The effect of monosodium glutamate on parotid salivary flow in comparison to the response to representatives of the other four basic tastes.

Parotid salivary flow was recorded from eight fit and healthy subjects using modified Lashley cups connected to an instantaneous flow meter in response to gustatory stimuli. The gustatory stimuli were monosodium glutamate (MSG), sodium chloride, sucrose, magnesium sulphate and citric acid. Stimuli were applied for 30 s, and repeated after the flows had returned to baseline following the rinse. Subjects were a significant source of variation for salivary response to each different test stimuli (p<0.001). The normalised salivary flow showed a strong correlation to concentration for all test stimuli (p<0.0001). The parotid salivary flow to MSG (umami) showed a dose-dependant response in which both Na(+) and glutamate ions contributed. The overall order of relative salivary flow responses from highest to lowest flows was citric acid (sour)>MSG (umami)>NaCl (salt)>sucrose (sweet)>=magnesium sulphate (bitter). The relative responses of the peak salivary flows showed the same ordered relation. The peak salivary flow provided a greater contribution to the response to citric acid, NaCl and MSG compared to the response to sucrose and magnesium sulphate.

Superior vena cava Doppler flow velocity patterns in pericardial disease.

Doppler superior vena cava (SVC) flow patterns were studied in 34 patients with pericardial disease and in 8 normal adults; the pulse transducer on the echocardiographic instrument was used for respiratory monitoring, rather than a separate nasal thermistor-based device. First expiratory SVC diastolic flow velocities (Dfe) did not differ in normal subjects and patients with hemodynamically insignificant pericardial effusions (23 +/- 3 cm/s and 29 +/- 13 cm/s, difference not significant). Dfe were less than 15 cm/s only in the 14 patients with cardiac tamponade (9 +/- 3 cm/s, p less than 0.01). A ratio of systolic to diastolic flow velocity less than or equal to 1.1 in the first expiratory beat distinguished constrictive pericarditis from all other groups (p less than 0.01), although not from restrictive cardiomyopathy. Expiratory ablation of diastolic SVC flow mimicking cardiac tamponade was not observed in constrictive pericarditis. Respiratory variation in SVC flow velocities was slight in normal subjects and patients with constrictive pericarditis, increased in patients with hemodynamically insignificant pericardial effusions (p less than 0.01) and greatest in patients with cardiac tamponade (p less than 0.01). Quantitative analysis of SVC flow velocity patterns is a useful addition to the echocardiographic evaluation of pericardial disease.

The physical properties of conventional and resin-modified glass-ionomer dental cements stored in saliva, proprietary acidic beverages, saline and water.

Specimens of three conventional and one resin-modified glass-ionomer cement were prepared for both compressive strength and biaxial flexure strength determination. They were stored either in neutral media (water, saline, unstimulated whole saliva or stimulated parotid saliva) or in acidic beverages (apple juice, orange juice or Coca-Cola) for time periods ranging from 1 day to 1 year. In neutral media, the compressive and biaxial flexural strengths of all cements studied showed similar results, with significant increases apparent in compressive strengths at 6 months and which continued to 1 year, but no significant differences between the media; and no significant differences with time for biaxial flexure strength in all media. These findings show that interactions of these cements with saliva, which are known to result in deposition of calcium and phosphate, do not affect strength. Results for specimens stored in Coca-Cola were the same as for those stored in neutral media. By contrast, in orange and apple juice specimens underwent severe erosion resulting in dissolution of the conventional glass-ionomers after 3-6 months, and/or significant loss of strength at 1-3 months. Erosion of the resin-modified glass-ionomer, Vitremer, led to a significant reduction in strength, but not in dissolution, even after 12 months. The chelating carboxylic acids in these fruit juices were assumed to be responsible for these effects.

The roles of periodontal ligament mechanoreceptors in the reflex control of human jaw-closing muscles.

Controlled mechanical stimuli were applied to an upper central incisor tooth in 19 human subjects and the resulting reflexes in the ipsilateral masseter muscle were examined electromyographically. In most cases the force profile of the stimuli consisted of a ramp leading to a sustained plateau at an intensity of 1 N. In addition 1 N tap stimuli were employed in some subjects. The 1 N ramp stimuli with a rise time of < or = 20 ms consistently evoked a single, short-latency (approximately 12 ms), inhibitory reflex which was often followed by an excitatory wave. The ramp stimuli with shorter rise times produced larger responses than those produced by ramp stimuli with longer rise times. By contrast the tap stimuli elicited a sequence of responses consisting of inhibitory-excitatory-inhibitory-excitatory components. The first inhibitory and excitatory responses evoked by tap stimuli had latencies similar to those of the responses evoked by the ramp stimuli. The latencies of the inhibitory responses evoked by 1 N ramps with rise times ranging between 2.5 and 20 ms did not vary significantly with the rise time. Consistent with this observation it was found that the median threshold force for evoking the short-latency inhibitory reflex was only 0.25 N. This was significantly less than the threshold for the excitatory response (median: 0.75 N). The responses to ramp-plateau forces were not dependent on the level of preloading of the tooth (at least within the range tested: < 0.25 to 1 N). These findings provide evidence that mechanoreceptors in the periodontal ligament contribute to the control of human jaw-closing muscles, notably to short-latency reflex responses. It may be concluded that the additional reflex responses produced by tapping stimuli result from the activation of receptors elsewhere due to vibration.

Mesencephalic innervation of the vibrissal follicle-sinus complex in the mouse embryo.

Peripheral projections of neurones whose cell bodies lie in the mesencephalic nucleus of the fifth cranial nerve, situated between the central grey and mesencephalic reticular formation, were studied in mouse embryos aged between day 9 and 15 and in postnatal day 1 mice. Nonspecific neural antibody staining allowed visualisation of the developing cranial nerves, in particular the descending mesencephalic tract. This facilitated successful dissection of the descending mesencephalic tract and trigeminal ganglion in the heads of fresh mouse embryos and postnatal mice. The fluorescent dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil), was injected into the descending mesencephalic tract in mouse embryos aged 12.5, 13.5 and 15 days of gestation and also into postnatal day 1 mice. Following a period of incubation, 100 microm sections were viewed under visible light and episcopic fluorescence. Mesencephalic neurones were observed to pass superiorly over the trigeminal ganglion and enter the maxillary division to innervate vibrissal follicle-sinus complexes, whilst none was observed innervating mandibular and maxillary intraoral structures. There was no fluorescent labelling in non-Dil injected control specimens. Using a highly specific neuronal tracer, this study shows that mesencephalic neurones in the periphery project exclusively to follicle sinus complexes in the developing mouse embryo and remain at least until postnatal day 1. These observations, contrary to those made in other animals, indicate a species specificity of mesencephalic peripheral projections.

Angiogenesis in human dental pulp following orthodontic tooth movement.

The pulpal response to orthodontic force is thought to involve cell damage, inflammation, and wound healing. These situations are likely to be associated with the release of angiogenic growth factors. We therefore investigated human dental pulps to determine if angiogenic changes could be detected after orthodontic force application. Fifteen premolar teeth were treated with straight-wire fixed orthodontic appliances for two weeks, and comparisons were made with 15 untreated control premolar teeth from the same subjects. The teeth were extracted and sectioned. The pulps were removed, divided into 1-mm sections, embedded in collagen, and cultured in growth media for up to four weeks. Cultures were examined daily, by light microscopy, for growth and number of microvessels. Apparent microvessels were observed within five days. Confirmation of microvessel identification was by electron microscopy for endothelial cell morphology. There were significantly greater numbers of microvessels at day five and day ten of culture in the pulp explants from orthodontically treated teeth compared with those from the pulps of control teeth. These results are consistent with the hypothesis that there is an increase in angiogenic growth factors in the pulp of orthodontically moved teeth.

The effect of odours on stimulated parotid salivary flow in humans.

We have previously shown that smell has no effect on resting parotid salivary flow in humans. In this study we investigated the effect of two odours on unilateral parotid salivary flow stimulated by either mastication or mastication with gustation. Neither odour stimulated flow above that elicited by either mastication or mastication with gustation. Removing an odour by sealing the nares has been reported to reduce stimulated parotid salivary flow, suggesting that smell contributes to stimulated salivary flow. However, in the present study, sealing the nares with a nose clip caused a significant reduction in the saliva elicited by an odourless stimulus. Even placing the nose clip over the bridge of the nose without sealing the nares significantly reduced the salivary flow, suggesting that the nose clip itself causes a reduction in stimulated parotid salivary flow. In conclusion, smell has no effect on stimulated parotid salivary flow in humans.

Is there a parotid-salivary reflex response to fat stimulation in humans?

The perception of fats in foods may involve gustatory, olfactory or textural cues. There is contradictory evidence as to whether the orosensory perception of fat is as a basic quality of taste or related to the physical characteristics of fat. A dose-response reflex parotid-salivary secretion has, however, been shown for the accepted basic taste qualities. The aim of this study was to establish whether varying fat concentration in two food types causes an associated dose-response reflex parotid secretion in humans. Parotid salivary flow was recorded using Lashley cups and cannulae connected to an instantaneous flow meter. Gustatory stimuli were achieved using 3 ml of skimmed (0.1% fat), semi-skimmed (1.7% fat) or full (3.6% fat) milk (Sainsbury) or 5 g of extra-light (5% fat), light (16% fat) or original (24% fat) cream cheese (Kraft). No significant differences in salivary flow rate were shown within the milk group (n=10, P=.93) or within the cream-cheese group (n=11, P=.82). Furthermore, no correlation was observed between increasing fat concentration and flow within either the milk (P=.98) or the cream-cheese group (P=.69; Pearson Product Moment Correlation). These results do not support the hypothesis that there is a fat-specific dose-response parotid reflex.

A "Border-Line detector" for recording locomotory activities of animals.

A T.V. Border-Line detector is described for making automatic long-term records of locomotory activity of animals.The apparatus is used in combination with a closed T.V. system. A video recorder is switched on for some seconds at the moment an animal passes a fictitious detection line corresponding with a scanning-line of a T.V.-picture.

A comparative physiological and morphological study of periodontal ligament mechanoreceptors represented in the trigeminal ganglion and the mesencephalic nucleus of the cat.

A correlative morphological study was carried out on two electrophysiologically identified and located periodontal ligament mechanoreceptors in anaesthetised cats. One mechanoreceptor had its cell body in the mesencephalic nucleus and the other had its cell body in the trigeminal ganglion. Physiological recordings were made from each of their cell bodies. The two receptors were located by punctate and electrical stimuli in the labial aspect of the periodontal ligament of the left mandibular canine tooth. Both receptors had similar positions relative to the tooth apex and fulcrum and were situated in the labial part of the ligament in each tooth. The receptor loci were marked, and these regions were studied in a series of semi-thin and ultra-thin sections. Only Ruffini nerve endings were observed under each ink mark. Both Ruffini nerve endings branched, were unencapsulated and were incompletely surrounded by terminal Schwann cells with extensions projecting towards collagen bundles. The results indicate that periodontal ligament mechanoreceptors with cell bodies in the mesencephalic nucleus and those with their cell bodies in the trigeminal ganglion can both be Ruffini nerve endings. Furthermore, there was no apparent morphological difference between the two periodontal ligament mechanoreceptors.

A possible explanation for the response characteristics of multi-tooth periodontal ligament mechanoreceptors in the cat.

During the course of a study on the morphology of periodontal ligament mechanoreceptors it was observed that a direct relation, without intervening bone, existed between the mandibular canine and first premolar tooth roots in the cat. An area, representing a window in the alveolar septal bone, extended 2-3 mm from the apex towards the tooth crown. Ruffini nerve terminals were observed amongst the collagen bundles in the ligament between the roots of the two teeth. Light and electron microscopy were used to identify the receptors. It is proposed that a periodontal ligament mechanoreceptor can respond to forces applied to adjacent teeth; movement of both teeth need not occur. This may explain the observation made in the past that single periodontal ligament mechanoreceptors respond to forces applied to more than one tooth.

The effects of sympathetic trunk stimulation on the position and mobility of the canine tooth of the cat.

The effects of cervical sympathetic trunk stimulation on the position of the maxillary canine tooth and its movements in response to mechanical loading were studied using an ultrasonic transit time technique. Stimulation of the ipsilateral sympathetic trunk for 10-60s and frequencies between 1 and 20 Hz caused both longitudinal and transverse movements of the tooth. Bilateral carotid occlusion caused negligible movements in either direction. When a controlled force was applied in the palatal direction, sympathetic stimulation caused a labial shift of the tip of the tooth and usually an increase in the load-induced palatal displacement; i.e. the mobility of the tooth was increased and appeared to be dependent on the amount of labial shift of the tooth. It is concluded that interference with the vascular component has little, if any, direct effect on the tooth mobility.

The response characteristics of mechanoreceptors related to their position in the cat canine periodontal ligament.

The relation between threshold, adaptation properties and position of these receptors was studied in anaesthetized cats. Electrophysiological recordings were made from functionally single fibres teased from the inferior alveolar nerve as forces were applied to the tip of the left mandibular canine tooth. Receptors were located within the periodontal ligament by paring away the overlying bone. Threshold and adaptation properties were related to the receptor position relative to the fulcrum and apex of the tooth. These results support the hypothesis that there is only one type of periodontal-ligament mechanoreceptor, and that their response characteristics depend on position.

The effect of rate of force application on the threshold of periodontal ligament mechanoreceptors in the cat canine tooth.

Mechanical stimuli in the form of ramp-plateau forces were applied to the tip of the crown of the left mandibular canine tooth in cats anaesthetized with alpha-chloralose. Electrophysiological recordings were made from functionally single fibres teased from the inferior alveolar nerve. The force threshold was determined for 34 periodontal ligament mechanoreceptors at different controlled rates of force application. Force threshold was dependent on the rate of force application to the crown tip. Rate sensitivity was present for all receptors across the range from rapidly to slowly adapting; the degree of rate sensitivity was graded according to the adaptation rate of the receptor. The results suggest that the velocity of mechanical stimulus application to teeth needs to be considered in studies involving periodontal mechanoreceptor responses and their reflexes.

The effect of tooth extraction on periodontal ligament mechanoreceptors represented in the mesencephalic nucleus of the cat.

When a force is applied to a tooth, mechanoreceptors in the periodontal ligament are stimulated. When teeth are extracted the remnants of the periodontal ligament break down and disappear, but it is not known what happens to the mechanoreceptor neurones that innervated it. The present study seeks to determine the effect of tooth extraction on the population of periodontal ligament mechanoreceptor neurones represented in the mesencephalic nucleus of the fifth cranial nerve. The incisor and canine teeth were extracted from adult cats; terminal experiments were performed between 7.5 months and 2 yr later. Recordings were made in the mesencephalic nucleus with microelectrodes, and neurones were identified in the inferior alveolar nerve that previously innervated the periodontal ligament of one of the extracted mandibular teeth. The majority of these neurones responded only to electrical stimuli applied to the edentulous ridge of the mandible in the area where the incisor or canine teeth had previously been. It was not possible to stimulate them mechanically, despite the use of large forces. A small number had reinnervated new soft-tissue sites. They could be mechanically stimulated and were found adjacent to the area in which the mandibular incisor and canine teeth had been. Thus the population of periodontal ligament mechanoreceptor neurones represented in the mesencephalic nucleus do not all degenerate after tooth extraction. As the majority of those still present do not appear to reinnervate new tissues in which they can be mechanically stimulated, it is unlikely that they have any functional role after tooth loss.

The effect of vibration on the discharge of periodontal ligament mechanoreceptors to controlled loading of the cat canine tooth.

This study observes the maximum 1:1 following frequencies of these mechanoreceptors, as well as their response characteristics before and after vibratory stimuli. Mechanical stimuli were applied to the tip of the crown of the left mandibular canine tooth in cats anaesthetized with alpha-chloralose while recordings were made from functionally single fibres teased from the inferior alveolar nerve. Vibratory stimuli were applied at various frequencies and durations at twice the threshold to that stimulus. Controlled ramp-plateau forces were applied before and after the period of vibration. A temporary rise in the receptor discharge was recorded and the threshold to ramp-plateau stimuli fell to about one-third of its original value. The increased post-vibration response was dependent on the frequency and duration of the stimulus. It is suggested that vibration has some temporary effect on the receptor environment.

Vascular endothelial growth factor, fibroblast growth factor 2, platelet derived growth factor and transforming growth factor beta released in human dental pulp following orthodontic force.

OBJECTIVE: The release of four diffusible angiogenic growth factors in human dental pulp following orthodontic force was investigated by using neutralising growth factor antibodies (NAs), individually and in four different combinations to block their effects. This study investigated if increasing the number of NAs (anti h vascular endothelial growth factor (VEGF), anti h fibroblast growth factor (FGF2), anti h platelet derived growth factor (PDGF) and anti Transforming growth factor beta (TGFbeta)) in combination resulted in a progressive reduction of the angiogenic response of the pulp. MATERIALS AND METHODS: The dental pulps from two groups of 40 premolar teeth, four teeth from each of 20 patients treated with fixed appliances for 2 weeks, were divided vertically, and sections from each half pulp co-cultured with sections of rat aorta in collagen. In one group, one of each of the four NAs, and in the other group, one of the four different NA combinations were added to the media of the co-cultures from one half of the pulp from each of the four teeth of each patient; the other half pulp co-cultures were controls. Cultures were examined daily by light microscopy for growth and number of microvessels. RESULTS: NAs significantly reduced microvessel numbers in the co-cultures when added individually (P<0.004), and in each of the four combinations (P<0.002), with a trend to progressively reduced microvessel numbers with increasing number of NAs in combination. CONCLUSIONS: Results indicated that all four angiogenic growth factors examined were released following orthodontic force application and play a role in the angiogenic response of the pulp, and that these factors may be more effective in combination.

Angiogenic growth factors released in human dental pulp following orthodontic force.

OBJECTIVE: The aim of this study was to investigate if a combination of five diffusible angiogenic growth factors were released in human dental pulp during orthodontic force application, by using growth factor neutralising antibodies (NAs) to block their effects. MATERIALS AND METHODS: Dental pulps from 18 premolar teeth treated with orthodontic fixed appliances for 2 weeks were divided vertically, and each half pulp further sectioned and co-cultured with a section of rat aorta in collagen surrounded by growth media. NAs (anti-h VEGF, anti-h FGF2, anti-h PDGF, anti-TGFbeta and anti-h EGF) were added to the media of the co-cultures from one half of each pulp from 10 teeth. The co-cultures from the remaining eight teeth acted as controls. Sections of rat aorta alone were also cultured with and without NAs. Cultures were examined daily by light microscopy for growth and number of microvessels. RESULTS: NAs significantly reduced microvessel numbers in the co-cultures, but not in the rat aorta alone cultures. CONCLUSIONS: The results show that a combination of these angiogenic growth factors are released in the pulp following orthodontic force.

The role of gingival mechanoreceptors in the reflex control of human jaw-closing muscles.

Electromyographic (EMG) experiments were undertaken to investigate the jaw reflexes evoked by activation of gingival receptors in 12 humans. EMG recordings were made from an active masseter muscle whilst ramp-plateau mechanical stimuli were applied to the gingiva. Stimuli with a constant rate of rise (0.2 N/msec) and a variable plateau force (up to 2 N), evoked a complex set of short- and long-latency inhibitory and excitatory responses. These occurred as a sequence of inhibition-excitation-inhibition-excitation, although not all of these elements were seen on every occasion. The median thresholds of these four responses ranged from 0.5 to 1 N but overall there were no significant differences between them (p > 0.05, Friedman's ANOVA). In other experiments, the same reflexes were recorded in response to application to the gingiva of 1 N ramp-plateau stimuli (5 msec rise time) and 1 N tap stimuli applied to the adjacent tooth. The application of a local anaesthetic agent to the stimulated gingiva produced reductions in the mean magnitude of almost all the responses but these were significant (p < 0.05; ANOVA) only for the long-latency inhibitions evoked by ramping the gingiva and the long-latency excitations evoked by either stimulus. It is concluded that mechanoreceptors in the gingiva can mediate long-latency inhibitory and excitatory jaw reflexes, and that these receptors may also contribute to long-latency reflexes evoked by tapping teeth. The scarcity of effects of gingival anaesthesia on the short-latency reflexes may be due to such responses being mediated by receptors deeper in the periodontium.

Taste.

When we eat or drink we perceive a sensation that is often described as taste. A better term for it would be flavour, because the experience is made up of different modalities of sensation. Amongst these modalities are those of smell, touch (texture), temperature, and, of course, the chemical sense of taste. In this paper only the sensations of oral chemoreception will be described. The distribution and the morphology of the chemoreceptors within the oral cavity, the mechanisms involved in the transduction of the signal and the central connections of the nerve fibres innervating the receptors will be discussed.