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Biomedical subjects

H Aars

Publications and source records attributed to H Aars.

At least 37 records · Page 2Linked to original sources
PubMed1987

Parotid salivary flow in response to mechanical and gustatory stimulation in man.

To examine further the role of the oral receptors in the masticatory-salivary reflex, a study with eight subjects was performed. The influence on mean parotid salivation of combined alterations in frequency and force of chewing and length of the chewing object was evaluated by group comparison. Salivary flow rate was recorded using a sensitive micromanometer, and the frequency (12, 60 and 90 cycles min-1) and force of chewing (10 and 40% of maximum) were controlled by a metronome and masseter muscle EMG, respectively. The maximum instantaneous flow and the latency of the masticatory-salivary reflex were examined in three subjects. For comparison with mean salivation rate during chewing, gustatory stimulation was performed with 0.5 or 5.0% citric acid. The masticatory-salivary reflex was mainly ipsilateral, and depended upon having an object between the teeth. Salivation increased with increases in frequency and force of chewing and with the number of teeth involved, each parameter of chewing having the greatest influence when increased from a low level of action. The salivation response to chewing showed two phases; the first, presumably due to contraction of the myoepithelial cells, had a latency of 0.2-0.4 s, while the second phase occurred about 1 s later. Our results support the hypothesis that the periodontal mechanoreceptors have a major role in the parotid response to chewing. Application of 0.5 and 5.0% citric acid on the back of the tongue induced dose-dependent parotid secretions, significantly higher than those of chewing. A negative correlation was found between the maximum fluid outputs during chewing and 5.0% citric acid stimulation.

Adolescent↗
PubMed1987

Acute changes in intra-alveolar tooth position and local clearance of 125I from the periodontal ligament.

Changes in intra-alveolar tooth position and local 125I clearance from the periodontal ligament (PDL) were monitored simultaneously in cats. Axial tooth movements, reflecting periodontal ligament volume changes, were measured with an ultrasonic transit time technique. Local blood flow changes in the PDL were studied indirectly by measuring the local clearance of 125I-. Stimulation of the cervical sympathetic trunk caused an intrusive movement of the tooth with a concomitant reduction of the 125I- clearance. Infusion of noradrenaline induced a similar response. Stimulation of the inferior alveolar nerve during systemic treatment with phentolamine caused an extrusive movement of the tooth with a concomitant increase in the clearance of the tracer from the PDL. Intra-arterial infusion of the vasodilator substance P mimicked that response. Fixation of the tooth to the jaw bone, thus preventing an intrusive movement, did not change the reductions in clearance seen on sympathetic stimulation, indicating that this blood flow reduction was not dependent on tooth movement. A qualitative relation between PDL blood flow (as measured by local 125I clearance) and PDL volume (as measured by tooth position) is shown. The two variables measured are suggested to reflect two aspects of blood flow in the PDL.

Alveolar Process↗
PubMed1983

Effects of sympathetic nerve activity on changes in the position of the rabbit incisor tooth evoked by acute alterations in arterial blood pressure.

The influence of the sympathetic innervation of periodontal blood vessels on the responses of the upper incisor tooth to sudden changes in mean arterial pressure was studied in 15 anaesthetized rabbits. Changes in axial position of the tooth were measured by ultrasonic transit time technique. With intact sympathetic nerves, the tooth showed small, if any, intrusive movements in response to 6-42 mm Hg reductions in arterial pressure evoked by stimulation of the aortic baroreceptor nerve. When exposed to similar periods of hypovolaemic hypotension, the intrusions were, on an average, 1 micron larger (p less than 0.01). After bilateral sectioning of the cervical sympathetic nerves, tooth intrusions in response to both types of pressure reduction became more marked, as did the extrusive movements evoked by abrupt increases in aortic pressure (produced by inflation of intra-aortic balloon). After sympathectomy, a 19 +/- 6 mm Hg rise in pressure caused extrusions of 6 +/- 3 microns, or 2 microns more than before the sympathectomy (p less than 0.01). The results suggest that the activity in sympathetic nerves to periodontal blood vessels may be inhibited by central nervous mechanisms and that the sympathetic innervation of the periodontal vasculature serves to minimize changes in tooth position brought on by sudden alterations in arterial pressure.

Animals↗
PubMed1983

Effects of sympathetic nerve activity on acute mobility of the rabbit incisor tooth.

The contribution of local blood flow to the buffering properties of the periodontal ligament was examined in 15 anesthetized rabbits. The position of the tooth was recorded by an ultrasonic transit time technique, and local vascular pressures and volumes were altered by electrical stimulation of the cervical sympathetic nerves. The unloaded tooth was shifted into a slightly intruded position by nerve stimulation, and from this position, intrusion movements evoked by 5- to 10-g loads were found to be 10-15% smaller than before the stimulation. Tooth mobility was unaffected by 20-30 mm Hg reductions in mean arterial pressure, but similar decreases in mobility as evoked by nerve stimulation were observed when the pressure was brought down to 10-25 mm Hg. This procedure also produced about the same intrusive shift of the unloaded tooth. Most likely, the sympathetic nerve activity decreased tooth mobility by causing a fall in periodontal vascular pressures, thereby moving the tooth into a position where it was more resistant to further, load-induced intrusion.

Animals↗
PubMed1982

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.

Animals↗
PubMed1982

The influence of sympathetic nerve activity on axial position of the rabbit incisor tooth.

Changes in position of the upper front tooth in response to sectioning and subsequent electrical stimulation of the cervical sympathetic nerves were studied in 25 anesthetized rabbits. The position was continuously recorded by an ultrasonic transit time technique. Sectioning of the nerves was found to induce an average tooth extrusion of about 7 microns. Sympathetic nerve stimulation for periods of 20-30 s caused intrusion of the tooth, with about 70% of maximum occurring at 2 Hz stimulations. The intrusive response was reduced by phentolamine. Neither atropine nor propranolol affected the stimulation response, but the latter drug led to marked extrusion of the tooth. In conclusion, the position of the rabbit's front tooth was found to be highly sensitive to alterations in sympathetic nerve activity to the vasculature of the tooth-supporting tissues.

Animals↗
PubMed1982

The influence of vascular beta-adrenoceptors on the position and mobility of the rabbit incisor tooth.

The influence of vascular beta-adrenoceptors on the tooth-supporting functions of the periodontal ligament were studied in 30 anesthetized rabbits. Propranolol and the beta 2-adrenoceptor antagonists ICI 118,551 and H 35/25 induced a marked extrusion of the incisor, probably due to reduced vasodilator tone in periodontal postcapillary blood vessels. Isoprenaline reversed the movement. beta 1- and beta 2-receptor antagonists decreased the intrusive responses to sympathetic nerve stimulation in teeth close to control position, but had no effect on responses in fully extruded teeth. Intrusive mobility, as tested by intermittent loading with 5-10 g, remained unaffected by beta-adrenoceptor blockade. The results suggest that vascular beta 2-adrenoceptors are important in the regulation of tooth position by their control of periodontal postcapillary resistance. Prejunctional beta-receptors enhancing the vasoconstrictor--and intrusive--responses to sympathetic nerve stimulation are probably a mixture of beta 1- and beta 2-receptors. It would seem that the periodontal vasculature is important for the position of the rabbit tooth but, due to rapid adaptive mechanisms of the tooth-supporting tissues, the vasculature contributes little to the resistance against load-induced intrusive movements of the tooth.

Adrenergic beta-Antagonists↗
PubMed1982

Neurotoxic effects of root filling materials on rat phrenic nerve in vitro.

Inhibitory effects of root filling materials on the conduction of action potentials evoked in rat phrenic nerves were evaluated in vitro. Endomethasone and N2 Normal completely and irreversibly inhibited conductance; ProcoSol caused complete but reversible inhibition; Kloroperka N-O caused total inhibition which was sometimes reversed; and AH26 and Diaket showed partial inhibition which was partially reversible.

Action Potentials↗
PubMed1980

Central interaction between reflex responses to activity in aortic nerve A- and C-fibres.

The question of whether or not activity in myelinated (A) and non-myelinated (C) afferents in a baroreceptor nerve shows interaction of their reflex effects, was investigated in 10 anesthetized rabbits. The central end of the cut left aortic nerve was stimulated by two sets of electrodes, one for selective high-frequency excitation of A-fibres (A-stimulation) and one for low-frequency activation of C- (and A-) fibres by another pulse generator (C-stimulation). The pulse rates in C-stimulations were too low to evoke reflex effects via A-fibres. The hypotensive response to combined stimulations of A- and C-fibres (AC-stimulation) was found to exceed the sum of responses to separate A- and C-stimulations in 21 of 22 stimulation series. For sympathetic activity to the kidney, a greater than additive effect was observed in 16 of 24 series (P = 0.08), while in 6 of the series, the responses were equal. Median values of the ratio AC/(A + C) were 1.28 for the reflex changes in pressure and 1.11 for the effects on renal nerve activity. Similarly, C-stimulation, which in comparison to A-stimulation affected sympathetic activity relatively more than blood pressure, in 13 of 16 series (P = 0.01) produced a greater sympathetic inhibition when added to a background of A-fibre activity than when alone. These results suggest that a synergistic interaction exists between central effects of afferent discharge in aortic nerve A- and C-fibres.

Animals↗
PubMed1979

Influences of axial load and blood pressure on the position of the rabbit's incisor tooth.

Changes in the axial position of the left upper incisor in response to loading by 5-20 g were measured with ultrasonic technique in anesthetized rabbits. The time-response of the load-induced intrusion described a biphasic curve, with a steep initial part followed by a slower part. Maximum amplitudes after 20 s increased with increasing loads. A rise in arterial blood pressure (aortic balloon inflation) resulted in extrusion, while i.v. injection of noradrenaline or papaverine caused intrusion and extrusion, respectively. The responses to loading and changes in blood pressure were largely unaffected by transection of the root, but the effects of pressure changes were severely diminished by local infiltration of the periodontium with noradrenaline. Participation of periodontal blood vessels in the damping of load-induced intrusion was excluded by the finding of roughly equal intrusion curves at low, normal and high blood pressure and up to 38 h after death. We conclude that the resting position of the rabbit's incisor is greatly influenced by arterial blood pressure, via the periodontal vessels. The intrusion in response to loading by up to 20 g is resisted by periodontal fibers only, the blood vessels or the pulpal and periapical tissues and pressure taking no part.

Animals↗
PubMed1978

The function of baroreceptor C fibres in the rabbit's aortic nerve.

The participation of aortic nerve C fibers in the baroreflex was investigated by recording changes in renal nerve activity in response to acute increases in arterial pressure, in two experimental situations: with the A and C fibres of the aortic nerve intact, and with the A fibres temporarily blocked by a hyperpolarizing current (anodal block). Pressure was increased by manual inflation of an intra-aortic balloon, and interference from other barorecptor areas was avoided by carotid occlusion and sectioning of the right aortic nerve. Rises in mean arterial pressure exceeding 20 mmHg, to levels above 110 mmHg, were needed to trigger sympathetic inhibition via C fibres. A rise of 45 mmHg caused 50% reduction in sympathetic activity, equal to that obtained by stimulation of aortic nerve C fibres at about 3 Hz. In contrast, a rise of 20-30 mmHg evoked more than 60% reduction in sympathetic activity when the A fibres were operative. Judged by these studies of peak reflex responses to brief pressure rises, baroreceptors with C fibres in the aortic nerve have a much higher threshold to pressure than their myelinated counterpart; the C fibres contribute to the baroreflex inhibition sympathetic discharge only when pressure is increased well above normal resting levels.

Action Potentials↗
PubMed1977

Inhibitory effect of propranolol on tetanic contraction in rabbit.

The effects of propranolol on electrical and mechanical activity during tetanic stimulation of the diaphragm and leg muscles, and on the heart rate, were studied in the anaesthetized rabbit. Propranolol (from 0.5 mg/kg) reduced the EMG evoked in diaphragm by phrenic nerve stimulation (50/sec) and the EMG and force of contraction during periods of increased respiratory drive obtained by partial tracheal obstruction. The heart rate was lowered by 10-25%. In the indirectly or directly stimulated leg muscles, the drug induced high frequency inhibition of EMG and tetanic contractions (100/sec) without affecting twitch contractions. The inhibitory effect of propranolol on skeletal muscle was probably not caused by beta-adrenergic block, but by stabilization of the sarcolemma. The results suggest that the high frequency inhibitory effect might contribute to the fatigue and reduced work capacity frequently observed when high doses of propranolol are given to man and animals.

Airway Obstruction↗
PubMed1977

Pressure-independent inhibition of sympathetic activity by noradrenaline: role of baroreceptor C fibres.

The effect of i.v. infusion of noradrenaline on activity in the renal sympathetic nerve was studied in rabbits anesthetized with chloralose and urethane. Noradrenaline (3--8 microgram/kg-min) initially increased mean arterial pressure 20--40 mmHg and consequently reduced renal nerve activity. However, studies over a wide range of pressures--obtained by changing the blood volume, revealed that noradrenaline after a few minutes had induced a pressure-independent reduction of sympathetic discharge. The effect disappeared with baroreceptor denervation. An unchanged relationship between arterial pressure and integrated activity in the whole left aortic nerve (which is largely a measure of activity in A fibres) suggested that the sympathetic depression was due to excitation of aortic nerve C fibres. This conclusion was supported by studies of sympathetic responses to selective stimulation of aortic nerve A and C fibres at equal pressures before and during infusion of noradrenaline. Compared to the reflex activity from A fibres, C fibre stimulation was invariably less effective in suppressing renal nerve activity during the infusion. Our studies indicate that noradrenaline may effect a negative feedback control of sympathetic discharge through activation of baroreceptor C fibres.

Animals↗