Submitted on October 17, 2007
Accepted on August 22, 2008
Synaptic Transmission from the Supratrigeminal Region to Jaw-closing and Jaw-opening Motoneurons in Developing Rats
Shiro Nakamura1, Tomio Inoue1*, Kan Nakajima2, Masayuki Moritani3, Kiyomi Nakayama4, Kenichi Tokita5, Atsushi Yoshida6, and Kohtaro Maki7
1 Oral Physiology, Showa University School of Dentistry, Tokyo, Japan
2 Orthodontics, Showa University school of Dentistry, Tokyo, Japan
3 Oral anatomy and Neurobiology, Faculty of Dentistry, Osaka University, Osaka, Japan
4 Tokyo, United States; Oral Physiology, Showa University School of Dentistry, Tokyo, Japan
5 Tokyo, Japan; Oral Physiology, Showa University School of Dentistry, Tokyo, Japan
6 Osaka, Japan; Oral anatomy and Neurobiology, Faculty of Dentistry, Osaka University, Osaka, Japan
7 Tokyo, Japan; Orthodontics, Showa University school of Dentistry, Tokyo, Japan
* To whom correspondence should be addressed. E-mail: inouet{at}dent.showa-u.ac.jp.
The supratrigeminal region (SupV) receives abundant orofacial sensory inputs and descending inputs from the cortical masticatory area and contains premotor neurons that target the trigeminal motor nucleus (MoV). Thus, it is possible that the SupV is involved in controlling jaw muscle activity via sensory inputs during mastication. We used voltage-sensitive dye, laser photostimulation, patch-clamp recordings and intracellular biocytin labeling to investigate synaptic transmission from the SupV to jaw-closing and jaw-opening motoneurons in the MoV in brainstem slice preparations from developing rats. Electrical stimulation of the SupV evoked optical responses in the MoV. An antidromic optical response was evoked in the SupV by MoV stimulation, whereas synaptic transmission was suppressed by substitution of external Ca2+ with Mn2+. Photostimulation of the SupV with caged glutamate evoked rapid inward currents in the trigeminal motoneurons. Gramicidin-perforated and whole-cell patch-clamp recordings from masseter motoneurons (MMNs) and digastric motoneurons (DMNs) revealed that glycinergic and GABAergic postsynaptic responses evoked in MMNs and DMNs by SupV stimulation were excitatory in P1-4 neonatal rats and inhibitory in P9-12 juvenile rats, whereas glutamatergic postsynaptic responses evoked by SupV stimulation were excitatory in both neonates and juveniles. Furthermore, the axons of biocytin-labeled SupV neurons that were antidromically activated by MoV stimulation terminated in the MoV. Our results suggest that inputs from the SupV excite MMNs and DMNs through activation of glutamate, glycine, and GABAA receptors in neonates, whereas glycinergic and GABAergic inputs from the SupV inhibit MMNs and DMNs in juveniles.
