IRS

[IRS-04] Neurons expressing the transcriptional regulator Phox2b may be involved in the induction of mastication-like jaw movements and salivation associated with mastication

〇Tomio Inoue¹, Kiyomi Nakayama², Ayako Mochizuki², Masanori Dantsuji², Shiro Nakamura² (1. Kyoto Koka Women's Col, 2. Dept Oral Physiol, Showa Univ Sch Dent)

Keywords:咀嚼、唾液分泌、Phox2b

A number of neurons expressing Phox2b (Phox2b⁺ neurons), a transcriptional regulator involved in the development of autonomic centers, are located in the medullary solitary nucleus, the supratrigeminal region, and t parvocellular and intermediate reticular formation (PCRt/IRt). We have shown that Phox2b⁺ neurons in these areas send axons to the trigeminal motor nucleus and may be involved in the regulation of jaw movements. Since Phox2b⁺ neurons located ventral to the facial nucleus are known to be involved in the respiratory rhythm generation, we investigated whether Phox2b⁺ neurons are involved in the masticatory rhythm generation. Using genetically modified rats that express the light-sensitive protein channelrhodopsin in Phox2b⁺ neurons, light irradiation of the solitary nucleus produced rhythmic muscle activity at 4-6 Hz in the jaw-opening muscle (digastric muscle), but only slight activity in the jaw-closing muscle (masseter muscle). Light irradiation to the supratrigeminal region elicited phase-synchronized rhythmic activity at 8-10 Hz in both jaw-opening and -closing muscles. On the other hand, light irradiation to the PCRt/IRt evoked synchronous activity at 4-6 Hz in both jaw-opening and -closing muscles, but out of phase with each other. Since Phox2b⁺ neurons in the brainstem are excitatory neurons, it is possible that Phox2b⁺ neurons excite superior salivatory nucleus neurons (preganglionic neurons controlling the salivary glands). Therefore, we examined whether Phox2b⁺ neurons are involved in salivary secretion using brain stem slice preparations from the same genetically modified rats as above. Light irradiation of the PCRt/IRt generated excitatory postsynaptic currents (EPSCs) in the superior salivatory nucleus neurons. These results suggest that Phox2b⁺ neurons are involved in the induction of rhythmic masticatory-like jaw movements and may have different effects on jaw movement induction depending on their location. In addition, Phox2b⁺ neurons may also be involved in the massive salivation associated with mastication.