Spontaneous functional viscerosensory regeneration into the adult brainstem.

The dorsal root entry zone of the vagus nerve (vDREZ) is uniquely characterized by peripheral tissue insertions (PTIs) deep to the brainstem surface, consisting of Schwann cells and a reticulum of astrocytic processes. Because Schwann cells permit peripheral axonal regeneration, the capacity of vagal medullary PTIs to allow centripetal regeneration of visceral afferents after vagal dorsal rhizotomy in adult rats was investigated. The present work shows that vagal axons spontaneously regenerate into appropriate and ectopic brainstem nuclei. They accomplish this by first growing along PTIs but then extend along basal laminas of medullary blood vessels. Electrically stimulated regenerated vagal afferents induced Fos expression (indicating functional connectivity) within appropriate but not ectopic nuclei. The unique structure of the vDREZ can thus support spontaneous functional regeneration of visceral primary afferent axons into the adult CNS.