BNST-projecting histaminergic circuits mediate state-dependent anxiety behavior through post-synaptic histamine H3 receptors on GABAergic neurons

Understanding the precise mechanisms underlying anxiety and anxiety disorders is crucial for identifying novel interventions. In this study, we report a histaminergic circuit targeting the bed nucleus of the stria terminalis (BNST) that mediates anxiety-like behavior in mice. First, we observed a significant decrease in both histamine signaling and histaminergic fiber activity in the BNST when mice entered an anxious environment. Selective modulation of the BNST-projecting histaminergic circuit mediated state-dependent anxiety behaviors: activation directly induced an anxiogenic effect on naive mice, while inhibition produced a significant anxiolytic effect in mice in an anxious state rather than normal state. Pharmacological intervention revealed that the inhibition of histamine H3 receptors (H3Rs), rather than histamine H1 receptors (H1Rs) or histamine H2 receptors (H2Rs), in the BNST abolished the anxiogenic effect of histaminergic circuit activation. Finally, through optogenetic manipulation of spatial-specific H3Rs, we identified a critical role for anxiety regulation by post-synaptic H3Rs in the BNST GABAergic neurons, rather than pre-synaptic H3Rs from upstream inputs. Together, our results revealed a histaminergic circuit targeting the BNST that mediates state-dependent anxiety-like behaviors through post-synaptic H3Rs. These findings provide new insights into the mechanism of anxiety and offer promising avenues for discovering novel pharmacological targets for the treatment of anxiety disorders.