Abstract
We have previously shown that the defense response against stressor was attenuated in prepro-orexin gene knockout mice and orexin neuron-ablated mice (Jpn J Physiol 55: S87, 2005). We have proposed that orexin plays as a master switch to elicit multiple efferent pathways of the defense response. It is still open question, however, how information of stressor activates the orexinergic neurons. In this experiment, we examined possible contribution of the amygdala as one of the afferent nuclei to activate orexinergic neurons. In urethane-anesthetized mice, a GABA-A receptor antagonist, bicuculline, was microinjected into the amygdala, of which electrical stimulation induced simultaneous increases in blood pressure, heart rate, and respiratory frequency. Bicuculline dose-dependently induced cardiorespiratory excitation in both orexin neuron-ablated mice and wild-type controls. However, dose-response curve was rightward shifted in the orexin neuron-ablated mice. We conclude that the amygdala constitutes one of the afferent pathways to the orexinergic neurons that involved in the defense response against stressor. [J Physiol Sci. 2006;56 Suppl:S94]
