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Biomedical subjects

R F Schmidt

Publications and source records attributed to R F Schmidt.

At least 109 records · Page 6Linked to original sources
PubMed1983

Afferent and efferent axons in the medial and posterior articular nerves of the cat.

The goal of this study is to determine the average numbers of afferent axons and postganglionic autonomic (sympathetic) efferent axons supplying the cat knee joint through the medial and posterior articular nerves. Interestingly, both nerves are composed primarily of unmyelinated axons. Only 20% of the axons in the medial articular nerve are myelinated, with the overwhelming majority, 80%, being unmyelinated. The posterior articular nerve has 78% unmyelinated and 22% myelinated axons. Neither nerve contains ventral root efferent axons. The sympathetic chain, in both nerves, contributes no myelinated and only 50% of the unmyelinated axons. The medial and posterior articular nerves are therefore predominantly afferent, since all myelinated and the remaining 50% of the unmyelinated axons arise from the dorsal root ganglion cell. The ratio of afferent unmyelinated to myelinated axons is 2:1. The roles of these afferent unmyelinated axons must now be considered in regard to joint kinesthetics and pain.

Animals↗
PubMed1982

Changes in heart rate and blood pressure upon injection of algesic agents into skeletal muscle.

In cats anaesthetized with chloralose and urethane algesic substances were injected intra-arterially into muscles of the left hindlimb and the resulting changes in heart rate and blood pressure recorded. The vagus nerves and both carotid sinus nerves were cut. Injection of KCl regularly induces acceleration of the heart rate and an increase in blood pressure. With bradykinin both accelerations and decelerations were observed (with or without accompanying pressor or depressor responses respectively). Injection of serotonin was rather ineffective in producing heart rate or blood pressure changes but subsequent injections of either KCl or bradykinin gave rise to enhanced acceleration and pressor responses. In the discussion it will be proposed that the diverse responses are due to differences in the composition of the afferent volleys elicited, probably because besides stimulating nociceptors these algesic substances activate to a varying extent non-nociceptive muscular fine afferent units of different modality and various central actions.

Animals↗
PubMed1981

Heart rate changes reflecting modifications of efferent cardiac sympathetic outflow by cutaneous and muscle afferent volleys.

In cats anesthetized with chloralose and urethane graded electrical stimulation of cutaneous and muscle nerves of the fore- and hindlimb was performed and the resulting changes in heart rate and blood pressure were recorded. The vagus nerves were cut and the right carotid artery was tied off. The left carotid sinus was intact. Repetitive stimulation of cutaneous group II afferents did not change the heart rate nor the blood pressure. Cutaneous group III afferent activity led to an increased heart rate in about 70% of all trials. Very consistent increases in heart rate were always seen when repetitive group IV cutaneous volleys were elicited. Volleys in group I and II muscle afferents were ineffective. With group III muscle volleys bradycardiac (in about 40% of all trials) or tachycardiac (in about 30%) responses were observed. The nature of the response depended on the experimental situation but was difficult to predict or to modify. Stimulation of group IV muscle afferents always induced definite increases in heart rate. The latency for the onset of the heart rate changes was of the order of 3--10 s, and the time of peak during prolonged stimulation was about 20--30 s. There was a marked early and a small late response adaptation during prolonged repetitive stimulation, but the control heart rate was only reached some 40--65 s after the end of the stimulation. For group IV volleys the minimal effective frequency of the repetitive stimulation was between 0.25 and 1.0 Hz, the optimal one between 6 and 15 Hz. At higher stimulus frequencies a decline of the responses was observed. At the optimal frequency about 5 volleys were sufficient to induce a just detectable heart rate change. Mainly from the results obtained with group III fiber stimulation it is concluded that the intensity and direction of somatically induced heart rate changes are not strictly related to the afferent fiber groups (i.e. fiber threshold and diameter), as suggested by the concept of "pressor" and "depressor" nerve fibers, but to the modality of the receptive units which the fibers subserve.

Adrenalectomy↗
PubMed1981

Muscle receptors with fine afferent fibers which may evoke circulatory reflexes.

The majority of afferent nerve fibers in mammalian skeletal muscle are thin myelinated (A delta or group III) and unmyelinated (C or group IV) afferents. Some 50% of these units appear to be responsible for the reception of noxious chemical, mechanical, and thermal stimuli, i.e., they are nociceptors. The other receptive units with fine afferent fibers presumably are activated by moderate innocuous stimuli such as light stretch, contractions, and light local touching. They possibly play a role in the circulatory and respiratory adjustments during exercise, i.e. they may be ergoreceptors. The data presently available suggest that the nociceptive as well as the ergoreceptive units are very heterogeneous groups with diverse receptive properties. The sensitivity of an individual unit may be restricted to the mechanical domain or to a single chemical substance, whereas other receptors respond to a great variety of chemical, mechanical, and probably thermal stimuli. Each receptor, however, seems to have a preferred susceptibility or "dominant sensitivity" to one or the other stimulus. This sensitivity may be modified by various factors, such as the local concentration of prostaglandins or serotonin. The concept of different types of fine afferent units is supported by preliminary ultrastructural findings showing a great structural diversity both in regard to the localization and the structural design of the receptive endings of these afferents.

Animals↗
PubMed1980

Reflex bladder activity induced by electrical stimulation of hind limb somatic afferents in the cat.

Methods used and results obtained in a study of reflex responses of the bladder were as follows. Intravesical pressure was recorded continuously by the balloon method in chloralose--urethane anaesthetized cats. Various afferent fibres of hind limb cutaneous and muscle nerves were stimulated electrically, and the resulting changes in vesical functions were examined. It was found that: (1) when the bladder was nearly empty and quiescent, repetitive stimulation of group III (thin myelinated) and IV (non-myelinated) cutaneous or muscle afferent fibres of hind limb nerves caused a reflex increase in the vesical tonus. This somato-vesical excitatory reflex was propriospinal with its efferent are mainly in the pelvic nerves; (2) when there were spontaneous, large (amplitude above 300--400 mm H2O), rhythmic (about 1.0--2.5/min) micturition contractions of the expanded bladder, these contractions were inhibited by repetitive stimulation of the group III and IV cutaneous or muscle afferent fibres of hind limb nerves. The inhibition was sometimes followed by subsequent larger micturition contractions. The efferent arc for this somato-vesical inhibitory reflex was also in the pelvic nerves. Supraspinal structures were essential for producing the micturition contractions; (3) stimulation of group III and IV afferent fibres together was more effective than stimulation of the group III afferent fibres alone in activating either the excitatory or inhibitory somato-vesical reflex pathways.

Animals↗
PubMed1979

Field potentials and excitation of primate spinothalamic neurones in response to volleys in muscle afferents.

1. In anesthetized monkeys, stimulation of muscle afferents results in a sequence of cord dorsum potentials. These include a group I volley followed by several negative potentials called here the NI, NII and NIII waves. 2. Evidence based on the effects of graded stimulus strengths, measurements of latencies, and the results of anodal blockade of large muscle afferents indicate that the NI, NII and NIII waves are evoked, respectively, by group I, II and III muscle afferents. 3. The NII and NIII waves appear to be confined to the lumbosacral enlargement when evoked by hind limb muscle afferents. However, the group I volley and NI wave can be detected at least as far rostrally as L 3. 4. The NII and NIII waves were mapped in the depth of the cord. The maxima for these waves were found in the neck of the dorsal horn. The waves reversed to become positive in the ventral horn. 5. Using graded electrical stimulation of muscle nerves it was possible to demonstrate that a few spinothalamic tract neurones could be activated monosynaptically by group I volleys; other spinothalamic cells may have been activated polysynaptically by group I volleys. The lack of any substantial excitation of spinothalamic neurones by intra-arterial injections of succinylcholine suggests that these group I actions may have been due to group Ib afferents from Golgi tendon organs. 6. The most potent excitation of spinothalamic tract cells was due to the action of middle sized and small muscle afferents. Evidence was obtained for an excitatory action of group II, III and IV afferents. There was a good correlation between the effects of graded stimulation in evoking discharges in separate bursts associated with the arrival of volleys in group II and group III afferents and the generation of the NII and NIII waves. 7. Some spinothalamic neurones, including several located in lamina I, were unaffected by the muscle afferent volleys used. It is suggested that such neurones might help to signal well localized pain, whereas the cells which respond to a variety of cutaneous and muscle afferents might be involved in signalling poorly localized pain which is subject to referral.

Animals↗
PubMed1979

Effects of mechanical and chemical stimulation of fine muscle afferents upon primate spinothalamic tract cells.

1. Injections of algesic chemicals were made into the arterial circulation of the triceps surae muscles in anaesthetized monkeys. 2. The responses of a sample of primary muscle afferents suggest that what is known about the activation of muscle afferents in the cat by algesic agents applies also to the monkey. One exception to this is the activation of many group I afferents by KCl in the monkey, but not in the cat. 3. Many spinothalamic tract cells were powerfully excited by the intra-arterial injection of algesic chemicals (bradykinin, 5-hydroxytryptamine (5-HT), KCl) in preparations in which the hind limb was denervated except for the nerves to the triceps surae muscles. The excitatory action of bradykinin had a slower time course than did that of 5-HT or KCl. 4. A number of the spinothalamic tract cells which failed to respond to chemical activation of muscle afferents were located in lamina I of the spinal cord. 5. Repeated injections of bradykinin produced similar responses, whereas the effects of 5-HT injections showed marked tachyphylaxis. 6. No evidence was obtained that activation of muscle spindle afferents by succinylcholine injections resulted in the excitation of spinothalamic tract neurones in the population sampled. 7. Injections of hypertonic NaCl into muscle or tendon produced a prolonged excitation of many spinothalamic tract cells. 8. It is concluded that a substantial proportion of primate spinothalamic tract cells receive a convergent input from cutaneous and muscle receptors. The muscle receptors involved appear to include primary afferents of group III and IV calibre. The possibility is suggested that such cells could play a role in the production of poorly localized pain.

Animals↗
PubMed1979

Descending influences on the responses of spinocervical tract neurones to chemical stimulation of fine muscle afferents.

1. In cats, extracellular micro-electrode recordings were made from axons of the spinocervical tract (s.c.t.) in both the decerebrate state and during cold block of the spinal cord (reversible spinal state) to examine the effects of intra-arterial injection of algesic agents (bradykinin, potassium, 5-hydroxytryptamine) into the gastrocnemius-soleus (g.s.) muscle on the discharge behaviour of s.c.t. neurones.2. In the decerebrate state without cooling the spinal cord 13% of the cells (eleven out of eighty-three) responded to intra-arterial injection of bradykinin, 33% (twenty-two out of sixty-nine) to 5-hydroxytryptamine, and 38% (thirty-five out of ninety-one) to potassium injection.3. The general time course and the latency of the responses of s.c.t. cells induced by injection of pain-producing substances into the g.s. muscle reflect in many respects the activations of g.s. group III and group IV primary afferent units studied previously.4. For twenty-seven s.c.t. neurones the period of recording was long enough to record the responses of the same cell to injections of algesic agents in both the decerebrate and the reversible spinal state. In the reversible spinal state 83% (nineteen out of twenty-three) of the s.c.t. neurones tested with all the three substances responded to at least one of the algesic agents. In the decerebrate state the percentage was lower (39%).5. Reversible spinalization led not only to a significant increase in the number of s.c.t. neurones responding to the algesic agents used but also to an increase in the magnitude of the chemically induced responses.6. The mean latency of the responses of neurones that were activated in both preparations were shorter in the reversible spinal state than in the decerebrate state.7. Control experiments showed that the responses to bradykinin and potassium were entirely due to the nervous outflow from the g.s. muscle. In contrast, intra-arterially applied 5-hydroxytryptamine influenced the s.c.t. cells via unknown additional sites of action.8. The results indicate that muscular group III and/or group IV units excitable by algesic substances do project on to neurones of the spinocervical tract. Furthermore it is concluded that the responses of s.c.t. neurones to activation of fine muscle afferents by algesic agents are subject to a descending control similar to the well known descending modulation of their responsiveness to cutaneous input. Therefore, in addition to serving as a cutaneous pathway the spinocervical tract may take part in muscular nociception.

Action Potentials↗
PubMed1978

Responses of group IV afferent units from skeletal muscle to stretch, contraction and chemical stimulation.

In an attempt to differentiate between nociceptive group IV muscle receptors and "ergoceptive" ones, the discharges of single group IV fibres from skeletal muscle in response to local pressure, sustained stretch, repetitive contraction and intra-arterial injections of bradykinin, 5-hydroxytryptamine (5-HT), potasssium, phosphate, and lactate were studied in anesthetized cats.

Animals↗
PubMed1978

Projections of primary afferent fibres from muscle to neurones of the spinocervical tract of the cat.

1. Micro-electrode recordings were made from axons in the spinocervical tract of decerebrate-spinal cats. 2. The effect of electrical stimulation of afferent fibres in muscle nerves was examined. 3. Stimulation of group III fibres in muscle nerves excited hair only and hair and pressure units in the spinocervical tract. Hair and pressure units also responded to electrical stimulation of group IV fibres. 4. Units of the spinocervical tract excited by stimulation of muscle nerves had receptive fields in the skin overlying the relevant muscles. 5. Stimulation of group III fibres in muscle nerves produced long lasting inhibition of spinocervical tract units. In two such units the inhibitory action of afferent myelinated fibres was enhanced by increasing the stimulus strength so that group IV fibres were recruited.

Animals↗
PubMed1977

Mossy and climbing fiber inputs from cutaneous mechanoreceptors to cerebellar Purkynĕ cells in unanesthetized cats.

1. Mossy and climbing fiber inputs from cutaneous mechanoreceptors to Purkynĕ cells of vermis and pars intermedia of the cerebellar anterior lobe were studied in locally anesthetized, paralyzed cats prepared for painless recording sessions. In this preparation the mossy fiber and climbing fiber pathways remain fully functional. Simple spikes and climbing fiber discharges were recorded simultaneously through extracellular glass micro-electrodes and thereafter filtered off from each other for separate, computer-assisted analysis. Controlled mechanical stimulation (air jets, taps, pressure) was performed on the foot pads of all four limbs and on the hairy skin of the limbs and the body. 2. Long term recording of the spontaneous activity of 110 Purkynĕ cells revealed a simple spike activity of 85 imp./s +/- 49 imp./s (mean +/- S.D.) and 1.00+/-0.78 climbing fiber responses per second. 3. Taps to foot pads and air jets to hairy skin revealed that most of the short latency responses via mossy fibers resulted from activation of the receptors of the ipsilateral forefoot. With the same stimuli climbing fiber discharges from the ipsilateral feet were more frequently evoked than from the contralateral feet. Both via mossy and climbing fibers the contralateral hindlimb gave the smallest contribution. 4. Simple spike responses were evoked more commonly by pad stimulation (tap stimuli) than by hair stimulation (air jets). For both types of stimuli excitatory responses were more frequent (3:1) than inhibitory ones. Similarly, pad stimulation was more effective than hair stimulation in inducing climbing fiber responses. Ipsilateral stimuli were much more effective than contralateral ones in evoking both simple spike and climbing fiber responses. 5. Steady pressure stimuli modify the Purkynĕ cell discharges via mossy and climbing fiber pathways. Excitatory and inhibitory effects often of very long duration have been observed via both pathways. Again the ipsilateral forelimb was more effective than the other limbs. Mossy fiber responses were at least three times as common as climbing fiber responses and excitatory responses were more frequent than inhibitory ones. 6. There is no apparent relation between the spontaneous discharge rates of the Purkynĕ cells and the response magnitudes of the mossy fiber and climbing fiber induced excitatory and inhibitory changes inthe impulse pattern of Purkynĕ cells during steady pressure stimuli.

Afferent Pathways↗
PubMed1977

Somatotopic studies on the vermal cortex of the cerebellar anterior lobe of unanaesthetized cats.

1. In unanaesthetized cats with intact neuraxis the relation between the cutaneous receptive fields of Purkynĕ cells and the position of these cells in the vermis of the cerebellar anterior lobe was studied with the specific question whether this cerebellar area exhibits any kind of somatotopy in the absence of central anaesthesia. To establish the receptive fields the skin of all four limbs and of the trunk was probed with mechanical stimuli (taps, air-jets, pressure). The recording sites in the vermis were determined histologically. 2. In regard to the mossy fiber transmitted input none of the four limbs showed a dominant representation in one or more of the lobules rostral of the fissura prima or in a parasagittal section. For the ipsilateral limbs there is a greater mossy fiber input to lobule V from the forelimb than from the hindlimb (84:59%), and a reversed preponderance for lobule II (45:80%) but this indication of a somatotopic arrangement is not unequivocally paralleled by the other mossy fiber inputs. 3. Also in regard to the climbing fiber input no distinct somatotopical arrangement has been detected. Again it has been noted that the ipsilateral inputs have a somewhat greater input to lobule V from the forelimb than from the hindlimb (35:22%), and the reverse finding holds true for lobule II (10:45%). 4. The overall results did not change appreciably when the responses were grouped according to their latencies or when the Purkynĕ cells were classified according to the patterns of convergence of their receptive fields. 5. The absence of a distinct somatotopic organization in the vermis is a direct consequence of the considerable convergence from the cutaneous mechanoreceptors of the limbs onto the individual Purkynĕ cells which occurs via the mossy and the climbing fiber pathways. It is suggested that this convergence indicates that the vermal Purkynĕ cells are particularly involved in coordinating the motor activity of forelimbs and hindlimbs.

Afferent Pathways↗