A novel model of care; Telemedicine and peer support for HCV care among HIV-infected people who inject drugs in remote Myanmar: a retrospective study.

Anxiety disorders (e.g., panic disorder and social anxiety disorder) are the most common mental disorders (, ). The high prevalence and functional disability caused by these disorders result in significant social and economic costs stemming from reduced patient productivity (–). Pharmacotherapy is one of the most commonly used treatments; however, it often lacks efficacy and may cause various unpleasant side effects in certain populations (). Therefore, a deeper understanding of the underlying neurophysiological mechanisms is essential to improve treatment outcomes. To address this, a reliable animal model for studying human anxiety is required, as animal models offer several advantages: the ability to control experimental conditions, access to tissue samples, and the possibility of manipulating specific neural cell types and circuits with spatial and temporal precision using transgenic, optogenetic, and chemogenetic techniques (). In rats, the communication through ultrasonic vocalizations (USVs), particularly the 22-kHz type, is considered one of the most reliable animal models for studying human anxiety, fulfilling physiological and ethological validity. Adult rats emit 22-kHz USVs with peak frequencies typically between 20 and 30 kHz, minimal frequency modulation, and durations usually exceeding 300 ms (). When exposed to predators (, ), involved in fighting (, ), or subjected to aversive stimuli such as foot shocks (, ), rats emit 22-kHz USVs that induce negative affective responses, including behavioral avoidance, in other conspecifics (, ). The perception of 22-kHz USVs activates specific brain regions, such as the amygdala, in a pattern similar to anxiety-related activation in the human brain (, ). Additionally, the emission of stress-induced 22-kHz USVs and the anxiety-related behavioral responses elicited by 22-kHz USV-like stimuli can be suppressed by anxiolytic pretreatment (, ). Mice, like rats, are also known to produce USVs for social communication. Mouse USVs are typically observed during three life stages: 1] in the neonatal stage, pups emit USVs upon separation from the nest to elicit maternal responses such as orientation, approach, and retrieval, similar to rats (); 2] in the juvenile stage, USVs are produced during intra- and intersex social interactions (); and 3] in the adult stage, both sexes emit USVs during specific social contexts. In male–female dyadic interactions, adult males emit most USVs to attract females during courtship (–), whereas females vocalize far less in comparison (–). In same-sex female dyads, resident females emit numerous USVs upon encountering an intruder, possibly for territorial signaling and to facilitate social information exchanges (, ). In same-sex male dyads, fewer USVs are produced, but they may serve to establish territorial dominance (). Across all ages, mouse USVs have been categorized into various vocalization types based on duration and spectrographic features (e.g., pitch shifts, frequency steps), though classification schemes vary among studies. However, the communicative function of individual USVs remains poorly understood. Notably, there is limited evidence in mice for stress-induced USVs that contain specific vocalizations associated with negative affective states and that evoke similar affective responses in conspecifics, unlike the well-documented affective communication of 22-kHz USVs in adult rats. From a socioethological perspective, we hypothesized that such communicative vocalizations likely exist in adult mice as well.