Tooth Pulp Stimulation Research Articles

Morphine and electroacupuncture: Comparison of the effects on the cortical evoked responses after tooth pulp stimulation in rats

The effects of morphine and electroacupuncture on the cortical evoked responses after tooth pulp stimulation were investigated in rats. Morphine suppressed these responses more strongly in secondary somatosensory areas than those in primary somatosensory areas, while electroacupuncture suppressed the response to the same degree in both areas. These results might suggest that there are some differences in noxious-suppressive action between morphine and the endogenous opiates released by electroacupuncture stimulation.

Altered pain perception in hypertensive humans

Sensory and pain thresholds to electrical stimulation of tooth pulps were measured in normotensive and essential hypertensive unmedicated human subjects. In both adult and young subjects there was a significant correlation between blood pressure and pain sensitivity: hypertensives had a higher threshold for sensation of pain in the tooth-pulp test than normotensive controls. An interrelationship between blood pressure and pain regulation is suggested.

Cell responses evoked by tooth pulp stimulation above the marginal layer of the cat's trigeminal nucleus caudalis.

In cats anesthetized with urethane, all-or-nothing, synaptically evoked recordings were made from 80 separate units in the descending spinal tract of the trigeminal nerve above the left trigeminal nucleus caudalis, at depths not exceeding 50 micrometer from the surface of the medulla. The units were excited by the left upper (21), left lower (25), either (28), or only on simultaneous stimulation of both (six) canine tooth pulps. There was no somototopic distribution. The latency of responses ranged from 4 to 82 msec. For the group of 28 units excited by upper and lower tooth pulps, there was close matching of response latencies from the two teeth. An abrupt decrease in latency upon increasing stimulation strength ("jumping"), and a gradual increase in latency during repetitive stimulation at a frequency between 1 and 20 Hz ("drifting") was characteristic of most, but not all, responses. Units evoked by stimulation of the inferior dental or infraorbital nerves had similar characteristics. Stimulation of a tooth pulp at threshold for a particular unit was used to test the excitability of that unit after suprathreshold stimulation of the same or a different canine tooth pulp. Stimulation of the upper left canine tooth pulp was generally only facilitatory, while stimulation of the lower left canine tooth pulp was initially facilitatory and later inhibitory. Stimulation of the upper or lower right canine tooth pulps did not excite but could inhibit units excited by the left canine tooth pulps. There was a significant correlation between the frequency at which a unit would follow repetitive stimulation and the duration of the inhibition generated by the first of a pair of stimuli. Long inhibition was associated with poor frequency following.

Local electrical stimulation: Effective needling points for suppressing jaw opening reflex in rat

Effects of electroacupuncture on the jaw opening reflex after tooth pulp stimulation were investigated in lightly anesthetized rats. Electroacupuncture stimulation (45 Hz, 5 msec) was delivered to 8 meridian points and 6 nonmeridian ones for 15 min so as to compare the degree of suppression elicited from each point. Significant suppressive effects on the reflex were observed in the cases of Yin-Hsiang, Ho-Ku and Shou-Sanli stimulation and these effects were antagonized by naloxone. However, stimulation of Hsia-Kuan, Chu-Chih, Neiting and Taichi, although these points were reported to suppress oro-facial or dental pain in man, scarcely produced suppressive effects. On the other hand, stimulation of some nonmeridian points produced moderate analgesic effects as gauged by the jaw opening reflex. The present study revealed that specificity of the meridian points is not absolute, but relative and that Yin-Hsiang, Ho-Ku and Shou-Sanli points were fairly effective in suppressing pulp-evoked jaw opening reflex in rat, which is presumably a noxious reflex. When the jaw opening reflex was evoked by non-pulpal stimulation, electroacupuncture was less effective on the reflex.

Presynaptic inhibition of tooth pulp afferents in the trigeminal nucleus during REM sleep.

In order to find whether presynaptic inhibition of tooth pulp afferents is enhanced in any phase of sleep or wakefulness, the orthodromic mass response of the trigeminal nucleus to electrical stimulation of the ipsilateral tooth pulp and the antidromic mass response of the tooth pulp to stimulation of the trigeminal nucleus were recorded in the cat. Both responses were stable in amplitude during different phases of sleep and wakefulness. However, attenuation of the orthodromic response and augmentation of the antidromic one were sometimes observed during the burst of rapid eye movements during paradoxical sleep, suggesting that presynaptic inhibition is massively enhanced only on those occasions.

Attenuation during paradoxical sleep of signals from tooth pulp to thalamus

Quantitative evaluation of the response of thalamic neurons to tooth pulp stimulation was made in chronically prepared cats. The latency, duration and intensity of the responses were measured from the post-stimulus time histograms to estimate, from various aspects, the alteration in the responsiveness during different phases of sleep and wakefulness. During slow wave sleep, tooth pulp-evoked impulses tended to be transmitted to the thalamus in a similar or slightly higher intensity compared to wakefulness. In contrast, during paradoxical sleep the signals were often attenuated in many aspects. The results seem to be in favor of the idea that the impairment of signal to noise ratio in a variety of neuronal networks is one of the characteristics of paradoxical sleep.

Bilateral projection of canine tooth pulps to neurons of the cat sensory trigeminal complex

The sensory trigeminal nuclei of cats were explored bilaterally with tungsten microelectrodes until neurons responsive to electrical stimulation of each canine tooth pulp were located. Then, the right trigeminal ganglion was transected and exploration was resumed. Stimulation of the left teeth generated 124 single-unit responses in 34 penetrations into the brain stem and evoked field potentials in 10 others after ganglionectomy. Although both left and right nuclear complexes yielded evoked activity, unit responses were obtained more frequently and field potentials attained higher amplitudes on the left. Stimulation of the right teeth, in contrast, triggered no unit discharges and evoked no field potentials in 51 postganglionectomy nuclear penetrations. Similarly, conditioning stimuli applied to the right teeth after ganglionectomy had no effect upon the responses to test stimuli applied to the left teeth. The data corroborate previous observations that many neurons in the trigeminal complex are innervated by bilateral projections from the canine dental pulps. In addition, they provide evidence that the projection from the contralateral canines is composed of primary and higher order afferent fibers which cross the midline exclusively within the brain stem to form a medullary-pontine pulpal decussation.

Quantitative relation between the intensity of tooth pulp stimulation and the magnitude of jaw opening reflex in the rat

The stimulus-response relation in the jaw opening reflex evoked by tooth pulp stimulation, which is considered as a “pain index”, follows the power function with an exponent of about six over a range of lower stimulus intensities.

Reports of Pain After Dental Treatment, Electrical Tooth Pulp Stimulation, and Cutaneous Shock

A growing body of literature suggests that pain is a crucial factor in the development and maintenance of apprehension toward dental treatment. These findings are often at variance with dental practitioners' impressions that routine dental treatment is virtually painless. Data from this study suggest that routine dental treatment is seldom perceived by regular patients as painless but is seen as low in intensity of pain compared with mild laboratory stressors. These data are interpreted as supporting the hypothesis that dental treatment is relatively painless. However, this conclusion conflicts with data supporting the importance of pain in dental fear, and possible reasons for the discrepancy are presented.

Coupling of membrane electrical processes and contractile activity of smooth muscle cells of the anococcygeus

The effect of low frequency auricular electroacupuncture (EAP) on electromyographic responses (EMGR) of the anterior belly of the digastruc muscle, elicited by stimulation of tooth pulp was studied in cat experiments. It was shown that observed augmentation of the EMGR amplitude produced by EAP depended on tonic activation of gamma-motoneurons of the muscle. This activation directly correlated with EAP intensity. At the same time the latent period of EMGR increased by one-two synapses on account of inhibiting shorter pathways in the afferent part of the reflex arch with intensive EAP. The inhibition of EAP-induced augmentation of EMGR can be achieved by administration of small doses of barbiturates that potentiate the analgetic action of EAP.

Interactions between nucleus centrum medianum and gigantocellular nociceptive neurons

Cells in nucleus reticularis gigantocellularis (NGC) and nucleus centrum medianum (CM) are known to respond to tooth pulp stimulation, which is a nociceptive trigeminal stimulus. We examined the effect of stimulation of CM on this class of neurons in NGC. Thirty-nine percent of the 57 neurons tested were antidromically activated by stimulation of the ipsilateral CM, while 28% of the 40 neurons tested were antidromically activated from the contralateral CM. In addition, the spontaneous activity of seven NGC neurons was altered by stimulation of the ipsilateral CM, while five cells were affected by stimulation of the contralateral CM. These data suggest a complex and reciprocal interaction between neurons in NGC and CM.

A problem in electrical stimulation of incisor tooth pulp in rats

The question of can electrical stimulation of the rat lower incisor pulp with a bipolar wire electrode selectively activate the pulp nerve without excitation of nerves outside the pulp was tested. Virtually all responses recorded from the mandibular nerve to stimulation of the pulp originated from the inferior alveolar nerve trunk and the response deriving from the pulp nerve was too small to be recorded.

Effects of substance P on nociceptive and non-nociceptive trigeminal brain stem neurons

As little information is available on the chemistry of synaptic transmission in trigeminal brain stem nuclei, an iontophoretic study was done on the effects of glutamate and substance P on single neurons in trigeminal nuclei oralis and caudalis in cats anesthetized with chloralose and paralyzed. The neurons were additionally studied for their responses to natural noxious and innocuous cutaneous and intraoral stimuli as well as to bipolar stimulation of the ipsilateral and contralateral canine tooth pulps, the exposed infraorbital and superior laryngeal nerves and forepaw. Glutamate excited all units tested. Substance P also had an excitatory effect, but only on some units. The slow time course of this effect was similar to that reported in other CNS regions. Units excited by substance P were located only in nucleus caudalis, and all responded to noxious cutaneous stimuli and/or to stimulation of tooth pulp; units responding only to innocuous orafacial stimulation were not excited by substance P. Levorphanol and opioid peptides were also applied iontophoretically to some of the neurons and were found to have depressant effects on nociceptive units. The data support the possibility that substance P and endogenous opioids play a role in chemical transmission in nociceptive pathways in trigeminal nucleus caudalis. The regional specificity of substance P excitation adds support to the earlier evidence of a differential distribution of sensory inputs to nuclei oralis vs. caudalis, with facial nociceptive afferents projecting only to caudalis. The functional specificity of substance P excitation also adds to the parallels found between the dorsal horn and nucleus caudalis. In addition, the similarity between the dorsal horn and nucleus caudalis with respect to the effects of substance P and of the opioids suggests a parallel in the neurochemistry of synaptic transmission at the two levels.

Feedback loop between locus coeruleus and spinal trigeminal nucleus neurons responding to tooth pulp stimulation in the rat Neurol. 186 (1979)_133–150 : S. Igarashi, M. Sasa and S. Takaori, Brain Res. Bull., 4 (1979) 75–83

Pain: February 1980 - Volume 8 - Issue 1 - p 125-126 doi: 10.1016/0304-3959(80)90103-7

Effects of morphine on evoked potentials recorded from the amygdala by tooth pulp stimulation in cats.

Effects of intravenously administered morphine on the evoked potentials of the amygdala elicited by tooth pulp stimulation were examined in cats. The various evoked potentials were observed in regions of the amygdala such as nucleus amygdaloideus centralis (pars lateralis), nucleus amygdaloideus basalis (pars magnocellularis), nucleus amygdaloideus basalis (pars parvocellularis) and nucleus amygdaloideus lateralis. Evoked potentials were significantly decreased by morphine in four of the recorded regions. Morphine had no effect on the latency at any site of the amygdala observed. Depressant effects of morphine on evoked potentials were antagonized by naloxone in all 14 cats. This study indicates that there is a receptive field of pain in the amygdala which undoubtedly plays a role in emotion.

Electroacupuncture suppresses the cortical evoked responses in somatosensory I and II areas after tooth pulp stimulation in rat.

Rat cortical evoked responses (CERs) of the somatosensory area I and II following tooth pulp stimulation were decreased in amplitude by electroacupuncture stimulation. Suppression was more marked with the contralateral CERs than with the ipsilateral ones. Onset latencies of somatosensory II CER of both sides were lengthened after electroacupuncture stimulation.

Diazepam-induced suppression of jaw opening reflex in rats.

Effec of an i.p. injection of diazepam on the jaw opening reflex evoked by electrical stimuli applied to the tooth pulp innervated by mainly high threshold afferents and the lower lip innervated by low threshold afferents was investigated using Wistar albino rats. Small doses of diazepam, less than 2.5 mg/kg, suppressed to the same degree the jaw opening reflexes evoked by stimulation of tooth pulp or lower lip. However, when larger doses thab 5.0 mg/kg were administered, the suppression of tooth pulp-evoked jaw opening reflex was greater than that of lower lip-evoked one. In this case, the period of suppression of tooth pulp-evoked jaw opening reflex was longer than that of lower lip-evoked one. It is concluded that (1) the pain relieving effect of diazepam appears only when larger doses tha 5.0 mg/kg are administered and that (2) the pain-relieving effect lasts longer than muscle-relaxative effect of diazepam.

Difference in effects of electro-acupuncture and morphine on thalamic-evoked responses in ventrobasal complex and the posterior nuclear group after tooth pulp stimulation in the rat

Electro-acupuncture suppressed the negative deflections of the thalamic-evoked responses both in the ventrobasal complex and in the posterior nuclear group, whereas morphine suppressed almost only those in the posterior nuclear group.

Effective conditions of electroacupuncture stimulation for suppressing tooth pulp-evoked jaw-opening reflex in the rat.

The effects of electroacupuncture (EA) on the rat jaw-opening reflex elicited by tooth pulp stimulation were studied to decide the effective stimulus conditions for electroacupuncture stimulation (EAS). The present study revealed that one of the most important factors for producing a strong EA effect was the stimulus pulse-frequency and that the stimulus pulse-duration was not an essential factor for this effect. In the rat, the following stimulus conditions were very useful for the quantitative study of the EA effect. (1) Stimulation time is 15 min. (2) Stimulus pulse-frequency is 30 to 150 Hz. (3) Stimulus pulse-duration is 0.1 to 5 ms. When the EAS was applied to the Ho-Ku point under these conditions, the degree of the suppression of the jaw-opening reflex was about 50% of the control.

The effect of local periodontal anaesthesia on the maximum biting force achieved by human subjects

Experiments were performed on 15 volunteers who clenched as hard as possible on a force transducer placed between canine and premolar teeth. Clenches were maintained for 5 s and repeated every 1.5 min. Initially, 10–15 clenches were recorded to establish a reference value for maximum static biting force (MBF). Local anaesthetic (LA; 4 per cent prilocaine) was injected around the biting teeth and clenches continued until the LA wore off. The duration and depth of the anaesthesia was assessed by monopolar tooth pulp stimulation. Adequate anaesthesia was obtained in 10 subjects; forces achieved during LA were greater than both pre-LA forces and also forces measured in unanaesthetized control subjects. Increases in force were most marked towards the end of the clench. The increase in MBF may be due to block of inhibitory pathways from the periodontium to elevator motoneurones, or to more complex mechanisms involving the cerebral cortex.