Musings on the wanderer: What's new in our understanding of vago-vagal reflexes? II. Integration of afferent signaling from the viscera by the nodose ganglia

To understand vago-vagal reflexes, one must have an appreciation of the events surrounding the encoding, integration, and central transfer of peripheral sensations by vagal afferent neurons. A large body of work has shown that vagal afferent neurons have nonuniform properties and that distinct subpopulations of neurons exist within the nodose ganglia. These sensory neurons display a considerable degree of plasticity; electrophysiological, pharmacological, and neurochemical properties have all been shown to alter after peripheral tissue injury. The validity of claims of selective recordings from populations of neurons activated by peripheral stimuli may be diminished, however, by the recent demonstration that stimulation of a subpopulation of nodose neurons can enhance the activity of unstimulated neuronal neighbors. To better understand the neurophysiological processes occurring after vagal afferent stimulation, it is essential that the electrophysiological, pharmacological, and neurochemical properties of nodose neurons are correlated with their sensory function or, at the very least, with their specific innervation target.