Adult rats produce two main types of ultrasonic vocalizations (USVs), occurring at 22 and 50 kHz USVs. These calls are associated with aversive and rewarding stimuli, respectively. The neural mechanism of amphetamine-induced calling was examined in lesion and antagonist studies. We also tested whether amphetamine-induced 50 kHz USVs could predict individual differences in intravenous self-administration or conditioned place preference behavior. Further experiments examined whether 50 kHz USVs could be evoked by amphetamine-conditioned sensory stimuli and by rewarding electrical brain stimulation. Overall, our experimental findings: (1) identify certain experimental conditions that increase amphetamine-induced 50 kHz calling, (2) provide evidence that these calls may be dependent on mesolimbic dopaminergic transmission, (3) relate individual differences in 50 kHz vocalizing to other behavioural measures of drug reward, and (4) show that in some situations, 50 kHz calls reflect anticipation of expected rewards.

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