Niigata Dent. J. 45（1）：7 － 17,

2015

7

－原著－
歯根膜ルフィニ神経終末の再生過程における ASIC3 発現様式の変化
井表千馨 1,2），齋藤功 1）

1）

新潟大学大学院医歯学総合研究科

歯科矯正学分野 （主任；齋藤2）

新潟大学大学院医歯学総合研究科

口腔解剖学分野 （主任；前田健康 教授）

功 教授）

Alterations in the Expression Pattern of the Acid-Sensing
Ion Channel 3（ASIC3）during the Regeneration of Periodontal Ruffini Endings
Chika Ihyo1, 2）, Isao Saito1）
1)
2)

Division of Orthodontics (Chief: Prof. Isao Saito), Niigata University Graduate School of Medical and Dental Sciences

Division of Oral Anatomy (Chief: Prof. Takeyasu Maeda), Niigata University Graduate School of Medical and Dental Sciences
平成 27 年３月２日受付

平成 27 年３月４日受理

キーワード：イオンチャネル，歯根膜ルフィニ神経終末，三叉神経節
Key words: ion channel, periodontal Ruffini ending, trigeminal ganglion
Abstract
The acid-sensing ion channel 3 (ASIC3), belonging to the epithelial sodium-channel/degenerin (ENaC/DEG)
superfamily, is regarded as an essential ion channel for mechanosensation. Our recent study has confirmed theexpression of ASIC3 in the mechanoreceptive Ruffini endings in the periodontal ligament of mice incisors,
indicating that this molecule is a new marker for mechanoreceptors. Although the periodontal Ruffini endings
have been reported to have a potential for high neuroplasticity, no information is available regarding the role of
ASIC3 during the regeneration process after nerve injury. This study was therefore undertaken to examinechanges in the expression pattern of ASIC3 in the periodontal ligament and trigeminal ganglion of the rats. Aftertransection of the inferior alveolar nerve (IAN), cryostat sections - including the lingual ligament of the lower
incisors and trigeminal ganglia - were processed for immunohistochemical procedures. As previously reported,the periodontal Ruffini endings disappeared on postoperative (PO) Day 3, and began regeneration from PO Day 7
to return to their normal morphology by PO Day 28, as shown by immunohistochemistry for protein gene product9.5, a neuronal marker. However, no apparent immunoreaction for ASIC3 was ever recognizable in the periodontal
ligament throughout this observation period. On the other hand, a strong immunoreaction for ASIC3 occurred in
the satellite cells encircling the trigeminal ganglion neurons on the ipsilateral side. These findings indicate that
ASIC3 is not directly involved in the axonal regeneration of the periodontal Ruffini endings but rather in neuronglial interactions such as control of the neuronal activity in the trigeminal ganglion.
抄録
Acid-sensing ion channel 3 (ASIC3) は，上皮性ナトリウムチャネル/ degenerin (ENaC/DEG) 遺伝子スーパーファミリーに属する非電位依存性陽イオンチャネルで，機械刺激受容に重要な役割を担う。近年，我々は ASIC3 が歯根膜の機械受容器である歯根膜ルフィニ神経終末に発現することを報告し，機械受容器の新たなマーカーとなり得ることを示した。歯根膜ルフィニ神経終末は，高い神経可塑性を有することが報告されているが，神経傷害後の再生過程における ASIC3 の役割については全く不明である。従って本研究では，ラットの歯根膜ルフィニ神経終末および三叉神経節における下歯槽神経傷害後の ASIC3 の発現様式の変化を検討した。下歯槽神経切断後，切歯舌側歯根膜を－7－新潟歯学会誌845（1）：2015

含む下顎骨と三叉神経節の凍結切片を作製し，神経線維のマーカーである protein gene product 9.5 (PGP 9.5) とASIC3 の局在を免疫組織化学的手法を用いて検索した。過去の報告と同様に，切歯歯根膜ルフィニ神経終末は，下歯槽神経切断 3 日後に完全に消失したが，7 日後には再生を開始し，切断後 28 日目には正常なルフィニ神経終末の形態に回復した。しかしながら，観察期間を通して ASIC3 の免疫陽性反応は歯根膜ルフィニ神経終末には認められなかった。一方，切断側の三叉神経節では神経細胞周囲の衛星細胞が強い ASIC3 免疫陽性反応を示した。これらのことから，ASIC3 は歯根膜ルフィニ神経終末の再生過程において，軸索終末の形態回復に直接的には関与しないが，三叉神経節における神経活性の調節といった neuron-glia interaction に関与する可能性が示唆された。

forces24). Indeed, it has been shown that the turnover

Introduction

rate of the collagen fibers in the periodontal ligaments
is about five times faster than that in other tissues25-27).

Acid-sensing ion channels (ASICs) belong to theThis indicates that the periodontal nerve fibers have toepithelial sodium-channel/degenerin (ENaC/DEG)

adapt to the active tissue remodeling of the periodontal

superfamily1-3）. ASICs consisting of 7 isoforms2，4） haveligament.

been reported to be distributed throughout the central
5-7)

movement

Previous experimental studies on tooth28，29)

and traumatic occlusion30，31) have shownand peripheral nervous systems in mammals . Previous

the rearrangement of the periodontal nerves andstudies have suggested the involvement of the neuronalchanges in the shape of the nerve endings. Further-ASICs in acid sensing as well as nociception andmore, when the inferior alveolar nerve (IAN) is cut at5，8-11)

mechanoception. In fact, ASIC1, 2, and 3 have been

the level of the mandibular foramen, the morphology

confirmed in the mechanoreceptive neurons of the dorsal

and density of the periodontal Ruffini ending almost re-root ganglia12) as have ASIC2a and ASIC3 in cutaneous

cover by postoperative 1 month32，33). Therefore, manymechanoreceptors including Meissner corpuscles, Merkel

researchers agree with the notion that the periodontal

nerve endings, and palisades of lanceolate nerve

Ruffini ending has a high potential for neuroplasticity.

endings

5，8，13)

Predominant expressions of sensory

Our regeneration studies using neurotrophin geneneurons have suggested that ASIC3 is an essential

knockout mice have indicated the possibility that vari-.

channel for mechanosensation

5，8，9，13，14), as confirmed byous kinds of molecules control the regeneration of theASIC3 expression in the trigeminal neurons, which

periodontal Ruffini endings in a stage-specific man-participate in the sensation and modulation of nocicep-

ner34-36). We have recently demonstrated ASIC3 immu-15-17)

tive and mechanoreceptive signals.

noreaction in the axoplasm of the periodontal Ruffini

The periodontal ligament is a dense connective

endings as well as in the medium-sized trigeminal neu-tissue which receives a rich supply of sensory nerves.

rons which mediate mechanotransduction 17) in theThe periodontal sensory endings are divided into

mouse, suggesting a possible role for ASIC3 during thenociceptive free endings and mechanoreceptive

regeneration process of the periodontal Ruffini endings.

specialized nerve terminals 18). In spite of variance

To date, however, no information is available regarding

among species or kinds of teeth, a series of morpholog-changes in the ASIC3 expression in the periodontal lig-

ical studies have suggested that the Ruffini ending is aament and trigeminal ganglion during nerve regenera-primary mechanoreceptor in the periodontal liga-tion. Therefore, this study investigated changes in thement 19，20). Although the periodontal Ruffini ending

localization of ASIC3 in the periodontal ligament andlacks a distinctive fibrous capsule different from thetrigeminal ganglion using a rat IAN injury model to de-Ruffini endings originally reported by Ruffini, thistermine the role of ASIC3 in the regenerating Ruffini

mechanoreceptive nerve terminal is morphologicallyendings.

characterized by dendritic ramifications of expanded

Materials and Methods

axon terminals filled with abundant mitochondria andby an association with the terminal Schwann cells, analogues to lamellar cells of the Pacinian corpuscle or18，19，21-23)

laminar cells of the Meissner corpuscle

Animal preparation
All animal experiments were approved and per-.

Active tissue remodeling takes place in the periodon-

formed according to the guidelines of the Niigata Uni-tal ligament with the constant exposure of occlusal

versity Intramural Animal Use and Care Committee－8－