A tool that most effectively determines the emotional states of rats is the registration and analysis of ultrasonic vocalizations (USVs). 50‑kHz USVs are a form of expression of positive emotions. USV measurement allows both identifying individual differences in processing information about the reward as well as reflecting, to a large extent, the level of individual motivation. We hypothesized that 50-kHz USV emission could have separate neurochemical backgrounds in different behavioral paradigms, as well as, some common neurochemical mechanisms reflected in examined neurotransmitters correlations. For example, re‑exposure to the context of morphine administration is associated with elevated serotonin concentrations in the amygdala, hippocampus, and medial prefrontal cortex (mPFC) and increased Glu/Gln ratio in the nucleus accumbens (Nacc). Machine learning based analysis indicates a strong correlation between serotonergic and glutamatergic systems in context‑induced conditioned response. In the case of social interaction paradigm, several neurochemical changes were detected. Depending on the duration of social interaction, neurotransmission pathways are activated in the cascade fashion. Thus, glutamatergic neurotransmission in amygdala, ventral tegmental area (VTA), Nacc, and hippocampus, and action in the serotonergic system in mPFC, Nacc, caudate, and putamen, dopaminergic neurotransmission in mPFC and hippocampus, and noradrenergic neurotransmission in the striatum, are activated under the influence of the elapsed time of social interaction.