Kainate receptor mediated presynaptic LTP in agranular insular cortex contributes to fear and anxiety in mice
Anxiety disorders represent serious social problems worldwide. Recent neuroimaging studies have found that elevated activity and altered connectivity of the insular cortex might account for the negative emotional states in highly anxious individuals. However, the exact synaptic mechanisms of specific insular subregions have yet to be studied in detail. To assess the electrophysiological properties of agranular insular cortex (AIC) neurons, basic synaptic transmission was recorded and different protocols were used to induce presynaptic and postsynaptic long-term potentiation in mice with anxiety-related behaviors. The presynaptic membrane expression of kainate receptors (KARs) and pharmacologic manipulations were quantified to examine the role of Gluk1 subtype in anxiety-like behaviors. Fear conditioning occludes electrically induced postsynaptic-LTP in the AIC. Quantal analysis of LTP expression in this region revealed a significant presynaptic component reflected by an increase in the probability of transmitter release. A form of presynaptic-LTP that requires KARs has been characterized. Interestingly, a simple emotional anxiety stimulus resulted in selective occlusion of presynaptic-LTP, but not of postsynaptic-LTP. Finally, injecting GluK1-specific antagonists into the AIC reduced behavioral responses to fear or anxiety stimuli in the mouse. These findings suggest that activity-dependent synaptic plasticity takes place in the AIC due to exposure to fear or anxiety, and inhibiting the presynaptic KAR function may help to prevent or treat anxiety disorder.