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Keywords:

  • amygdala;
  • freezing;
  • rat;
  • social buffering;
  • stress-induced hyperthermia

Abstract

In a phenomenon known as ‘social buffering’ in various species, signals from a conspecific animal can mitigate stress responses. This buffering can be achieved either by ‘pair-housing’ after a stressful event or by ‘pair-exposure’ to an acute stressor with a conspecific animal. In this study, we compared the impacts of these two types of social buffering on auditory conditioned fear responses in male rats. When subjects were exposed to an auditory conditioned stimulus (CS) that had been paired with foot shocks on the previous day, they clearly exhibited behavioral (freezing), autonomic (aggravated stress-induced hyperthermia) and neural (Fos expression) responses. Pair-housing for 24 h with an unfamiliar rat following fear conditioning resulted in a suppressed autonomic, but not behavioral, response, with Fos expression in the lateral nucleus of the amygdala and ventrolateral periaqueductal gray. On the other hand, pair-exposure to the CS with an unfamiliar rat eliminated the behavioral, but not the autonomic, response, with Fos expression in the basal nucleus of the amygdala and infralimbic region of the prefrontal cortex. Furthermore, subjects that had been pair-housed and then pair-exposed showed no behavioral, autonomic or neural responses, suggesting that the combination of the two procedures can completely block the fear conditioning sequence. These results demonstrate that two types of social buffering differentially relieve conditioned fear responses, by influencing different neural pathways in the amygdala.