Ultrasonic vocalization in rats self-administering heroin and cocaine in different settings: evidence of substance-specific interactions between drug and setting

Rationale Clinical and preclinical evidence indicates that the setting of drug use affects drug reward in a substance-specific manner. Heroin and cocaine co-abusers, for example, indicated distinct settings for the two drugs: heroin being used preferentially at home and cocaine preferentially outside the home. Similar results were obtained in rats that were given the opportunity to self-administer intravenously both heroin and cocaine. Objectives The goal of the present study was to investigate the possibility that the positive affective state induced by cocaine is enhanced when the drug is taken at home relative to a non-home environment, and vice versa for heroin. Methods To test this hypothesis, we trained male rats to self-administer both heroin and cocaine on alternate days and simultaneously recorded the emission of ultrasonic vocalizations (USVs), as it has been reported that rats emit 50-kHz USVs when exposed to rewarding stimuli, suggesting that these USVs reflect positive affective states. Results We found that Non-Resident rats emitted more 50-kHz USVs when they self-administered cocaine than when self-administered heroin whereas Resident rats emitted more 50-kHz USVs when self-administering heroin than when self-administering cocaine. Differences in USVs in Non-Resident rats were more pronounced during the first self-administration (SA) session, when the SA chambers were completely novel to them. In contrast, the differences in USVs in Resident rats were more pronounced during the last SA sessions. Conclusion These findings indicate that the setting of drug taking exerts a substance-specific influence on the ability of drugs to induce positive affective states

Dopamine D1 and μ-opioid receptor antagonism blocks anticipatory 50 kHz ultrasonic vocalizations induced by palatable food cues in Wistar rats

RATIONALE: Fifty kilohertz ultrasonic vocalizations (USVs) have been sometimes shown to reflect positive affective-like states in rats. Rewarding events, such as access to palatable food or drugs of abuse, increase the number of anticipatory 50 kHz USVs. However, little is known about the predictability of USVs, subtypes of USVs involved, and underlying neurobiological mechanisms. OBJECTIVES: We examined whether cue-induced anticipatory 50 kHz USVs predict palatable food intake and tested the effects of dopamine D(1) and μ-opioid receptor antagonism on anticipatory USVs. MATERIALS: Food-restricted rats received repeated sessions of a 2 min cue light immediately followed by 5 min access to palatable food. Ultrasonic vocalizations were recorded during cue presentation. After 24 pairing sessions, the rats were pretreated with the D(1) receptor antagonist SCH 23390 (5, 10, and 20 μg/kg) and μ-opioid receptor antagonist naltrexone (0.03, 0.06, 0.13, 0.25, 0.5, and 1 mg/kg) in a Latin-square design, and USVs were recorded during cue presentation. RESULTS: Rats emitted 50 kHz USVs during cue presentation, and the number of USVs increased across sessions with robust and stable interindividual differences. Escalation in USVs was subtype-dependent, with non-trill calls significantly increasing over time. Palatable food intake was positively correlated with anticipatory 50 kHz USVs. Moreover, anticipatory USVs were dose-dependently prevented by antagonism of D(1) and μ-opioid receptors. CONCLUSIONS: These findings demonstrate that anticipatory 50 kHz USVs represent a stable phenotype of increased motivation for food, and dopamine and opioid systems appear to mediate anticipatory 50 kHz USVs