Elsevier

Physiology & Behavior

Volume 66, Issue 4, June 1999, Pages 639-643
Physiology & Behavior

Articles
High-Frequency Ultrasonic Vocalizations Index Conditioned Pharmacological Reward in Rats

https://doi.org/10.1016/S0031-9384(98)00337-0Get rights and content

Abstract

We have proposed that short (<0.5 s), high-frequency (∼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.

Section snippets

Experiment 1

Experiment 1 was designed to determine whether an environment associated with AMPH treatment would facilitate 50-kHz USVs. We were also interested in determining whether USVs versus place-preference measures would exhibit comparable sensitivity as markers of prior AMPH treatment.

Experiment 2

As with Experiment 1, Experiment 2 was designed to determine whether an environment associated with prior MORPH treatment would elicit increased 50-kHz USVs, even after correcting for place preference.

General discussion

These studies are the first to demonstrate that 50-kHz USVs may serve as a marker of pharmacological reward. Rats made more 50-kHz USVs in the chamber where they had previously received a rewarding compound (i.e., AMPH and MORPH), even after statistically controlling for differences in chamber occupancy. Within groups, the proportion of vocalizations that rats made on the drug-paired side was correlated with place preference, suggesting that the two measures indexed a similar construct.

Acknowledgements

This work was supported in part by NIMH Postdoctoral Training Grant MH18931 to Brian Knutson, and NIMH Grant HD30387 to Jaak Panksepp. Additional support for was provided by Wright–Patterson Contract #F336016 and ONR Grant NOOO14-96-1-0589. We thank Douglas Pruitt for consultation on design issues and two anonymous reviewers for comments on the manuscript.

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