Autonomic modulation of olfactory signaling.

The olfactory epithelium is extensively innervated by sympathetic nerve endings, which release norepinephrine, and parasympathetic nerve endings, which release acetylcholine. Because olfactory sensory neurons have adrenergic and muscarinic receptors in addition to odorant receptors, autonomic stimulation can modulate the responses of olfactory sensory neurons to odorants. Recent studies have shed light on the molecular mechanisms that underlie crosstalk between muscarinic and odorant receptor signaling. The emerging view is that the stimulation of odorant receptor signaling by odorants, which is the earliest step in olfaction, can be substantially regulated by the autonomic nervous system.