Role of the anterior insular cortex microcircuits in observation fear of mice / 中国药理学与毒理学杂志

ABSTRACT

OBJECTIVE Fear can be learned indi-rectly,but excessive transmission of fear is essential for the development of mental illness.Previous research has indicated that the anterior insular cortex(AIC)may play a crucial role in the process of fear transmission,and abnormal AIC activity is a possible mechanism under-lying various affective disorders.Inhibitory neurons are crucial for maintaining local microcircuit homeostasis.With the support of novel specific neuroregulatory tech-niques,it is now possible to monitor and regulate differ-ent types of neurons in real-time.Therefore,investigating distinct subtypes of inhibitory neurons in the AIC that are involved in fear contagion may provide valuable insights into potential mechanisms underlying mental disorders.METHODS We established a modified observational fear(OF)model.A demonstrator(DM)mouse was placed in an acrylic cup at the center of the apparatus,and two observer(OB)mice were allowed to explore the DM mouse simultaneously from separate areas on either side.During the OF training,electric foot shocks were administered to the DM mouse and freezing,the side and corner time,and social interaction behavior were scored.Next,we characterized the activity patterns of distinct neuronal subtypes in the AIC using GCaMP-based calcium recording.Finally,we employed a Cre-dependent optogenetic approach to selectively modulate excitatory or inhibitory neurons in the AIC,and investigat-ed empathic fear behavior across different Cre transgenic mouse lines(CK2-Cre,PV-Cre,SOM-Cre,VIP-Cre).RESULTS During the training phase,the OB mice exhib-ited significantly higher levels of fear compared to the control group(which did not observe a traumatic event),as evidenced by increased freezing time,decreased interaction time,and increased corner zone time.Calcium fiber recording results suggested that CK2 neurons are involved in risk prediction,while PV and VIP neurons exert inhibitory control on this behavior.Optogenetic silencing of CK2-positive neurons in the AIC through injection of AAV-DIO-NpHR-mCherry in mice demon-strated a significant reduction in empathic fear.Similarly,activation of PV or VIP inhibitory neurons expressing ChR2-eYFP also resulted in a similar effect.However,activation of SOM neurons led to a significant increase in empathic fear.CONCLUSION Our study demonstrated that VIP and PV neuron activity in the AIC attenuates empathetic fear,while SOM and CK2 neuron activity enhances fear expression.These findings shed light on the distinct contributions of various inhibitory interneu-rons in the AIC to fear contagion,indicating their mutual interaction for maintaining local microcircuit homeostasis that regulates empathetic fear behaviors.