Primary vagal projection to the contralateral non-NTS region in the embryonic chick brainstem revealed by optical recording.

Using multiple-site optical recording with the voltage-sensitive dye, NK2761, we found that vagus nerve stimulation in the embryonic chick brainstem elicits postsynaptic responses in an undefined region on the contralateral side. The characteristics of the contralateral optical signals suggested that they correspond to the monosynaptic response that is related to the vagal afferent fibers. The location of the contralateral response was different from the vagal motor nucleus (the dorsal motor nucleus of the vagus nerve) and sensory nucleus (the nucleus of the tractus solitarius), and other brainstem nuclei that receive primary vagal projection. These results show that the vagus nerve innervates and makes functional synaptic connections in a previously unreported region of the brainstem, and suggest that sensory information processing mediated by the vagus nerve is more complex than expected.