Orexin links emotional stress to autonomic functions.

We studied autonomic functions in orexin-deficient mice and found abnormalities in the emotional state-dependent adjustment of the central autonomic regulation on circulation and respiration. These are summarized as follows. 1) Orexin-deficient mice exposed to a stressor exhibited an attenuated fight-or-flight response, including increases in respiration and blood pressure and stress-induced analgesia. 2) Stimulation to the amygdala (AMG) or the bed nucleus of the stria terminalis (BNST), both of which are implicated in the stress-induced autonomic responses, induced long-lasting cardiorespiratory excitation in wild-type mice but not in the orexin neuron-ablated mice. Hence, it is likely that the orexin system is one of the essential modulators required for orchestrating the neural circuits controlling autonomic functions and emotional behaviors.