Social and contextual modulation of ultrasonic distress vocalizations in wistar rats

Rats emit ultrasonic vocalizations when they perceive danger, but what they "say" and how often they "speak" may depend on how they perceive the immediacy of a perceived threat and who is around them. This thesis investigated how social context (presence of a same-sex conspecific during aversive experiences), sex (male or female), and the perceived threat intensity modulate 22 kHz ultrasonic distress vocalizations (USVs) of Wistar rats tested in increasing-intensity contextual fear conditioning, context tests, and acoustic startle tests. The results reveal that all three factors -sex, social context, and threat intensity- interact with one another to influence USV emission rates. Notably, pair-tested male rats exhibited a significantly higher amount of, and more sustained distress vocalizations compared to all other groups, particularly under high-threat conditions. The male dyads also displayed a significant increase in the principal frequency of their calls with repeated aversive stimuli during high context-shock contingency contextual fear conditioning and produced numerous overlapping, temporally coordinated calls. In contrast, single-tested females, despite initially vocalizing at similar levels to the other groups in low-intensity fear conditioning, remained completely silent in all subsequent tests. Pair-tested female rats emitted higher amounts of distress vocalizations compared to single females in higher-stress situations but still vocalized less than male pairs. These findings underscore that 22 kHz USVs are not static distress signals, but constitute communicative signals dynamically shaped by the animal's social environment, sex, and perceived threat level.