Extrasynaptic homomeric glycine receptors in neurons of the rat trigeminal mesencephalic nucleus
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The neurons in the trigeminal mesencephalic nucleus (Vmes) innervate jaw-closing muscle spindles and periodontal ligaments, and play a crucial role in the regulation of jaw movements. Recently, it was shown that many boutons that form synapses on them are immunopositive for glycine (Gly+), suggesting that these neurons receive glycinergic input. Information about the glycine receptors that mediate this input is needed to help understand the role of glycine in controlling Vmes neuron excitability. For this, we investigated the expression of glycine receptor subunit alpha 3 (GlyRα3) and gephyrin in neurons in Vmes and the trigeminal motor nucleus (Vmo), and the Gly+ boutons that contact them by light- and electron-microscopic immunocytochemistry and quantitative ultrastructural analysis. The somata of the Vmes neurons were immunostained for GlyRα3, but not gephyrin, indicating expression of homomeric GlyR. The immunostaining for GlyRα3 was localized away from the synapses in the Vmes neuron somata, in contrast to the Vmo neurons, where the staining for GlyRα3 and gephyrin were localized at the subsynaptic zones in somata and dendrites. Additionally, the ultrastructural determinants of synaptic strength, bouton volume, mitochondrial volume, and active zone area, were significantly smaller in Gly+ boutons on the Vmes neurons than in those on the Vmo neurons. These findings support the notion that the Vmes neurons receive glycinergic input via putative extrasynaptic homomeric glycine receptors, likely mediating a slow, tonic modulation of the Vmes neuron excitability.
KeywordsMesencephalic trigeminal nucleus Glycine receptor Homomeric Jaw movement Ultrastructure Immunohistochemistry
The authors sincerely thank Dr. Juli Valtschanoff for helpful discussion and careful reading of the manuscript.
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (NRF-2017R1A5A2015391, NRF-2017R1A2B2003561).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted.
- Bae YC, Choi BJ, Lee MG, Lee HJ, Park KP, Zhang LF, Honma S, Fukami H, Yoshida A, Ottersen OP, Shigenaga Y (2002) Quantitative ultrastructural analysis of glycine- and gamma-aminobutyric acid-immunoreactive terminals on trigeminal alpha- and gamma-motoneuron somata in the rat. J Comp Neurol 442:308–319CrossRefPubMedGoogle Scholar
- Fekete CD, Chiou T-T, Miralles CP, Harris RS, Fiondella CG, Loturco JJ, De Blas AL (2015) In vivo clonal overexpression of neuroligin 3 and neuroligin 2 in neurons of the rat cerebral cortex: differential effects on GABAergic synapses and neuronal migration. J Comp Neurol 523:1359–1378CrossRefPubMedPubMedCentralGoogle Scholar
- Paik SK, Bae JY, Park SE, Moritani M, Yoshida A, Yeo EJ, Choi KS, Ahn DK, Moon C, Shigenaga Y, Bae YC (2007) Developmental changes in distribution of gamma-aminobutyric acid- and glycine-immunoreactive boutons on rat trigeminal motoneurons. I. Jaw-closing motoneurons. J Comp Neurol 503:779–789CrossRefPubMedGoogle Scholar
- Paik SK, Kwak MK, Bae JY, Yi HW, Yoshida A, Ahn DK, Bae YC (2012) γ-Aminobutyric acid-, glycine-, and glutamate-immunopositive boutons on mesencephalic trigeminal neurons that innervate jaw-closing muscle spindles in the rat: ultrastructure and development. J Comp Neurol 520:3414–3427CrossRefPubMedGoogle Scholar