Biomedical subjects

R F Schmidt

Publications and source records attributed to R F Schmidt.

At least 91 records · Page 5Linked to original sources

PubMed1987

Enhancement of the responses of ascending tract cells in the cat spinal cord by acute inflammation of the knee joint.

Recordings were made from 16 ascending tract cells in the spinal cords of anaesthetized, spinalized cats before and after an acute arthritis was produced by injection of kaolin and carrageenan into the knee joint. The responses tested routinely were to passive flexion of the knee, an innocuous movement. In some cases, responses to other movements were also tested, and changes in background discharge rates were monitored. Control recordings for a period of 1 h or in 3 cases of 3 h indicated that the responses to flexion were reasonably stationary. Four tract cells that initially showed little or no response to flexion of the knee joint developed large responses within 1 to 2 h after inflammation of the joint. Another 9 cells were tested that had responses to flexion of the knee joint prior to inflammation. In 6 cases, inflammation produced enhanced static or transient responses. In 2 cases, the effect of flexion was initially inhibitory or variable, but after inflammation these cells showed large excitatory responses. In the other case, inflammation had no effect. Background discharges were increased by inflammation in 6 of these 9 cells. The effect of inflammation of the knee joint was tested on 3 tract cells that had no clearly defined receptive field in the knee. In 1 case, a response developed to knee flexion after acute inflammation was produced. In the other 2 cases, there were initially responses to knee flexion, but these were unchanged by inflammation. Two of the cells tested had bilateral receptive fields in or around the knee joints. Inflammation of one knee joint enhanced the responses to flexion of the same but not of the contralateral knee in one case but greatly increased the responses to flexion of both knees in the other case. Injections of prostaglandin (PGE2) caused an enhancement of the responses to knee flexion beyond that caused by inflammation in 5 of 7 cases. One cell whose responses to flexion of the knee were unaffected by inflammation showed inhibitory responses to prostaglandin injections into the inflamed knee joint. The effects of inflammation on the responses of ascending tract cells of the spinal cord appear to serve as a useful neural model of the events responsible for the development of arthritic pain.

Acute Disease↗

PubMed1987

Nerve fibres and their terminals of the dura mater encephali of the rat.

The dura mater encephali of the rat is richly supplied by myelinated (A-axons) and unmyelinated (C-axons) nerve fibres. For the supratentorial part the main nerve supply stems from all three branches of the trigeminal nerve. Finally, 250 myelinated and 800 unmyelinated nerve fibres innervate one side of the supratentorial part. The vascular bed of the dura mater exhibits long postcapillary venules up to 200 micron in length with segments of endothelial fenestration. Lymphatic vessels occur within the dura mater. They leave the cranial cavity through the openings of the cribriform plate, rostral to the bulla tympani together with the transverse sinus, and the middle meningeal artery. The perineural sheath builds up a tube-like net containing the A- and C-axons. It is spacious in the parietal dura mater and dense at the sagittal sinus along its extension from rostral to caudal and at the confluence of sinuses. Terminals of both the A- and C-axons are of the unencapsulated type. Unencapsulated Ruffini-like receptors stemming from A-axons are found in the dural connective tissue at sites where superficial cerebral veins enter the sagittal sinus and at the confluence of sinuses. The terminations of single A-axons together with C-fibre bundles mix up in their final course in one Schwann cell to build up multiaxonal units or terminations (up to 15 axonal profiles). A morphological differentiation is made due to the topography of these terminations; firstly, in different segments of the vascular bed: postcapillary venule, venule, the sinus wall, lymphatic vessel wall, and secondly, within the dura mater: inner periosteal layer, collagenous fibre bundles of the meningeal layer and at the mesothelial cell layer of the subdural space.

Animals↗

PubMed1987

The modulation of visceral functions by somatic afferent activity.

We began by briefly reviewing the historical background of neurophysiological studies of the somato-autonomic reflexes and then discussed recent studies on somatic-visceral reflexes in combination with autonomic efferent nerve activity and effector organ responses. Most of the studies that have advanced our knowledge in this area have been carried out on anesthetized animals, thus eliminating emotional factors. We would like to emphasize again that the functions of many, or perhaps all visceral organs can be modulated by somato-sympathetic or somato-parasympathetic reflex activity induced by a appropriate somatic afferent stimulation in anesthetized animals. As mentioned previously, some autonomic nervous outflow, e.g. the adrenal sympathetic nerve activity, is involved in the control of hormonal secretion. John F. Fulton wrote in his famous textbook "Physiology of the Nervous System" (1949) that the posterior pituitary neurosecretion system (i.e. for oxytocin and vasopressin) could be considered a part of the parasympathetic nervous system. In the study of body homeostasis and environmental adaptation it would seem very important to further analyze the contribution of somatic afferent input to the autonomic nervous and hormonal regulation of visceral organ activity. Also, some immunological functions have been found to be influenced by autonomic nerves or hormones (e.g. adrenal cortical hormone and catecholamines). Finally, we must take into account, as we have briefly discussed, that visceral functions can be modulated by somatic afferent input via various degrees of integration of autonomic nerves, hormones, and immunological processes. We trust that such research will be expanded to higher species of mammals, and that ultimately this knowledge of somato-visceral reflexes obtained in the physiological laboratory will become clinically useful in influencing visceral functions.

Afferent Pathways↗

PubMed1986

Effects of acetylsalicylic acid and indomethacin on single groups III and IV sensory units from acutely inflamed joints.

In cats with an acute experimental inflammation in the right knee joint the effects of acetylsalicylic acid (ASA) and indomethacin on the discharge properties of single fine myelinated and unmyelinated articular afferent units were tested. The knee joint was inflamed by injection of kaolin and carrageenan into the joint cavity some hours before the recording period. Before drug application the single afferent fibres showed resting activity and responses to movements of the joint within its working range which is common for units from the inflamed knee. Resting activity was reduced significantly in most units within 0.5 h after the intravenous injection of the drugs. Within the observation time of about 1-2 h there was no recovery. In a few units a transient increase of resting activity was observed immediately after the injection of a drug. After the initial observation period of 1-2 h the responses to movements were tested. They were reduced in all units except one myelinated afferent. Also during this testing period the resting discharges did not recover. Intra-arterial injection of prostaglandin E2 in low doses close to the joint temporarily nullified the depressing effects of aspirin and indomethacin. Resting activity and movement evoked responses were increased up to the level before the treatment with analgesic drugs. The effects of prostaglandin E2 lasted for several minutes to more than 1 h. The depression of resting and evoked activity in single afferent articular units from inflamed joints is discussed in relation to the analgesic properties of aspirin and indomethacin.

Afferent Pathways↗

PubMed1986

[Correlation of scintigraphic and x-ray findings in Marie-Bamberger secondary hypertrophic osteoarthropathy].

The radiological and scintigraphic findings in the rare condition of hypertrophic osteoarthropathy (Marie-Bamberger) were followed up for a period of two years. They are described and compared. Skeletal scintigraphy shows the abnormalities in the skeleton at an earlier stage than does radiology and also shows more extensive manifestations. The specific symmetrical distribution of abnormally increased uptake in the diaphyses and metaphyses of the long bones of the extremities, with sparing of the axial skeleton, produces highly specific appearances which can be considered as diagnostic.

Adolescent↗

PubMed1986

Responses of spinal cord neurones to stimulation of articular afferent fibres in the cat.

Responses of spinal cord neurones to excitatory input from myelinated and non-myelinated afferent fibres of the knee joint were investigated in spinalized cats that were anaesthetized with alpha-chloralose. The hind limb was largely denervated except for the knee joint. The action of joint afferent volleys on populations of spinal cord neurones was assessed by recordings of cord dorsum potentials and of field potentials within the substance of the spinal cord. Three different negative cord dorsum potentials (NI, NII and NIII waves) were produced by volleys in progressively smaller sized myelinated afferent fibres of the posterior articular nerve of the knee. Volleys in non-myelinated joint afferent fibres did not evoke a detectable cord dorsum potential. The NII and NIII waves could be recorded at segmental levels L4-S2. Field potentials corresponding to the cord dorsum negative waves were recorded with a tungsten micro-electrode inserted into the substance of the cord. The potentials were negative when the recording electrode was in the dorsal horn, but reversed to become positive in the ventral horn. There were differences in the depths at which the different components of the field potential sequence reversed in sign. Single unit recordings revealed that afferent volleys in the posterior articular nerve could excite neurones in segments L5-S1 and at depths from less than 1 to 4 mm below the dorsal surface of the cord. Most marked recording sites were in laminae I, IV-VI or VIII. Many units were activated just by the A fibre component of the joint afferent volley, but others could also be excited by the C fibre component. None were excited just by C fibres. All units tested had a convergent excitatory input from fibres belonging to cutaneous, muscle and mixed nerves. Neurones excited by joint afferent volleys were tested for a receptive field using several forms of local mechanical stimulation of the knee joint and joint movements. Most cells could be activated by one or more of these stimuli. Although many of the effective mechanical stimuli were innocuous, noxious stimuli could often excite the cells more effectively, and some neurones were only activated by noxious stimuli. A few cells with receptive fields in the knee joint did not respond to joint movements.

Action Potentials↗

PubMed1986

Catecholamine secretion and adrenal nerve activity in response to movements of normal and inflamed knee joints in cats.

The effects of articular stimulation on adrenal catecholamine secretion and adrenal sympathetic nerve activity were studied using halothane anaesthetized cats. Various natural passive movements were applied to the normal and inflamed knee joints. Rhythmic flexions and extensions as well as rhythmic inward and outward rotation of normal knee joints within their physiological range of motion did not change nerve activity or the secretion of adrenal catecholamines. Static outward rotation in the normal working range was also ineffective. However, as soon as this static rotation was extended into the noxious range, significant increases in both of these variables were elicited. In the acutely inflamed knee joint, various passive movements produced increases in both adrenal sympathetic and catecholamine secretion. Especially noteworthy was the finding that movements of the inflamed knee joint that were within the normal range of motion produced increases in all variables. Articularly induced increases in adrenal sympathetic nerve activity were diminished by severing various hind-limb somatic afferent nerves and abolished by complete denervation of the knee joint. Additionally, section of the adrenal sympathetic nerves eliminated the catecholamine secretion response. From these data it was concluded that the responses observed in these experiments were reflexes having an afferent limb in hind-limb nerves and an efferent limb in the adrenal sympathetic nerves. A contribution of supraspinal structures was suggested for the reflex responses of sympatho-adrenal medullary function evoked by knee joint stimulations, since spinal transection at the C2 level completely abolished the responses.

Action Potentials↗

PubMed1986

Mechanical sensitivity of group III and IV afferents from posterior articular nerve in normal and inflamed cat knee.

Recordings were performed from sciatic nerve or dorsal root filaments in 28 cats to study single group III (conduction velocity 2.5-20 m/s) and group IV (conduction velocity less than 2.5 m/s) units supplying the knee joint via the posterior articular nerve (PAN). In seven of these cats the knee joint had been inflamed artificially. Recordings from sciatic nerve filaments revealed responses to local mechanical stimulation of the joint in only 3 of 41 group IV units and in 12 of 18 group III units from the normal joint. In the inflamed joint 14 of 36 group IV units and 24 of 36 group III units were excited with local mechanical stimulation. In recordings from dorsal root filaments (normal joint) 4 of 11 group IV units and 7 of 13 group III units were activated by stimulating the joint locally. In the normal joint four group IV units (recorded from dorsal root filaments) responded only to rotations against the resistance of the tissue, whereas the majority of the fibers did not respond even to forceful movements. Group III units with local mechanosensitivity in the normal joint reacted strongly or weakly to movements in the working range of the joint or only to movements against resistance of the tissue. In the inflamed joint, group IV fibers (recorded in sciatic nerve filaments) with detectable receptive fields responded strongly to gentle movements or only to movements against resistance of tissue. Some did not react to movements. Group III units reacted strongly or weakly to gentle movements or only to movements against resistance of the tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1986

Discharge characteristics of receptors with fine afferents from normal and inflamed joints: influence of analgesics and prostaglandins.

This contribution presents several aspects of our work which are relevant in order to understand how pyrazolone drugs act. They include the discharge characteristics of individual fine afferent nerve fibres from the normal intact joint, the changes that acute experimental inflammation can induce in them, and the effects of prostaglandins and non-steroidal anti-inflammatory drugs.

Action Potentials↗

PubMed1985

Activation of fine articular afferent units by bradykinin.

The responses of single fine articular afferent units to close intra-arterial injection of KCl and bradykinin were recorded from filaments of the saphenous nerve of the cat's right hindlimb. All units included in this study were sensitive to local mechanical probing of the medial and anteromedial aspects of the knee joint. The units were identified by conduction velocity as belonging either to group III (2.5-20 m/s, 17 units) or group IV (less than 2.5 m/s, 23 units). Prior to bradykinin administration the responses of all units to passive limb movements were recorded in order to classify the units as belonging to one of the following 4 categories: activated by non-noxious movements; weakly activated by non-noxious movements; activated only by noxious movements; not activated by movements. Bolus injections of KCl were used to test the accessibility of the units via the blood vessels. Such injections elicited a rapid burst of impulses at short latencies of less than 1 s. If this discharge did not occur, no test with bradykinin was carried out. There was no difference in latency and time course between such discharges in group III and group IV units. With only 3 exceptions the 40 units excited by KCl were also activated by bradykinin which was applied in doses from 0.026 to 26 micrograms. Higher doses were not used. For most group III and IV units the minimal effective dose of bradykinin for a clear excitation was usually either 0.26 or 2.6 micrograms. In both groups of units the bradykinin-evoked discharge generally had a uniform latency and a time course with a total duration well under 1 min. In the course of repetitive injections at intervals of 3-5 min, the latency of the evoked discharge increased gradually and its magnitude became successively smaller. This tachyphylaxis was usually very pronounced, regardless of whether low or high doses of bradykinin were administered. No differences in the bradykinin sensitivity were found between units with very low to very high thresholds to local mechanical stimulation (tested with von Frey hairs) and between units belonging to the 4 different categories of response behavior to passive innocuous and noxious joint movements. These results indicate that the sensitivity to bradykinin is shared by all fine articular afferent units, regardless of their thresholds to local mechanical stimulation and joint movement and, hence, their functional role in signaling innocuous or noxious mechanical events at the knee joint.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1985

Degeneration patterns of postganglionic fibers following sympathectomy.

In cats the time course of degeneration following lumbal sympathectomy was studied in the ramus communicans griseus (rcg) and in the nerves to the triceps surae muscle using light and electron microscopic methods. The left lumbar sympathetic trunk including its rami communicantes was removed from L2 to S1 using a lateral approach. The animals were sacrificed between 2 and 48 days after the sympathectomy. Tissue samples were taken (a) one cm proximal to the entrance of the rcg into the spinal nerve, and (b) one cm proximal to the entrance of the nerve into the muscle belly. In the rcg signs of degeneration can already be recognized in the myelinated as well as in the unmyelinated axons 48 h after sympathectomy. The degenerative processes in the axons reach their peak activity at about 4 days p.o. They end a week later. Signs of the reactions of the Schwann cells and of the endoneural cells can first be seen 2 days p.o. They are most pronounced around the 8th day p.o., and last at least up to the third week. Thereafter the cicatrization processes settled to a rather steady state (total observation period 7 weeks). In the muscle nerves the first signs of an axonal degeneration of the sympathetic fibers can be recognized 4 days after surgery. The signs of axonal degeneration are most striking about 8 days p.o. They have more or less disappeared another week later. The reactions of the Schwann cells also start on the fourth day but outlast the degenerative processes by some 8 days. Thus the degenerative and reactive processes in the rcg precede those in the muscle nerves by 2 days early after surgery and by 6 days 3 weeks later. Seven weeks after surgery, fragments of folded basement lamella and Remak bundles with condensed cytoplasm and numerous flat processes are persisting signs of the degeneration. In addition to the differences in time course between the proximal and the distal site of observation, it was also noted that both the axonal degeneration and the reactions of the Schwann cells are more pronounced in the rcg than in the muscle nerve. For example there was abundant mitotic activity in the central endoneural and Schwann cells whereas we could not detect such activity in the periphery.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1985

Sensory innervation of the Achilles tendon by group III and IV afferent fibers.

In sympathectomized cats the innervation of the Achilles tendon by fine afferent nerve fibers was studied with semithin and ultrathin sections. Several different types of sensory endings of group III and group IV nerve fibers were identified. Of the five different types of endings in the group III range (T III endings), two are located within vessel walls. One of them ends in the circumference of the venous vessels (T III/VV). Its lanceolate terminals have characteristic receptor areas at their edges. The second type ends in the adventitia of lymphatic vessels (T III/LV). Its receptive areas are scattered along their terminal course. Two further group III endings ramify within the connective tissue compartments of the vessel-nerve-fascicles of the peritenonium externum and internum. One type is tightly surrounded by collagen fibrils (T III/PTic); the other terminates between the collagen fiber bundles (T III/PTgc). The latter arrangement recalls the ultrastructural relation between nerve terminals and collagen tissue in Golgi tendon organs. The fifth type innervates the endoneural connective tissue of small nerve fiber bundles (T III/EN). At least some of them come into close contact with bundles of collagen fibers which penetrate the perineural sheath to terminate within the endoneurium. The endings of group IV afferents (T IV endings) show a striking topographic relationship to the blood and lymphatic vessels of all connective tissue compartments of the Achilles tendon. They form penicillate endings which may contain granulated vesicles. In any event, they can easily be discriminated from the T III endings in the vessel walls. In close neighborhood to Remak bundles, a cell has been regularly found which fulfilled all ultrastructural criteria for mast cells. But this cell is not a mast cell proper because it is surrounded by a basal lamina (pseudo mast cell).

Achilles Tendon↗

PubMed1985

Reactions of cardiac postganglionic sympathetic neurons to movements of normal and inflamed knee joints.

The effects of passive movements of normal and inflamed knee joints on unitary activity in filaments of the inferior cardiac nerve (ICN) were studied in cats anesthetized with chloralose and urethane. The effects were compared with those obtained by electrical stimulation of afferent A- and C-fibers in the medial articular nerve, in muscle and in cutaneous hind limb nerves. The vagus nerves were cut and the right carotid artery was tied off. The left carotid sinus was intact. All ICN units used in this study displayed spontaneous activity which was usually related to the cardiac and respiratory rhythms. The ICN units were regularly excited by electrically evoked single or short repetitive A-volleys in articular, cutaneous and muscle nerves. The excitation was followed by a silent period. Inclusion of C-fibers in the afferent volleys gave a second, long-latency burst of impulses which was seen only with short repetitive stimulation. Passive movements in the normal working range of the joint did not influence the activity of ICN units. However, noxious joint movements, particularly of inflamed joints, led to pronounced excitation of ICN units accompanied by rises in blood pressure. Most of these effects could still be seen after all nerves to the hind limbs, except the medial articular nerve, were cut. It is proposed (a) that ICN units form a homogeneous population of sympathetic postganglionic units whose reaction pattern to somatovisceral input is distinctly different from that of other sympathetic subsystems, and (b) that articular receptors make a substantial contribution to the ICN input particularly when many fine afferent units are sensitized to mechanical stimulation by an acute joint inflammation.

Afferent Pathways↗

PubMed1985

Effects of an experimental arthritis on the sensory properties of fine articular afferent units.

An acute experimental arthritis was induced in the right knee joint of adult cats anesthetized with chloralose, and the activity of single fine afferent units of the medial articular nerve was recorded from filaments of the saphenous nerve. All units included in this study were sensitive to local mechanical probing of the medial and anteromedial aspects of the knee joint. The units were identified by their conduction velocity as belonging either to group III (2.5-20 m/s, 48 U) or group IV (less than 2.5 m/s, 29 U). After the identification, the resting activity was measured, and the evoked activity was determined using local mechanical stimulation with glass rods and von Frey hairs, and passive movements of the knee joint. The results were compared with those obtained in a similar study of fine articular units from normal joints. Resting activity was observed in 75% of the group III and 83% of the group IV units. The discharges were irregular and often of high frequency. Both the percentages of units with resting activity and the frequencies of their discharges were more than twice as high as in the control sample. Nearly all units from inflamed joints had low threshold to movements (group III 89%, group IV 72%), and most units responded well to flexion and extension. In contrast, in units from normal joints only 33% of the group III and 10% of the group IV units responded well to passive movements in the normal working range of the joint. In inflamed as well as in normal joints the responses were mostly tonic in character and adapted slowly or not at all when the joint was held in a new position. In normal joints 24% of the group III and 36.5% of the group IV afferent units with local mechanosensitive receptive fields could not be excited by any physiological or noxious joint movements. Such units were only very occasionally seen in the present sample. The average number of receptive fields per unit found in inflamed joints exceeded considerably that in normal units, but no systematic drop in von Frey thresholds was seen when comparing the control sample with the inflamed one. From the above data we conclude that an acute inflammation sensitizes many fine articular units, making them active at rest and increasing the responsiveness more readily to normally innocuous joint movements. Both nociceptors and units with low threshold to movement seem to become sensitized by the inflammation.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1984

Changes in blood pressure and heart rate induced by movements of normal and inflamed knee joints.

The effects of passive movements of normal and inflamed knee joints on blood pressure and heart rate were recorded in baroreceptor denervated cats anesthetized with halothane, and these effects were compared with those obtained by severe noxious squeezing of the hind paw. Rhythmic flexions and extensions as well as rhythmic inward and outward rotations of a normal knee joint in its physiological working range did not have any significant influence on blood pressure and heart rate. However, on the inflamed side, the same movements caused definite increases in blood pressure and heart rate (e.g. mean increases for flexion-extension movements were 13 mmHg and 4 beats/min, respectively, P less than 0.01). Static outward rotations in the normal working range were ineffective in both joints, but as soon as these static rotations were extended into the noxious range significant increases in blood pressure and heart rate were elicited. The respective mean increases induced from the normal and inflamed sides were 17 and 38 mmHg for the blood pressure and 4 and 8 beats/min for the heart rate. The increases in blood pressure and heart rate induced by noxious outward rotation of the inflamed joint regularly exceeded those elicited by noxious squeezing of the hind paw. It is concluded that impulses in articular nociceptors and possibly other fine articular afferent units activate sympathetic outflow to the cardiovascular system, and that these effects are particularly prominent when the joint receptors are sensitized by

Animals↗

PubMed1983

Types of afferents from the knee joint evoking sympathetic reflexes in cat inferior cardiac nerves.

In anesthetized cats electrical stimulation of the medial articular nerve of the knee joint evoked sympathetic reflex discharges in inferior cardiac nerves. Low intensity single stimuli elicited early reflex discharges (A-reflexes, latency 70-90 ms, duration 110-200 ms) whereas short tetanic stimulation at higher intensities evoked, in addition, late reflexes (C-reflexes, latency 390-480 ms, duration 230-400 ms). An analysis of the relation between the conduction velocity and the electrical threshold of 231 single medial articular nerve fibers revealed that the A-reflex is mainly due to activation of Group II units, whereas the C-reflex is evoked by activity in unmyelinated Group IV fibers.

Animals↗

PubMed1983

Discharge characteristics of fine medial articular afferents at rest and during passive movements of inflamed knee joints.

After induction of an experimental knee joint inflammation, the activity of single Group III and IV afferent units in the medial articular nerve of the cat was recorded at rest and during passive movements. The properties of these units were compared to those sampled from normal knee joints. The proportion of units displaying resting discharges was higher in the inflamed group. The frequency of discharges was also higher. The receptive fields were larger than those in the control units. Passive movements in the normal working range of the joint activated many more units in the inflamed joint than in the control sample. We conclude that joint inflammation sensitizes articular nociceptors to be active not only at rest, but also during normally innocuous joint movements.

Animals↗

PubMed1983

An electron microscopic analysis of the left phrenic nerve in the rat.

In this electron microscopic study, the axonal categories in the left phrenic nerve at its entrance to the diaphragm have been determined. At a level 3 mm rostral to the diaphragm, the left phrenic nerve contains approximately 700 axons: 57% are myelinated and 43% are unmyelinated. The dorsal root ganglion cells give rise to 31% of the myelinated axons and the ventral root contributes 69%. Of the unmyelinated axons, the dorsal root ganglion cell contributes 59%, the cervical sympathetic chain 24%, and 17% course through the ventral roots. These ventral root unmyelinated axons are presumably preganglionic efferents since the proximal stump of the ventral root showed no decrease in unmyelinated axons after ventral rhizotomy.

Animals↗