Comparison of short-latency trigeminal evoked potentials elicited by painful dental and gingival stimulation

Opioid and Endocannabinoid System in Orofacial Pain

Orofacial pain disorders are frequent in the general population and their pharmacological treatment is difficult and controversial. Therefore, the search for novel, safe and efficient analgesics is an important but still elusive goal for contemporary medicine. In the recent years, the antinociceptive potential of endocannabinoids and opioids has been emphasized. However, concerns for the safety of their use limit their clinical applications. the possibility of modulating the activity of endocannabinoids by regulation of their synthesis and/or degradation offers an innovative approach to the treatment of pain. A rat model of trigeminal pain, utilizing tongue jerks evoked by electrical tooth pulp stimulation during perfusion of the cerebral ventricles with various neurotransmitter solutions can be used in the pharmacological studies of nociception in the orofacial area. The aim of this review is to present the effects of pharmacological activity of opioids and endocannabinoids affecting the transmission of the sensory information from the orofacial area on the example of trigemino-hypoglossal reflex in rats.

Electrophysiology of Cranial Nerve Testing: Trigeminal and Facial Nerves

The clinical examination of the trigeminal and facial nerves provides significant diagnostic value, especially in the localization of lesions in disorders affecting the central and/or peripheral nervous system. The electrodiagnostic evaluation of these nerves and their pathways adds further accuracy and reliability to the diagnostic investigation and the localization process, especially when different testing methods are combined based on the clinical presentation and the electrophysiological findings. The diagnostic uniqueness of the trigeminal and facial nerves is their connectivity and their coparticipation in reflexes commonly used in clinical practice, namely the blink and corneal reflexes. The other reflexes used in the diagnostic process and lesion localization are very nerve specific and add more diagnostic yield to the workup of certain disorders of the nervous system. This article provides a review of commonly used electrodiagnostic studies and techniques in the evaluation and lesion localization of cranial nerves V and VII.

Effects of centrally administered endocannabinoids and opioids on orofacial pain perception in rats

BACKGROUND AND PURPOSE

Endocannabinoids and opioids play a vital role in mediating pain-induced analgesia. The specific effects of these compounds within the orofacial region are largely unknown. In this study, we tried to determine whether an increase in cannabinoid and opioid concentration in the CSF affects impulse transmission between the motor centres localized in the vicinity of the third and fourth cerebral ventricles.

EXPERIMENTAL APPROACH

The study objectives were realized on rats using a method that allows the recording of the amplitude of evoked tongue jerks (ETJ) in response to noxious tooth pulp stimulation. The amplitude of ETJ was a measure of the effect of neurotransmitters on neural structures.

KEY RESULTS

Perfusion of cerebral ventricles with anandamide (AEA), endomorphin-2 (EM-2), URB597, an inhibitor of fatty acid amide hydrolase (FAAH) and JZL195, a dual inhibitor of FAAH and monoacylglycerol lipase (MAGL) reduced the ETJ amplitude. The antinociceptive effect of AEA, EM-2, URB597 and JZL195 was blocked by CB₁ receptor antagonist, AM251 and by μ receptor-antagonist, β-funaltrexamine. In contrast to AEA, 2-arachidonoylglycerol alone did not decrease ETJ amplitude.

CONCLUSIONS AND IMPLICATIONS

We demonstrated that in the orofacial area, analgesic activity is modulated by AEA and that EM-2-induced antinociception was mediated by μ and CB₁ receptors. The action of AEA and EM-2 is tightly regulated by FAAH and FAAH/MAGL, by preventing the breakdown of endogenous cannabinoids in regions where they are produced on demand. Therefore, the current findings support the therapeutic potential of FAAH and FAAH/MAGL inhibitors as novel pharmacotherapeutic agents for orofacial pain.

Analysis of trigeminal nerve disorders after oral and maxillofacial intervention

Background

Quantitative sensory testing (QST) is applied to evaluate somatosensory nerve fiber function in the spinal system. This study uses QST in patients with sensory dysfunctions after oral and maxillofacial surgery.

Methods

Orofacial sensory functions were investigated by psychophysical means in 60 volunteers (30 patients with sensory disturbances and 30 control subjects) in innervation areas of the infraorbital, mental and lingual nerves. The patients were tested 1 week, 4 weeks, 7 weeks and 10 weeks following oral and maxillofacial surgery.

Results

QST monitored somatosensory deficits and recovery of trigeminal nerve functions in all patients. Significant differences (p < 0.05) between control group and patients were shown for cold, warm and mechanical detection thresholds and for cold, heat and mechanical pain thresholds. Additionally, QST monitored recovery of nerve functions in all patients.

Conclusion

QST can be applied for non-invasive assessment of sensory nerve function (Aβ-, Aδ- and C-fiber) in the orofacial region and is useful in the diagnosis of trigeminal nerve disorders in patients.

Somatosensory evoked potentials of inferior alveolar nerve

PURPOSE

The use of inferior alveolar nerve somatosensory evoked potentials may represent an objective means of evaluating sensory nerve function in the maxillofacial region. The aim of this work was to confirm the existence of a standard sequence of prominent events in the trigeminal somatosensory evoked potentials (TSEPs) of inferior alveolar nerve (IAN) waveform, examine those components and their normal variability by statistical analysis, and discuss TSEPs' nervous origin and some patterns of TSEPs' abnormalities due to dysfunctional nerves.

MATERIALS AND METHODS

TSEPs were obtained following electrical stimulation (square wave pulses 0.2 millisecond [ms] in duration, 4 to 6.5 mA, 0.7/second repetition rate, 200 averages) of the gum at the mental foramen level via intraoral surface electrodes and recorded from the contralateral central scalp sites.

RESULTS

We successfully recognized steady waveforms of sufficient quality and consistently recorded a "W"-shaped response: latency onset and peak of the initial deflection of positive polarity were approximately 12 ms and 20 ms, respectively. Negative and positive deflections followed with respective peak latencies at around 26 ms and 36 ms. One side of the lower lip can be compared with the contralateral side and patients may serve as their own control in cases of unilateral nerve injury. The anaesthetic block showed the total abolition of responses. Reproducible TSEP waveform was only obtained during nerve stimulation and not during masseter muscle stimulation.

CONCLUSIONS

TSEPs, obtained with the present technique, may represent an objective, low-invasive, and reliable way of testing sensory nerve function in the maxillofacial region.

Pharmacokinetic-pharmacodynamic modelling of the analgesic effect of alfentanil in the rat using tooth pulp evoked potentials

The purpose of the present study was to develop an animal model for the investigation of the concentration-effect relationship of alfentanil using tooth pulp evoked potentials (TPEP). Six chronically instrumented, freely moving rats received a computer-controlled intravenous infusion of alfentanil resulting in seven pseudo-steady-state blood concentration levels, each maintained for 30 min. At each concentration level, the tooth pulp of the rat upper incisor was electrically stimulated in a time-randomized order with different current intensities (400-800 microA, 1 msec duration) and the electroencephalogram (EEG) was recorded concomitantly. Arterial blood samples were collected serially and assayed for alfentanil using RIA. Repetitive evoked EEG responses were averaged per stimulus intensity and per session. The decrease of the area under the negative peak 15 msec after stimulation (% of preadministration value) was used as pharmacological endpoint. The concentration-TPEP effect of alfentanil was investigated by nonlinear mixed effect modeling (NONMEM). When the observed TPEP effect was plotted versus the alfentanil blood concentration no hysteresis or proteresis was observed, and the two could directly be related to each other on the basis of the sigmoidal Emax pharmacodynamic model. The (population) pharmacodynamic estimates were (+/-S.E.): Emax = 108 +/- 10%, EC50 = 24 +/- 17 ng/ml, Hill factor = 0.81 +/- 0.37. A large interindividual variability for EC50 (omegaEC50) of 164 +/- 107% was observed. The residual variability was 14 +/- 10%. It is concluded that the TPEP is a useful tool for the systematic investigation of the concentration-analgesic effect relationship of centrally acting analgesics in the freely moving rat.

Non-invasive trigeminal evoked potentials: normative aging data

A mild electric shock applied to the lower lip was used to elicit reliable evoked potentials from the trigeminal nerve in 50 normal adults who ranged in age from 20 to 69 years. The waveforms were morphologically similar to those observed with invasive procedures. No substantial effects for subject age, side of stimulation, or recording electrode were obtained for any of the individual trigeminal evoked potential amplitudes or latencies. Female subjects tended to have somewhat larger amplitudes and shorter latencies than male subjects. The results suggest that non-invasive procedures produce reliable evoked potential measures of trigeminal nerve function for patients of all ages.

Laser evoked brain potentials in response to painful trigeminal nerve activation

Long latency brain potentials were evoked by infrared laser stimuli (LEPs) applied to the right forehead in order to activate the thinnest cutaneous A-delta afferents of the upper branch of the trigeminal nerve thus inducing a painful sensation. Ten healthy male subjects participated in 4 identical subsequent sessions, one week apart, receiving 4 blocks of 40 stimuli each. This way the individual trigeminal LEPs, as well as their inter- and intraindividual reliability were determined. Five major components could be identified, denoted by polarity and peak latencies: N150, P230, N300, P360, N480. The LEP waveforms were found to be highly stable within subjects, peak latencies varied by less than 5%. Great variation in waveform appeared amongst subjects, peak latencies varied by more than 15%. The last two components exhibited the largest variability and were not identified in all subjects.

Chemo-somatosensory event-related potentials in response to repetitive painful chemical stimulation of the nasal mucosa

The aim of the study was to investigate how chemo-somatosensory event-related potentials (CSSERPs) and pain ratings are modified by repetitive painful stimulation of the nasal mucosa (58% v/v CO2, 200 msec duration). Twenty-two subjects performed 3 experiments during which trains of stimuli were applied. The interstimulus interval (ISI) between stimuli was constant for each experiment, but varied between experiments (8, 4, and 2 sec). CSSERPs were obtained from 5 positions (Fz, C3, Cz, C4, and Pz). The subjects not only rated the overall perceived intensities but also reported the quality of the stimuli. At an ISI of 8 sec estimates decreased and only stinging sensations were reported. In contrast, at an interval of 2 sec estimates increased being accompanied by the buildup of burning pain. This phenomenon was interpreted in terms of the superposition of first (sharp and stinging pain: A delta fibers) and second pain (dull and burning pain: C fibers), respectively. However, given the special circumstances of short ISIs CSSERP amplitudes decreased the more the shorter the ISI was. In line with previous investigations it is hypothesised that CSSERPs predominantly reflect nociceptive information transmitted via A delta fibers.

The trigeminal evoked potential: Part I. Long-latency responses in awake or anesthetized subjects

Trigeminal evoked potentials have been elicited with differing methodologies that render responses almost as numerous as the number of laboratories reporting them. Forty-six trigeminal nerves were studied to investigate trigeminal evoked potentials in 20 awake, normal subjects and 20 patients undergoing surgery with general anesthesia. A comparison was made between different methods of surface stimulation and subdermal stimulation. It was concluded that these techniques had no practical use in intraoperative monitoring.

Short latency trigeminal evoked potentials: normative data and clinical correlations

A very short latency trigeminal evoked potential (STEP) to electrical stimulation of the upper lip has been recorded from over the scalp. This potential consists of 5 distinct peaks within the 12 msec range. Normative data were obtained from 25 healthy volunteers. The impact of the stimulus rate and intensity on the response was studied in each subject. These results were compared to those of 19 patients suffering from lesions involving the trigeminal system in its peripheral aspect or the brain-stem. The STEP was consistently abnormal whenever the involved side was stimulated. Changes in peak latencies and in interpeak latency differences (IPLD) correlated well with clinical and radiological findings and improved with the removal of the offending lesion. The STEP proved to be a reliable method for evaluating the trigeminal system in its peripheral and central pathways; it may thus serve as an additional parameter for studying brain-stem functions.