Emotional and state-dependent modification of cardiorespiratory function: Role of orexinergic neurons

Our daily life not only involves calm, resting states but is filled with perturbations that induce active conditions, such as movements, eating, and communicating. During such active periods, cardiorespiratory regulation must be adjusted for bodily demands, which differ from those during resting states, by modulating or resetting baseline levels. To explore neural mechanisms of state-dependent adjustments of central autonomic regulation, we recently focused on the following two states: 1), stress-induced defense (fight-or-flight) responses, because stressors induce both cognitive, emotional, and behavioral changes and autonomic alterations, and 2), sleep/wake differences. Basal respiration and respiratory reflex regulation significantly differ during waking and sleep states. In this review, we will summarize our recent findings with orexin knockout and orexin neuron-ablated mice to determine possible contributions of orexin, a hypothalamic neuropeptide, to state-dependent adjustments of central autonomic regulation. The diversity of synaptic control of cardiovascular and respiratory neurons appears to be necessary for animals to adapt to ever-changing life circumstances and behavioral states. The orexin system likely functions as one essential modulator for coordinating circuits controlling autonomic functions and behaviors. (C) 2008 Elsevier B.V. All rights reserved.