Quantitative and qualitative assessment of sensory changes induced by local anesthetics block of two different trigeminal nerve branches.

OBJECTIVES: The aims were to use different techniques to assess the degree of sensory changes and magnitude of perceived size changes in the facial region induced by nerve blocks of two different trigeminal nerve branches in healthy participants. MATERIALS AND METHODS: This placebo-controlled study included 30 healthy volunteers. The participants underwent quantitative and qualitative sensory testing (QST and QualST) thrice: before, 10 min, and 2 h after mental (n = 15) and infraorbital (n = 15) nerve blocks and during control (saline) sessions. Perceived numbness, temperature changes, and perceptual distortion were also measured at all time points during the nerve block and control sessions. Differences in outcome parameters between the sessions and time points were analyzed using analyses of variance and McNemar's tests. RESULTS: There was a significant degree of sensory loss to most QST and all QualST parameters, with significant numbness and increased perceived size at the injection site 10 min and 2 h after the nerve blocks compared with saline (P < 0.030) and the baseline (P < 0.042). Two hours after the nerve blocks, the sensitivity was significantly closer to baseline than after 10 min to most of the QST parameters (P < 0.011). CONCLUSIONS: QST and QualST revealed that the nerve blocks in the orofacial region resulted in complete or partial blockade of afferent nerve fibers mediating thermal and mechanical function for more than 2 h with significant numbness and perceptual distortion. CLINICAL RELEVANCE: Both QST and QualST can provide information on the degree of blockade of afferent nerve fibers after nerve blocks in the orofacial region.

Automated assessment of intranasal trigeminal function.

BACKGROUND: The intranasal trigeminal system is a key player in the perception of intranasal airflow. Why it has not been studied very well may be due to the lack of techniques that allow for fast, reliable and inexpensive routine investigation of the system. The basis of the current study is the notion that--within limits--the intranasal trigeminal system detects the overall mass of a stimulus and not just its concentration. Thus, changing the duration of the stimulus at a given concentration has a similar effect as changing its concentration. METHODOLOGY: Ninety-nine normosmic subjects participated [48 women and 51 men; mean (range) age = 45 years (20-88 years)]. In addition, 50 patients with olfactory loss were investigated once (28 women, 22 men; mean age 58 years, SD = 14 years; age range 24-88 years; causes of olfactory loss: viral infections n = 22, head trauma n = 8, chronic sinunasal disease n = 3, idiopathic n = 17). CO2-stimuli with various durations (multiples of 50 ms) were presented through a standard bilateral nasal cannula at an interval of 10 s; stimulus duration was increased by 50 ms from one stimulus presentation to the next, until the subject pushed a button indicating a painful sensation. This was the basis for automated assessment of CO2-pain responsiveness. RESULTS: This current study had four main findings: (1) Using the new, automated device CO2 pain responsiveness can be measured reliably, (2) CO2 pain responsiveness correlates with olfactory function, (3) as with olfaction, women are more sensitive to CO2 , and CO2-pain responsiveness also correlates with aging, (4) CO2-pain responsiveness is lower in patients with olfactory loss compared to normosmic, healthy controls, even when controlling for age. CONCLUSION: We have demonstrated that the current approach is a reliable and valid measure of intranasal trigeminal function.

Pathological assessment of the nervous and male reproductive systems of rat offspring exposed maternally to acrylamide during the gestation and lactation periods - a preliminary study.

To evaluate the developmental effects of exposure to acrylamide (ACR) on the nervous and male reproductive systems, pregnant Sprague-Dawley rats were given ACR at 0, 50, 100 or 200 ppm in the drinking water from gestational day 10 to postnatal day 21 and histopathological assessment of offspring was performed at weaning and postnatal week 11. Neurotoxicity was quantitatively assessed with reference to nerve fiber density, percentages of degenerated and small caliber axons in the sciatic nerves, and numbers of aberrant dot-like structures immunoreactive for synaptophysin in the cerebellar molecular layer. Although maternal neurotoxicity was evident from 100 ppm, no changes suggestive of neurotoxicity or testicular toxicity were observed in offspring. However, lowering of body weights was dose-dependently observed from birth at the dose levels of > or =50 ppm in males and > or =100 ppm in females. Maternal malnutrition was apparent at >/=100 ppm during the lactation period. Therefore, poor lactational ACR-exposure due to maternal toxicity might account for the lack of ACR-induced offspring toxicity other than retarded body growth.

Assessment of oral trigeminal sensitivity in humans.

The aim of this prospective study was to establish a clinical test for the assessment of oral trigeminal sensitivity. Capsaicin-impregnated filter paper strips (five concentrations: 0.0001-1%) were used to measure trigeminal thresholds. The strips were placed on the anterior tongue for 10 s. Subjects were asked to report the onset of any sensory perception, quality and duration of sensory perception. Thresholds were estimated in two ways: (1) threshold (THR1) related to sensory perception and (2) intensity related threshold (THR2). The test was applied to 63 healthy subjects (mean age 40 years; 34 women, 29 men). For whole-mouth testing with capsaicin, a small but significant correlation was found between THR1 and THR2 (r (63) = 0.41). Coefficients of correlation between test and re-test were r (30) = 0.60 for THR1 and r (30) = 0.78 THR2. Neither THR1 nor THR2 indicated either side or sex-related differences. Age-related differences were only found in THR2 scores, which were lower in young subjects (<40 years). Reliable assessment of intraoral trigeminal sensitivity appears to be possible using the presently described technique.

Application, function, and effects of menthol in cigarettes: a survey of tobacco industry documents.

Menthol cigarettes are the only cigarette market category identified by use of a flavor additive and constitute more than a quarter of the overall market. Menthol also is used at reduced levels in many nonmenthol brands. Public health research has suggested patterns of use of mentholated brands as a potential explanation for the health disparities between Black (largely menthol) and White (largely nonmenthol) smokers and has explored the effects of menthol on smoker behavior, consumption patterns, and consequent delivery of smoke constituents. However, relatively few published studies have directly examined the physiological impact and function of menthol delivery in cigarettes. In this study, we review internal tobacco industry documents to assess industry research on function and effects of menthol in cigarettes. Industry documents describe a range of physiological effects of menthol, with important implications for use and consumption patterns. These effects include altered perception of tobacco smoke and its constituents via cooling, smoothing, and anesthetic effects; increased impact through stimulation of trigeminal receptors; interaction with nicotine controlling its perception, delivery, and uptake; and increased respiratory irritation and toxic effects. Further studies are needed to evaluate these findings. We conclude that the unique differences between menthol cigarettes and nonmenthol cigarettes must be considered in research, cessation treatment, and enactment of tobacco product regulations.

The effect of peripheral glycerol on trigeminal neuropathic pain examined by quantitative assessment of abnormal pain and sensory perception.

In nine patients with trigeminal neuropathic pain after nerve injury, we examined prospectively the effect of peripheral glycerol neurolysis on abnormal pain and sensory perception. In the painful facial skin area of these patients, we found increased temperature and tactile thresholds and the presence of abnormal temporal summation of pain. In seven patients, neuropathic pain was peripheral and disappeared after application of local anaesthesia at or proximal to the site of nerve injury. Neuropathic pain was central in two patients, and unresponsive to local anaesthesia applied proximal to the site of nerve injury. Six weeks after injection of glycerol proximal to the site of nerve injury, no or marginal pain relief was found in 8 patients with peripheral or central trigeminal neuropathic pain. On the other hand, in one of the patients with peripheral trigeminal neuropathic pain, glycerol was given at the site of nerve injury, and produced total pain relief for the whole observation period of 7 months. In this patient, pain relief was associated with normalisation of abnormal temporal summation of pain, which was not observed in the 8 patients with no or marginal pain relief. No further changes in temperature or tactile thresholds were found in any of the 9 patients after a single injection of absolute glycerol. Total pain relief in one of the patients probably is related to the ability of glycerol to inhibit ongoing ectopic impulse generation at the site of nerve injury. We suggest that glycerol-induced reduction of primary afferent hyperactivity may secondarily result in down-regulation of central neuronal hyperexcitability. The efficacy of application of glycerol at the site of nerve injury in patients with peripheral trigeminal neuropathic pain may warrant further investigation. However, this prospective study does not provide evidence that application of glycerol proximal to the site of nerve injury has a place in the treatment of trigeminal neuropathic pain.

Evaluation of the sensory irritation test for the assessment of occupational health risk.

Many occupational exposure limits (OELs) are based on irritation. A sensory irritation test has been developed based on trigeminal nerve stimulation in the nasal mucosa of rodents which results in a decreased respiratory frequency. The RD50, the concentration inducing a 50% decrease in the respiratory rate, was proposed for the assessment of OELs. The reproducibility within one laboratory appeared to be satisfactory, but interlaboratory differences may be larger. Intra- and interspecies differences were inconsistent. Other effects (pulmonary irritation, toxicity) may interfere with trigeminal nerve stimulation. The effects of mixed and repeated exposures (the occurrence of "sensitization" and "(cross-)tolerance") are evaluated. Severe toxicity was observed in animals exposed below the RD50 for some compounds. A quantitative evaluation with respect to human data was not possible. The suitability of the test for the assessment of an OEL is doubted. The best purpose will be as an upper range-finding study for subacute or chronic toxicity experiments.