di Sistema, Istituto Superiore di Sanità, Viale Regina Elena, 299, 00161 Roma, Italy b Department of Pharmacology and General Physiology, University of Rome “La Sapienza”, P.le Aldo Moro 5, 00185 Roma, Italy Received 6 May 2003; received in revised form 30 July 2003; accepted 30 July 2003 Abstract 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 0.8 mg/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. © 2003 Elsevier B.V. All rights reserved. Keywords: Ultrasonic vocalizations; Behavior; Neonatal mouse; Cholinergic; Scopolamine; Locomotion; Ontogeny; Maternal potentiation 1. Introduction The developing cholinergic system is affected in a num- ber of neurodevelopmental disorders of different etiology [4,30], including autism [37] and Rett syndrome [32,53]. Furthermore, developmental exposure to several disrup- tors of cholinergic function, such as alcohol and pesticides [16,38,45], induces marked brain and behavioral alteration [30]. Therefore, the assessment of cholinergic function dur- ing early ontogeny is of particular interest as a precocious marker of brain abnormalities and would help investigating the role of this neurotransmitter system in brain develop- ment under both physiological and pathological conditions. Since laboratory animals, especially mice, are increasingly used for modeling and investigating child health issues, the need for appropriate and reliable experimental protocols to assess cholinergic function during early phases of mouse development is clearly emerging. ∗ Corresponding author. Tel: +39-6-49902039; fax: +39-6-4957821. E-mail address: branchi@iss.it (I. Branchi). In altricial rodents, the central cholinergic system attains full functional maturity around the third-fourth post-natal week [17,49]. At this age, animals clearly respond to admin- istration of cholinergic antagonists, such as scopolamine, with a marked increase in locomotor activity [2,11]. How- ever, neurochemical markers of cholinergic function appear already before post-natal day (PND) 7 [17,49] and sev- eral behavioral responses, such as suckling behavior, la- tency to choice in a T-maze, spontaneous alternation, and conditioned response suppression, are affected by choliner- gic pharmacological manipulation as early as the first week [10,19,42,47]. Infant mice and rats emit ultrasonic vocalizations (USVs) when isolated from the mother and littermates [7,23,57]. These vocalizations promote maternal behavior, eliciting a prompt response of orienting, searching and retrieving [20,21,33,48]. USV emission rate is strongly modulated by several environmental variables, such as temperature [34], olfactory and tactile stimuli [8,15,36], as well as by manipu- lations of the social context [8,26,50]. In the last 20 years, it has been shown that pharmacological treatments markedly 0166-4328/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0166-4328(03)00277-8