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Biomedical subjects

Alain Woda

Publications and source records attributed to Alain Woda.

13 recordsLinked to original sources
PubMed2006

The challenge of mastication: preparing a bolus suitable for deglutition.

The main function of mastication is to transform a solid food into a bolus that can be swallowed safely. The bolus characteristics such as particles size or cohesiveness, are continuously sensed during mastication and they are important in initiating deglutition. This study examined the following question: What is the condition of the bolus just before swallowing? Ten subjects with normal dentition aged 37.5 +/- 3.7 years were asked to chew without swallowing six different foods (three nuts and three vegetables) while the number of cycles and the duration of the sequence were recorded. The particle size distribution shown by the expectorated food bolus just before swallowing was examined by image analysis. The results showed that, for a given food, the sizes of the bolus particles just before swallowing were comparable in all subjects. However, the number of cycles and duration of the sequence varied between subjects. Taken together these data strongly suggest that the granularity of the bolus before swallowing has to reach a predetermined state which is obtained by using an individual chewing strategy. This suggests that the bolus structure reflects a key factor for homeostasis and explains the large interindividual variability of the mastication physiologic parameters.

Adult↗
PubMed2005

Activity of masticatory muscles in subjects with different orofacial pain conditions.

The existence of a pathophysiological link between tonic muscle activity and chronic muscle pain is still being debated. The purpose of this retrospective, controlled study was to evaluate the electromyographic (EMG) activity of masticatory muscles in subjects with different orofacial pain conditions. The temporal and masseter EMG activity at rest and the masseteric reflex were recorded in two groups of patients with either myofascial pain (n=33) or neuropathic pain (n=20), one group of non-pain patients with disc derangement disorders (n=27) and one control group of healthy, asymptomatic subjects (n=32). The EMG activities of both muscles at rest were significantly higher in the pain patient groups compared to the asymptomatic control group. There was no significant difference between the disc derangement disorder group and the control group. The masseteric reflex amplitude was reduced in all patient groups when compared with the control group. In pain patient groups, the increased EMG activity at rest and the reduction of the masseteric reflex amplitude were equally distributed in the pain and non-pain sides. In addition, subjects presenting with bilateral pain showed higher EMG activity at rest than those with unilateral pain. These results suggested that the modulation of muscle activity was not the direct consequence of a peripheral nociceptive mechanism and seemed to indicate that a central mechanism was at work. The contrast between the increased EMG activity at rest and the reduction of the masseteric reflex amplitude may reflect modulations of motoneurones that differed in tonic versus phasic conditions in chronic pain patients.

Adolescent↗
PubMed2005

Towards a new taxonomy of idiopathic orofacial pain.

There is no current consensus on the taxonomy of the different forms of idiopathic orofacial pain (stomatodynia, atypical odontalgia, atypical facial pain, facial arthromyalgia), which are sometimes considered as separate entities and sometimes grouped together. In the present prospective multicentric study, we used a systematic approach to help to place these different painful syndromes in the general classification of chronic facial pain. This multicenter study was carried out on 245 consecutive patients presenting with chronic facial pain (>4 months duration). Each patient was seen by two experts who proposed a diagnosis, administered a 111-item questionnaire and filled out a standardized 68-item examination form. Statistical processing included univariate analysis and several forms of multidimensional analysis. Migraines (n=37), tension-type headache (n=26), post-traumatic neuralgia (n=20) and trigeminal neuralgia (n=13) tended to cluster independently. When signs and symptoms describing topographic features were not included in the list of variables, the idiopathic orofacial pain patients tended to cluster in a single group. Inside this large cluster, only stomatodynia (n=42) emerged as a distinct homogenous subgroup. In contrast, facial arthromyalgia (n=46) and an entity formed with atypical facial pain (n=25) and atypical odontalgia (n=13) could only be individualised by variables reflecting topographical characteristics. These data provide grounds for an evidence-based classification of idiopathic facial pain entities and indicate that the current sub-classification of these syndromes relies primarily on the topography of the symptoms.

Adult↗
PubMed2005

Mechanisms associated with unusual orofacial pain.

This article presents an overview of possible mechanisms associated with pain perception, with a specific focus on understanding unusual manifestations of orofacial pain associated with nerve insult. It includes recent evidence concerning neurobiological changes that occur in the periphery at tissue and nerve sites, or within the central nervous system, and that may involve chemical and inflammatory responses, sensitization, or alterations of cellular function. Moreover, the contribution of the autonomic nervous system, changes in emotional reactivity and vigilance, the roles of high brain centers such as the basal ganglia (nigro-striatal) system, and the influence of aging and gender, are briefly described.

Afferent Pathways↗
PubMed2004

Topical clonazepam in stomatodynia: a randomised placebo-controlled study.

Stomatodynia is characterised by a spontaneous burning pain in the oral mucosa without known cause or recognised treatment. The purpose of this double-blind, randomised, multicentre parallel group study was to evaluate the efficacy of the topical use of clonazepam. Forty-eight patients (4 men and 44 women, aged 65+/-2.1 years) were included, of whom 41 completed the study. The patients were instructed to suck a tablet of 1 mg of either clonazepam or placebo and hold their saliva near the pain sites in the mouth without swallowing for 3 min and then to spit. This protocol was repeated three times a day for 14 days. The intensity was evaluated by a 11-point numerical scale before the first administration and then after 14 days. Two weeks after the beginning of treatment, the decrease in pain scores was 2.4+/-0.6 and 0.6+/-0.4 in the clonazepam and placebo group, respectively (P = 0.014). Similar effects were obtained in an intent-to-treat analysis (P = 0.027). The blood concentration of clonazepam was similar whether it was measured 14 days after sucking a tablet three times a day or during the 5 h that followed sucking a single tablet (n = 5). It is hypothesised that clonazepam acts locally to disrupt the mechanism(s) underlying stomatodynia.

Administration, Topical↗
PubMed2004

Bidirectional modulation of windup by NMDA receptors in the rat spinal trigeminal nucleus.

Activation of afferent nociceptive pathways is subject to activity-dependent plasticity, which may manifest as windup, a progressive increase in the response of dorsal horn nociceptive neurons to repeated stimuli. At the cellular level, N-methyl-d-aspartate (NMDA) receptor activation by glutamate released from nociceptive C-afferent terminals is currently thought to generate windup. Most of the wide dynamic range nociceptive neurons that display windup, however, do not receive direct C-fibre input. It is thus unknown where the NMDA mechanisms for windup operate. Here, using the Sprague-Dawley rat trigeminal system as a model, we anatomically identify a subpopulation of interneurons that relay nociceptive information from the superficial dorsal horn where C-fibres terminate, to downstream wide dynamic range nociceptive neurons. Using in vivo electrophysiological recordings, we show that at the end of this pathway, windup was reduced (24 +/- 6%, n = 7) by the NMDA receptor antagonist AP-5 (2.0 fmol) and enhanced (62 +/- 19%, n = 12) by NMDA (1 nmol). In contrast, microinjections of AP-5 (1.0 fmol) within the superficial laminae increased windup (83 +/- 44%, n = 9), whereas NMDA dose dependently decreased windup (n = 19). These results indicate that NMDA receptor function at the segmental level depends on their precise location in nociceptive neural networks. While some NMDA receptors actually amplify pain information, the new evidence for NMDA dependent inhibition of windup we show here indicates that, simultaneously, others act in the opposite direction. Working together, the two mechanisms may provide a fine tuning of gain in pain.

Action Potentials↗
PubMed2004

Influence of age on adaptability of human mastication.

The objective of this work was to study the influence of age on the ability of subjects to adapt mastication to changes in the hardness of foods. The study was carried out on 67 volunteers aged from 25 to 75 yr (29 males, 38 females) who had complete healthy dentitions. Surface electromyograms of the left and right masseter and temporalis muscles were recorded simultaneously with jaw movements using an electromagnetic transducer. Each volunteer was asked to chew and swallow four visco-elastic model foods of different hardness, each presented three times in random order. The number of masticatory cycles, their frequency, and the sum of all electromyographic (EMG) activity in all four muscles were calculated for each masticatory sequence. Multiple linear regression analyses were used to assess the effects of hardness, age, and gender. Hardness was associated to an increase in the mean number of cycles and mean summed EMG activity per sequence. It also increased mean vertical amplitude. Mean vertical amplitude and mean summed EMG activity per sequence were higher in males. These adaptations were present at all ages. Age was associated with an increase of 0.3 cycles per sequence per year of life and with a progressive increase in mean summed EMG activity per sequence. Cycle and opening duration early in the sequence also fell with age. We concluded that although the number of cycles needed to chew a standard piece of food increases progressively with age, the capacity to adapt to changes in the hardness of food is maintained.

Adaptation, Physiological↗
PubMed2003

[Neurobiology of trigeminal pain].

The brainstem trigeminal complex integrates somatosensory inputs from orofacial areas and meninges. Recent studies have shown the existence of a double representation of pain within the brainstem, at the level of both caudalis and oralis subnuclei. Noxious messages are mainly conveyed by C-fibers that activate the subnucleus caudalis neurons. These neurons in turn activate the subnucleus oralis whose neurons share similar features with the deep spinal dorsal horn neurons. In contrast with the nearness of the laminar organization of the dorsal horn, the vertical organization of the trigeminal complex offers an easier access for the study of segmental mechanisms of nociceptive processing. This model allowed us to show the existence of subtle NMDA-related mechanisms of segmental nocious processing. The trigeminal complex conveys nociceptive messages to several brainstem and thalamic relays that activate a number of cortical areas responsible for pain sensations and reactions. Cortical processing is sustained by reciprocal interactions with thalamic areas and also by a direct modulation of their pre-thalamic relays. The dysfunction of these multiple modulatory mechanisms probably plays a key role in the pathophysiology of chronic trigeminal pain.

Afferent Pathways↗
PubMed2002

Influence of impaired mastication on nutrition.

It has been suggested that people who suffer from impaired masticatory function may adapt food consistency to their oral status (which may lead to deficient nutrient intake) or rely on the digestive system to compensate for the lack of oral preparation of food (which may increase the likelihood of digestive diseases and decrease gut absorption). Masticatory deficiency thus may be detrimental to health. This article reviews evidence of the effects of masticatory deficiency on nutrition. The selection of relevant literature was based on Medline queries using the following key words: mastication, nutrition, digestion, diet, and disease risk. Earlier work not listed in Medline but related to the subject also was reviewed. Only publications available in English were selected for inclusion. It is difficult to draw conclusions from many of the reviewed studies due to issues related to study design, confounding variables, and the subjective nature of the measurements. In particular, data supporting a link between masticatory function and deficient dietary intake often are based on relatively weak correlations and cannot confer a causal relationship.

Animals↗
PubMed1995

Evidence for a peripheral origin of the tonic nociceptive response to subcutaneous formalin.

The orofacial formalin test in the rat is a valid and reliable model of nociception and is sensitive to various classes of analgesic drugs. The noxious stimulus consists in an injection of diluted formalin (2.5% in saline) into the upper lip. The behavioural nociceptive response is measured in terms of the amount of time the animal spends rubbing the injected area. Two distinct periods of intense rubbing activity can be identified, a first phase occurring in the first 3 min and a second phase lasting from 12 to 39 min after formalin injection. The present study verified the peripheral origin of the first phase of the formalin response and examined whether the second phase is produced by peripheral activation of afferent fibres and/or by a phenomenon of central facilitation induced by the neural activity that occurs during the first phase. This was determined by assessing the effect of a local anaesthetic agent (lidocaine) administered into the formalin injection site, before or after the first phase of the formalin response. Local injection of 50 microliters of lidocaine prior to formalin completely abolished the first phase of the formalin response but this blockade did not significantly influence the appearance and development of the second phase. Thus, the primary afferent activity that normally occurs during the first phase of the formalin response is not a prerequisite for the expression of the second phase. A higher dose of lidocaine (150 microliters) induced, in addition, inhibition of the first part of the second phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1995

The orofacial formalin test in rats: effects of different formalin concentrations.

In this study of the orofacial formalin test in rats, the effects of different formalin concentrations (0.2%, 0.5%, 1.5%, 2.5%, 5% and 10%) on the behavioural nociceptive response (face rubbing) was investigated. The histological responses of the skin were also evaluated. Increasing the concentration of formalin caused a parallel aggravation of histological signs of tissue inflammation and injury. All concentrations provoked an early phase of nociceptive response, but its intensity was not concentration-dependent. The 2nd phase of response to formalin only occurred for concentrations of 1.5% and higher. A positive relationship between the formalin concentration and the amplitude of the rubbing activity measured between 12 and 45 min after injection could be observed until 2.5% but with the highest concentrations (5 and 10%), the amplitude of the response decreased. Our findings indicate that the orofacial formalin test should be carried out using concentration between 0.5 and 2.5%. This is essential to assess increase as well as decrease in pain intensity. Moreover, this will have the effect of minimizing the suffering of the experimental animal.

Animals↗