Infralimbic Endothelin1 Is Critical for the Modulation of Anxiety-Like Behaviors

Amygdalar Endothelin-1 Regulates Pyramidal Neuron Excitability and Affects Anxiety

An abnormal neuronal activity in the amygdala is involved in the pathogenesis of anxiety disorders. However, little is known about the mechanisms. High-anxiety mice and low-anxiety mice, representing the innate extremes of anxiety-related behaviors, were first grouped according to their anxiety levels in the elevated plus maze test. We found that the mRNA for endothelin-1 (ET1) and ET1 B-type receptors (ETBRs) in the amygdala was down-regulated in high-anxiety mice compared with low-anxiety mice. Knocking down basolateral amygdala (BLA) ET1 expression enhanced anxiety-like behaviors, whereas over-expressing ETBRs, but not A-type receptors (ETARs), had an anxiolytic effect. The combined down-regulation of ETBR and ET1 had no additional anxiogenic effect compared to knocking down the ETBR gene alone, suggesting that BLA ET1 acts through ETBRs to regulate anxiety-like behaviors. To explore the mechanism underlying this phenomenon further, we verified that most of the ET1 and the ET1 receptors in the BLA were expressed in pyramidal neurons. The ET1–ETBR signaling pathway decreased the firing frequencies and threshold currents for the action potentials of BLA pyramidal neurons but did not alter BLA synaptic neurotransmission. Together, these results indicate that amygdalar ET1-ETBR signaling could attenuate anxiety-like behaviors by directly decreasing the excitability of glutamatergic neurons.

Hippocampal Endothelin-1 decreases excitability of pyramidal neurons and produces anxiolytic effects

Anxiety disorders contribute to the pathophysiology of psychiatric diseases, including major depression, substance abuse, and schizophrenia. The hippocampus is important for anxiety modulation. However, the mechanisms that control the neuronal activity of the hippocampus in anxiety are still not clear. We found that Endothelin-1 (ET1) mRNA in the hippocampus was down-regulated in high-anxiety mice. Neutralizing endogenous ET1 in the hippocampal CA1 enhanced anxiety-like behaviors. We next revealed that most expression of ET1 and its receptors in the CA1 takes place in pyramidal neurons, and the ET1 signaling pathway directly regulated the excitability of CA1 pyramidal neurons and glutamatergic synaptic neurotransmission. Finally, we proved that neutralizing endogenous CA1 ET1 produces anxiogenic effects on low-anxiety mice, whereas infusing exogenous ET1 into the CA1 alleviates the anxiety susceptibility of high-anxiety mice. Together, these results indicate that ET1 signaling is critical in maintaining the excitability of glutamatergic neurons in the hippocampus and, thus, in modulating anxiety-like behaviors. Because ET1 is a risk factor for ischemic stroke, our findings might also help to explain the potential mechanism of emotional abnormality in stroke.