Abstract
The multiple-site optical recording of transmembrane potential activity with a voltage-sensitive merocyanine-rhodanine dye, NK2761, was used to survey extensively the early functional organization of neural circuits related to the vagus nerve in the embryonic chick brainstem. In addition to the response area on the stimulated side, including the vagal sensory nucleus (the nucleus of the tractus solitarius (NTS)) and the motor nucleus (the dorsal motor nucleus of the vagus nerve (DMNV)), vagal stimulation induced an additional response area at the level of the cerebellum on the contralateral side. This response appeared to come through the second synaptic pathway from the NTS to the contralateral side. Blockade of non-NMDA receptors in the NTS abolished the responses on the contralateral side, while blockade of NMDA receptors did not abolish the responses. The responses on the contralateral side were first detected from the 7-day old embryonic stage, when the glutamatergic EPSP in the NTS was first observed. This result suggests that the second synaptic pathway from the NTS to the contralateral side is already generated when the primary vagal afferents make functional synapses on the NTS neurons. [Jpn J Physiol 54 Suppl:S153 (2004)]
