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H Lohmann

Publications and source records attributed to H Lohmann.

At least 37 records · Page 2Linked to original sources
PubMed1994

Long-range horizontal connections between supragranular pyramidal cells in the extrastriate visual cortex of the rat.

In this study, we examined the morphological structure and synaptic physiology of long-range axon projections among supragranular pyramidal cells in the extrastriate visual cortex of the rat. Intra- and extracellular recordings from layer II/III pyramidal cells were performed in brain slices of area 18a following extracellular stimulation of either the underlying white matter or within layer II/III. Neurons were injected with biocytin for two-dimensional reconstruction of their axon arborizations. The conduction velocity of afferent fibers (0.58 m/s) was twice as high as that of intracortical tangential fibers (0.28 m/s). Layer II/III cells were mainly di- or polysynaptically driven by afferent activation, but predominantly monosynaptically driven from intracortical stimulation sites. The afferent as well as intracortically evoked postsynaptic potentials showed a very similar time course and shape. From both stimulation sites, suprathreshold action potentials could be elicited. The current threshold for a postsynaptic response and the slope and width of excitatory postsynaptic potentials (EPSPs) increased with the distance of lateral stimulation. The morphological properties of layer II/III pyramidal cell axon collaterals closely corresponded to the electrophysiological results. Long-range intraareal axon collaterals could be followed up to 1 mm within the supragranular layers. Their length-distance distribution showed an inverse relationship to the threshold currents of EPSPs. Pyramidal cells exhibited regularly spaced patches of horizontal axon collaterals with an interpatch distance of about 250 microns. We concluded that the supragranular horizontal network in the extrastriate visual cortex of the rat is qualitatively very similar to that of cats and monkeys. However, quantitative differences exist in its spatial extent and physiological characteristics.

Animals↗
PubMed1988

Acute lead exposure transiently inhibits hippocampal neuronal activities in vitro.

The effects of acute lead exposure on extracellularly recorded evoked responses in the CA1 region of hippocampal slices were investigated. Field potentials in response to paired-pulse stimulation were assessed while perfusing the slices with normal media and media containing lead in concentrations of 0.2 microM to 53 microM. The evoked population excitatory postsynaptic potentials decreased during lead exposure to a lesser extent than the orthodromically evoked population spike, whereas the presynaptic fiber volley remained unchanged. The maximal inhibition of the orthodromically evoked responses depended strongly on the lead concentration. The input-output relations of the orthodromic responses obtained during perfusion with lead significantly differed from those during control conditions. The somatic short-term potentiation obtained by paired-pulse stimulation increased during the lead exposure. Lead seemed to inhibit the evoked activities only transiently: within 20 min after lead onset, the recorded responses had reached the control level again in spite of further lead perfusion. In contrast to the orthodromically evoked responses, the antidromically evoked population spikes remained constant at all concentrations used. It is concluded from these results that lead acts presynaptically in the hippocampal slice preparation. Additionally, lead interferes with non-synaptic processes at the pyramidal neurons in the CA1. Possible influences of lead over different neurotransmitter systems are discussed.

Action Potentials↗
PubMed1988

Visual receptive fields of local intracortical potentials.

We have developed a method to define a spatial-temporal receptive field (RF) for local, intracortically recorded field potentials in the visual cortex. In analogy to the classic RF concept, a relation between stimulus position and a single recording location is evaluated. Our receptive field cinematogram (RF-Cine) approach, additionally, includes the temporal dynamics between stimulus and response: A sequence ('movie') of successive 'frames' is calculated, which shows the field potential amplitudes plotted with reference to the position in visual space of a randomly moving stimulus. The exploration of the receptive fields via a randomly jumping disk stimulus is especially suitable for multi-electrode cortex mapping, because the RF-Cines of all electrodes can be evaluated simultaneously within a single stimulation period of 100 s duration. Field potential RF-Cines showed concentrical or ellipsoidal antagonistic center-surround structures with biphasic or triphasic time courses. The size of these structures increases with retinal eccentricity. The cortical surface coverage of the RF-Cine centers was calculated to be 0.8 mm2 for area 17 and 1.3 mm2 for area 18, being nearly constant within the 0-10 degrees cortical representation of the lower visual field. These values approximately correspond to the extent of one hypercolumn. The absolute positions of the RF-Cine structures can be determined with an accuracy of 0.1-0.2 mm in cortical coordinates.

Animals↗
PubMed1988

Miniature endplate potentials as a tool in neurotoxicology.

The toxic effect of thallium added to the bath solution was studied with intra- and extracellular recordings from mammalian nerve-muscle preparations. To elucidate the target region, 3 different functional parameters were studied: (1) Post-synaptic endplate potentials (EPPs) resulting from evoked transmitter release; (2) Post-synaptic miniature endplate potentials (MEPPSs) resulting from spontaneous transmitter release; and (3) Presynaptic ion currents at the nerve terminal. At a concentration of 0.5 mM/l thallium acetate, EPP amplitudes were irreversibly decreased while MEPP amplitudes remained unaffected. MEPP frequencies were reversibly increased, indicating a presynaptic rather than a post-synaptic target site of thallium toxicity. The subpopulation of small MEPPs (sub-MEPPs) behaved like the MEPP population, except that upon addition of 4-AP, the sub-MEPP population was augmented at the cost of the MEPP population. In view of the slow time course of the toxic effects (30 min for a 10-fold increase of MEPP frequency, 100-180 min for a 50% reduction of EPP amplitudes), it is concluded that thallium needs to be transported across the cell membrane before it finally interferes with release mechanisms. It is hypothesised that thallium reduces the number of active sites recruited by one action potential (reduced EPP amplitude), while at the same time the probability of transmitter liberation is enhanced (increased MEPP frequency). The rather indirect mode of action of thallium was also found when presynaptic ion currents were recorded using extracellular electrodes. In proportion to the decrease of the EPP amplitudes, a reduction of all inward and outward currents was observed. This effect was also irreversible. It is concluded that in spite of some similarities, thallium behaves quite differently from bivalent heavy metals like cobalt and cadmium, which act as competitive calcium antagonists at the presynaptic nerve terminal. In these toxic substances, the time course of intoxication is much faster, the required concentration is much lower, and the inhibition of the slow calcium current is reversible.

4-Aminopyridine↗
PubMed1987

Pharmacodynamics of the new H1-antagonist 3-amino-9,13b-dihydro-1H-dibenz[c,f]imidazo[1,5-a]azepine hydrochloride in volunteers.

The inhibitory effects of 3-amino-9,13b-dihydro-1H-dibenz[1,5-a]azepine hydrochloride (WAL 801 CL), a new H1-receptor antagonist, on histamine-induced skin wheals were studied in 9 volunteers. The study was a double-blind, randomized (Latin square) change-over, intraindividual comparison of the effects of single doses of 2,6 and 18 mg WAL 801 CL and of placebo and 2 mg ketotifen on skin wheals induced by intradermal injections of 5 micrograms hystamine 1, 2, 4, 6 and 8 h after administration of the drugs. The injection of 5 micrograms was also made prior to each drug administration. The effects on psychological performance and the subjective state were also evaluated. The following tests were employed: simple visual reaction time (RT), critical flicker fusion frequency (C3F) and von Zerssen's self-rating scale Bf-S, assessing state of mood. There was a washout period of at least 72 h between each course of treatment. A decrease in the size of the histamine wheal was observed 1 h after WAL 801 CL and was maintained for at least 8 h. The reduction in the size of the histamine wheal was between 44% (2.0 mg) and 71% (18.0 mg). After ketotifen a marked decrease in the wheal area was observed between 4 and 8 h after administration of the drug, with maximum histamine antagonism of 59% after 6 h. The inhibitory effects of 6 and 18 mg WAL 801 CL and 2 mg ketotifen were statistically significant compared with placebo. 8 of 9 subjects felt tired (subjective report) after ketotifen, corresponding changes could be detected by Zerssen's state of mood scale Bf-S, but not by other psychological performance measures (RT, C3F).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

[Pseudarthrosis of the scaphoid bone. Experiences in 240 cases].

The results after treatment of 197 non-union of scaphoid fractures are reported. The operative technique of Matti-Russe, called also Russe I, has proved successful in cases in which the fracture is located in the middle or distal third of the scaphoid or where there is a viable small proximal fragment. Bone healing depends more on the age of the pseudarthrosis than on the age of the patient. In 86% of 83 cases the technique of Russe I was successful and in this group the period between accident and treatment was no longer than two years. After a period of more than four years after the accident the success rate is only 54%. The combination of the technique of Russe I with styloidectomy of the radius diminishes the number of good results. The operative technique known as Russe II assumes a good blood supply of the distal fragment of the scaphoid. In 15 cases, after resection of the necrotic small proximal fragment of the scaphoid, a fungiform bonegraft from the iliac crest was placed in the cavity and the success rate was 80%. The findings after palliative treatment of 43 non-unions of the scaphoid are based on subjective criticisms by the patients. The denervation of the wrist and the wrist arthrodesis were done in 28 cases. After resection of the necrotic proximal fragment, a tendon interposition arthroplasty was performed in nine cases, and in six cases a prosthesis for the proximal part of the scaphoid was implanted.

Bone Transplantation↗
PubMed1987

[Alternative surgical procedure in pseudarthrosis of the scaphoid bone with a small proximal fragment].

The management of non-union of the scaphoid with a Herbert screw assumes a specific size of the proximal pole fragment. In cases of extremely small proximal pole fragments the length of the leading thread of the screw can cause blockage of the proximal pole fragment. In these instances a dorsal approach is used and the Herbert screw is inserted in a proximal-to-distal direction rather than the usual distal-to-proximal insertion. The advantages are a stable internal fixation and an abbreviated period of immobilization in plaster; however, the small number of cases reported does not permit us to draw conclusions regarding indications for use of this technique.

Bone Screws↗
PubMed1986

The action of thallium acetate on phasic transmitter release in the mouse neuromuscular junction.

Endplate potentials (EPP's) and miniature endplate potentials (MEPP's) were recorded from neuromuscular junctions of the mouse phrenic nerve-diaphragm preparation, blocked by high Mg++ (12 X 10(-3) mol/l)-Ringer. Superfusion of the preparations with Mg++-Ringer solutions containing thallium acetate (5 X 10(-4) mol/l Tlac) decreased phasic transmitter release as judged by EPP amplitudes as well as average quantal content, until total synaptic blockade (within about 300 min) occurred. Simultaneously MEPP amplitudes remained unchanged, whereas the frequency of MEPP's increased. When EPP amplitudes and/or quantal content were reduced by 50% (usually within about 180 min), superfusion with Mg++-Ringer solution without Tlac did not restore phasic transmitter release. However, the increase in spontaneous transmitter release was reversible, as MEPP frequencies returned to normal values. 4-Aminopyridine (5 X 10(-4) mol/l 4-AP) as added to the bath solution in the state of 50%-reduced phasic release temporarily restored EPP amplitudes and average quantal content, whereas MEPP amplitudes remained unchanged. It is concluded that thallium irreversibly blocks phasic transmitter release, whereas spontaneous transmitter release is reversibly enhanced.

4-Aminopyridine↗
PubMed1986

Effects of a kappa-opioid agonist on adrenocorticotropic and diuretic function in man.

Although kappa-opiate receptors represent an important fraction of the total opiate receptor capacity in human brain their endocrine function is unknown. We determined the effects of a kappa-opiate receptor agonist on the secretion of vasopressin, ACTH and cortisol and on diuresis. The racemic benzomorphan kappa agonist MR 2033 or its opiate active (-)-isomer, MR 2034, inhibited the release of cortisol and ACTH in 12 trials in a naloxone reversible manner; plasma levels of vasopressin were not altered. The (+)-isomer, MR 2035, did not affect the secretion of cortisol or ACTH. Surprisingly, in five other subjects large increases were observed in vasopressin, ACTH and cortisol following the kappa-agonist, which were probably elicited indirectly by aversive effects of the opioid. The subjects in whom vasopressin release was not altered by MR 2033 and MR 2034 displayed large decreases in urine osmolality which were not antagonized by naloxone. The opiate inactive (+)-isomer, MR 2035, caused no diuretic response. Subjects in whom vasopressin release was stimulated did not show decreases in urine osmolality indicating that vasopressin is capable of antagonizing the diuretic action of the kappa-agonist. Our data show that a kappa-agonist inhibits secretion of cortisol and ACTH by acting at stereospecific opiate receptors and elicits diuresis by acting at stereospecific, but naloxone-insensitive non-classical opioid receptors. These data support the concept that different types of kappa-receptors can be distinguished in man.

Adrenocorticotropic Hormone↗
PubMed1985

Pharmacokinetics of adimolol after single and multiple dose administration in healthy volunteers.

The pharmacokinetic properties of adimolol (MEN 935), a new antihypertensive agents with predominantly beta-receptor blocking and additional alpha-adrenolytic activity were investigated in healthy volunteers. Study A subjects (n = 6) received single intravenous doses of 5 mg adimolol and single oral doses of 200 mg capsules, 200 mg tablets and 100 mg tablets on four occasions separated by at least two weeks. Study B subjects (n = 6) were given single intravenous doses of 5 mg and single oral doses of 100 mg of the 14C-labelled drug on two different occasions. Study C subjects (n = 6) were administered multiple oral doses of 100 mg adimolol daily for five days, and three weeks later 50 mg daily for five days. Adimolol plasma concentrations were assayed over seven days following each single dose using a specific and sensitive high-pressure liquid chromatographic method. The plasma concentration data obtained from the single i.v. dose studies were individually fitted to an open four-compartment model. To describe mathematically the single oral dose plasma level data, two compartments were added to the model to take care of the absorption. Irrespective of the route of administration, the doses and formulations given, all plasma concentration curves could be described with similar pharmacokinetic parameters. Plasma concentration curves predicted by the open four-compartment model were fully confirmed by the actual data obtained after chronic oral administration. The terminal half-life averaged 12 h following intravenous and 15 h after oral administration. The peak plasma concentration was reached on average 4 h following oral administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1985

[Improvement of suture technic in flexor tendon injuries. Clinical and experimental study].

Multiple causes for the rupture of sutured tendons have been reported. At the time of exploration, loosening of the knot and breakage of the suture have been found to explain failure. A knot with four throws is frequently mentioned in various series as the smallest secure knot which can be made when employing a braided polyester suture material. Experiments have shown that the distance between the ends of the tendons affects the healing process and the tensile strength of the injured tendons. In order to avoid increasing the gap between the sutured ends of the tendons with the thick knot, it can be placed away from the cut surface of the tendons and displaced into the proximal or distal end of the tendons with a small additional incision. Through a longitudinal incision, the suture is easily passed in a criss cross fashion through the tendon and the knot can be buried in the tendon. This technique assures a very delicate and exact coaptation of the tendon ends. Almost 100% of the tendons remain intact during the healing phase. According to this experience, the risk of tendon rupture is reduced as a result of an increase in the tensile strength of the suture and the displacement of the knot away from the cut surface of the tendon.

Finger Injuries↗
PubMed1985

[Severe skin burns caused by a photochemotherapeutic agent].

By uncontrolled application without indication of a photoactive drug methoxypsoralen (Meladinine) which is sold only on prescription a 20-year-old man sustained a large burn injury of 71% of body surface. Because he was admitted to the hospital relatively late, a life-threatening condition developed as it is well known after large body burns. Adequate intensive care including artificial respiration and proper local treatment to prevent infection were decisive for successful treatment.

Adult↗
PubMed1983

Comparative studies on the efficacy of brotizolam and nitrazepam: a multi-centre study.

Efficacy and tolerability of brotizolam (0.25 and 0.5 mg) were compared over a 6-day period with nitrazepam (5.0 mg) in middle-aged patients (less than 65 years) with sleep disturbances requiring medication. The study was double-blind and randomised with a cross-over design. Each preparation reduced sleep onset latency and frequency of awakenings, and improved quality and duration of sleep as well as subjective condition on awakening. Brotizolam 0.25 mg was found to be equally effective as 0.5 mg, and so the lower dose is recommended for the middle aged.

Adolescent↗
PubMed1982

[Indications and results of arthrodesis of the wrist].

Between 1966 and 1980, fusion of the wrist joint was performed on 113 patients. Follow-up was possible on 98 (86,6%). Stable fixation with a plate using a corticocancellous bone graft from the ilium improved the technique. Particularly striking was the reduction of postoperative immobilisation from an average of four months between 1966 and 1972 (before the introduction of the plate) to three weeks between 1973 and 1980. This improvement and the increased incidence of permanent wrist joint damage after injury have broadened the indications for wrist joint fusion. In 57 of the 113 cases (58,2%), good and excellent results were obtained. 92 patients (93,9%) pronounced themselves satisfied with the result compared to the preoperative situation. The one exception was wrist joint fusion in childhood, even though the growing epiphyses of the radius was protected.

Adolescent↗
PubMed1981

[Rare localization of a small sweat gland adenoma of the skin].

This case report of a chondroid syringoma (t. h.) arising in a finger is of interest because of the unusual site, its usual location being the region of the head and neck. Characteristically it is benign, slow growing and compresses adjoining structures. In skin lesions generally histological confirmation of the diagnosis is essential in order to exclude malignancy, but particularly when the site of the lesion is an unusual one.

Female↗
PubMed1980

[Debrisorb therapy of severe hand infections].

Treatment with DEBRISORB, a new topical agent formed by three dimensional network of dextran polymers in porous hydrophilic beads, was used in 26 cases of infected wounds in the hand. These were of traumatic and postoperative origin, often with remaining necrotic areas and in a few cases with a considerable oedema. The special effect of DEBRISORB was in absorbing the exudate and in reducing the inflammation and swelling of the discharging wounds. Within a few days secretion was diminished and healthy granulation tissue appeared. For covering the defects we employed local transposition flaps, direct flaps and split-skin grafts without complications. Local treatment with DEBRISORB is an effective method to clean infected wounds, to reduce inflammation and oedema, and is useful as treatment before grafting.

Administration, Topical↗