Acute and long-term effects elicited by psychoactive drugs on 50-kHz ultrasonic vocalizations in rats: development of a new experimental tool for the study of drug-mediated reward.
Ultrasonic vocalizations (USVs) have recently emerged as an indicator of the emotional state of
rats, and the evaluation of the USVs in the 50-kHz range has been proposed as a tool to investigate the affective
properties of drugs of abuse. To clarify the relevance of 50-kHz USVs to drug-induced reward, the acute and
long-term effects elicited by different psychoactive drugs
[
amphetamine, 3,4-methylenedioxymethamphetamine
(MDMA, ecstasy), methylphenidate, morphine, and nicotine
]
were characterized in adult male rats.
Amphetamine and methylphenidate were the only drugs that stimulated the emission of 50-kHz USVs by rats
after their acute administration. Moreover, amphetamine was the only drug that elicited a significant emission
of 50-kHz USVs after repeated administration. However, rats in all the treatment groups emitted 50-kHz USVs
when later re-exposed to the environment previously paired with repeated drug administration, likely indicative
of drug-mediated environmental conditioning. Taken together, these results demonstrate the existence of major
differences in the acute and long-term effects of different psychoactive drugs on the emission of 50-kHz USVs
by rats. Moreover, these results provide a better understanding of the usefulness of 50-kHz USVs as a new tool
for the assessment of drug-mediated reward, with implications for the preclinical study of addictive behavior
