Abstract
Infant rat ultrasonic vocalizations (USVs) are widely believed to result from the induction of an emotional state of anxiety or distress. This perspective, however, is not easily reconciled with the demonstration by W. J. Farrell and J. R. Alberts 2000 that norepinephrine, a nonselective betaβadrenoceptor agonist with anxiogenic properties, inhibits production of USVs. Here, Farrell and Alberts' finding was replicated and extended with 12βdayβold rats using a conventional isolation paradigm. First, treatment with norepinephrine (1 mg/kg) significantly inhibited ultrasound production while also increasing body temperature. Next, treatment with the betaβ2 agonist terbutaline (1 mg/kg) and the betaβ3 agonist CLβ316243 (1 mg/kg), but not the betaβ1 agonist dobutamine (1 mg/kg), inhibited ultrasound production; only CLβ316243 increased body temperature. The unexpected inhibition of USVs by terbutaline, a potent bronchodilator, was replicated using a slightly modified procedure; again, body temperature was unaffected by terbutaline administration. In no experiment was inhibition of USVs related to changes in motor activity. Altogether, these results suggest either that ultrasound production is not a valid indicator of anxiety or that anxiety in infant rats is produced by neuropharmacological mechanisms that differ fundamentally from those in adults. Β© 2005 Wiley Periodicals, Inc. Dev Psychobiol 47: 66β76, 2005.