Observational Fear Learning in Rats: Role of Trait Anxiety and Ultrasonic Vocalization

Abstract

Rats can acquire fear by observing conspecifics that express fear in the presence of conditioned fear stimuli. This process is called observational fear learning and is based on the social transmission of the demonstrator rat’s emotion and the induction of an empathy-like or anxiety state in the observer. The aim of the present study was to investigate the role of trait anxiety and ultrasonic vocalization in observational fear learning. Two experiments with male Wistar rats were performed. In the first experiment, trait anxiety was assessed in a light–dark box test before the rats were submitted to the observational fear learning procedure. In the second experiment, ultrasonic vocalization was recorded throughout the whole observational fear learning procedure, and 22 kHz and 50 kHz calls were analyzed. The results of our study show that trait anxiety differently affects direct fear learning and observational fear learning. Direct fear learning was more pronounced with higher trait anxiety, while observational fear learning was the best with a medium-level of trait anxiety. There were no indications in the present study that ultrasonic vocalization, especially emission of 22 kHz calls, but also 50 kHz calls, are critical for observational fear learning.

Fear Extinction and Predictive Trait-Like Inter-Individual Differences in Rats Lacking the Serotonin Transporter

“…In contrast, the increase in anxiety-related behavior displayed by rats lacking SERT might underlie the higher level of immobility during the recovery phase of the differential fear conditioning paradigm. In fact, trait anxiety was found to predict enhanced fear memory after fear conditioning in mice [89] and rats [68]. Moreover, rats selectively bred for high anxiety display deficits in extinction and extinction recall [90].…”

“…Other than solely expressing anxiety and fear, 22-kHz USV are thought to function as alarm calls to warn conspecifics about threats and were shown to evoke a fear response in receiver rats [42,65]. The latter was also observed during social fear conditioning [59,67,68] and confirmed in playback studies, where 22-kHz USV induced behavioral inhibition in receiver rats [43,69]. Supporting a communicative function, 22-kHz USV emission was reported to be potentiated by the presence of conspecifics [42] and it appears possible that this audience effect is more prominent in female than male rats.…”

Biological Functions of Rat Ultrasonic Vocalizations, Arousal Mechanisms, and Call Initiation

“…The alarm calls are directed to the members of the entire social group (audience effect) and related to the approaching danger. However, the social effect may not be present, i.e., a rat may emit alarm calls when it is isolated from the group (particularly in the laboratory) or when it may not know where other conspecifics are [ 172 ]. Alarm calls are emitted from the place of a relative safety (not in the immediate reach of the predator when the fear response appears) and are not directed to the predator [ 173 ].…”

Social Behavior and Ultrasonic Vocalizations in a Genetic Rat Model Haploinsufficient for the Cross-Disorder Risk Gene Cacna1c

“…Consistent with studies on social transmission of food preferences in wild rats, laboratory studies demonstrated that rats can learn about positive and negative events through observing others. This includes the transfer of information concerning distant foods [34] and observational learning of fear [35]. Laboratory studies further revealed that rats engage in cooperative actions [36], prefer mutually rewarding options [37], follow rules of general and direct reciprocity [38], and display empathy-driven helping behavior [39].…”