Empathy is crucial for our emotional experience and social interactions, and its abnormalities manifest in various psychiatric disorders. Observational fear is a useful behavioral paradigm for assessing affective empathy in rodents. However, specific genes that regulate observational fear remain unknown. Here we showed that 129S1/SvImJ mice carrying a unique missense variant in neurexin 3 (Nrxn3) exhibited a profound and selective enhancement in observational fear. Using the CRISPR/Cas9 system, the arginine-to-tryptophan (R498W) change in Nrxn3 was confirmed to be the causative variant. Selective deletion of Nrxn3 in somatostatin-expressing (SST+) interneurons in the anterior cingulate cortex (ACC) markedly increased observational fear and impaired inhibitory synaptic transmission from SST+ neurons. Concordantly, optogenetic manipulation revealed that SST+ neurons in the ACC bidirectionally controlled the degree of socially transmitted fear. Together, these results provide insights into the genetic basis of behavioral variability and the neurophysiological mechanism controlling empathy in mammalian brains.

Empathy enables social mammals to recognize and share emotion with others and is well‐documented in non‐human primates. During the past few years, systematic observations have showed that a primal form of empathy also exists in rodents, indicating that empathy has an evolutionary continuity. Now, using rodents exhibiting emotional empathy, the molecular and cellular study of empathy in animals has begun in earnest. In this article, we will review recent reports that indicate that rodents can share states of fear with others, and will try to highlight new understandings of the neural circuitry, biochemistry and genetics of empathic fear. We hope that the use of rodent models will enhance understanding of the mechanisms of human empathy and provide insights into how to treat social deficits in neuropsychiatric disorders characterized by empathy impairment.

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