Rats can convey information about their internal states through ultrasonic vocalizations (USVs). In male and female TH:cre rats and wildtype littermates, amphetamine (2 mg/kg) elicited high-frequency USVs and increased locomotion, heroin (0.25 mg/kg) elicited low-frequency USVs in some rats without altering high-frequency USVs or locomotion, and ketamine (30 mg/kg) suppressed high-frequency USVs while transiently increasing locomotion. Chemogenetically inhibiting or stimulating ventral tegmental area dopamine neurons suppressed amphetamine- or ketamine-induced locomotion and amphetamine-induced USVs. USVs provide a behavioral readout of drug and brain manipulation effects that locomotion alone cannot capture, potentially helping bridge human and rodent neuroscience.
Adolescent THC exposure in rats leads to sex-dependent effects on learning to seek rewards guided by cues, but has minimal impact on cognitive flexibility or decision-making under uncertainty. Adult rats treated with THC during adolescence showed reduced discounting of improbable reward options when given amphetamine, indicating heightened sensitivity to dopamine augmentation. Direct chemogenetic stimulation of dopamine neurons in the ventral tegmental area or their projections to the medial prefrontal cortex did not alter decision-making in control rats, but slightly disrupted choices in THC-exposed rats. These findings suggest that adolescent THC exposure produces specific, persistent cognitive changes that may alter responses to amphetamine through mechanisms independent of the VTA-mPFC dopamine pathway.