Tension Receptors Research Articles

Mechanical properties and sensitivity to CCK of vagal gastric slowly adapting mechanoreceptors

Sixty single afferent fibers with endings in the stomach wall were isolated from the cervical vagus of urethan-anesthetized Sprague-Dawley rats. All the fibers, most of which were spontaneously active, increased their discharge after gastric distension or during spontaneous contractions of the stomach. Because of this and the characteristic dynamic and static features of their response to inflation and deflation, they were identified as in-series tension receptors. Certain features of their responses, previously suspected from studies on reflex modulation of vagal efferent fibers or brain stem neurons, were directly confirmed. These included a broad range of mechanical thresholds and spontaneous firing frequencies that were correlated and a sensitivity only to dynamic stretch and active contraction in the highest threshold endings. The tension receptors could also be activated by circulating cholecystokinin, an effect unrelated to changes in intraluminal pressure and hence gastric wall tension, suggesting that there may be humoral modulation of visceral sensory signals that might be relevant to several behavioral situations, such as food intake regulation.

Vagal afferent discharge from gastric mechanoreceptors during contraction and relaxation of the ferret corpus

Vagal afferent fibres with mechanoreceptive fields in the gastric corpus were studied electrophysiologically in the urethaneanaesthetized ferret in an attempt to assess how changes in muscle tension and length modulate receptor discharge. Single afferent units were spontaneously active and increased their firing on distension of the corpus. During vagally evoked isovolumetric contractions and relaxations, the afferent discharge closely followed changes in intracorpus pressure. Under near-isotonic conditions, changes in both intracorpus pressure and afferent discharge were attenuated to similar degrees despite large changes in corpus volume, although the latter had a modulating influence on afferent discharge. These mechanoreceptors appeared to behave as tension receptors but were also influenced by muscle length as would occur if the receptor were associated with the laminar intramuscular septa of connective tissue which may serve as intramuscular tendons in this tissue.

Contrôle nerveux de la motricité du réticulo-rumen

This paper reviews the nervous mechanisms involved in the control of motility of the forestomach compartments in ruminants. The first part of the review reports the efferent vagal discharge which consists of several distinct and independent types of urinary activity and passes from the gastric centres to the reticulo-rumen. The patterns of each of these activities are temporally related to the contractions of special parts of the forestomach and occur in a sequence which could produce the coordinated series of movements found in the reticulum and rumen. The orderly sequence of motor events that constitutes the gastric cycle is due to this coordination of efferent vagal outputs arising in the gastric centres. The focal point of the second part of the paper is sensory feedback from the complex stomach to the centres. Four types of receptor have been identified according to their location and stimulus; these are tension receptors and epithelial receptors in the reticulo-rumen and tension receptors and mucosal receptors in the abomasum. Mechanical or chemical stimulation of these distinct receptor types leads to either facilitation or inhibition of reticulo-ruminal motility. The third part of the paper deals with the organization of the medullary gastric centres. The gastric vagal motoneurons are controlled by interneurons organized in two functionally distinct networks. The "rate" network for which the periodicity of its activity depends on the cumulative integrated afferent inputs from central and peripheral sources, determines the rhythm of gastric cycles. It is postulated to drive the "amplitude and form" network which adjusts vagal output to instantaneous gastric afferents, enabling the amplitude of gastric contractions to be adapted to peripheral stimulations. The role of the sensory feedback from the complex stomach in the control of the "frequency" network is discussed, taking into account new experiments on vagal deafferentation and the concept of an oscillating generator that would be more or less permanently inhibited by vagal afferents is reviewed. The respective roles of local regulation mechanisms, mediated in the intramural plexus, and of central mechanisms, in the control of forestomach motility, are briefly discussed.

Tension receptors on the closer muscle apodeme in the walking legs of the blue crab,Callinectes sapidus

1. Receptors responsive to muscle tension have been located on the closer apodeme of walking legs of the blue crabCallinectes sapidus. The axons form a discrete nerve, the closer apodeme sensory nerve (CASN) which joins the PD organ nerve. 2. The receptors are 25–35 bipolar cells whose cell bodies measure between 25–60 μn, located on the distal end of the apodeme. The dendrite of each is inserted through the hypocuticle into the endocuticle of the apodeme. No receptors are found directly associated with muscle fibers. 3. The apodeme receptors exhibit no spontaneous activity at any rest position of the dactyl, and are unresponsive to passive movement of the dactyl. 4. Isometric tension causes the apodeme receptors to fire. Increased tension increases the frequency of output with the recruitment of additional units. 5. Upon isotonic contraction against increasing loads, the receptors show increased output and the recruitment of additional units. Isotonic contraction of the unloaded closer muscle evokes no response by the receptors. 6. The combined anatomical and physiological evidence supports the theory that these sensory cells are series tension receptors.

Cold-sensitive mechanoreceptors with afferent C-fibres in the sheep duodenum

The effect of changes of temperature on the impulse activity of duodenal mechanoreceptors with afferent C-fibres was studied in acute electrophysiological experiments in chloralose-anaesthetised sheep. The impulse activity of 4 tension receptor units increased when the duodenal mucosa was cooled over the range 0-39 degrees C. The impulse activity of 10 tension receptors was reduced when the mucosa was cooled. Temperature changes between 39 degrees C and 52 degrees C did not alter the discharge pattern of either type of tension receptor response. An additional unit, which may have been associated with pyloric circular muscle, was excited by cooling over the temperature range 0-39 degrees C. This unit was insensitive to compression and was excited by close-intra-arterial injections of pentagastrin, nor-adrenaline, prostaglandin F2a and prostaglandin E2. The cold-sensitivity of mechanoreceptors in the duodenal muscularis externa may play a role in the reflexes regulating gastric emptying in experimental situations when duodenal chyme is cold.

EFFECT OF ALTERING THE RUMEN LOAD ON THE FEEDING BEHAVIOR IN SHEEP

Fistula feeding before a morning meal increased rumen load and suppressed feeding of the sheep. The removal of food residues from the rumen decreased rumen load and stimulated subsequent feeding. The rumen load, estimated from the torque values of rumen content, seems to affect the tension receptor in the rumen. Key words: Sheep, rumen load, rumen digesta, food intake

Tension receptors with vagal afferent fibres in the proximal duodenum and pyloric sphincter of sheep.

Single-unit afferent activity was recorded from the hepatic-duodenal branch of the vagus nerve of chloralose-anaesthetized sheep during acute electrophysiological experiments. The impulse activity of sixty-seven slowly adapting mechanoreceptors situated in the muscularis externa of the proximal duodenum and pyloric sphincter was synchronous with alterations in electromyographic and tension records. Afferent units were excited during passive distension, compression and drug-induced increases in muscle tension, thus satisfying the criteria for 'in series' tension receptors (Iggo, 1955). From the responses to compression some evidence was found for the existence of separate populations of tension receptors with different mechanical thresholds. Two fibre populations were found: non-myelinated (0.70 +/- 0.26 S.D. ms-1) and myelinated (7.6 +/- 1.6 S.D. m s-1). Mucosal application of solutions of hydrochloric acid, volatile fatty acids, alkali and amino acids, and mucosal probing modified the activity of most units. These changes were reduced by anaesthesia of the mucosa. It is concluded that tension receptors in the sheep duodenum occupy a position 'in series' with longitudinal muscle, and that their activity can be modified by the particulate and chemical composition of chyme by a mechanism involving local nerve plexuses. The activity of tension receptors is compared with that of two other mechanoreceptor classes located serosally (five units) and in the lesser omentum (eleven units). Receptors in neither of these two classes were directly excited by active contraction of the duodenum.

The responses of duodenal tension receptors in sheep to pentagastrin, cholecystokinin and some other drugs.

The proposal that some post-prandially released alimentary hormones modify ingestive behaviour and gastric emptying by altering impulse activity in alimentary enteroceptors has been tested using a number of gastrointestinal peptide hormone analogues. These and other drugs were applied to single-unit afferent preparations of duodenal tension receptors in chloralose-anaesthetized sheep. In separate experiments the effect of pentagastrin and cholecystokinin on duodenal motor activity was recorded without unitary afferent activity measurements. Local intra-arterial bolus injections of pentagastrin, cholecystokinin, insulin, prostaglandin, acetylcholine, phenylbiguanide, veratrine, 5-hydroxytryptamine and bradykinin aroused or enhanced activity in tension receptors. With the exception of a short-latency effect of insulin B.P., these responses occurred together with local increases in tension and electromyographic activity of the duodenum. Combinations of atropine and hexamethonium reduced duodenal motor activity and abolished most drug-evoked afferent responses. Intracarotid bolus injections of pentagastrin at first increased, then reduced duodenal tension, electromyographic activity and impulse activity of tension receptors. Cholecystokinin (CCK-8) injected by this route caused similar alterations of these parameters, and the response was characterized by periods of reduced activity followed by a prolonged excitation of duodenal motility. From the responses to bolus injections of humoral agents it is concluded that some alimentary hormones released after a meal may have a peripheral excitatory action on the tension receptor environment which causes increased afferent activity. The mechanism probably involves both an alteration in duodenal motility and a sensitization of the receptor ending. In addition, the peptide hormones gastrin and cholecystokinin may act centrally to alter duodenal motor control and thus may influence gastric emptying and post-prandial satiety mechanisms.

Sensory representation of a non‐planar joint in the walking legs of the horseshoe crab,Limulus polyphemus

The patello‐tibial joint in the walking leg of the horseshoe crab can move in the flexion‐extension and promotion‐remotion planes with the freedom of movement of a ball‐and‐socket joint. Its mechanical status is represented by at least seven populations of sensory neurons and these include three different types of proprioceptors; articular membrane receptors, muscle length receptors and muscle tension receptors. A population of each of these types of proprioceptor is associated with structures on the anterior and posterior sides of each leg. In this report we describe the representation of joint movement in both planes by two populations of each type of proprioceptor. In general, the articular membrane receptors were most sensitive to joint flexion; receptors on the anterior side of the leg were biased toward promotion, while those on the posterior were biased toward remotion. Muscle length receptor activity was increased by joint extension and was slightly augmented, in posterior and anterior length receptors, by promotion and remotion, respectively. Length receptor tonic activity was a linear function of muscle length for extension but a non‐linear function of muscle flexion. Tension receptor activity was always highly dependent upon active muscular contraction. Tension receptors associated with posterior tibial flexor showed enhanced activity when the joint was promoted; the activity of those associated with the anterior flexor was enhanced by remotion. The relationships between tension receptor activity and muscle length, and between tension receptor activity and joint position, were also explored. While no single receptor population appears capable of representing the status of this joint in both planes, the output of all of the receptor populations studied appears to provide the CNS with unambiguous information about several parameters representing the status of this complex joint.

The relationship between sensory activity and muscle tension in the anterior flexor muscle of horseshoe crab walking legs

A population of series tension receptors associated with the anterior tibial flexor muscle in the walking legs of the horseshoe carb was studied. Active contraction of the muscle readily elicited receptor activity but the receptors were largely insensitive to imposed extension or flexion of the passive muscle. The anterior flexor muscle inserts on the tibia. One of the three heads of the muscle originates in the patella and the other two originate in the femur. For a given contraction, a higher frequency sensory discharge was observed when the muscle was fixed at greater lengths. This relationship held whether muscle length was changed by manipulation of the femero‐tibial joint, the patello‐tibial joint, or both. For most of the units studied (12 of 15) the relationship between receptor spike frequency and whole muscle tension was highly linear. The results of this study suggest that the sensory endings measure the tension in apodemes common to the three heads of the muscle, define the relationship betwee...

Clinical diseases of the rumen: a physiologist's view.

An interpretation of many of the classical signs of ruminal dysfunction is possible by extrapolation from the results of research in rumen physiology. Correlation of motility and ruminal fluid characteristics will often provide a means of establishing the degree, the duration and the differential diagnosis of the dysfunction detected. In the case of disorders of ruminal motility, general anaesthesia and diseases at any sites which produce pain or fever can inhibit the hindbrain reflex centres responsible for evoking primary and secondary cycle contractions of the reticulorumen. Simple indigestion/rumen impaction, vagus indigestion and hypocalcaemic milk fever cause ruminal stasis, probably because they relax the reticuloruminal smooth muscle and hence decrease the reflexly excitable sensory inputs from tension receptors. Grain engorgement/ruminal acidosis and extreme bloat are likely to excite other sensory receptors (epithelial receptors), which reflexly inhibit cyclical motility. Bloat occurs when eructation is inadequate either because the oesophagus is obstructed or because cardiac opening is reflexly inhibited by the presence of ruminal fluid rather than gas at the cardia in conditions of subnormal motility or of leguminous frothing.

Effect of thoracic deafferentation on load-compensating mechanisms in humans.

First-breath responses to graded elastic (delta E) and resistive (delta R) loads in 29 cervical cord-injured and 80 normal men were compared with those predicted assuming identical respiratory muscle pressure (Pmus) wave forms in the unloaded and loaded states. The cord-injured group's mean actual and predicted inspiratory duration (TI) responses were equal, indicating that the average duration of their phrenic discharge remained constant during both delta E and delta R. Their mean expiratory duration (TE) responses fell short of predictions with delta E but exceeded predictions with delta R, signifying that a neural mechanism hastened inspiration following delta E but postponed it following delta R. TE/(pred TE) values (an index of phrenic timing) from different loads were proportional to concomitant TI responses but not to indices of diaphragmatic force [peak Pmus, (VT/TI)/(pred VT/TI)], movement (VT, VT/TI), or duration of contraction [TI/(pred TI)]. These findings suggest that oropharyngeal and/or pulmonary receptors signaling airflow duration, rather than diaphragmatic length or tension receptors, adjust phrenic motoneuron timing during mechanical loading. The cord-injured group produced a normal tidal volume (VT) defense coupled with a depressed frequency (f) response to delta E and, conversely, a weak VT defense coupled with a normal f response to delta R. Since both groups' VT/TI responses surpassed predictions equally, the cord-injured group's deficit was attributable entirely to impaired regulation of TE during delta E and TI during delta R. Thus chest wall receptors modulate duration and timing, but probably not average intensity, of the phrenic output during loading. Nearly one-third of the normal, but virtually none of the cord-injured, samples prolonged TI against large delta R and shortened TI agaist large delta E, suggesting that thoracic deafferentation impairs human ability to distinguish large delta R from delta E. These latter findings support the hypothesis that chest wall afferents subserve perception of respiratory force or position in humans.

Local regulation of subcutaneous blood flow in normal subjects and in migraine patients before and after single-dose ergotamine tartrate.

Local blood flow regulation of the foot was studied in 15 normal subjects and in nine migraine patients. Changes in arterial and venous pressures were induced by lowering and elevation of the limb. Changes in blood flow were estimated from the changes in the wash-out rate of a subcutaneous 133-Xenon depot. The local vasoconstrictor response to increased venous pressure elicited during lowering was identical in the normal subjects and in the migraine patients. During elevation, however, an abnormality in the autoregulation of blood flow could be demonstrated, as a decrease in blood flow during elevation to +40 cm was more pronounced in the patients than in the normal subjects (P = 0.04). About 3 h after 0.5 mg ergotamine tartrate/70 kg body weight i.v. the local regulation of blood flow had markedly changed in normal subjects as well as in migraine patients. During elevation to +20 and to +40 cm, blood flow increased significantly (P = 0.01 and P = 0.02). In two subjects the isotope depot was infiltrated with lidocaine and the ergotamine-induced increase in blood flow during elevation was blocked. The results may indicate that the veno-receptor of the veno-arteriolar reflex underlying the local vasoconstrictor response is a tension receptor, which due to the veno-constrictor effect of ergotamine is triggered even at heart level.

Modulation of reflex and centrally generated motor activity by tension receptor afference in Cancer pagurus (Decapoda, Brachyura)

1. 1. Electrical stimulation of the tension receptor nerve of the flexor of the carpus inhibits not only resistance reflex activity in the flexor motor nerve but also motor activity evoked by a variety of other external stimuli. 2. 2. Not all units in the flexor motor nerve respond in the same way to a given level of flexor tension nerve stimulation. 3. 3. A resistance reflex to imposed extension occurs as a result of MCl chordotonal organ input alone. A modified resistance reflex to extension also occurs in the presence of isometric contraction of the flexor muscle produced by centrally generated activity in the flexor motor nerve. 4. 4. The resistance reflex present when there is no centrally generated activity in the flexor motor nerve is abolished by cutting the MC1 nerve; at least part of the reflex which occurs during centrally generated activity remains after the MC1 nerve has been cut. This remaining part of the reflex is abolished when the tension receptor nerve is cut. 5. 5. These results indicate that the sign of the effect that tension receptor afference has on the flexor motor neurons depends on whether the neurons are activated reflexly or centrally. Ways in which this could occur are discussed.

Responses and central interactions of tension receptors in the leg flexor muscle of Carcinus

1. 1. The physiology of the detection of tension in the limb flexor muscle of Carcinus is described. The tension receptors respond primarily to the rate of tension increase in the muscle, and their activity is closely related to movement of the apodeme, whether induced by external forces or by flexor muscle contraction. 2. 2. The immediate effect of tension afference in whole animal preparations in all cases is short-term excitation of flexor motoneurones. 3. 3. If there is spontaneous activity in the motoneurones, or if activity is induced by stimulation of non-limb areas, tension afference also evokes long-term excitation. 4. 4. Resistance reflexes are always inhibited by tension afference.

Multiple receptor types for octopamine in the locust.

1. Three different pharmacological classes of octopamine receptor mediate the actions of octopamine on the locust extensor-tibiae neuromuscular preparation. A receptor classification scheme is proposed based on the results of detailed studies with agonists and antagonists. 2. Octopamine1 class receptors mediate the slowing of a myogenic rhythm found in a specialized proximal bundle of muscle fibres. Octopamine2A class receptors mediate the increase in amplitude of slow motoneurone twitch tension and octopamine2B class receptors mediate the increase in relaxation rate of twitch tension induced by firing either the fast or the slow motoneurones. 3. Octopamine1 receptors can be distinguished from the 2A and 2B classes since chlorpromazine (and yohimbine) are much better blocking agents than metoclopramide at the former receptors, whereas the converse is true for the latter class. Also clonidine is a more effective agonist than naphazoline for the former receptors and the converse is true for the latter class. 4. Octopamine 2A can be distinguished for octopamine 2B receptors since metoclopramide, mianserin and cyproheptadine show a strong preference for blocking the former class. Also naphazoline is a much better agonist than tolazoline at the former receptors and tolazoline is a much better agonist than clonidine at a latter. 5. The results are discussed in terms of the location of the various classes of octopamine receptors, their possible relationship to vertebrate alpha-adrenoreceptors, and the significance of the results for studies on octopamine receptors in the vertebrate central nervous system.

Cardiovascular changes in elicited by vagal gastric afferents in the rat.

Cardiovascular changes elicited by gastric distension in the urethane anaesthetized rat are described. Heart rate changes were mediated via a vago-vagal pathway with 'in-series' tension receptors in the stomach wall providing the afferent input and cholinergic cardio-inhibitory fibres forming the efferent pathway. Blood pressure changes occurred independently of the heart rate changes; the main afferent pathway was again vagal but the efferent outflow was non-cholinergic and probably sympathetic.

Postural Reflexes Coordinating Walking Legs in a Rock Lobster

Postural Reflexes Coordinating Walking Legs in a Rock Lobster

The morphology and ultrastructure of tension receptors in the walking legs of the crab, Carcinus maenas.

The tension receptor system of the crab merus consists of two size classes of receptor cell body distributed along one face of the flexor muscle apodeme. The receptors show the general arthropod mechanoreceptor structure of cell body, connecting cilium, and sheathed sensory processes, but there are several differences. Many processes show convolutions, and the distal portion of the sensory process is embedded in the apodeme cuticle. The terminations of the sensory processes lack the usual structural specialisations for mechanotransduction. Tension transduction appears to occur by flexion of the cuticle-embedded sensory process.

Vagal afferent discharge from mechanoreceptors in different regions of the ferret stomach.

1. The rate and volume of gastric filling was estimated in conscious ferrets by measuring the amount of milk they would drink after an overnight fast. The mean volume was 94.5 +/- 7.5 ml. at a rate of 13.0 +/- 0.74 ml./min. An intragastric infusion rate of 10 ml./min to a total of 50 ml. was selected as a standard distension stimulus. 2. Action potentials were recorded from single gastric afferent fibres in the cervical vagus. All but two of thirty-six afferent units were tonically active when the stomach was deflated. 3. Afferent fibres arising from receptors in the antrum showed modulation in phase with spontaneously occurring antral contractions. Afferent fibres from the corpus and fundus, however, discharged at irregular rates between 0.35 and 7.5 Hz with no correlation with the intragastric pressure rises associated with the antral contractions. 4. Inflation of the stomach with 50 ml. 0.9% NaCl at a rate of 10 ml./min stimulated antral motility and the rhythmic afferent discharge from the antrum was enhanced Receptors in the corpus and fundus increased their rate of discharge with increasing gastric volumes. Receptors in the region between the antrum and the corpus had the property of both types so that they responded to both distension and contractions. 5. On distension with 0.9% NaCl, fluid is distributed unevenly in the stomach. 80% was accommodated in the corpus and fundus, the remainder of the fluid entering the antrum. 6. The tension was measured in strips of stomach wall taken from corpus and antrum. For equal increments of stretch the development of tension was greater in the antral than in corpus strips. This physical property together with neurally mediated receptive relaxation of the corpus is the reason for the fluid distribution described above. 7. It is concluded that the properties of the tension receptor are determined by their site in the stomach. Those in the body and fundus signal the degree of distension and those in the antrum signal information concerning the amplitude, rate and duration of antral contractions.