Biomedical subjects

B Ströhmann

Publications and source records attributed to B Ströhmann.

6 recordsLinked to original sources

PubMed1995

Electrical resonances in central auditory neurons.

In the auditory pathway, signal processing depends on the filter functions of neurons. We used frequency analysis to investigate the contributions of intrinsic membrane properties to the input-output relationships in neurons. The whole-cell tight-seal recording technique in brain slices of chicks was used to study neurons at four levels of the auditory pathway. Neurons displayed resonant peaks in their voltage responses to injected sinusoidal currents that swept through a specified frequency range. Higher resonant frequencies tended to predominate at relatively lower stations in the auditory pathway (approximately 100 Hz in the nucleus magnocellularis, 24 Hz in the nucleus laminaris, 6 Hz in the nucleus ovoidalis). Field L neurons (cortex homologue) displayed low pass filter characteristics without resonance. We propose that the subthreshold membrane resonances amplify synaptic inputs at specific frequencies and contribute to the chick's ability to decode temporal sound parameters.

Animals↗

PubMed1994

Mode of firing and rectifying properties of nucleus ovoidalis neurons in the avian auditory thalamus.

1. We studied neurons of the nucleus ovoidalis, the principal auditory thalamic relay nucleus of the chicken, with tight-seal whole-cell recording techniques in in vitro slice preparations. Nucleus ovoidalis, marked by anterograde labeling of afferents from the inferior colliculus, consists of a clearly delineated group of densely packed, multipolar cells of approximately uniform diameter. We measured a wide range of non covarying resting potentials (-60 +/- 9 mV, mean +/- SD) and input resistances (277 +/- 168 M omega). All neurons discharged overshooting fast spikes. The observed electrophysiological properties may have a decisive role in the transfer of sensory signals. 2. We grouped neurons on the basis of their firing patterns, in response to intracellular injections of depolarizing current pulses from various membrane potentials. The majority of neurons (86%) displayed weakly adapting, tonic firing. A smaller group of neurons (14%) exhibited qualitative changes in firing modes. They fired repetitively when the stimulus pulse was superimposed on relatively depolarized levels, usually including the resting potential. DC-hyperpolarization led to burst responses consisting of fast action potentials on top of slow potentials. 3. In all neurons, application of 300 nM tetrodotoxin blocked the action potentials and reduced a depolarization-activated inward rectification, observed during 1-s current pulses in a range of membrane potentials depolarized from rest. This rectification is interpreted as a partial result of a persistent Na+ current. 4. During the applications of tetrodotoxin in neurons with burst firing capability, two other slow potentials were visible in isolation. Depolarizing current pulses evoked slow, transient depolarizations at the onset whereas rebound slow potentials occurred on termination of hyperpolarizing current pulses. The slow potentials were blocked by application of 0.5 mM Ni2+ and are likely a result of a low threshold Ca2+ current, such as a T-current. 5. A distinctive property of all ovoidalis neurons was a hyperpolarization-activated inward rectification. Application of Cs+ (3 mM) but not Ba2+ (3 mM), tetraethylammonium (10 mM), or 4-aminopyridine (4 mM) reversibly blocked the current that produced this rectification. The activation time constants for the current varied between approximately 50 and 400 ms and were voltage dependent in some neurons. Thus the hyperpolarization-activated current (IH), responsible for thalamic sleep mechanisms in mammals, also is present in a submammalian thalamus. 6. We suggest that the voltage and time dependencies of the persistent Na+ current and IH participate in generation of the sub- and suprathreshold temporal activity patterns in the neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Subthreshold frequency selectivity in avian auditory thalamus.

1. We studied the frequency responses of neurons in the nucleus ovoidalis (OV), the principal thalamic auditory relay nucleus of the chicken, in the subthreshold range of membrane potentials. The frequency response is the impedance amplitude profile evident in the voltage response to a broadband stimulus. The stimulus was a deterministic periodic current input of small amplitude, sweeping through a specified frequency range. We used whole-cell, tight-seal recording techniques in slices to study the voltage responses and membrane properties in current and voltage clamp. 2. Generally, low-frequency resonant humps with peak impedances of approximately 6 Hz characterized the frequency responses of OV neurons. This resonance was the principal determinant for frequency selectivity in the majority of OV neurons expressing only a tonic mode of firing. 3. The 6-Hz resonance was voltage dependent and most distinct where the activation ranges of a hyperpolarization activated inward current (IH) and a persistent Na+ current tend to overlap. The potential range for optimal resonance often included the resting potential. 4. Application of the Na+ current antagonist, tetrodotoxin, blocked the persistent Na+ current and most of the resonant hump at depolarized levels but did not affect the resonant peak along the frequency axis. Thus the persistent Na+ current may serve to amplify the resonance. 5. Extracellular application of Cs+, but not Ba2+, blocked a voltage sag during pulsed hyperpolarization as well as the IH current. Application of Cs+ also eliminated the 6-Hz resonance. An IH seems, therefore, instrumental for the resonance. 6. A minority of neurons that expressed low-threshold Ca2+ spikes and burst firing at hyperpolarized states displayed voltage oscillations at 2-4 Hz, spontaneously or in response to pulsatile stimuli. Application of Ni2+ blocked the oscillations and the low-threshold spikes, presumably produced by a T-type Ca2+ current. The resonance at 6 Hz, however, was only slightly affected by Ni2+. A T-type current, therefore, is critical for the 2- to 4-Hz oscillations. 7. Membrane resonance may dominate the power spectrum of subthreshold potential fluctuations. The resonance demonstrated in vitro may be stabilized by experimental procedures; its frequency may be different and more variable in vivo. Resonances in thalamic neurons may play a role in auditory signal processing in birds.

Animals↗

PubMed1991

[Nasal cavity and paranasal sinus malignancies in the ENT clinic of Charité since 1959].

A retrospective analysis of 235 cases suffering from nasal and/or paranasal sinus malignant tumours who were admitted to the Charité ENT-Clinic between 1959 and 1989, is presented. 94 of the patients were women and 141 men, the mean age being 63.8 years (women) and 61.8 years (men), respectively. The most common histomorphological diagnosis was carcinoma (66%), followed by lymphoma/sarcoma (17%). 35% of all tumours originated in the nasal cavity, 38% in the maxillary sinus, 22% in the ethmoidal sinuses. At the time of admission many tumours had already invaded surrounding structures. Tumour invasion of the pterygopalatine fossa was noted in 52 patients, invasion of the orbit in 89 and of the skull base in 65 cases. Our therapy mainly depended on the histology of the tumours. 19% of all carcinomas were treated by surgery only, in 48% surgery and postoperative radiation was the therapy of choice. 59% of lymphomas/sarcomas were treated by radiation only. 100 out of these 227 patients treated because of sinus malignancy developed recurrencies. The 5-year survival rate was 30% in general, 29% for the years 1959-1970, 31% for the years 1971-1984 and for the T1 to T4 type cancers 54%, 38%, 19% and 19%, respectively.

Adolescent↗

PubMed1991

[Kimura disease--2 case reports].

Two histologically confirmed cases of Kimura's disease are reported in the present article. Emphasis is placed on the clinical symptoms in conjunction with the histological picture. Recent studies in the literature are discussed with respect to differential diagnosis, etiology and therapy. In all ENT-tumours of unknown origin this relatively uncommon disease should also be considered.

Angiolymphoid Hyperplasia with Eosinophilia↗

PubMed1989

[The clinical course of fatal aneurysm rupture of the base of the skull].

At the Institut of Pathology and the Institut of Forensic Medicine at the Charité Clinics of the Humboldt-University Berlin from 1979 to 1984 took place 13,622 necropsies. Among them were 75 cases of fatal ruptures of intracranial aneurysms. This paper gives a description of the resulting subarachnoid hemorrhages (SAH) and compares them with the pathologic-anatomical findings. 65 cases have been utilized, in 50% of them the patients died on the day of bleeding, in no case the aneurysm was verified before death. 31% of the patients survived longer than one week. A sufficient prognostic sign was the degree of unconsciousness during the 24 hours following SAH. The morphological findings (intracranial hematomas, brain edema) and the time of further survival did not correlate. Ventricular hematomas were found in 49% of the autopsy subjects. Patients with ventricular hematomas from the initial SAH evolved a bad clinical state (Botterell Grading 'IV or 'V). Every nontraumatic SAH is a case of emergency which requires a fast diagnostic procedure. Ruptured aneurysms have to be excluded. A good clinical state after SAH need not keep stable. Grading systems reflect intracranial processes only incompletely.

Adult↗