Biomedical subjects

Peter Svensson

Publications and source records attributed to Peter Svensson.

At least 19 recordsLinked to original sources

PubMed2007

What can human experimental pain models teach us about clinical TMD?

Human experimental pain (HEP) models applied to the orofacial area have been widely used over the last decades and several reviews are available on the interaction between HEP and jaw-motor function. In this selective review some of the possibilities and limitations with HEP models are discussed based on the current experience with HEP models. For example, it is appropriate to consider how closely HEP models may mimic the clinical phenomenon, i.e., do they represent a reasonable "proxy" of temporomandibular disorders (TMD) and what can HEP models offer for the understanding of jaw-motor function in relation to painful TMD conditions. Finally, are there any clinical implications of the knowledge derived from HEP studies? This present review suggests that HEP models, indeed, are valuable and can provide clinically relevant information by serving as a bridge between basic animal experiments and studies in pain populations; however, there are several caveats to this suggestion which needs to be acknowledged.

Adaptation, Physiological↗

PubMed2006

Increased muscle pain sensitivity in patients with tension-type headache.

Nociceptive mechanisms in tension-type headache are poorly understood. The aim was to investigate the pain sensitivity of pericranial muscles and a limb muscle in patients with tension-type headache. Experimental muscle pain was induced by standardized infusions of 0.5 ml of 1 M hypertonic saline into two craniofacial muscles (anterior temporalis (TPA) and masseter (MAS)) and a limb muscle (anterior tibial (TA)) in 24 frequent episodic tension-type headache patients (FETTH), 22 chronic tension-type headache patients (CTTH) and 26 age and gender matched healthy subjects. Headache patients were examined twice, both on days with and on days without headache. The pressure pain thresholds (PPTs) were determined before and after infusions. The subjects continuously reported intensity of saline-induced pain on an electronic visual analogue scale (VAS) and the perceived area of pain was drawn on anatomical maps. Headache patients demonstrated significantly lower PPTs, higher saline-evoked VAS pain scores and greater pain areas than healthy subjects at all the tested muscle sites (P<0.05). There was a significant gender difference for the PPTs in all three groups of participants (P<0.05) and for VAS pain scores in the CTTH patients (P<0.05). There was no difference in pain sensitivity between FETTH and CTTH or between patients with or without headache. In conclusion, the present study demonstrates the presence of generalized pain hypersensitivity both in FETTH and CTTH compared to controls which is unrelated to actual headache status and extends to include responses to longer-lasting stimuli which are clinically highly relevant. Gender differences in deep pain sensitivity seem to be a consistent finding both in healthy controls and patients with tension-type headache.

Female↗

PubMed2006

Differential effect of intravenous S-ketamine and fentanyl on atypical odontalgia and capsaicin-evoked pain.

Atypical odontalgia (AO) is an intraoral pain condition of currently unknown mechanisms. In 10 AO patients and 10 matched healthy controls, we examined the effect of intravenous infusion of an N-methyl-D-aspartate (NMDA) receptor antagonist S-ketamine and a mu-opioid agonist fentanyl on spontaneous AO pain and on an acute intraoral nociceptive input evoked by topical application of capsaicin. The drugs were administered in a randomized, placebo-controlled, cross-over manner. Furthermore, measures of intraoral sensitivity to mechanical and thermal quantitative sensory testing (QST) including temporal summation were compared between groups and sides. Both drugs failed to produce an analgesic effect on spontaneous AO pain, but fentanyl effectively reduced capsaicin-evoked pain. AO patients showed increased sensitivity to capsaicin and heat pain, but no significant differences in cold and mechanical sensitivity compared with healthy controls. No side-to-side differences in QST measures were found in AO patients. The present study demonstrates that AO is unlikely to be primarily due to a persistent afferent barrage from the peripheral region. Furthermore, in contrast to studies on various neuropathic pain conditions, fentanyl and S-ketamine in the present doses failed to attenuate AO pain.

Adult↗

PubMed2006

Validation of a musculo-skeletal model of the mandible and its application to mandibular distraction osteogenesis.

Mandibular distraction osteogenesis will lead to a change in muscle coordination and load transfer to the temporomandibular joints (TMJ). The objective of this work is to present and validate a rigid-body musculo-skeletal model of the mandible based on inverse dynamics for calculation of the muscle activations, muscle forces and TMJ reaction forces for different types of clenching tasks and dynamic tasks. This approach is validated on a symmetric mandible model and an application will be presented where the TMJ reaction forces during unilateral clenching are estimated for a virtual distraction patient with a shortened left ramus. The mandible model consists of 2 rigid segments and has 4 degrees-of-freedom. The model was equipped with 24 hill-type musculotendon actuators. During the validation experiment one subject was asked to do several tasks while measuring EMG activity, bite force and kinematics. The bite force and kinematics were used as input for the simulations of the same tasks after which the estimated muscle activities were compared with the measured muscle activities. This resulted in an average correlation coefficient of 0.580 and an average of the Mean Absolute Error of 0.109. The virtual distraction model showed a large difference in the TMJ reaction forces between left and right compared with the symmetric model for the same loading case. The present work is a step in the direction of building patient-specific mandible models, which can assess the mechanical effects on the TMJ before mandibular distraction osteogenesis surgery.

Adult↗

PubMed2006

Effects of subcutaneous administration of glutamate on pain, sensitization and vasomotor responses in healthy men and women.

The present study aimed to investigate if (1) subcutaneous injection of glutamate induces pain, sensitization and vasomotor responses in humans and (2) if sex differences exist in these responses. Thirty healthy volunteers (men-15 and women-15) were included. Each subject received four subcutaneous injections (0.1ml; glutamate 100, 10, 1mM and isotonic saline 0.9%) into the forehead skin in two sessions separated by one week. Assessments of pain intensity (VAS), quality, distribution; area of pinprick hyperalgesia; pressure pain threshold (PPT) at the injection site; surface skin temperature and local blood flow were performed at predetermined time points. The highest concentration of glutamate evoked the highest pain intensity, the longest duration of pain and the largest pain area under the VAS-time curve (P<0.001) in both men and women, although responses in women were larger than in men (P<0.05). The face-chart pain area was the largest for the highest concentration of glutamate (P<0.001) and women drew a larger pain area than men (P=0.024). The area of pinprick hyperalgesia was the largest for glutamate 100mM (P<0.001) and women indicated a larger area than men (P<0.001). Concentration-dependent local vasomotor responses were found following the subcutaneous injection of glutamate but there was no sex difference in this effect. Glutamate 100mM significantly reduced the PPT values (P<0.001) without sex-related differences. The present study demonstrates for the first time that subcutaneous injection of glutamate evokes pain, vasomotor responses and pinprick hyperalgesia in human volunteers and that there are sex-related differences in some of these responses.

Adult↗

PubMed2006

Correlation and cluster analysis of sensory, pain, and reflex thresholds to various stimulus modalities in symptom-free subjects.

OBJECTIVE: In order to evaluate the possible relation between the psychophysical response and a motor reflex, sensory and pain thresholds to various stimuli were analyzed in combination with the occurrence threshold of the late masseteric exteroceptive suppression (ES2) period. METHODS: Twenty men and 20 women participated. The tactile detection threshold and the filament-prick pain detection threshold were measured on the cheek skin overlying the left masseter muscles. The pressure pain threshold and pressure pain tolerance threshold were measured at the left masseter muscle. The surface EMG was recorded from the left masseter muscle, while electrical stimuli with 13 fixed intensities were applied to the skin above the left mental nerve. The stimulation intensity at which the ES2 appeared for the first time and the lowest stimulus intensity at which the subjects reported to be painful were defined as the ES2 and pain threshold, respectively. RESULTS: There were significant positive correlations between the tactile detection threshold and the pain thresholds determined using the different stimulus modalities, and the ES2 threshold was also significantly correlated with the pain thresholds (P<0.05). Cluster analysis could significantly discriminate two distinct groups with high versus low tactile, pain and ES2 thresholds (P<0.05). CONCLUSIONS: The present findings suggested that the ES2 reflex response has a relation with the individual sensory and pain sensitivity in symptom-free subjects. SIGNIFICANCE: Combined examination of sensory, pain, and ES2 thresholds might provide complementary information on the pathophysiology underlying orofacial pain.

Adult↗

PubMed2006

Effects of muscle fatigue induced by low-level clenching on experimental muscle pain and resting jaw muscle activity: gender differences.

The purpose of this study was to investigate the effects of jaw-muscle fatigue evoked by low-level tooth-clenching followed by the induction of experimental muscle pain by injection of glutamate on the perception of fatigue and pain and on the resting electromyographic (EMG) activity. In addition, the role of gender on these interactions was studied. The EMG activities of bilateral masseter (MAL, MAR) and temporalis (TAL, TAR) muscles in 11 healthy young women and 12 men were measured before (Baseline) and after tooth-clenching for 30 min at 10% of maximal force (Post1), after subsequent glutamate (Glu) or isotonic saline (Iso) injection into the MAL following the tooth-clenching (Post2) and 60 min after tooth-clenching (Post3). The intensities of fatigue, fatigue-related muscle pain and headache-like symptoms were scored on 0-10 cm visual analog scales (VAS). The glutamate-evoked pain was continuously scored on an electronic VAS. Sustained low-level tooth-clenching consistently produced fatigue sensation, fatigue-related muscle pain and headache-like symptoms in both genders with significantly higher fatigue VAS scores in men than in women, while the accompanying increase in the resting EMG activity appears higher in women than in men in the masseter muscles. In this study no gender differences were found for the perceived amount of experimental pain induced by glutamate injection. Additional increases of the resting EMG activity after injections occurred only in men in the injected masseter muscle and non-injected temporalis muscles. The present findings provide new information on the complex influence of gender on sensory-motor integration in the trigeminal system which may contribute to differences in susceptibility to develop musculoskeletal pain problems.

Adult↗

PubMed2006

Effect of local anesthesia on atypical odontalgia--a randomized controlled trial.

The aim of the study was to evaluate the analgesic effect of lidocaine in a double-blind, controlled multi-center study on patients with atypical odontalgia (AO)--a possible orofacial neuropathic pain condition. Thirty-five consecutive AO patients (range 31-81 years) with a mean pain duration of 7.2 years (range 1-30 years) were recruited from four different orofacial pain clinics in Sweden. In a randomized cross-over design, 1.5 ml local anesthesia (20mg/ml lidocaine and 12.5 microg/ml adrenaline) or 1.5 ml saline (9 mg/ml NaCl solution) (placebo) was injected to block the painful area. The VAS pain scores showed an overall effect of time (ANOVA: P<0.001) and treatment (ANOVA: P=0.018) with a significant interaction between the factors (ANOVA: P<0.001). Overall, VAS pain relief was significantly greater at 15-120 min following the lidocaine injections compared to the placebo injections (Tukey: P<0.05). All patients demonstrated significant disturbances in somatosensory function on the painful side compared to the non-painful side as revealed by quantitative sensory tests, however, only one significant inverse correlation was found between percentage pain relief and the magnitude of brush-evoked allodynia (Spearman: P<0.01). In conclusion, AO patients experienced significant, but not complete, pain relief from administration of local anesthetics compared with placebo. The findings indicate that the spontaneous pain in AO patients only to some extent is dependent on peripheral afferent inputs and that sensitization of higher order neurons may be involved in the pathophysiology of AO.

Adult↗

PubMed2006

Blink reflexes in patients with atypical odontalgia and matched healthy controls.

Atypical odontalgia (AO) is an orofacial pain condition which has been suggested to involve neuropathic pain mechanisms. The aim of this study was to use a brain stem reflex to investigate craniofacial nociceptive mechanisms in AO. In 38 AO patients and 27 matched healthy controls, the R2 component of the blink reflex (BR) was elicited using a "nociceptive-specific" electrode and recorded with surface electromyography electrodes on both orbicularis oculi muscles. The BR was tested by stimulation of both sides of the face of the participants before, during, and after an intraoral pain provocation test with capsaicin. The data were analyzed with three- and four-way mixed-model analyses of variance. The root mean square value of the ipsilateral R2 (R2i) was significantly reduced in patients compared with controls (P=0.046). No differences in R2 between stimulation sides were detected in either group (P>0.757). In all participants, R2 responses and the intensity of the pain evoked by the electrical stimulus were decreased during and after application of capsaicin compared with baseline (P<0.001). In patients, R2i onset latencies were significantly prolonged compared with controls (P=0.031). The present data show disturbances in the central processing of craniofacial information and that endogenous pain inhibitory systems in AO patients and healthy controls were activated to a similar degree by an acute intraoral nociceptive input. Additional clinical research with AO patients will be needed to determine to what extent neuropathic pain mechanisms are involved in this pain condition.

Adult↗

PubMed2006

Influence of age and gender on the jaw-stretch and blink reflexes.

The aim of this study is to investigate the influence of age and gender on jaw-stretch and blink reflexes (BR). Thirty "young" (26.5+/-0.7 years) and thirty "old" (47.8+/-1.8 years) healthy adults were included. Short-latency stretch reflex responses were evoked in the masseter and temporalis muscles by fast jaw-stretches, and BR in orbicularis oculi muscle were evoked by painful electrical pulses (0.5 ms duration), delivered by a concentric electrode placed on the left lower forehead close to the supraorbital foramen. For the jaw-stretch reflex, the pre-stimulus EMG activity in the old subjects was significantly lower than that of the young subjects in the right and left masseter and temporalis muscles (P<0.006), whereas there was no difference in the results between males and females. The normalized peak-to-peak amplitude of the EMG in the left masseter and left and right temporalis muscles was significantly lower in the old subjects compared with the young subjects (P<0.02). Females had significantly higher normalized peak-to-peak EMG amplitudes compared with males in the right masseter and left temporalis muscles (P<0.05). The old subjects had significantly lower root mean square (RMS) (P=0.01) and average (P<0.02) BR values in the right and left orbicularis oculi muscles, and lower area under the curve (AUC) (P=0.02) values in the left orbicularis oculi muscle compared with the young subjects. Female subjects had significantly lower AUC (P=0.02) in the left orbicularis oculi muscle compared with males. The old subjects had significantly later offset (P<0.003) and longer duration (P<0.001) in the left orbicularis oculi compared with the young subjects. The results of the present study demonstrated a significant effect of both age and gender on stretch and BR and suggested that these variables should be taken into consideration in the interpretation of brainstem reflexes in basic and clinical studies.

Adult↗

PubMed2006

Open reduction and rigid internal fixation of mandibular condylar fractures by an intraoral approach: a long-term follow-up study of 15 patients.

PURPOSE: To evaluate the long-term results obtained with open reduction and rigid internal fixation of mandibular condylar fractures by an intraoral approach. PATIENTS AND METHODS: Fifteen patients with 24 mandibular condylar fractures were retrospectively examined with an average follow-up of 23 months (range, 6-63 months). Clinical and radiographic examination was conducted according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD), including an evaluation of maximum voluntary bite force measurements and facial nerve function. Statistical analysis was performed on maximum voluntary bite force measurements and maximum pressure pain threshold. RESULTS: Two patients fulfilled the criteria for a RDC/TMD diagnosis. Myofacial pain (group I) and bilateral arthralgia (group III), combined with a moderate nonspecific physical symptom score, was diagnosed in 1 patient and 1 patient received a diagnosis of disc displacement with reduction (group II). Satisfying radiographic fracture healing was seen in 12 joints. However, miniplate fracture occurred in 3 patients and severe bone resorption of the condylar head was seen in one patient. Minor adjustment of the postoperative occlusion was necessary in 6 patients. No significant difference between maximum voluntary isometric bite force measurements or maximum pressure pain threshold was found between the fracture side and the opposite side in unilateral cases or between the operated and nonoperated side in bilateral cases. None of the patients showed facial nerve injury or visible facial scars. CONCLUSION: Within the limitations of a retrospective study, the present study emphasized that optimal management of dislocated bilateral condylar injuries combined with other fractures of the facial skeleton constitute a challenging issue in maxillofacial trauma. Moreover, open reduction and rigid internal fixation of mandibular condylar fractures by an intraoral approach is a technically demanding surgical procedure associated with a high risk of postoperative complications in these injuries.

Adolescent↗

PubMed2006

Recalibration improves inter-examiner reliability of TMD examination.

OBJECTIVE: The purpose of this study was to assess whether recalibration of examiners would improve the reliability of gathering clinical findings and related diagnoses of temporomandibular disorders (TMD) in accordance with the Research Diagnostic Criteria for TMD (RDC/TMD). MATERIAL AND METHODS: Two clinicians independently examined a total of 48 symptomatic and asymptomatic subjects according to the RDC/TMD on two occasions: examination 1 (E1). Aarhus, Denmark (n=24; 18 female, ages 18-59 years); examination 2 (E2). Malmö, Sweden (n=24; 18 female, ages 18-86 years). The clinicians were calibrated in the use of the RDC/TMD Axis-I examination on the day before E1. Six months later, they were recalibrated on the day before E2. Intra-class correlation coefficients (ICCs) were used to examine the inter-examiner reliability of the two clinicians on the two occasions (E1, E2). RESULTS: The intra-class correlation coefficients of vertical range of jaw motion differed little between E1 and E2. At E2, all other examination components consistently improved in reliability relative to E1. Similar improvements were seen for the frequently occurring RDC/TMD clinical diagnoses: Ia. Myofascial pain [ICC = 0.83 (E1) and 1.00 (E2)], IIa. Disk displacement with reduction [ICC = 0.26 (E1) and 0.64 (E2)], and IIIa. Arthralgia [ICC = 0.16 (E1) and 0.73 (E2)]. CONCLUSION: Recalibration considerably improved inter-examiner reliability for assessing RDC/TMD clinical variables and diagnoses, which are critically dependent on reliable assessment of clinical signs; improvement was most marked when initial inter-examiner reliability was low. Final inter-examiner reliabilities after recalibration were all associated with acceptable to excellent levels.

Adolescent↗

PubMed2006

Long-lasting mechanical sensitization following third molar surgery.

AIMS: To investigate the degree and duration of neuronal hyperexcitability due to local inflammatory trauma after surgical removal of an impacted mandibular third molar. METHODS: A total of 32 healthy men (16 patients, 16 control subjects) underwent quantitative sensory tests (QST) at baseline (preoperatively) and 2, 7, and 30 days following surgical removal of a mandibular third molar. Thermal and mechanical QST was applied to the extraoral and intraoral regions as well as to the dominant forearm. RESULTS: Detection thresholds for thermal and mechanical stimuli did not change over time in patients and control subjects, but pain thresholds (thermal, pressure, electrical) in the control group increased significantly. Patients showed significantly decreased pain pressure thresholds and pressure pain tolerance (P < .05 for both) on the operated side and absence of adaptation to the tests for up to 30 days postoperatively. CONCLUSION: These results indicate that even a minor surgical procedure in the orofacial region may be sufficient to evoke hyperexcitability in an area adjacent to the surgical wound for up to 30 days. The decreased adaptive capacity in the patient group also suggests the involvement of central pain-regulatory mechanisms in response to the surgical trauma.

Adult↗

PubMed2006

Increased pain sensitivity to intraoral capsaicin in patients with atypical odontalgia.

AIMS: To use 2 well-characterized stimuli, the intraoral capsaicin model and the "nociceptive-specific" electrode, to compare superficial nociceptive function between patients with atypical odontalgia (AO) and matched healthy controls. Furthermore, the authors aimed to describe the sensitivity, specificity, and positive predictive values (PPV) of the techniques if group differences could be established. METHODS: Thirty-eight patients with AO and 27 matched healthy controls participated in this study. Thirty microliters of 5% capsaicin was applied to the gingiva on the left and right sides of all participants as a pain-provocation test. The participants scored the capsaicin-evoked pain continuously on a 0-to-10 visual analog scale (VAS). Furthermore, individual electrical sensory and pain thresholds to stimulation with a "nociceptive-specific" electrode on the facial skin above the infraorbital or mental nerve were determined. RESULTS: AO patients had higher VAS pain scores for capsaicin application than healthy controls (ANOVA: F > 4.88; P < .029). No differences between the painful sides and the nonpainful sides of the patients were found (ANOVA: F < 1.26; P > .262). No main effects of group or stimulation side on the electrical sensory and pain thresholds were detected (ANOVA: F < 0.309; P > .579). Sensitivity was 0.51; specificity, 0.81; and PPV, 0.77 when a VAS value of > or = 8 for capsaicin-evoked pain was used. CONCLUSION: AO patients show increased sensitivity to intraoral capsaicin but normal sensitivity to "nociceptive-specific" electrical stimulation of the face in an area proximal to the painful site. The use of the intraoral pain-provocation test with capsaicin as a possible adjunct to the diagnostic workup is hampered by the only moderately good sensitivity and specificity.

Analysis of Variance↗

PubMed2006

Influence of intramuscular nerve growth factor injection on the response properties of rat masseter muscle afferent fibers.

AIMS: To investigate whether local administration of nerve growth factor (NGF) decreases the mechanical threshold (MT) of putative nociceptive masseter afferent fibers as part of its mechanism of mechanical sensitization. METHODS: Electrophysiologic recordings were made from masseter afferents and a randomized, blinded approach was used to test the effects of intramuscular injection of NGF (2.5 or 25 microg/mL) into the rat masseter muscle on the MT of masseter afferents (n=65) and plasma protein extravasation. RESULTS: The plasma protein extravasation data and electrophysiological recordings indicated that rat NGF injection was not inflammatory and did not evoke afferent discharge or induce mechanical sensitization (as reflected in a decreased MT) in masseter afferents in either male or female rats. To investigate whether the lack of effect of NGF injection might be due to differences between human and rat NGF, additional experiments with human NGF injection (25 microg/mL) were undertaken. Intramuscular injection of human NGF into the rat masseter muscle also failed to evoke afferent discharges; however, it did decrease the MT of masseter afferent fibers. CONCLUSION: The finding that neither rat nor human NGF excited putative nociceptive masseter afferent fibers is consistent with a previous report that intramuscular NGF injections are not acutely painful in human subjects. The ability of human NGF injection into the rat masseter muscle to induce afferent mechanical sensitization suggests that this experimental approach may be useful for the study of peripheral mechanisms of myofascial pain and tenderness associated with temporomandibular disorders.

Afferent Pathways↗

PubMed2005

A PET activation study of brush-evoked allodynia in patients with nerve injury pain.

Acute experimental brush-evoked allodynia induces a cortical activation pattern that differs from that typically seen during experimental nociceptive pain. In this study, we used positron emission tomography to measure changes in regional cerebral blood flow (rCBF) in patients with clinical allodynia. Nine patients with peripheral nerve injury were scanned during rest, brush-evoked allodynia, and brushing of normal contralateral skin. PET data were analyzed for the whole group and for single subjects. Allodynic stimulation activated the contralateral orbitofrontal cortex (BA 11) in every patient. Whereas normal brushing activated most strongly the contralateral insular cortex, allodynic brushing produced an ipsilateral activation in this area. Another important difference between normal and allodynic brushing was the absence of a contralateral primary somatosensory cortex (SI) activation during allodynic brushing. No thalamic activation was observed during allodynic or control brushing. Although no anterior cingulate cortex (ACC) activation could be demonstrated in the group analysis, single subject analysis revealed that four patients activated this region during brush-evoked allodynia. A direct post hoc comparison of brush -and allodynia-induced rCBF changes showed that allodynia was associated with significantly stronger activations in orbitofrontal cortex and ipsilateral insula whereas non-painful brushing more strongly activated SI and BA 5/7. These findings indicate that activity in the cortical network involved in the sensory-discriminative processing of nociceptive pain is downregulated in neuropathic pain. Instead, there is an upregulation of activity in the orbitofrontal and insular cortices, which is probably due to the stronger emotional load of neuropathic pain and higher computational demands of processing a mixed sensation of brush and pain.

Adult↗

PubMed2005

Ketamine attenuates glutamate-induced mechanical sensitization of the masseter muscle in human males.

The purpose of the present study was to determine whether glutamate-induced mechanical sensitization of the masseter muscle in human volunteers involves activation of peripheral N-methyl-D-aspartate (NMDA) receptors. Healthy male volunteers (n=18) participated in this randomized, two-session study. During each session, the volunteers received two injections into the right masseter muscle. An initial injection of glutamate (1 M, 0.2 ml) alone was followed 30 min later by a second injection of glutamate alone or glutamate combined with ketamine (10 mM). Pressure pain threshold (PPT) was assessed over the right masseter muscle at and 2 cm above the injection site, as well as over the right temporalis muscle and left masseter muscle prior to the first injection. The PPT was reassessed at all four sites every 5 min from 10 to 30 min after the second injection and once again 60 min after the second injection. Glutamate-evoked muscle pain, pain area and the sensory pain response index of the McGill pain questionnaire were all significantly reduced by co-injection of ketamine. The mean PPT values were significantly decreased by approximately 10%, 10, 15 and 25 min after injection of glutamate, but only over the site of injection. Co-injection of ketamine with glutamate also completely blocked the glutamate-induced mechanical sensitization 15 min post-injection as compared with glutamate alone. The lack of spread of mechanical sensitization outside the area of glutamate injection is consistent with the view that glutamate-induced mechanical sensitization results from a peripheral mechanism. The attenuation of glutamate-induced mechanical sensitization by ketamine suggests that this effect is mediated, in part, through activation of peripheral NMDA receptors.

Adult↗

PubMed2005

Gender difference in masseteric exteroceptive suppression period and pain perception.

OBJECTIVE: Use of brain stem reflexes in the assessment of orofacial function requires insight into the influence of demographic factors such as gender. The aim of this study was to characterize possible gender differences in the relation between quantitative measures of the masseteric exteroceptive suppression (ES) reflex response and pain perception evoked by incrementally increasing electrical stimulation. METHODS: In 12 men and 12 women, the surface electromyogram was recorded from the left masseter muscle. Thirteen fixed stimulus intensities from 5 to 35 mA at 2.5 mA increments were applied to the skin above the left mental nerve. The stimulation intensity at which the late ES appeared first and the first intensity at which the subjects reported the stimulus intensity to be painful were defined as the reflex threshold (RT) and pain threshold (PT), respectively. Furthermore, data were analyzed using stimulus-response curves, and the reflex appearance levels (RAL), the saturation level, the slope from appearance to saturation of the reflex (SLP), and the pain appearance level (PAL) were determined. RESULTS: The PT was equal to or higher than the RT in 9 of the 12 men, but only in 4 of the 12 women. Further, women had significantly lower PAL, RAL, and SLP (12.7 +/- 0.8, 12.9 +/- 1.4, and 3.0 +/- 0.9 mA, respectively) compared to men (20.3 +/- 1.6 mA, 16.7 +/- 1.1 T, and 4.1 +/- 0.4, respectively) (P < 0.05). CONCLUSIONS: The present results document that women have a lower reflex threshold and pain threshold to cutaneous electrical stimulation than men. SIGNIFICANCE: These findings suggest that gender differences may exist in the sensory-motor integration of primary afferent input from the orofacial region and that these differences should be considered in the design of future reflex studies.

Adult↗