While several studies have investigated mouse ultrasonic vocalizations (USVs) emitted by isolated pups or by males in mating contexts, studies of behavioral contexts other than mating and vocalization categories other than USVs have been limited. By improving our understanding of the vocalizations emitted by mice across behavioral contexts, we will better understand the natural vocal behavior of mice and better interpret vocalizations from mouse models of disease. Hypothesizing that mouse vocal behavior would differ depending on behavioral context, we recorded vocalizations from male CBA/CaJ mice across three behavioral contexts including mating, isolation, and restraint. We found that brief restraint elevated blood corticosterone levels of mice, indicating increased stress relative to isolation. Further, after 3 days of brief restraint, mice displayed behavioral changes indicative of stress. These persisted for at least 2 days after restraint. Contextual differences in mouse vocal behavior were striking and robust across animals. Thus, while USVs were the most common vocalization type across contexts, the spectrotemporal features of USVs were context-dependent. Compared to the mating context, vocalizations during isolation and restraint displayed a broader frequency range, with a greater emphasis on frequencies below 50 kHz. These contexts also included more non-USV vocal categories and different vocal patterns. We identified a new Mid-Frequency Vocalization, a tonal vocalization with fundamental frequencies below 18 kHz, which was almost exclusively emitted by mice undergoing restraint stress. These differences combine to form vocal behavior that is grossly different among behavioral contexts and may reflect the level of anxiety in these contexts.

A common symptom of anxiety disorders is the overgeneralization of fear across a broad range of contextual cues. We previously found that the ACC and ventral hippocampus (vHPC) regulate generalized fear. Here, we investigate the functional projections from the ACC and vHPC to the amygdala and their role in governing generalized fear in a preclinical rodent model. A chemogenetic approach (designer receptor exclusively activated by designer drugs) was used to inhibit glutamatergic projections from the ACC or vHPC that terminate within the BLA at recent (1 d) or remote (28 d) time points after contextually fear conditioning male mice. Inactivating ACC or vHPC projections to the BLA significantly reduced generalized fear to a novel, nonthreatening context but had no effect on fear to the training context. Further, our data indicate that the ACC-BLA circuit supports generalization in a time-independent manner. We also identified, for the first time, a strictly time-dependent role of the vHPC-BLA circuit in supporting remote generalized contextual fear. Dysfunctional signaling to the amygdala from the ACC or the HPC could underlie overgeneralized fear responses that are associated with anxiety disorders. Our findings demonstrate that the ACC and vHPC regulate fear expressed in novel, nonthreatening environments via projections to the BLA but do so as a result of training intensity or time, respectively.

Genetic variation in the serotonergic system within the brain has been a significant focus of psychiatric research over the last several decades. In particular, the serotonin transporter (5-HTT) gene (SLC6A4) has been tied to early emotion processing biases. However, a clear understanding of how genetic variation of SLC6A4 may influence clinically salient emotional phenomena is still elusive. In this investigation, we focused on examining variation in the 5-HTT-linked polymorphic region (5-HTTLPR; including the single nucleotide polymorphism rs25531 which alters genotype interpretation) and real-time emotion responses evoked in the laboratory using a paradigm designed to spontaneously induce emotion regulation. Across 2 studies we show that for healthy individuals with 2 copies of the functional short (S=) allele there is weakened downregulation of negative emotion. In addition, we found greater electrodermal responses as well as both negative and positive emotion in association with the S= allele in 1 of the 2 samples. These findings provide evidence that the S= allele may promote system-wide heightened emotional reactivity in healthy subjects. Both phenomena, observed here in a healthy population, are strongly linked to the development of psychiatric disease. As such, these findings have implications for S= carriers' vulnerability to affective disorders, as well as suggest potential targets for future clinical investigation.

No abstract