The brainstem premotor neurons of the facial nucleus (VII) and hypoglossal (XII) nucleus can integrate orofacial nociceptive input from the caudal spinal trigeminal nucleus (Vc) and coordinate orofacial nociceptive reflex (ONR) responses. However, the synaptoarchitectures of the ONR pathways are still unknown. In the current study, we examined the distribution of GABAergic premotor neurons in the brainstem local ONR pathways, their connections with the Vc projections joining the brainstem ONR pathways and the neurochemical properties of these connections. Retrograde tracer fluoro-gold (FG) was injected into the VII or XII, and anterograde tracer biotinylated dextran amine (BDA) was injected into the Vc. Immunofluorescence histochemical labeling for inhibitory/excitatory neurotransmitters combined with BDA/FG tracing showed that GABAergic premotor neurons were mainly distributed bilaterally in the ponto-medullary reticular formation with an ipsilateral dominance. Some GABAergic premotor neurons made close appositions to the BDA-labeled fibers coming from the Vc, and these appostions were mainly distributed in the parvicellular reticular formation (PCRt), dorsal medullary reticular formation (MdD), and supratrigeminal nucleus (Vsup). We further examined the synaptic relationships between the Vc projecting fibers and premotor neurons in the VII or XII under the confocal laser-scanning microscope and electron microscope, and found that the BDA-labeled axonal terminals that made asymmetric synapses on premotor neurons showed vesicular glutamate transporter 2 (VGluT2) like immunoreactivity. These results indicate that the GABAergic premotor neurons receive excitatory neurotransmission from the Vc and may contribute to modulating the generation of the tonic ONR.
References
[1]
Clarke RW (1985) The effects of decerebration and destruction of nucleus raphe magnus, periaqueductal grey matter and brainstem lateral reticular formation on the depression due to surgical trauma of the jaw-opening reflex evoked by tooth-pulp stimulation in the cat. Brain Res 332: 231–236.
[2]
Westberg KG, Clavelou P, Schwartz G, Lund JP (1997) Effects of chemical stimulation of masseter muscle nociceptors on trigeminal motoneuron and interneuron activities during fictive mastication in the rabbit. Pain 73: 295–308.
[3]
Tsai C-M (1999a) The caudal subnucleus caudalis_medullary dorsal horn.acts as an interneuronal relay site in craniofacial ociceptive reflex activity. Brain Research 826: 293–297.
[4]
Yoshida A, Bae YC, Shigenaga Y, Sessle BJ (1995) Physiology and morphology of the neuronal circuits of jaw reflexes in cats,. In: Taylor A, Gladden MH, Durbaba R, editors. Alpha and Gamma Motor Systems. Plenum, New York. pp. 57–59.
[5]
Li JL, Wu SX, Tomioka R, Okamoto K, Nakamura K, et al. (2005) Efferent and afferent connections of GABAergic neurons in the supratrigeminal and the intertrigeminal regions. An immunohistochemical tract-tracing study in the GAD67-GFP knock-in mouse. Neurosci Res 51: 81–91.
[6]
Dong YL, Li JL, Zhang FX, Li YQ (2011) Nociceptive afferents to the premotor neurons that send axons simultaneously to the facial and hypoglossal motoneurons by means of axon collaterals. PloS ONE 6: e25615.
[7]
Li YQ, Takada M, Kanako T, Mizuno N (1997a) GABAergic and glycinergic interneurons projecting to the trigeminal motor nucleus: a double-labeling study in the rat. J Comp Neurol 373: 498–510.
[8]
Li YQ, Takada M, Kanako T, Mizuno N (1997b) Distribution of GABAergic and glycinergic premotor neurons projecting to the facial and hypoglossal nuclei in the rat. J Comp Neurol 378: 283–294.
[9]
Tsai CM, Chiang CY, Yu XM, Sessle BJ (1999b) Involvement of trigeminal subnucleus caudalis (medullary dorsal horn) in craniofacial nociceptive reflex activity. Pain 81: 115–128.
[10]
Saha S, Appenteng K, Batten TF (1991) Quantitative analysis and postsynaptic targets or GABA-immunoreactive bouton within the rat trigeminal motor nucleus. Brain Res 561: 128–138.
[11]
Kolta A (1997) In vitro investigation of synaptic relations between interneurons surrounding the trigeminal motor nucleus and masseteric motoneurons. J Neurophysiol 78: 1720–1725.
[12]
Streppel M, Popratiloff A, Gruart A, Angelov DN, Guntinas-Lichius O, et al. (2000) Morphological connections between the hypoglassal and facial nerve in the brain stem of the rat. HNO 48: 911–916.
[13]
Luccarini P, Cadet R, Duale C, Woda A (1998) Effects of lesions in the trigeminal oralis and caudalis subnuclei on different orofacial nociceptive responses in the rat. Brain Res 803: 79–85.
[14]
Bellocchio EE, Reimer RJ, Fremeau RT, Edwards RH (2000) Uptake ofglutamate into synaptic vesicles by an inorganic phosphatetransporter. Science 289: 957–960.
[15]
Fremeau RT, Troyer MD, Pahner I, Nygaard G, Tran CH, et al. (2001) The expression of vesicular glutamate transportersdefines two classes of excitatory synapse. Neuron 31: 247–260.
[16]
Fremeau RT, Voglmaier S, Seal RP, Edwards RH (2004) VGLUTs definesubsets of excitatory neurons and suggest novel roles for glutamate. Trends Neurosci 27: 98–103.
[17]
Varoqui H, Schafer MK, Zhu H, Weihe E, Erickson JD (2002) Identification of the differentiation-associated Na+/PI transporter as a novel vesicular glutamate transporter expressed in the distinct set of glutamatergic synapses. J Neurosci 22: 142–155.
[18]
Li JL, Fujiyama F, Kaneko T, Mizuno N (2003) Expression of vesicular glutamate transporters, VgluT1 and VgluT2, in axon terminals of nociceptive primary afferent fibers in the superficial layers of the medullary and spinal dorsal horns of the rat. J Comp Neurol 457: 236–249.
[19]
Liu Y, Abdel Samad O, Zhang L, Duan B, Tong Q, et al. (2010) VGLUT2-dependent glutamate release from nociceptors is required to sense pain and suppress itch. Neuron 68: 543–556.
