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Biomedical subjects

C Weidner

Publications and source records attributed to C Weidner.

At least 19 recordsLinked to original sources
PubMed2005

Can receptor potentials be detected with threshold tracking in rat cutaneous nociceptive terminals?

Threshold tracking of individual polymodal C- and Adelta-fiber terminals was used to assess membrane potential changes induced by de- or hyperpolarizing stimuli in the isolated rat skin-nerve preparation. Constant current pulses were delivered (1 Hz) through a tungsten microelectrode inserted in the receptive field, and the current amplitude was controlled by feedback with a laboratory computer programmed to serially determine the electrical threshold using the method of limits. During threshold tracking, the receptive fields of the fibers were heated (32-46 degrees C in 210 s) or superfused with modified synthetic interstitial fluid containing either 0, 20, 40, 50, or 60 mM [K+], phosphate buffer to pH 5.2 or 6.1, or bradykinin (BK, 10(-8)-10(-5) M). High [K+]e decreased the current threshold for activation by 6-14% over 120 s, whereas K+-free superfusion augmented the threshold by >5%, and after some delay, also induced ongoing discharge in 60% of units. pH 6.1 and 5.2 caused an increase in threshold of 6 and 18%, respectively, and 30% of the fibers were excited by low pH, although the change in threshold of pH responsive and unresponsive fibers did not differ significantly, suggesting a general excitability decrease induced by protons. Heat stimulation increased the mean threshold and conduction velocity of the fibers tested and resulted in activity in 78% of units. Additionally, for these units, activation was preceded by a significant decrease in threshold compared with the tracked thresholds of fibers unresponsive to heat. Bradykinin also led to a significant threshold decrease before activation. In conclusion, the technique of threshold tracking proved suitable to assess changes in excitability resulting from receptor currents evoked by noxious heat and bradykinin in the terminal arborization of cutaneous nociceptors.

Adaptation, Physiological↗
PubMed2005

[Work disability from mental disorders].

Sick leave certifications allow patients to stay away from work without negative consequences. German regulations state that patients can be granted sick leave when duties can no longer be fulfilled or may endanger health status and when there is a causal relationship between illness and disability. Relevant is not the presence of illness but of a disability which interferes with work requirements. In Germany, an average of 4% of workers are on sick leave at any given time, corresponding to about 2 weeks per year and person. The level of sick leave depends not only on the patient's health status but also on social factors. Mental disorders are a major reason for sick leave. Sick leave can have negative effects by fostering chronicity. In 75% of cases, physicians have been found to grant sick leave incorrectly. It must be kept in mind that not illness per se but only disorders of participation justify sick leave.

Disability Evaluation↗
PubMed2005

Bioenergetics of archaea: ATP synthesis under harsh environmental conditions.

Archaea are a heterogeneous group of microorganisms that often thrive under harsh environmental conditions such as high temperatures, extreme pHs and high salinity. As other living cells, they use chemiosmotic mechanisms along with substrate level phosphorylation to conserve energy in form of ATP. Because some archaea are rooted close to the origin in the tree of life, these unusual mechanisms are considered to have developed very early in the history of life and, therefore, may represent first energy-conserving mechanisms. A key component in cellular bioenergetics is the ATP synthase. The enzyme from archaea represents a new class of ATPases, the A1A0 ATP synthases. They are composed of two domains that function as a pair of rotary motors connected by a central and peripheral stalk(s). The structure of the chemically-driven motor (A1) was solved by small-angle X-ray scattering in solution, and the structure of the first A1A0 ATP synthases was obtained recently by single particle analyses. These studies revealed novel structural features such as a second peripheral stalk and a collar-like structure. In addition, the membrane-embedded electrically-driven motor (A0) is very different in archaea with sometimes novel, exceptional subunit composition and coupling stoichiometries that may reflect the differences in energy-conserving mechanisms as well as adaptation to temperatures at or above 100 degrees C.

Adenosine Triphosphate↗
PubMed2004

Spinal anesthesia for cesarean section following inadequate labor epidural analgesia: a retrospective audit.

BACKGROUND: High blocks have been reported when spinal anesthesia is used for cesarean section following inadequate labor epidural analgesia. We have therefore modified the practice at our institution to minimize this risk and conducted a retrospective observational study of outcome following the change of practice. METHOD: The records of 115 women with inadequate epidural labor analgesia who required cesarean section between July 1998 and January 2002 were studied. No epidural boluses were administered in the 30 min preceding spinal anesthesia and a reduced spinal dose, median (range) 9.38 mg (7.5-11.3 mg) of 0.75% hyperbaric bupivacaine and fentanyl 15 microg (10-25 microg) was used. Patients were left sitting for 2 min and then positioned supine with left uterine displacement and were closely monitored for symptoms or signs that would suggest a high block. RESULTS: No parturient developed a high spinal necessitating intubation, and there was no adverse neonatal outcome. CONCLUSION: These findings do not conclusively establish this method as safe, but should spinal anesthesia for cesarean section following suboptimal labor epidural analgesia be considered, avoiding epidural boluses immediately preceding spinal injection, using a lower spinal dose, and delayed supine positioning following spinal injection may be advisable.

Adult↗
PubMed2003

Active "itch fibers" in chronic pruritus.

An itch-specific neuronal pathway was recently discovered in healthy humans and animals. Here the authors report that activity in this specific pathway coincides with itch under pathophysiologic conditions in a patient with chronic pruritus. Microneurographic recordings from the symptomatic area revealed spontaneous activity in six single C-fiber afferents that had the characteristic features of "itch fibers." Itch may be caused by activity in a specific subpopulation of C-fiber afferents.

Chronic Disease↗
PubMed2003

[Finding the reasons for "workplace phobia". Sick leave can cause damage].

Anxiety engendered by the workplace leads to an inability to work and earn one's living. The term workplace phobia is applied when anxiety leads to avoidance of the workplace. As in the case of school phobia, a range of differential diagnoses may be involved, requiring careful clarification. Such may include post-traumatic stress disease, posttraumatic embitterment, social phobia, personality disorders, depression and organic brain disease. The treatment of workplace-related phobia differs from that of other phobias because of the peculiarities of the workplace. Simply giving the patient sick leave may do more harm than good, and as such needs to be carefully weighed up.

Anxiety Disorders↗
PubMed2003

Action potential conduction in the terminal arborisation of nociceptive C-fibre afferents.

Recordings of single human peroneal C-fibres and rat saphenous C-fibres confirm two different patterns of conduction at branching points. In general, an action potential (AP) arising from one terminal branch may be propagated not only centrally, but also antidromically into the other branches of the terminal arborisation. If a stimulus activates several converging branches of one unit, at each branching point only the AP arriving first from the simultaneously activated daughter branches will be propagated centrally, resetting the slower branches. However, occasionally a single electrical stimulus may evoke a double response in the parent axon. In this case, these two responses apparently originate from different terminal branches and require unidirectional conduction block to prevent the faster AP from invading and resetting the slower-conducting terminal. This conclusion is supported by the notion that when such a double response occurs, both responses immediately show additional activity-dependent slowing of the conduction velocity due to frequency increase in the parent axon (two spikes per stimulus, one from each of the two excited branches). A comparable discharge pattern in the stem axon can be induced by repetitive paired stimulation of one terminal branch. Then the slowing is induced by the doubled frequency along the whole nerve fibre including the terminal branch. Since in this case not only the stem axon, but also the terminal branches carry two spikes per pulse, activity-dependent slowing is predictably more pronounced. Unidirectional block thus provides insight into the differential amount of activity-dependent slowing (and hence postexcitatory hyperpolarisation) in the stem axon and terminal branches of cutaneous C-fibres. This comparison reveals that more than two-thirds of the slowing can be attributed to the terminal branches, since it is two- to fourfold that observed during double stimulation as compared with the unidirectional block condition. This indicates that the terminal branches are equipped with membrane proteins that are different from those of the parent axon.

Action Potentials↗
PubMed2003

Chemical response pattern of different classes of C-nociceptors to pruritogens and algogens.

Vasoneuroactive substances were applied through intradermal microdialysis membranes and characterized as itch- or pain-inducing in psychophysical experiments. Histamine always provoked itching and rarely pain, capsaicin always pain but never itching. Prostaglandin E(2) (PGE(2)) led preferentially to moderate itching. Serotonin, acetylcholine, and bradykinin induced pain more often than itching. Subsequently the same substances were used in microneurography experiments to characterize the sensitivity profile of human cutaneous C-nociceptors. The responses of 89 mechanoresponsive (CMH, polymodal nociceptors), 52 mechanoinsensitive, histamine-negative (CMi(His-)), and 24 mechanoinsensitive, histamine-positive (CMi(His+)) units were compared. CMi(His+) units were most responsive to histamine and to PGE(2) and less to serotonin, ACh, bradykinin, and capsaicin. CMH units (polymodal nociceptors) and CMi(His-) units showed significantly weaker responses to histamine, PGE(2), and acetylcholine. Capsaicin and bradykinin responses were not significantly different in the two classes of mechano-insensitive units. We conclude that CMi(His+) units are "selective," but not "specific" for pruritogenic substances and that the pruritic potency of a mediator increases with its ability to activate CMi(His+) units but decreases with activation of CMH and CMi(His-) units.

Acetylcholine↗
PubMed2002

Innervation territories of mechano-insensitive C nociceptors in human skin.

Microneurographic recordings were obtained in the peroneal nerve from 20 mechano-insensitive units (CMi) and six mechano-heat responsive C units (CMH) in healthy human subjects. Their innervation territories in the skin of the leg or foot were assessed by transcutaneous electrical stimulation with a pointed probe at intensities of 10 to 100 mA (0.2 ms) and, when applicable, by mechanical von Frey hair stimulation. Electro-receptive fields (eRFs) of CMH units had a median area of 1.95 cm(2) when mapped with 10 mA that coincided approximately with mechano-receptive fields (mRFs) as mapped with a 750-mN von Frey hair. Fifty-milliampere stimuli increased the eRFs to 3.08 cm(2) in a concentric manner. This was probably due to current spread since these units are known to have low electrical thresholds. Further increase of the stimulus strength to 70 or 100 mA increased the eRFs only marginally. Mechano-insensitive units had much smaller eRFs (median: 0.35 cm(2)) than CMH units when mapped with the same pointed probe at 10 mA (n = 13). The receptive territories consisted of one distinct spot or of several spots separated by distances of more than 1 cm. However, when mapping stimuli of 50 mA were applied, eRFs became continuous and grew to a median area of 5.34 cm(2), i.e., larger than those of CMHs. The borders of eRFs of CMi units were significantly more irregular compared with CMH units. A further increase of the stimulus intensity to a maximum of 100 mA only marginally enlarged the eRFs. The CMi units could be activated by heat or chemical substances applied inside the 50-mA eRF, indicating that receptive nerve endings were mapped. Responsiveness to these stimuli was inhomogeneous within the eRFs. It was concluded that innervation territories of CMi units in human skin exceed those of CMH units in size by a factor of approximately 3. The widely branched terminals underlying the large fields are consistent with a role of this nociceptor class in axon reflex flare and preclude a role in exact spatial discrimination of noxious stimuli.

Adult↗
PubMed2000

Time course of post-excitatory effects separates afferent human C fibre classes.

1. To study post-excitatory changes of conduction velocity, action potentials were recorded from 132 unmyelinated nerve fibres (C fibres) in cutaneous fascicles of the peroneal nerve using microneurography in healthy human subjects. The 'marking' technique was used to assess responsiveness to mechanical and heat stimuli or sympathetic reflex provocation. 2. C fibres were classified into three major classes: mechano-responsive afferent (n = 76), mechano-insensitive afferent (n = 48) and sympathetic efferent C fibres (n = 8). 3. During regular stimulation at 0.25 Hz, conditioning pulses were intermittently interposed. Changes of conduction velocity were assessed for different numbers of conditioning impulses and varying interstimulus intervals (ISIs). For all three fibre classes the latency shift following conditioning pulses at an ISI of 1000 ms increased linearly with their number (n = 1, 2 and 4). However, the absolute degree of conduction velocity slowing was much higher in the 32 mechano-insensitive fibres as compared with 56 mechano-responsive or 8 sympathetic fibres. 4. Single additional pulses were interposed at different ISIs from 20 to 2000 ms. For 20 mechano-responsive fibres conduction velocity slowing increased with decreasing ISI (subnormal phase). In contrast, for 16 mechano-insensitive C fibres the conduction velocity slowing decreased with shorter ISIs, and at values lower than 417 +/- 49 ms (mean +/- s.e.m.) the conduction velocity of the conditioned action potential was faster than before (conduction velocity speeding). This supernormal phase had its maximum at 69 +/- 10 ms. 5. In this study we provide, for the first time, direct evidence of relative supernormal conduction in human mechano-insensitive C fibres. The implications for temporal coding in different afferent C fibre classes are discussed.

Action Potentials↗
PubMed2000

Which nerve fibers mediate the axon reflex flare in human skin?

Axon reflex vasodilatation due to transcutaneous electrical stimulation in human skin was measured by laser Doppler imaging. Constant current pulses of 10 mA, 0.2 ms, delivered at 1 or 10 Hz for 2 min through a probe of 30 mm2 surface area did not induce a significant flare response, though this stimulus previously has been found supra-maximal for cutaneous polymodal (mechano-heat responsive) C-nociceptors in microneurography experiments. Pulses of the same strength from a pointed probe yielding a higher current density induced an extended and persistent flare. This type of stimulus previously has been proven to recruit mechano-insensitive C-units in microneurography experiments, in contrast to stimuli from the 30 mm2 probe. It is concluded that mechano-insensitive C-nociceptors and not polymodal C-units mediate the axon reflex flare in human skin.

Adult↗
PubMed2000

Low-dose lidocaine reduces secondary hyperalgesia by a central mode of action.

Sodium channel blockers are approved for intravenous administration in the treatment of neuropathic pain states. Preclinical studies have suggested antihyperalgesic effects on the peripheral as well as the central nervous system. The objective of this study was to determine mechanisms of action of low-dose lidocaine in experimental induced, secondary hyperalgesia. In a first experimental trial, participants (n=12) received lidocaine systemically (a bolus injection of 2 mg/kg in 10 min followed by an intravenous infusion of 2 mg kg(-1)h(-1) for another 50 min). In a second trial, a modified intravenous regional anesthesia (IVRA) was administered to exclude possible central analgesic effects. In one arm, patients received an infusion of 40 ml lidocaine, 0.05%; in the other arm 40 ml NaCl, 0.9%, served as a control. In both trials capsaicin, 20 microgram, was injected intradermally and time course of capsaicin-induced pain, allodynia and hyperalgesia as well as axon reflex flare was determined. The capsaicin-induced pain was slightly reduced after systemic and regional application of the anesthetic. The area of pin-prick hyperalgesia was significantly reduced by systemic lidocaine, whereas the inhibition of hyperalgesia was absent during regional administration of lidocaine. In contrast, capsaicin-induced flare was significantly decreased after both treatments. We conclude that systemic lidocaine reduces pin-prick hyperalgesia by a central mode of action, which could involve blockade of terminal branches of nociceptors. A possible role for tetrodotoxin resistant sodium channels in the antihyperalgesic effect of low-dose lidocaine is discussed.

Adult↗
PubMed2000

Acute effects of substance P and calcitonin gene-related peptide in human skin--a microdialysis study.

Upon activation nociceptors release neuropeptides in the skin provoking vasodilation and plasma protein extravasation in rodents, but only vasodilation in humans. Pivotal peptides in the induction of neurogenic inflammation comprise calcitonin gene-related peptide and substance P, the latter being suggested to act partly via degranulation of mast cells. In this study substance P and calcitonin gene-related peptide-induced vasodilation, protein extravasation, histamine release, and sensory effects were investigated simultaneously in human skin by dermal microdialysis. The vasodilatory prostaglandin E(2) and the mast cell activator codeine served as positive controls. Substance P and calcitonin gene-related peptide applied intradermally via large cut-off plasmapheresis capillaries induced dose-dependent local vasodilation, but only SP provoked protein extravasation in concentrations greater than 10(-9) M. Substance P-induced (10(-8)-10(-6) M) protein extravasation was not accompanied by histamine release and was unaffected by cetirizine (histamine H1 blocker, 200 microg per ml). Only the highest concentration of substance P (10(-5) M) induced significant histamine release. Neither neuropeptide caused any axon reflex erythema or any itch or pain sensation, whereas mast cell degranulation by codeine dose dependently provoked itch, flare, protein extravasation, and histamine release. In human skin calcitonin gene-related peptide and substance P induce vasodilation by a mechanism not involving histamine. No evidence for neuropeptide-induced activation of nociceptors was obtained. Our results suggest that endogenous calcitonin gene-related peptide and substance P have no acute sensory function in human skin. The lack of neurogenic protein extravasation in humans can most probably be attributed to low local concentrations of this neuropeptide still sufficient to exert trophic and immunomodulatory effects (10(-11) M), but too low to induce protein extravasation (10(-8) M) or even mast cell degranulation (10(-5) M). J Invest Dermatol 115:1015-1020 2000

Adult↗
PubMed1999

Functional attributes discriminating mechano-insensitive and mechano-responsive C nociceptors in human skin.

Microneurography was used in healthy human subjects to record action potentials from unmyelinated nerve fibers (C units) in cutaneous fascicles of the peroneal nerve. Activity-dependent slowing (n = 96) and transcutaneous electrical thresholds (n = 67) were determined. Eight units were sympathetic efferents according to their responses to sympathetic reflex provocations. Mechano-heat-responsive C units (CMH) (n = 56) had thresholds to von Frey hair stimulation </=90 mN (6.5 bar). Mechano-insensitive C units (n = 32) were unresponsive to 750 mN (18 bar). Twenty-six mechano-insensitive units responded to heat (CH), and the remaining six units did not respond to physical stimuli but were proven to be afferent by their response to intracutaneous capsaicin (CM(i)H(i)). Mechano-insensitive units had significantly slower conduction velocity (0.81 +/- 0.03 m/sec), and CH units had higher heat thresholds (48.0 +/- 0.6 degrees C) compared with CMH units (1.01 +/- 0.01 m/sec; 40.7 +/- 0.4 degrees C). Transcutaneous electrical thresholds were <9 mA for CMH units and >35 mA for CH and CM(i)H(i) units. Activity-dependent slowing was much more pronounced in mechano-insensitive than in mechano-responsive units, without overlap. Sympathetic efferent C units showed intermediate slowing, significantly different from CMH, and completely separate from CH and CM(i)H(i) units. The activity-dependent slowing of conduction provides evidence for different membrane attributes of different classes of C fibers in humans.

Adult↗
PubMed1999

[Control of referral and duration of rehabilitation in federal insurance office provided rehabilitation].

Presented is a computer-based system for interactive assignment control, designed to cope with the increasing requirements in rehabilitation and health care concerning quality assurance, greater flexibility, as well as enhanced effectiveness and efficiency. Thanks to multi-factor control, medical, organizational and economic parameters can be taken into account selectively. In addition, an unbureaucratic approach to determining length of rehabilitation programme participation is described, which has been implemented successfully for the last three years.

Germany↗
PubMed1995

Interspecific variation in the chelonian primary visual system.

The primary visual system of 21 species of turtles, distributed among nine of the existing 12 families, were studied by autoradiography. In all species, contralateral visual projections exist to 15 targets: two hypothalamic structures (nucleus suprachiasmaticus and n. periventricularis), three major thalamic visual centres (nucleus ovalis, n. geniculatus lateralis ventralis and n. geniculatus lateralis dorsalis) and two minor thalamic targets (nucleus dorsolateralis anterior and n. ventrolateralis), five pretectal sites (nucleus geniculatus pretectalis, n. opticus pretectalis ventrolateralis, n. lentiformis mesencephali, n. posterodorsalis and n. griseus tectalis), two strata of the optic tectum (stratum opticum and s. fibrosum et griseum superficiale), and a single tegmental target (nucleus opticus tegmenti). In contrast to the stability of contralateral visual projections, their ipsilateral counterparts varied considerably between species, being limited to the hypothalamus in some species, and involving the majority of the primary visual centres in others. This variation is not readily explainable in terms of taxonomic position or of differences in mode of life.

Animals↗
PubMed1988

Visual system degeneration in the glaucomatous albino quail.

The peripheral (eye, retina, optic nerve) and central (primary optic tracti and centers, centrifugal visual tractus and nucleus) visual system of an imperfect albino quail mutant with a sex linked recessive gene was examined in 32 specimens ages 1 week - 16 months-hatch using various histological techniques. During the first weeks the visual system was normal and comparable in its overall organization to that found in the pigmented quail. However, the ipsilateral retinal projections were observed to be weaker in the young mutant, then completely disappeared two months after birth. Initial signs of the bupthalmos, a form of spontaneous glaucoma, appeared between the 3rd and 5th months. This was characterized by a distention of the eye linked to an increase in intraocular pressure. The pathological process was progressive and at 16 months the eye was very prominent, the anterior chamber deep and a large and globular cornea was noted. The glaucoma progressively induced different histopathological changes in the visual system including: cupping of the optic disc, degeneration of optic axons and their parent ganglion and centrifugal cells and cavernous degeneration. All of these phenomena were identifiable at about the 10th post-natal month and progressed in a relatively constant and orderly manner. The retinal projections to the nucleus ectomamillaris, ventral and lateral optic tectum and ventral pretectum were the first to degenerate. The degeneration of optic fibers attaining the dorsal pretectum and dorsal thalamus occurred later. Furthermore the retrograde degeneration in the centrifugal isthmo-optic nucleus progressed from the external to the internal pole. The mechanisms involved in the selective degeneration of centrifugal and centripetal optic fibers is discussed.

Age Factors↗