Time-dependent and side-specific c-Fos responses of the nucleus tractus solitarius and hypoglossal nucleus after unilateral nerve transection in mice.

How the medullary nucleus tractus solitarius (NTS) and hypoglossal nucleus (HN) respond when peripheral input or output is lost is unclear. In adult mice, we unilaterally transected the superior laryngeal (input) and hypoglossal (output) nerves and mapped c-Fos in the NTS and HN at 12, 24 and 72h. Both nuclei showed a transient c-Fos increase relative to sham. In the HN, c-Fos shifted over time from the ipsilateral to the intact contralateral side, whereas the NTS responded bilaterally. Because the contralateral HN response arose in non-axotomized neurons, it reflects an activity-dependent component, not injury alone.