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Biomedical subjects

R W Linden

Publications and source records attributed to R W Linden.

At least 19 recordsLinked to original sources
PubMed1998

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.

Adult↗
PubMed1998

The masticatory-parotid salivary reflex in edentulous subjects.

The parotid-masticatory salivary reflex has been studied in edentulous subjects. Salivary flow was recorded by siting a modified Lashley cup over the orifice of the parotid duct on one side of the mouth. Subjects chewed on small pieces of silicone rubber with their complete dentures for 1 min periods which resulted in a reflex secretion of parotid saliva. The secretion was greatest when the subject chewed on the same side of the mouth (ipsilateral) as the salivary flow was recorded. Less salivary flow resulted when the subjects chewed on the opposite side of the mouth (contralateral). Anaesthesia of the mucosa of the maxillary and mandibular denture-bearing area was achieved by placing a thin layer of anaesthetic ointment in the fitting surface of the dentures on the side ipsilateral to the Lashley cup. This resulted in a reduction of salivary flow in response to similar chewing cycles. The results confirmed the presence of a parotid-masticatory salivary reflex in edentulous subjects which appears similar in many respects to that of dentate subjects. It is likely that receptors in the oral mucosa are stimulated when an edentulous subject masticates with complete dentures and that activity in these mechanoreceptive neurones results in the reflex salivary secretion.

Denture, Complete↗
PubMed1996

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.

Adolescent↗
PubMed1996

Glycoproteins in human parotid saliva assessed by lectin probes after resolution by sodium dodecyl sulphate-polyacrylamide gel electrophoresis.

Human parotid salivary glycoproteins separated by gradient sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and electroblotted onto nitrocellulose have been investigated using a battery of biotinylated lectin probes of characterized sugar specificity. Lectin binding, detected on blots using avidin-biotin complex (ABC) and a chemiluminescence generating substrate, was recorded on photographic film and compared with the original fluorescein isothiocyanate (FITC) stained blots or with Coomassie Brilliant Blue R-250-stained gels run in parallel. A number of glycoprotein bands which were undetected by protein stains or the periodic acid Schiff reaction were revealed by lectins. Binding by lectins from Concanavalia ensiformis, Lens culinaris, Limax flavus, Phaseolus vulgaris, Ricinus communis, Triticum vulgaris, Lotus tetragonobulus and Ulex europaeus indicated that sialylated and fucosylated triantennary and bisected, N-linked complex sugar chains were present on many glycoproteins in addition to the major glycosylated proline-rich glycoprotein (GI). Binding with lectins from Arachis hypogaea and Dolichos biflorus indicated that the O-linked sugar chains were confined to the alpha-heavy chain of Ig A. Comparison of lectin binding in samples from five healthy individuals revealed differences in a number of glycoproteins in addition to the previously characterized G1 and CON 1/CON 2 polymorphisms and demonstrated that the H blood group antigen was expressed mainly on G1 in parotid saliva. This study will be used as a basis upon which to study salivary glycoproteins in diseases affecting parotid glands.

Adult↗
PubMed1996

The effects of unilateral and bilateral chewing, empty clenching and simulated bruxism, on the masticatory-parotid salivary reflex in man.

In man, parotid flow has been recorded, using modified Lashley cups, in response to mechanical stimulation of the teeth by repeated chewing and clenching manoeuvres. The rectified and integrated masseter electromyographic activity was used as an indirect measure of the stimulus intensity where necessary. Following the observation that "empty clenching' failed to evoke a parotid salivary response, a series of three experiments has been undertaken to address the following questions. (1) Is a lateral component of force required to evoke a flow during empty clenching? (2) Does contralateral inhibition of salivary secretion explain this observation? (3) What is the threshold for the masticatory-salivary reflex? The results suggest that: (i) empty clenching together with a lateral component of force does not result in a secretion above resting flows; (ii) there is no evidence for the existence of contralateral inhibition of salivary secretion; and (iii) the threshold for the masticatory-salivary reflex is lower than 5% of comfortable chewing forces. We are still unable to offer an explanation for the lack of parotid secretion during empty clenching.

Bruxism↗
PubMed1996

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.

Angiogenesis Inducing Agents↗
PubMed1994

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.

Animals↗
PubMed1994

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.

Alveolar Process↗
PubMed1994

The effect of temperature on the discharge of periodontal ligament mechanoreceptors in the cat canine tooth.

The response of periodontal ligament mechanoreceptors to mechanical stimuli was studied at different temperatures in anaesthetized cats. Recordings were made from functionally single fibres in the inferior alveolar nerve from mechanoreceptors which were located in the ligament by dissection and punctate stimulation and electrical stimulation. A thermode was used to alter and maintain small areas of periodontal ligament at temperatures ranging from thermode tip temperatures of 3 degrees C to 57 degrees C. The response to ramp-plateau mechanical stimuli applied to the tip of the crown of the canine tooth was greatest when the thermode temperature was 37.5 degrees C +/- 6.5 degrees C. The effect was similar for all receptors studied.

Adaptation, Physiological↗
PubMed1993

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.

Afferent Pathways↗
PubMed1993

Role of periodontal mechanoreceptors in evoking reflexes in the jaw-closing muscles of the cat.

1. In anaesthetized cats the left maxillary and mandibular canine and incisor teeth were extracted. Nine weeks later the animals were anaesthetized again and titanium implants were placed into the edentulous ridge of the maxilla and mandible. 2. Terminal experiments were performed between 9 weeks and 10 months after inserting the implants. Recordings were made from the trigeminal ganglia and peripheral nerves of anaesthetized cats. Neurones were identified which responded to forces applied to the maxillary teeth but none was found which responded to forces applied to the implant. 3. The responses of motor units in the temporalis muscle were studied in response to ramp-plateau forces applied to the maxillary canine tooth and maxillary implant using peristimulus time histograms and cumulative sum (cusum) analysis. A small amount of inhibition of the motor units was observed in response to the applied forces to the implant. However, the inhibition was much more profound when similar forces were applied to the tooth. 4. The results confirm that when forces are applied to a tooth, periodontal mechanoreceptors are stimulated which evoke reflex inhibitions to motor units in the jaw-closing muscles. However, there is evidence that mechanoreceptors situated distant to the periodontium can also evoke such reflexes. 5. The results are discussed in relation to the overall functional role of periodontal mechanoreceptors in the reflexes of mastication.

Animals↗
PubMed1992

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.

Adult↗
PubMed1992

An olfactory-submandibular salivary reflex in humans.

In a previous study we concluded that there is no olfactory-parotid salivary reflex in humans (Lee & Linden, 1991). The present study examines the olfactory-submandibular salivary reflex. Bilateral submandibular saliva was collected using custom-made collection devices for each of nine subjects. Salivary flow was measured in response to six appetizing odours: peppermint, vanilla, chocolate, beef, tomato and lemon. A significant increase in salivary flow was seen in response to each. There was no significant response to distilled water. We conclude that an olfactory-submandibular salivary reflex does exist in humans.

Adult↗
PubMed1992

The relation between the response properties and the position of reinnervated periodontal ligament mechanoreceptors in the cat.

Electrophysiological recordings were made from functional single fibres teased from the inferior alveolar nerve 12 weeks after nerve section. The force thresholds, adaptation times and conduction velocities of 10 located periodontal ligament mechanoreceptors in 2 cats were recorded and compared with results for normal located receptors from a previous study using similar techniques. The relation of both threshold and the adaptation rate to the position of the reinnervated receptors was statistically significant and similar to the relation for normal units. These results support the hypothesis that the range of response characteristics of periodontal ligament mechanoreceptors depends on their position relative to the tooth's fulcrum.

Adaptation, Physiological↗
PubMed1991

An olfactory-parotid salivary reflex in humans?

It is commonly stated that smell elicits a parotid salivary reflex in humans. However, this assumption seems to be supported only by experiments in which either a lemon or an irritating odour has been used as the primary stimulus. In this study six pleasant odours, chocolate, vanilla, peppermint, beef, tomato and lemon, were administered to ten subjects. Air was passed through a solution of the stimulant and the resultant odour was administered to the subject via a face mask. Unilateral parotid saliva was collected via a Lashley cup and salivary flow was measured using an instantaneous flowmeter sensitive to flows as low as 0.008 ml min-1. Citric acid, lemon juice, chocolate and distilled water were also delivered to the subjects at increasing concentrations. At low concentrations none of these stimuli significantly increased the parotid salivary flow above resting levels. However, an increase in salivary flow was seen when lemon juice or odourless citric acid was sniffed or delivered to the subject at high concentrations, causing irritation in the nasal cavity and/or the back of the throat. Our results suggest that there is no true olfactory-parotid salivary reflex in humans, and that acidic stimuli can cause irritation with a concomitant increase in the salivary flow.

Adult↗
PubMed1990

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.

Adult↗
PubMed1989

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.

Animals↗