Effects of NMDA and MK-801 injected into the substantia nigra pars reticulata on jaw movements evoked by dopamine D1-/D2 receptor stimulation in the ventrolateral striatum: studies in freely moving rats.

The effects of NMDA and MK-801 injected into the substantia nigra pars reticulata on jaw movements evoked by dopamine D1/D2 receptor stimulation in the ventrolateral striatum were examined in freely moving rats, by using a magnet-sensing system combined with intracerebral drug microinjection technique. Bilateral injections of a mixture of SKF 82958 (5 microg) and quinpirole (10 microg), agonist at dopamine D1 and D2 receptors respectively, into the ventrolateral striatum elicited repetitive jaw movements. Bilateral injections of NMDA (0.01 and 0.05 microg/0.2 microl in each side) into the substantia nigra pars reticulata, which alone did not produce jaw movements, reduced the repetitive jaw movements evoked by the dopamine D1/D2 receptor agonist mixture in a dose-dependent manner. Injection of the non-competitive NMDA receptor antagonist, MK-801 (0.1 and 0.5 microg/0.2 microl in each side), into the substantia nigra pars reticulata, which alone did not produce jaw movements, prevented the dopaminergic jaw movements in a dose-dependent manner. Moreover, other behaviors such as grooming, rearing, yawning, vacuous chewing, and locomotor activity that occurred after injections of the dopamine receptor agonist mixture were not significantly altered by the bilateral injections of NMDA or MK-801 into the substantia nigra pars reticulata. Given our previous results showing that both agonist and antagonist of GABA(A) receptors injected into the substantia nigra pars reticulata inhibit the jaw movements elicited by dopamine D1/D2 receptor stimulation in the ventrolateral striatum, the present results suggest that there are complex functional interactions between NMDA and GABA(A) receptors within the substantia nigra pars reticulata that may be responsible for the common profiles in the effects of NMDA and GABA(A) receptor agents.

Denture wearing during sleep doubles the risk of pneumonia in the very elderly.

Poor oral health and hygiene are increasingly recognized as major risk factors for pneumonia among the elderly. To identify modifiable oral health-related risk factors, we prospectively investigated associations between a constellation of oral health behaviors and incident pneumonia in the community-living very elderly (i.e., 85 years of age or older). At baseline, 524 randomly selected seniors (228 men and 296 women; mean age, 87.8 years) were examined for oral health status and oral hygiene behaviors as well as medical assessment, including blood chemistry analysis, and followed up annually until first hospitalization for or death from pneumonia. During a 3-year follow-up period, 48 events associated with pneumonia (20 deaths and 28 acute hospitalizations) were identified. Among 453 denture wearers, 186 (40.8%) who wore their dentures during sleep were at higher risk for pneumonia than those who removed their dentures at night (log rank P = 0.021). In a multivariate Cox model, both perceived swallowing difficulties and overnight denture wearing were independently associated with an approximately 2.3-fold higher risk of the incidence of pneumonia (for perceived swallowing difficulties, hazard ratio [HR], 2.31; and 95% confidence interval [CI], 1.11-4.82; and for denture wearing during sleep, HR, 2.38; and 95% CI, 1.25-4.56), which was comparable with the HR attributable to cognitive impairment (HR, 2.15; 95% CI, 1.06-4.34), history of stroke (HR, 2.46; 95% CI, 1.13-5.35), and respiratory disease (HR, 2.25; 95% CI, 1.20-4.23). In addition, those who wore dentures during sleep were more likely to have tongue and denture plaque, gum inflammation, positive culture for Candida albicans, and higher levels of circulating interleukin-6 as compared with their counterparts. This study provided empirical evidence that denture wearing during sleep is associated not only with oral inflammatory and microbial burden but also with incident pneumonia, suggesting potential implications of oral hygiene programs for pneumonia prevention in the community.

Relationship between jaw muscle volume and craniofacial form.

To study the relationship between craniofacial form and jaw muscle function, we evaluated 25 adult male subjects with Obstructive Sleep Apnea (age, 30-61 years; weight, 58-122 kg) on the basis of CT scans obtained for routine diagnostic purposes. All scans were obtained with the Frankfort horizontal plane at right angles to the floor; each CT slice was 8 mm thick. Masseter and medial pterygoid muscle outlines were traced, digitized, and stored, and three-dimensional reconstructions were made for calculation of muscle volume. Lateral cephalometric radiographs were analyzed for quantification of selected craniofacial variables. Significant correlations could not be identified between physiological apnea variables and jaw muscle volume. An intersubject variability in masseter muscle volume was identified (range, 22.4-38.1 cm3). Medial pterygoid muscle volume revealed more variability (range, 7.4-15.2 cm3). Masseter muscle volume had a negative correlation with mandibular plane and gonial angle, and a positive correlation with posterior face height, ramus height, posterior face length, condylar center to first molar point length, gonion to pterygomaxillary fissure length, and the ramus height/anterior face height ratio. Medial pterygoid muscle volume showed a positive correlation with posterior face height, ramus height, posterior face length, and the lengths between condylar center to first molar contact point, gonion to pterygomaxillary fissure, and antegonion to key ridge. Subjects with large masseter and medial pterygoid muscle volumes had flat mandibular and occlusal planes, and small gonial angles.

Measurement of dopamine receptor-mediated jaw movements by a magnet-sensing system in freely moving rats.

This study tested a system for monitoring jaw movements in freely moving rats. A Hall-effect transducer was fixed to the skull in order to sense voltage changes induced by variations in the position of a magnet fixed to the mandible. By measuring dopamine receptor-mediated jaw movements, this system produces data comparable to that obtained using a light-sensitive transducer system in anesthetized rats, while also measuring the vertical component of jaw movements in freely moving rats. In combination with conventional visual observation, this system may provide a useful tool for assessing movements of the orofacial region during spontaneous and drug-evoked behavior.

Evidence that angiotensin II enhances apomorphine-induced jaw movements via AT1 receptors in the ventrolateral striatum: studies by magnet-sensing system in freely moving rats.

The role of angiotensin AT(1) receptors in the ventrolateral striatum in modulating apomorphine-induced jaw movements was studied using a magnet-sensing system combined with an intracerebral drug microinjection technique in freely moving rats. Bilateral injections of angiotensin II (1 and 2 micro g/0.2 micro l in each side) into the ventrolateral striatum, which alone did not significantly elicit jaw movements, dose-dependently enhanced apomorphine (1 mg/kg i.v.)-induced repetitive jaw movements. The enhancement of apomorphine-induced jaw movements by angiotensin II (2 micro g) was dose-dependently antagonized by the angiotensin AT(1) receptor antagonist losartan (15 and 30 mg/kg i.p.), given 3 h before, while losartan (30 mg/kg i.p.) alone did not significantly affect the apomorphine (1 mg/kg)-induced jaw movements. These results indicate that angiotensin II enhances apomorphine-induced jaw movements via stimulation of angiotensin AT(1) receptors located in the ventrolateral striatum.

The influence of craniofacial form on bite force and EMG activity of masticatory muscles. VIII-1. Bite force of complete denture wearers.

Today, Japan as a society is aging. The average life expectancy of Japanese people is approximately 80 years. One result of this is that preservation of masticatory functions in elderly people has become increasingly important from the viewpoint of quality of life. In the future, the use of dentures in facilitating masticatory functions as a substitute for teeth that are lost during the aging process will assume greater significance. Accordingly, appropriate evaluation and judgment of complete dentures for edentate jaws is crucial. This study was designed to elucidate the effects of the craniofacial form in complete denture wearers on the mode of activity of gnathic functions. First, subjects wearing complete dentures in both the upper and lower jaws were instructed to carry out vertical clenching, and bite force direction was determined. These data were then related to the subject's craniofacial morphology. These results suggest that the bite force direction in complete denture wearers is not affected by gender differences, but is closely associated with lateral craniofacial morphology, and that appropriate setting of occlusal plane and the occluded vertical dimension is extremely important in the preparation of complete dentures.