High-frequency ultrasonic vocalizations index conditioned pharmacological reward in rats

Physiol Behav. 1999 Jun;66(4):639-43. doi: 10.1016/s0031-9384(98)00337-0.


We have proposed that short (<0.5 s), high-frequency (approximately 50 kHz) ultrasonic vocalizations ("50-kHz USVs") index a positive affective state in adult rats, because they occur prior to rewarding social interactions (i.e., rough-and-tumble play, sex). To evaluate this hypothesis in the case of nonsocial stimuli, we examined whether rats would make increased 50-kHz USVs in places associated with the administration of rewarding pharmacological compounds [i.e., amphetamine (AMPH) and morphine (MORPH)]. In Experiment 1, rats made a greater percentage of 50-kHz USVs on the AMPH-paired side of a two-compartment chamber than on the vehicle-paired side, even after statistical correction for place preference. In Experiment 2, rats made a higher percentage of 50-kHz USVs on the MORPH-paired side than on the vehicle-paired side, despite nonsignificant place preference. These findings support the hypothesis that 50-kHz USVs mark a positive affective state in rats and introduce a novel and rapid marker of pharmacological reward.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Affect / drug effects*
  • Amphetamine / pharmacology*
  • Animals
  • Arousal / drug effects
  • Association Learning / drug effects
  • Conditioning, Classical / drug effects*
  • Female
  • Male
  • Morphine / pharmacology*
  • Motivation*
  • Rats
  • Rats, Long-Evans
  • Social Behavior*
  • Social Environment
  • Sound Spectrography
  • Ultrasonics


  • Morphine
  • Amphetamine