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

Abstract

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.

Anticipatory 50kHz ultrasonic vocalizations are associated with escalated alcohol intake in dependent rats

“…Consistent with this hypothesis, in dependent rats but not nondependent rats, we observed that a subset of rats that displayed high alcoholin take also had higher levels of anticipatory 50 kHz USVs compared with low-alcohol-intake rats. Previous studies have reported an increase in 50 kHz USVs in response to cues paired with appetitive stimuli, such as food [8,9], copulation [10,11], and cocaine [11,12]. Rats that had extinguished methamphetamine self-administration and then given a methamphetamine priming injection or exposed to drug-paired cues robustly emitted 50 kHz USVs and rein-stated drug-seeking behavior [12].…”

“…Ultrasonic vocalizations between 10 and 100 kHz were recorded and analyzed using Avisoft SASLab Pro (version 5.1, Avisoft Bioacoustics). Spectrograms were generated with a fast Fourier transform length of 512 points and overlap of 50% (FlatTop window, 100% frame size), providing a frequency resolution of 419 Hz and time resolution of 1.19 ms. Vocalizations were categorized as trill, other FM, or flat using criteria described in Buck et al [9]. Here, trill calls included the “trill FM”and “step-trill FM” categories.…”

“…Here, trill calls included the “trill FM”and “step-trill FM” categories. Other FM calls included “other FM” and “step FM.” Flat calls included the “flat” category from Buck et al[9]. Microphones were placed inside the sound-attenuating cubicle and outside a grate in the wall of the operant chamber.…”

“…However, these calls are also elicited by aversive stimuli [6,7], and the affective state(s) that they represent are not well understood. Previous reports have shown that 50 kHz USVs are elicited by cues that predict rewarding stimuli, such as food [8,9], copulation [10], cocaine [11], and rewarding brain stimulation [8]. Thus, 50 kHz USVs may be an index of motivation during reward anticipation [1,11,12].…”

Exercise reward induces appetitive 50-kHz calls in rats

“…However, as running also releases endogenous opioids [63], the calls could also reflect liking, although conflicting evidence exists whether opioid agonists or antagonists increase 50-kHz calls [64][65][66][67].…”