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Response characteristics of primary periodontal mechanoreceptive neurons
simultaneously recorded in the trigeminal ganglion and mesencephalictrigeminal nucleus of the rat in response to trapezoidal and rectangularmechanical stimulation of a single tooth
Shigeru Miyata１, Niichiro Amano１, Takahiro Satoda２,
Takatoshi Murata３, Shigenori Kawagishi４, Kenichi Yoshino５,
Keiko Hayashi１, and Yasuo Nishikawa６（formerly）Division of Oral Neuroscience ; ４Division of Multidisciplinary Studies ;１

Department of Oral Health Management ; Kyushu Dental University, Kitakyushu 803-8580, Japan
Department of Oral Health Science, Faculty of Dentistry, Hiroshima University, Hiroshima 734-8553, Japan

５
２

Department of Translational Research, Tsurumi University School of Dental Medicine, Yokohama 230-8501, Japan
Department of Physiology, Osaka Dental University, Osaka 573-1121, Japan３
６

E-mail: sxkk@nifty.com
Received 2013, 6, 7.
Accepted 2013, 9, 25.

Abstract
Periodontal mechanoreceptors are dually innervated by primary neurons whose cell bodies exist in the trigeminal
ganglion（TG）and the mesencephalic trigeminal nucleus（MTN）. We obtained simultaneous recordings of singleunit responses of primary periodontal mechanoreceptive neurons located in the TG and MTN of the same animal tocontrolled experimental forces applied to a single tooth. Simultaneous single-unit recordings of electrophysiologically
identified primary periodontal mechanoreceptive neurons in a rat’s TG and MTN were performed while isosceles
trapezoidal or rectangular mechanical stimuli were being applied in either the linguolabial or the labiolingual
direction to the ipsilateral maxillary incisor. Fifty-four single units were recorded in 27 rats and classified as rapidly
adapting（RA）or slowly adapting（SA）periodontal neurons on the basis of their responses to a decisive rectangularmechanical stimulus applied in the linguolabial direction. Significantly more RA neurons existed in the MTN than
the TG（P < 0.05）. The response characteristics of the SA and RA periodontal neurons were quite similar between
the TG and MTN. The trapezoidal and rectangular stimuli applied in the linguolabial direction elicited a vigorous
sustained spike discharge in SA periodontal neurons in both the TG and MTN, whereas both stimuli applied in the
opposite（labiolingual）direction did not elicit any SA responses. Rectangular stimuli applied in both directions
elicited high-threshold ON-OFF spike responses in the RA periodontal neurons in both the TG and MTN. We
also found an unreported burst-type periodontal neuron; its responsiveness was characterized by a brief repetitive

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Periodontal neurons in V ganglion & mesencephalic nucleus （Miyata et al.）

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spike discharge of high frequency in response to a slight tapping applied in both directions. Six of the 17 TG-RA
neurons examined were this burst-type neuron. From the above results, it is presumed that during incisive processof rat chewing cycle, rapidly repeated chopping or chiselling movements bring about transient, forceful periodontalmasseteric reflex, which can be produced by abundant periodontal inputs from both the MTN and TG.

Key words：Primary periodontal neuron / Trigeminal ganglion / Mesencephalic trigeminal nucleus /Simultaneous recording / Rat
Introduction
Periodontal mechanoreceptors are dually
innervated by primary neurons whose cell bodies
exist in the trigeminal ganglion （ TG ） and themesencephalic trigeminal nucleus （ MTN ）. Wellover 75% of the periodontal mechanoreceptors aresupplied by the TG, with a lesser number by theMTN１）. MTN periodontal mechanoreceptors of acat’s canine tooth are known to be concentrated
near the root apex, whereas TG periodontal
mechanoreceptors are found around the middleof the root ２）. We reported that MTN primary
periodontal mechanoreceptive neurons innervating a
rat maxillary incisor showed the highest frequency
of one- to-one following in repetitive tapping at
100 Hz, and all tested neurons exhibited suchvery rapid adaptation as to show only ON-OFF
responses to trapezoidal mechanical stimuli applied
more rapidly than 0.6 Newton/sec（N/sec）３）.
Tabata and Hayashi （1994）４） documented thatabout 90 % of TG periodontal mechanoreceptive
primary neurons innervating a rat incisor weredirectionally selective, and the ratio of the numberof sustained - and transient - response neurons
was about 10 to 1. To the best of our knowledge,
there is no report on simultaneous recordings ofsingle-unit responses of the primary periodontal
mechanoreceptive neurons located in the TG and
MTN of the same rat to controlled mechanicalstimuli applied to a single tooth.
The purpose of the present study was to compare
the response characteristics to trapezoidal orrectangular mechanical stimulation of the ipsilateralmaxillary incisor between electrophysiologically
identified primary periodontal mechanoreceptive

neurons simultaneously recorded in a rat’s TG and
MTN. Preliminary reports of this research havebeen presented previously５,６）.

Materials and Methods
A total of 27 male Wistar albino rats weighing

440 - 560 g were used in the present study. All pro-cedures of the experiments were approved by the
Animal Care and Use Committee at Kyushu Dental
University, and were carried out in strict accordance with the National Institute of Health Guide
for the Care and Use of Laboratory Animals. During experiments all efforts were made to minimize
pain and the number of the rats used. Each rat wasanesthetized with sodium pentobarbital（50 mg/kg,
i.p.）and tracheotomized. During unit recording, therat was paralyzed with pancuronium bromide（0.1mg/kg, i.m., every hr）and artificially ventilated.
The rat’s rectal temperature was maintained at
37 - 38°
C with a thermostatically controlled heating pad. The crowns of the left maxillary incisorand both mandibular incisors were cut off.
Figure 1 shows the schematic representationof stimulating and recording procedures used inthis study. In the right maxillary incisor, a small
notch was cut in its incisal edge, metal applicators’
point was inserted into the notch, and the junction
was covered with dental self-curing acrylic resin.
Therefore, ramp-and-hold（i.e., isosceles trapezoidal）mechanical stimuli could be applied easily ineither the linguolabial or the labiolingual direction through the applicator of an electromechanicalforce generator（DPS-250H, Dia Medical System,
Tokyo, Japan ） incorporating a vibrator （ Model
101, Ling Dynamic Systems, CT, USA）
. Foil strain
gauges bonded to the applicator arm provided a

― 78 ―

Fig. 1. Experimental arrangements for simultaneous single unit recordings of electrophysiologically identified primary
periodontal mechanoreceptive neurons in a rat’s trigeminal
ganglion (TG) and mesencephalic trigeminal nucleus (MTN)
during controlled experimental forces applied in either the
linguolabial or the labiolingual direction to the ipsilateralmaxillary incisor.

continuous recording of the forces applied. The
forces with the rates of application of 1, 3 and 5 N/
sec will be referred to in this paper as trapezoidal
mechanical stimuli, while those with the rates ofapplication of 50, 75 and 83 N/sec will be referred
to as rectangular mechanical stimuli.
After the rat’s head was set in a Narishige stereotaxic instrument（Model SR-5R）, the right anterior superior alveolar nerve was exposed by removing the eyeball. The exposed anterior superior
alveolar nerve was not sectioned but was left intact
for later electrophysiological testing for identifying
a unit as the primary afferent. On the right side, atemporal craniotomy was performed, and restrictedtemporal lobe aspiration was performed to expose
the floor of the middle cranial fossa. With gentle
retraction of the base of the brain, the dorsal surface of the right TG was exposed, and its three
peripheral divisions were confirmed with a surgicalmicroscope. A 5-mm rostrocaudally elongated holeintersecting the right lambdoid suture was drilled,
making it possible to insert a recording microelectrode vertically into all regions of the caudal MTN.
A varnish-coated Elgiloy microelectrode（15.3 17.8 MΩ at 5 Hz）was directed laterally at a 60-degree angle from the vertical plane in order toinsert into the rostrocentral part of the TG by astepping microdrive, in which maxillary incisorsensitive units were distributed ４）. Another micro-

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electrode was guided to the caudal part of the right
MTN, in which spindle afferent potentials could be
evoked by probing the jaw-closing muscles or bycyclic depressing of the mandible. Thereafter, themicroelectrode was moved to a caudal side at intervals of 200 µm until periodontal afferent potentials
could be elicited by manual pressure on the maxillary incisor. Single-unit activity was continuously
monitored on a digital memory oscilloscope（VC-11,
Nihon Kohden Corp., Tokyo, Japan）and stored onmagnetic tape for off-line analysis. Iron was deposited from the microelectrode tip by passing anodal
DC current（20 µA for 3 - 15 min）, which was later
converted to Prussian Blue spots for histologicalconfirmation７）. The chi-squared test was used tocompare the incidence of unit types between the
TG and MTN. The differences with P < 0.05 wereconsidered as statistically significant.

Results
When unitary activity was detected in theright TG or MTN responding to manual pressure
on the right maxillary incisor, the unit waselectrophysiologically identified as a primaryafferent by its ability to follow faithfully double
pulse stimuli delivered at rates of 500 Hz８） to theright anterior superior alveolar nerve. Figure 2
exemplifies the electrophysiological examination
to identify a periodontal mechanoreceptive unit
recorded in the MTN as the primary afferent.
Successful simultaneous recordings of single units
in both the TG and MTN of the same animal wereattained in 19 rats. In the remaining eight rats,
single units were recorded only in the TG or MTN
of each animal. A total of 54 single units wererecorded in the 27 rats.
On the basis of the response to a decisive
rectangular mechanical stimulus（magnitude 0.3 N,
velocity 75 N/sec, ramp time 4 msec, and plateau
time 400 msec）applied in the linguolabial direction（see the middle of the bottom traces in Fig. 3B）,
all 54 single units could be broadly classified aseither rapidly adapting （RA）or slowly adapting（ SA ） periodontal neurons. The RA periodontal

Periodontal neurons in V ganglion & mesencephalic nucleus （Miyata et al.）neurons only generated action potentials during
the dynamic phase of the rectangular mechanicalstimulus, whereas the SA periodontal neurons fired
action potentials in a repetitive fashion during

Figure 2. An example of the electrophysiological identification ofa primary periodontal mechanoreceptiv unit in the MTN by meansof double pulse stimulation of the anterior superior alveolar nerve.
In each record, upper and lower traces show unitary responses
and stimulus signals, respectively. A, this single unit responding to
manual pressure on the maxillary incisor exhibited a single spike
potential with a consistent latency of 0.6 msec in response to asingle suprathreshold stimulus（3.8 mA, 0.2 msec duration）. B, theunit followed faithfully double pulse stimuli separated by 2 msec
（i.e., 500 Hz）. The upgoing arrow indicates unit response to thesecond stimulus. C, the unit was not able to follow double pulse
stimuli separated by 1 msec（i.e., 1 kHz）
, which was shorter than
the refractory period. The time and voltage calibrations are thesame for all records.

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the dynamic and static phases of the rectangularmechanical stimulus９）. Table 1 shows the neuronaltype（RA, SA）distribution of the 54 units in thetwo recording sites（TG, MTN）. Looking at all 54
units, the proportion of the RA and SA periodontal
neurons was significantly different between the TG
and MTN（chi-squared test, P < 0.05）.
Figure 3 shows typical discharge patterns of
a TG - SA and an MTN - RA periodontal neuron
that were encountered in three of the 19 rats.
Under the same magnitude of loading applied in
the linguolabial direction, the SA responses of
the TG periodontal neuron showed greater spike
numbers and spike frequencies to the trapezoidal
stimuli compared to the rectangular stimuli（Fig. 3A, B）. The maximum frequency of the SA
spike responses amounted to 107 Hz during thetrapezoidal stimulation at 5 N/sec velocity and
0.5 N magnitude. This TG-SA periodontal neuron
exhibited directional preference properties justlike an SA periodontal mechanosensitive unit in
the dog, as illustrated in Figure 2 in a 1970 study
by Hannam10）. When the incisor was stimulated 180
degrees from its sensitive linguolabial direction,
the vigorous sustained spike responses of the
TG- SA neuron were abolished and OFF spikes
occurred. Such OFF responses to the trapezoidal
and rectangular mechanical stimuli were an
OFF spike and double OFF spikes, respectively（ Fig. 3 C, D ）. The stretch receptor, a Ruffini like corpuscle, located in the lingual periodontal
ligament of rats１,11） appears to be a preeminent

Table 1. Distribution of the neuronal types (RA, SA) of 54 periodontal neurons in two recording sites (TG,MTN) in the rat

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Fig. 3. Simultaneous recordings of a slowly adapting (SA) and a rapidly adapting (RA) periodontal mechanoreceptive primary neuron locatedin the TG and MTN of the same rat, respectively, to isosceles trapezoidal (bottom traces in A and C) and rectangular (bottom traces in B
and D) tooth-pressing stimuli applied in the linguolabial (downward stimuli in A and B) or labiolingual (upward stimuli in C and D) direction.
Trapezoidal stimuli were stepwisely increased in velocity and magnitude as follows: 1 Newton/sec (N/sec) and 0.1 N; 3 N/sec and 0.3 N; 5 N/
sec and 0.5 N (from the left to the right in the bottom traces in A and C). In the rectangular stimuli, graded velocities and magnitudes were as
follows: 50 N/sec and 0.1 N; 75 N/sec and 0.3 N; 83 N/sec and 0.5 N (from the left to the right in the bottom traces in B and D). Sustained
spike responses were elicited in this TG-SA neuron, while ON-OFF spike responses were elicited in the MTN-RA neuron. The voltage, time,and force calibrations in C were also applied in A, B and D.

Periodontal neurons in V ganglion & mesencephalic nucleus （Miyata et al.）

― 81 ―

the TG - RA and MTN - RA periodontal neurons
were unexcitable even at high intensities of
the trapezoidal mechanical stimuli （ data notshown）. As shown in Figure 5A, when the gradedrectangular mechanical stimuli were applied in
the linguolabial direction, the TG-RA and MTNFig. 4. Photomicrographs showing the recording sites (PrussianBlue spots) of the MTN-RA (A) and the TG-SA (B) periodontal
neuron illustrated in Figure 3. A, Prussian Blue spot (asterisk) was
located at the termination of the electrode track 2 (Tr 2) within
the MTN. A large oval cell body of another primary afferent MTN
neuron was seen just at the lower left of the spot. B, Prussian Blue
spot (asterisk) was found in the rostrocentral part of the TG. LC,
locus coeruleus; scp, superior cerebellar peduncle; Op, ophthalmic
nerve; Mx, maxillary nerve; Md, mandibular nerve. Scale bar, 1 mm
for A and B.

candidate for this TG-SA periodontal neuron.
As shown in Figure 3 A - D, the MTN - RAperiodontal neuron did not respond at all unlessthe incisor was stimulated by the rectangularmechanical stimuli applied more rapidly than 50
N/sec. The response of the MTN-RA neuron to
linguolabially applied stimuli was only one ON-

OFF spike. It was noted that the rectangularmechanical stimuli in the reverse （labiolingual）
direction produced a very similar ON-OFF spike
whose appearance was a mirror image of the ONOFF spike evoked by the linguolabially applied
stimuli. Figure 4 shows the histological verificationof recording sites of the TG-SA and the MTN-RA
periodontal neuron illustrated in Figure 3.
In this study, a small number of spontaneously
active SA units （ three ） were obtained in the
TG of three rats. In common with these units,a spontaneous spike discharge at about 60 Hz
increased to about 130 Hz while the trapezoidal
mechanical stimuli were being applied in the
linguolabial direction, whereas the spontaneous
spike discharge completely disappeared while
the trapezoidal stimuli were being applied in thelabiolingual direction（not illustrated）.
Figure 5 is a typical record of the combinationof a TG-RA and an MTN-RA periodontal neuron,
which was the most frequently encounteredcombination in this study （9 / 19 rats ）. BothRA periodontal neurons responded with a patternof ON-OFF spikes, similar to the response of the
MTN-RA periodontal neuron illustrated in Figure

3. As seen in Figure 5A, the ON spike responses of

the TG-RA periodontal neuron were characterized
by a burst consisting of about 15 spikes within
50-msec duration, which presented an appearanceof a tapered delta shape because the spike size
decreased exponentially with time. The numberof spikes increased with the increase in stimulus
intensity.
When an extremely shortened and weakened（8-msec duration and 0.03 N magnitude）rectangularmechanical stimulus（tapping）was applied in the
linguolabial direction, this TG - RA periodontal
neuron produced a brief ON spike response alone
consisting of a burst of five spikes with 20-msec
duration（Fig. 5B）. We therefore suspected thatthe waning event of the amplitude of the spikeburst was not due to transmission of the mechanicalvibration to the recording microelectrode after the
tooth-tapping, but rather it was a characteristic of
the generation mechanism of the action potentials
from this burst-type TG-RA neuron. Furthermore,
the possibility of a multiunit recording waseliminated following the waveform analysis of ahigh-speed trace. Six of the 17 TG-RA neurons
examined displayed such burst-type spike
responses.
The rectangular mechanical stimuli applied in thereverse（labiolingual）direction produced ON-OFF
spike responses in both the TG - RA and MTN -RA periodontal neurons（Fig. 5C）. Waveforms ofthese ON-OFF spike responses corresponded tothose in which the ON-OFF spike responses to the
linguolabially applied stimuli interchanged theirpositions（Fig. 5A, C）.
Both the TG and the MTN are collections of

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Fig. 5. Responses of a TG-RA and an MTN-RA periodontal neuron in the same rat. Both RA neurons were unexcitable even at high intensitiesof trapezoidal tooth-pressing stimuli, but showed ON-OFF spike responses to rectangular stimuli (A-C). B, when an extremely shortened andweakened (8 msec duration and 0.03 N magnitude) rectangular tapping was applied linguolabially, a brief ON spike response alone was elicitedin the TG-RA neuron. This ON spike response was characterized by a high-frequency burst of five spikes within 20-msec duration. The
waveform of ON and OFF spike responses were interchanged mutually according to the change of the direction of tooth-pressing. Note thatthe direction of rectangular tapping signal (second trace from bottom) is reversed in B.

cell bodies of primary trigeminal afferent neurons.
In the rat MTN, there are numerous cells ranging
in size from 200 to 300 µm in diameter, clusteringwith soma - soma contacts 12 , 13）. In the rat TG,
intraganglionic synapses have become a focus ofattention14,15）. In the present study, there wereseven rats in which the activity of two periodontal
single units was recorded simultaneously by one
microelectrode inserted into the TG （6 rats ）or MTN （2 rats ）. When two periodontal single

Periodontal neurons in V ganglion & mesencephalic nucleus （Miyata et al.）― 83 ―

Fig. 6. Simultaneous recordings of an SA and an RA periodontal neuron through respective microelectrodes placed in a rat’s TG and MTN.
(A, B) Both TG-SA and MTN-SA neurons exhibited a clear directional sensitivity and responded with vigorous sustained spike discharges
exclusively to linguolabially applied tooth-pressing, whereas vigorous continuous spike responses were abolished by labiolingually applied
tooth-pressing (C, D). In contrast, large-amplitude TG- and MTN-RA neurons responded with ON-OFF spikes to both linguolabially andlabiolingually applied rectangular tooth-pressings. Voltage, time, and force calibrations in B apply to A, C and D.

― 84 ―

units were caught in the same microelectrode,the activity of each unit was identified from its
waveform in a stationary state of a high - speed
trace on the memory oscilloscope.
Figure 6 shows the simultaneous recordingsof an SA and an RA periodontal neuron throughrespective microelectrodes placed in the TG and
MTN of the same rat. The MTN-SA periodontal
neuron is one of the three which were obtained
from the MTN of all animals （ see Table 1）.
There was a strong resemblance in the response
characteristics of the SA and RA periodontal
neurons between the TG and MTN. Both the TGSA and MTN-SA periodontal neurons exhibited

prominent directional preference, and respondedwith a continuous spike activity exclusively to the
linguolabially applied mechanical stimuli （ Fig.
6A, B）, whereas the labiolingually applied stimuli
abolished the sustained spike activity in bothneurons, and evoked an OFF spike in the TG-SA
periodontal neuron（Fig. 6C, D）.
The continuous spike responses of the TG SA and MTN-SA periodontal neurons were more

remarkable as to the total number of evoked spikes
and the discharge frequency to the trapezoidal
than to the rectangular mechanical stimuli withthe same magnitude（Fig. 6A, B）. The maximum
frequency of the SA spike activity amounted to
120 Hz and 70 Hz in the MTN and TG periodontal
neurons, respectively, during the trapezoidal
mechanical stimulation at 5 N/sec velocity and
0.5 N magnitude; it decreased to 83 Hz and 40 Hz,
respectively, during the rectangular stimulation at
83 N/sec velocity and 0.5 N magnitude（Fig. 6A, B）.
This MTN SA periodontal neuron showed greater
maximum discharge frequency compared to the
TG-SA periodontal neurons illustrated in Figures
3 and 6 . In addition, the MTN - SA periodontal
neuron was slightly high - threshold, and thus it
could not respond to the trapezoidal as well as therectangular mechanical stimuli with the smallest
magnitude.
As seen in Figure 6B and D, both the TG-RA
and MTN-RA periodontal neurons responded with

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ON - OFF spikes exclusively to the rectangularmechanical stimuli in both directions. Although thiswas the same event as that illustrated in Figure 5A
and C, a substitution of the waveforms of the ON-

OFF spike responses arose between the linguolabial
and labiolingual stimulations（Fig. 6B, D）. Suchan exchange of ON and OFF spike responses
would be effective to provide sensory information
about changing the direction of forces delivered
to the maxillary incisor. The TG-RA periodontal
neuron in Figure 6B was the same as the TG-RA
periodontal neuron in Figure 5 regarding its ON
discharge of a brief burst of high-frequency spikes
in response to the linguolabially applied stimuli.

Discussion
We observed an absolute majority of the RAtype periodontal neurons in the MTN comparedto the TG （P < 0.05, see Table 1）. Taking into
consideration that an excessive dynamic loading
as steep as 75 N/sec was used as the criterion forclassifying the neurons as the RA versus SA type,the above result provides further evidence thatthe rat MTN periodontal neurons may be involved
in information transmission of the displacement
velocity and the vibration delivered to the incisor３）.
We found six TG-RA periodontal neurons which
exhibited a brief repetitive spike discharge of highfrequency in response to a slight tapping applied
linguolabially. Unlike the TG - SA periodontal
neurons probably supplying the Ruffini - like
corpuscles in the lingual periodontal ligament １,11）,
these burst-type TG-RA neurons were devoid of
directional sensitivity, and they responded to boththe linguolabially and labiolingually applied stimuli.
In addition, the burst - type TG - RA periodontal
neurons were so sensitive to mechanical transientsthat they could not respond at all unless the incisor
was stimulated more rapidly than 50 N/sec.
Any discussion concerning the nature of theperiodontal receptors innervated by the burst type TG-RA periodontal neurons must of course
be speculative. However, there are two candidates
for this periodontal receptor. Although thePeriodontal neurons in V ganglion & mesencephalic nucleus （Miyata et al.）existence of Pacinian corpuscles in the periodontal
ligament has been denied 16）, an unknown burst type mechanoreceptor resembling Pacinian
corpuscles（which are activated best by 60 - 300-

Hz vibration17））might exist in the rat periodontall i g a m e n t . B e r k o v i t z a n d S h o r e ’ s （ 1 9 7 8 ）1 8 ）ultrastructural observation in the periodontal
ligament of the rat incisor has referred tothe presence of lamellar, knob - like, neuralterminations where single myelinated nerve fibers
are surrounded by bundles of small myelinatedfibers in close apposition. Such structures are
generally similar to those reported by Bonnaud etal.（1978）19） in the cat and by Harris and Griffin（1974）20） in humans, which were described by
Bonnaud et al.19） as resembling the structure ofPacinian corpuscles.
Another candidate for the burst-type periodontal
receptor might be included in the nociceptive
category with the greatest response to damaging
stimuli. Unfortunately, there is little publishedinformation regarding nociceptive afferents in
the rat periodontal ligament, although a studyof the feline periodontal ligament is available21）.
We are planning further experiments to clarify
the structural and functional properties of theperiodontal receptors innervated by the newly
identified burst-type TG neurons.
The direction in which a rat maxillary incisor
is pressed has been reported to determine
the production of the excitatory or inhibitory
periodontal - masseteric reflex （ PMR ）22 , 23）. In
the excitatory PMR, a linguolabial tapping on
the maxillary incisor induced a fast transient
electromyographic （EMG） activity and asubsequent tonic EMG activity in the ipsilateral
masseter muscle22）. As seen in Figure 6B, the earlytransient RA and the following tonic SA spike
discharges in the TG-RA and TG-SA periodontal
neurons bear a close resemblance to the EMG
pattern of the excitatory PMR. In particular,
repetitive excitatory inputs of the large-amplitude
ON spikes from the burst - type TG - RA neuron
would be the most advantageous to evoke the early― 85 ―

transient excitation in the masseteric motoneurons.
On the other hand, the existence of the inhibitory
PMR was disclosed from the finding thatlabiolingual pressing on the rat maxillary incisor
induced an inhibition of ongoing spontaneous EMG
activity in the ipsilateral masseter muscle23）. Thisphenomenon could be explained from our findingthat the labiolingually applied tooth - pressing
completely depressed the spontaneous spike
discharge in the three spontaneously active TG-SA
neurons, in contrast to the linguolabially applied
tooth-pressing, which resulted in a facilitation of
the spontaneous spike activity. These properties
may be a reflection of the direction of occlusal
forces during masticatory movements.

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Periodontal neurons in V ganglion & mesencephalic nucleus （Miyata et al.）

― 87 ―

ラット三叉神経節および三叉神経中脳路核において同時記録された一次歯根膜機械受容ニューロンの単一歯台形状
および矩形状機械刺激に対する応答特性
宮
河

田
岸

重

茂１・天
則４・吉

九州歯科大学１

仁一朗１・里賢 一５・林

野
野

田

隆
恵

博２・村
子１・西

田
川

（旧）摂食神経科学分野；４総合科学分野；５口腔保健管理学講座

貴
泰

俊３
央６

２

広島大学大学院口腔健康科学講座
３

鶴見大学歯学部探索歯学講座
６

大阪歯科大学生理学講座

抄録

歯根膜機械受容器は三叉神経節および三叉神経中脳路核の一次求心性ニューロンによって二重支配されている。単一歯に加えた実験的制御力に対する同一動物の三叉神経節および中脳路核の一次歯根膜機械受容ニューロンの単一ユニット応答を同時記録した。具体的には、人工呼吸を施したネンブタール麻酔・パンクロニゥム非動化ラットの右側
上顎切歯に二等辺台形状または矩形状機械刺激を舌唇または唇舌方向に加えている間に、同側三叉神経節および中脳路核において電気生理学的に同定した一次歯根膜機械受容ニューロンから同時に単一ユニット記録を行った。27匹のラットから54個の単一ユニットが記録された。それらのユニットは舌唇方向に加えた基準の矩形状機械刺激（刺激の大きさ＝0.3 Newton、刺激速度＝75 N/sec、ランプタイム＝4 msec、プラートタイム＝400 msec）
に対する応答に基づいて速順応性あるいは遅順応性歯根膜ニューロンに分類された。中脳路核には三叉神経節に比べて統計学的に有意に多数の速順応性歯根膜ニューロンが存在した(P < 0.05)。遅順応性および速順応性歯根膜ニューロンの応答特性は三叉神経節と中脳路核間で非常に類似していた。舌唇方向に加えた台形状および矩形状刺激は三叉神経節、中脳路核両方の遅順応性歯根膜ニューロンに活発な持続するスパイク発射を誘発するのに反して、反対方向（唇舌方向）に加えた台形状および矩形状刺激はいかなる遅順応性応答も誘発しなかった。両方向に加えた矩形状刺激は三叉神経節と中脳路核両方の速順応性歯根膜ニューロンに高閾値のオン-オフ・スパイク応答を誘発した。著者らはまた、未だ報告のないバースト型歯根膜ニューロンを発見した。その応答性は、両方向に加えた軽いタッピングに応答して短い反復性の高頻度スパイク発射を示すという特徴を持っていた。記録した17個の三叉神経節の速順応性ニューロンのうち、６個がこのバースト型ニューロンであった。以上の結果から、ラットの咀嚼サイクルの咬断期に急速に繰り返されるchoppingあるいは chiselling動作は、中脳路核と三叉神経節の両方からの豊富な歯根膜入力に起因する一過性で強力な歯根膜・咬筋反射をもたらすと考えられる。
キーワード：一次歯根膜ニューロン／三叉神経節／三叉神経中脳路核／同時記録/ ラット