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Biomedical subjects

M Michaelis

Publications and source records attributed to M Michaelis.

At least 55 records · Page 3Linked to original sources
PubMed1996

[Occupational medicine in public health service--evaluation results of an continuing education symposium].

The demand for a quality controlled and quality proved continuing medical education (CME) has grown in the past. Especially the German "Bundesärztekammer" (society of physicians of Germany) has developed new models for CME and it's evaluation. This paper presents the background, methodology and results of two evaluations of CME for occupational physicians in health care institutions. The two symposia in 1994 and 1995 were evaluated using the same questionnaire. The comparative analysis of the results indicates the feasibility of the instrument and the validity of the results when used together with the results on an open discussion at the end of the symposium. It also demonstrates the value of the evaluation for future planning of comparable programs.

Adult↗
PubMed1995

Development of spontaneous activity and mechanosensitivity in axotomized afferent nerve fibers during the first hours after nerve transection in rats.

1. Spontaneous activity and ectopic mechanical excitability of axotomized unmyelinated and myelinated fibers in the sural nerve were examined in anesthetized rats. The analysis was performed within 30 h after the nerve lesion using single-fiber recordings that were performed proximal to the severed nerve end. 2. Among all unmyelinated fibers tested (n = 865), 4-8% exhibited persistent spontaneous activity of low and irregular frequency. The percentage of spontaneously active C fibers did not change significantly during the first 30 h. Only 6 of 796 A fibers had spontaneous activity. 3. Mechanical stimulation of the cut nerve end excited 5-8% of all C fibers under investigation. No development with time could be detected in the frequency of mechanically excitable C fibers. In contrast, beginning 6 h after nerve transection, the number of mechanically excitable A fibers rose with time, reaching 27% after 22-30 h. 4. Among the A fibers (C fibers) that exhibited mechanical excitability or spontaneous activity, only 4% (25%) had both properties, whereas 96% (75%) were either mechanosensitive or spontaneously active. 5. With time after the nerve lesion, the mean discharge rate of all spontaneously discharging C fibers decreased significantly from 49 imp/min (0.5-9 h after nerve lesion) to 11 imp/min after 22-30 h. The mean discharge rate of C fibers exhibiting solely spontaneous activity and those C fibers that were additionally mechanosensitive did not differ significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1995

[Epidemiology of spinal diseases in nurses].

Epidemiology of spinal pathology among nurses. A cross-sectional study of 3300 German nurses was carried out in the course of an investigation of the prevention of occupation--related back problems. A much higher incidence of lumbar-spinal problems was observed than in a control group of office staff, not required to lift or carry. Evidence of much greater risk, especially of severe sciatic symptoms, was supported by a case-controlled study of patients with the diagnosis of disc-prolapse or disc-protrusion, carried out in two neuroradiology units. Nurses were significantly over represented. A lack of preventive measures for carrying and lifting patients was clearly demonstrated (availability and use of mechanical aids). To what extent the perception of spinal problems is influenced by psychological factors and not only by physical factors will be demonstrated by the recording of stress factors.

Humans↗
PubMed1994

Monosynaptic excitation of preganglionic vasomotor neurons by subretrofacial neurons of the rostral ventrolateral medulla.

Extracellular single unit recordings were made from barosensitive neurons in the subretrofacial nucleus (SRF) of the rostral ventrolateral medulla in chloralose-anaesthetised cats. At the same time, single preganglionic neuron activity was recorded from filaments of the cervical sympathetic trunk (CST); barosensitive units were selected for study. Evidence for monosynaptic connections between the two neuron groups was sought by cross-correlation analysis of their ongoing activity. Cross-correlograms of 16/16 SRF/CST neuron pairs showed a broad peak (100-200ms wide), reflecting the synchronizing action of arterial baroreceptors on both neurons' activity. Two of the 16 cross-correlograms additionally showed a robust, statistically significant, narrow peak of a single 2 ms bin width, providing the first physiological demonstration that ventrolateral medullary neurons monosynaptically excite preganglionic sympathetic neurons. Deductions are made about the strength, convergence and divergence of the connection.

Animals↗
PubMed1994

Properties of afferent nerve fibres supplying the saphenous vein in the cat.

1. We examined the responses of primary afferent neurones supplying a vascularly isolated segment of the saphenous vein to mechanical and chemical stimuli in anaesthetized cats. Activity was recorded from centrally cut axons of afferent nerve fibres which were isolated from the saphenous nerve near its junction with the femoral nerve. 2. A total of thirty units responded to one of these stimuli and twenty-three of them were activated by local mechanical stimulation of the venous wall. Most receptive fields were circular spots. The response of the isolated venous segment to distension was tested in fifteen out of thirty units and eight out of fifteen were activated. Intravasal threshold pressures inducing discharges were in the range of 35-250 mmHg with a mean of 120 mmHg. 3. Twenty-seven out of the thirty units were tested for both mechano- and chemosensitivity. Thirteen were classified as A fibres and fourteen as C fibres with conduction velocities of 5-30 m s-1 and less than 2.5 m s-1 respectively. Twenty fibres (12/13 A, 8/14 C) were mechanosensitive. Two-thirds of the mechanosensitive A (8/12) and all of the mechanosensitive C fibres (8/8) responded to at least one of the chemical stimuli used: hypertonic saline, bradykinin (BK) or capsaicin. 4. The remaining seven units (6 C, 1 A) were activated by injection of BK into the isolated venous segment but failed to respond to mechanical stimuli. Six were found during five experiments in which BK was used as a search stimulus. Injection of bradykinin into the isolated venous segment repeatedly induced an increase in systemic blood pressure. 5. The proportion of unmyelinated fibres responding to mechanical stimulation of the venous segment was systematically examined in three experiments and amounted to about 1% of the unmyelinated afferents in the saphenous nerve. 6. In conclusion, a small proportion of afferent nerve fibres in the saphenous nerve responds to presumably noxious mechanical and/or chemical stimuli applied to the saphenous vein. These fibres, together with some chemospecific venous afferents, may be capable of encoding nociceptive information from the vein especially under pathological conditions.

Animals↗
PubMed1994

Modulation of activity in dorsal root ganglion neurons by sympathetic activation in nerve-injured rats.

1. Teased-fiber recordings were made from the axons of dorsal root ganglion (DRG) neurons in rats that underwent transection of the sciatic nerve 4-22 days previously. Many of the neurons had spontaneous ectopic discharge originating from within the DRG. 2. When postganglionic sympathetic efferents ending in the DRG were activated by tetanic stimulation of the T13 and L1 ventral roots (VRs), the ongoing afferent discharge was altered in more than one-half of the DRG neurons sampled. In most of the responsive units (62%), activity was augmented by this sympathetic stimulation; in the remainder (38%), activity was suppressed. Single-pulse stimuli of sympathetic efferents had no effect. 3. Responses to sympathetic stimulation began after a substantial delay (mean 14.3 s), peaked after 10-20 s, and then returned toward baseline over an additional 20-30 s. 4. Both excitatory and suppressive responses to sympathetic stimulation, as well as corresponding responses to systemically applied adrenaline, were blocked by the alpha-adrenoreceptor antagonist phentolamine. 5. Most of the active DRG neurons that responded to sympathetic stimulation, as well as others that did not, were excited by tetanic stimulation of neighboring afferent neurons that share the same DRG. These "crossed afterdischarge" responses were not blocked by phentolamine. Single-pulse stimuli of neighboring afferents had no effect. 6. Sympathetic-sensory coupling in DRGs of nerve-injured animals provides a previously unsuspected substrate for sympathetic involvement in neuropathic sensory dysfunction.

Animals↗
PubMed1994

[The epidemiologic significance of varicella].

A total of 552 persons working in the university hospital of Freiburg, Germany (nurses, pediatric nurses, administration--and technical personnel) was screened for antibodies to varicella zoster virus. Prevalence of antibodies to VZV among men was higher than among women. While the degree of immunity of nurses and administration/technical personnel was comparable, pediatric nurses had a significantly higher seroprevalence (< 20 years 89.3%, -30 years 95.7%, > 30 years 98.6%). Therefore, pediatric nurses should be screened and susceptible persons should be vaccinated.

Adult↗
PubMed1994

[Acceptance of preventive vaccinations by physicians and the general population].

The acceptance of vaccinations depends on the quality of information on effects and side effects. This publication deals with the results of three questionnaire studies: Questionnaire 1 was directed to the general population and contained questions on vaccination history and acceptance of vaccinations, questionnaire two and three were addressed to practitioners (general medicine/paediatrics/internal medicine) with additional questions on the number of vaccinations performed per year. An average of 50% of the persons taking part in the questionnaire study had been vaccinated within the last 10 years against diphtheria, tetanus, polio and/or influenza. The acceptance of these vaccinations was quite satisfactory whereas opinions on mumps and measles vaccinations were quite negative. In the course of the questionnaire study with practitioners it could be demonstrated that vaccinations against diphtheria, tetanus, polio and influenza were regarded as useful while immunisation against mumps, measles, tuberculosis, pertussis and chicken-pox were not regarded as useful. Information programes on vaccinations and the need for further investigations are discussed as well as the problem of mandatory vaccinations.

Adolescent↗
PubMed1993

Receptive properties of afferent nerve fibres associated with the rat saphenous vein.

We tested afferent fibres isolated from the saphenous nerve for their responses to mechanical, osmotic and chemical stimuli applied to a vascularly isolated segment of the saphenous vein in the rat. Fifteen units were excited by local mechanical stimulation and many of them were also activated by distension of the venous segment, however exclusively by presumably noxious pressures. Most mechanosensitive fibres were excited by one of the three pain-producing substances, hyperosmotic saline (HS), potassium chloride (KCl) and bradykinin. Three fibres which were insensitive to mechanical stimulation, responded to injection of HS or KCl into the venous segment. We conclude that the venous afferents most likely have nociceptive function. Most are considered to be polymodal.

Animals↗
PubMed1993

Peripheral nerve injury triggers noradrenergic sprouting within dorsal root ganglia.

In humans, trauma to a peripheral nerve may be followed by chronic pain syndromes which are only relieved by blockade of the effects of sympathetic impulse traffic. It is presumed that, after the lesion, noradrenaline released by activity of sympathetic postganglionic axons excites primary afferent neurons by activating alpha-adrenoceptors, generating signals that enter the 'pain pathways' of the central nervous system. The site of coupling is unclear. In some patients local anaesthesia of the relevant peripheral nerve does not alleviate pain, implying that ectopic impulses arise either within the central nervous system, or in proximal parts of the primary afferent neurons. In experimentally lesioned rats, activity can originate within the dorsal root ganglia. Here we report that, after sciatic nerve ligation, noradrenergic perivascular axons in rats sprout into dorsal root ganglia and form basket-like structures around large-diameter axotomized sensory neurons; sympathetic stimulation can activate such neurons repetitively. These unusual connections provide a possible origin for abnormal discharge following peripheral nerve damage. Further, in contrast to the sprouting of intact nerve terminals into nearby denervated effector tissues in skin, muscle, sympathetic ganglia and sweat glands, the axons sprout into a target which has not been partially denervated.

Animals↗
PubMed1993

Spontaneous activity, conduction velocity and segmental origin of different classes of thoracic preganglionic neurons projecting into the cat cervical sympathetic trunk.

Previously, in the anesthetized cat, thoracic preganglionic neurons projecting to the superior cervical ganglion were divided into four classes (groups I-IV) by way of their reflex pattern. Neurons of each class are probably involved in a distinct function, such as regulation of peripheral vascular resistance, regulation of blood flow through skin, regulation of pupil diameter, etc. Here it was tested whether the functionally different classes of thoracic preganglionic neurons also differ in the distribution of their segmental origin, their spontaneous activity and the conduction velocity of their axons. The segmental distribution of preganglionic neurons was almost identical to that determined previously with tracer methods. Distinct classes of neurons had different, although overlapping segmental distributions. Most group III neurons were located in segments T1 and T2, whereas group I, II and IV neurons showed a broader distribution. The subpopulations of preganglionic neurons did not differ in their rate of spontaneous activity. No significant difference was found in segmental distribution between neurons with spontaneous activity and silent neurons. No correlation was found between conduction velocity and spontaneous activity. The proportion of unmyelinated units was greater among group I (16.3%), group II (24.1%) and group IV (22.2%) neurons than among group III neurons (8%). The distributions of conduction velocity were significantly different between group I and group III and between group II and group III neurons. Axons of preganglionic neurons located in segments T1 and T2 conducted faster than axons of neurons located more caudally. The present study shows that distinct subpopulations of preganglionic neurons, as defined by their reflex patterns, differ in their segmental location within the spinal cord and with respect to the conduction velocity of their axons.

Animals↗
PubMed1993

Responses of lumbar vasoconstrictor neurons supplying different vascular beds to graded baroreceptor stimuli in the cat.

Lumbar sympathetic vasoconstrictor neurons supplying skeletal muscle, hairy skin and pelvic organs were tested for their responses to carotid baroreceptor stimulation in chloralose-anaesthetized cats. Using single- and few-fibre recordings, the responses of the different types of vasoconstrictor neuron to graded steps of non-pulsatile pressure ranging from 110 to 260 mmHg in a vascularly isolated carotid sinus were analyzed quantitatively during the first 10 s of stimulation. The activity in all postganglionic muscle vasoconstrictor (MVC) neurons, preganglionic visceral vasoconstrictor (VVC) neurons and one third of the postganglionic cutaneous vasoconstrictor (CVC1) neurons was strongly depressed by maximal baroreceptor stimulation. Moreover, quantitative analysis revealed no significant differences of the baroreceptor sensitivity of MVC and CVC1 neurons as compared with VVC neurons at all levels of carotid sinus pressure. In contrast, two-thirds of the postganglionic cutaneous vasoconstrictor (CVC2) neurons exhibited a significantly weaker barosensitivity. The functional implications are discussed.

Animals↗
PubMed1992

Viscero-sympathetic reflex responses to mechanical stimulation of pelvic viscera in the cat.

Viscero-sympathetic reflex responses to mechanical stimulation of urinary bladder and colon were studied in cutaneous vasoconstrictor (CVC) neurones supplying hairy skin, in muscle vasoconstrictor (MVC) neurones supplying skeletal muscle and in sudomotor (SM) neurones supplying the sweat glands of the central paw pad of the cat hindlimb. The cats were anaesthetized, paralysed and artificially ventilated. The vasoconstrictor activity was recorded from the axons of the postganglionic fibres that were isolated in filaments from the respective peripheral hindlimb nerves. The activity in the sudomotor neurones was monitored by recording the fast skin potential changes occurring on the surface of the central paw pad. Afferents from the urinary bladder and from the colon were stimulated by isotonic distension and isovolumetric contraction of the organs. Most CVC neurones with ongoing activity were inhibited by these stimuli; only a few CVC neurones were excited. The MVC and SM neurones were generally excited by the visceral stimuli, yet the size of the evoked skin potential changes was variable. The reflex responses elicited in the sympathetic outflow to the cat hindlimb by stimulation of visceral afferents from the pelvic organs are uniform with respect to the different types of afferent input system but differentiated with respect to the efferent output systems. Graded stimulation of the visceral afferents from the urinary bladder by isotonic pressure steps elicited graded reflex responses in CVC (threshold less than 30 mmHg) and MVC neurones (threshold less than 20 mmHg) and a graded increase of the arterial blood pressure (threshold less than 20 mmHg). These graded reflex responses are closely related to the quantitative activation of sacral afferent neurones with thin myelinated axons innervating the urinary bladder that are also responsible for eliciting the micturition reflex, but not to the quantitative activation of sacral afferent neurones with unmyelinated axons. The latter have thresholds of 40-50 mmHg intravesical pressure at which the size of the vesico-sympathetic reflexes in the vasoconstrictor neurones was about 50% of maximal size. This does not exclude the fact that activation of unmyelinated vesical afferents contributes to the vesico-sympathetic reflexes.

Animals↗
PubMed1992

Production of the cytostatic agent aeroplysinin by the sponge Verongia aerophoba in in vitro culture.

1. The marine sponge Verongia aerophoba contains two bioactive secondary metabolites from tyrosine, (+)-aeroplysinin-1 [3',5'-dibromo-1',2'-dihydroxy-4'- methoxycyclohexa-3',5'-dien-1'-yl-methyl-cyanide; abbreviated AP] and dibromoverongia-quinol [3',5'-dibromo-1'-hydroxy- 4'-oxocyclohexa-2',5'-dien-1'-yl-acetamide; abbreviated DV], which display strong cytostatic activity. 2. The concentrations causing 50% inhibition of cell growth are 0.47 microM (AP) and 1.21 microM (DV), resp. 3. Depending on depth regions from which the sponges were collected, differences in occurrence of metabolites were observed. 4. AP and DV were found to be present in sponges collected at a depth of 5-10 m, whereas only DV could be detected in material from deeper regions (20-30 m). 5. AP is present only in the surface layers (both the outer and oscular region) of the sponge, while in the centre of the sponge only DV is detected. 6. Cubes from sponges, collected at a depth of 30 m, were cultivated in seawater in vitro and were found to have the capacity (i) to synthesize AP, and (ii) to release this bioactive material into the medium under defined conditions. Under optimal conditions (light and aeration) 100 g of sponge synthesize and release 13.02 mg of AP during a 10-day incubation period. 7. In the dark and without aeration this synthesis was prevented. 8. These data show that also under in vitro conditions sponges retain the capability of producing bioactive compounds and can be induced to produce even substances which they did not secrete in their natural environment.

Acetamides↗
PubMed1992

Respiratory modulation of the activity in sympathetic neurones supplying muscle, skin and pelvic organs in the cat.

1. The respiratory-related modulation of activity in neurones of the lumbar sympathetic outflow to skeletal muscle, skin and pelvic organs was investigated in anaesthetized, paralysed and artificially ventilated cats, using single- and multi-unit recordings. The activity of the neurones was analysed with respect to the phrenic nerve discharge under various experimental conditions. 2. Neurones tentatively classified as muscle vasoconstrictor and visceral vasoconstrictor neurones exhibited two activity peaks, one caused by baroreceptor unloading during the declining phase of the second order blood pressure waves and a respiratory drive-dependent peak in parallel with inspiration. The two peaks were separated by depressions of activity in early inspiration and post-inspiration. After cutting vagus and buffer nerves the activity peak during inspiration remained and was followed and sometimes preceded by a depression of activity. 3. The majority of the neurones tentatively classified as cutaneous vasoconstrictor neurones exhibited no respiratory modulation in their activity. Others exhibited an activity peak in expiration, an activity peak in inspiration, or a respiratory profile similar to that in muscle vasoconstrictor neurones. During increased respiratory drive (induced by hypercapnia) some neurones with unmodulated activity changed to an inspiratory or an expiratory pattern. Neurones discharging predominantly in inspiration projected preferentially to hairless skin. 4. Neurones which were tentatively classified as sudomotor neurones discharged predominantly in early expiration. 5. Some preganglionic neurones which were tentatively classified as motility-regulating neurones discharged during expiration. The majority of these neurones disclosed no respiratory modulation of their activity. 6. The study shows that different types of neurone of the lumbar sympathetic system exhibit distinct patterns of respiratory modulation in their activity. We conclude that the type and degree of central coupling between respiratory system and sympathetic nervous system may vary according to the destination of the sympathetic neurones.

Animals↗
PubMed1992

Classification of preganglionic neurones projecting into the cat cervical sympathetic trunk.

1. The spontaneous and reflex activity patterns of 167 single preganglionic axons dissected from the cervical sympathetic trunk were examined in chloralose-anaesthetized cats. Each neurone was classified into one of four major groups, on the basis of three principal criteria: the presence or absence of significant cardiac rhythmicity of the activity, the response to noxious stimulation of the skin, and the coupling of its activity to central inspiratory drive (phrenic nerve activity). Most neurones were also subjected to additional tests, which included carotid chemoreceptor stimulation, nasopharyngeal probing, systemic hypercapnia (ventilation with 8% CO2), hyperventilation, adrenaline-induced blood pressure rises and retinal illumination. 2. Group I neurones (n = 69; 41%) showed significant cardiac rhythmicity, indicating strong baroreceptor control. Most (54/69) were excited by noxious stimuli, the rest being unaffected. Their activity showed variable degrees of excitatory coupling to the central inspiratory drive, and was enhanced by hypercapnia (35/39). Their responses to stimulation of arterial chemoreceptors (12/15) and nasopharyngeal receptors (24/35) were excitatory. 3. Group II neurones (n = 39; 23%) were inhibited by noxious stimulation of skin. With nine exceptions, they showed no significant cardiac rhythmicity, although they were weakly inhibited by an adrenaline-induced blood pressure rise. Their coupling to central inspiratory drive was weak or absent, and their responses to hypercapnia and hyperventilation were variable. By contrast to other groups, they were inhibited by both chemoreceptor stimulation (9/10) and nasopharyngeal stimulation (17/18). 4. Group III neurones (n = 33; 20%) showed no significant cardiac rhythmicity, but their activity was closely coupled to central inspiratory drive. They were inhibited by hyperventilation (9/9) and excited by hypercapnia (20/21), but only fired during the central inspiratory phase and sometimes during late expiration. Their responses to noxious stimulation (28/33), chemoreceptor stimulation (8/11) and nasopharyngeal probing (24/24) were excitatory, but the induced activity was 'gated' by the respiratory cycle, occurring primarily during inspiration and avoiding the postinspiratory phase. 5. Group IV neurones (n = 26; 16%) showed no significant cardiac or respiratory related activity and were either excited (n = 22) or unaffected (n = 4) by noxious stimuli. One of the latter and three group II neurones were inhibited by retinal illumination; thirty-one other neurones of all classes were unaffected. 6. Approximately 45% of thoracic sympathetic neurones were silent under the experimental conditions. About 25% of these could be recruited by systemic hypercapnia leaving 34% without spontaneous and reflex activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Respiratory-related activity patterns in preganglionic neurones projecting into the cat cervical sympathetic trunk.

1. Activity in 233 single sympathetic preganglionic neurones that project to the superior cervical ganglion was analysed with respect to central components of respiration (phrenic nerve discharge) and to the afferent feedback generated by mechanical events occurring with ventilation in anaesthetized and artificially ventilated cats. 2. The activity in ninety-one neurones was modulated during the respiratory cycle in two ways: directly by the central inspiratory drive, and indirectly by ventilation-related blood pressure changes, acting via the systemic baroreceptors. The direct influence was prominent in vagotomized animals or those with a raised respiratory drive, and consisted of an inspiratory increase in activity and decreases of activity in early inspiration and postinspiration. The indirect influence (excitation due to baroreceptor unloading) usually dominated in normocapnic cats with intact vagus nerves. This population of neurones showed both similar reflex responses and a similar respiratory modulation of activity as postganglionic neurones supplying hindlimb skeletal muscle. 3. Sixty-one neurones discharged exclusively, or almost exclusively, during central inspiration. This discharge pattern neither depended on the integrity of vagal nor baroreceptor afferents. The activity of these neurones was abolished during hyperventilation and enhanced during hypercapnia. In the latter state, a small activation was often seen in stage II expiration. 4. In normocapnia the remainder of neurones (n = 81) exhibited no, or no pronounced, respiratory modulation of activity, except three neurones which showed a prominent expiratory pattern being of central and not of reflex origin. They were not a homogeneous population and included neurones exhibiting reflex responses similar to those of postganglionic neurones supplying hindlimb skin (n = 36), neurones responding to light (n = 4), and others (n = 41). 5. It is concluded that distinct types of thoracic preganglionic neurone differ with respect to respiratory modulation of their activity stemming from both central and reflex sources. Thus, the temporal profile of activity in these neurones in relation to respiration is another functional characteristic which can be used to distinguish between populations of sympathetic neurones.

Animals↗