, Volume 224, Issue 4, pp 477–487

Failure of rewarding and locomotor stimulant doses of morphine to promote adult rat 50-kHz ultrasonic vocalizations

  • Jennifer M. Wright
  • Lan Deng
  • Paul B. S. Clarke
Original Investigation

DOI: 10.1007/s00213-012-2776-z

Cite this article as:
Wright, J.M., Deng, L. & Clarke, P.B.S. Psychopharmacology (2012) 224: 477. doi:10.1007/s00213-012-2776-z



Frequency-modulated 50-kHz ultrasonic vocalizations (USVs) are emitted by adult rats in response to psychostimulants and non-pharmacological appetitive stimuli and thus have been proposed to model positive affect.


The main aim was to determine whether rewarding doses of morphine increase 50-kHz call rate or alter the relative prevalence of the trill call subtype.


In experiment 1, USVs were recorded from adult male Long–Evans rats after subchronic morphine (1 mg/kg subcutaneous (SC)) administration, acute challenge with morphine (1 and 3 mg/kg SC) or amphetamine (1 mg/kg IP, positive control), and in conjunction with locomotor activity tests with morphine (1 and 3 mg/kg SC). In experiments 2 and 3, the USV altering, rewarding, and locomotor effects of morphine were examined using a conditioned place preference (CPP) procedure.


In experiment 1, morphine (1 mg/kg) initially suppressed calling; rats became tolerant to this effect with repeated exposure. Tested subsequently in singly- and pair-tested rats, morphine markedly decreased USVs but significantly increased locomotor activity. In experiments 2 and 3, morphine produced a significant CPP without increasing either unconditioned or conditioned USV emission. Morphine did not detectably alter the relative prevalence of 50-kHz call subtypes.


Although 50-kHz calls, and the trill call subtype in particular, have been proposed as an animal model of positive mood, not all euphoriant drugs acutely increase the rate of 50-kHz calling or consistently promote trill calls.


Ultrasonic vocalizations Rat Morphine Opioid Amphetamine Reward Conditioned place preference Locomotor activity 

Supplementary material

213_2012_2776_MOESM1_ESM.doc (246 kb)
ESM 1(DOC 245 kb)

Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Jennifer M. Wright
    • 1
  • Lan Deng
    • 1
  • Paul B. S. Clarke
    • 1
  1. 1.Department of Pharmacology and TherapeuticsMcGill UniversityMontrealCanada

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