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Biomedical subjects

G Langner

Publications and source records attributed to G Langner.

29 records · Page 2Linked to original sources
PubMed1987

Covariation of latency and temporal resolution in the inferior colliculus of the cat.

Onset latency of single-unit and multiunit responses was measured in the central nucleus of the inferior colliculus (ICC) of barbiturate anesthetized cats. The relationship of the units' onset latency with their characteristic frequency (CF), their best modulation frequency (BMF), and their location within the ICC was studied. Latencies were significantly correlated to BMF; they were only weakly correlated to CF. The contribution of CF to the delays can be attributed to the traveling wave mechanism; covariation of latency and temporal resolution (BMF) likely manifests neuronal mechanisms underlying periodicity coding.

Acoustic Stimulation↗
PubMed1984

Infrasound responses in the midbrain of the guinea fowl.

The electrophysiological audiogram of the Guinea fowl has been obtained using auditory evoked potentials from the MLD of unanesthetized birds. In restricted regions of MLD, phase-coupled responses to extreme low-frequency sinusoids (2-10 Hz) could be recorded at moderate intensities. The tonotopy of MLD extends continuously to the infrasound region at the rostrodorsal margin. Single-cell recording of infrasound responses show phase-locked firing of neurons with different phase delays for different cells.

Animals↗
PubMed1983

Evidence for neuronal periodicity detection in the auditory system of the Guinea fowl: implications for pitch analysis in the time domain.

Evidence for periodicity analysis was obtained by recording from 420 single units in the auditory midbrain nucleus (MLD) of awake Guinea fowls (Numida meleagris). The results were compatible with a neuronal correlation model consisting of three main components: an oscillator, an interval multiplier and a coincidence unit. The model makes use of a neuronal time constant in order to measure the periodicities of auditory signals. For 180 units the sequence of spike intervals in response to tone bursts and amplitude modulations (AM) was studied with 10 microseconds resolution. In 69 of these units (38%) amplitude fluctuations like stimulus onset or the modulation cycles produced periodic spike trains resembling damped oscillations. The periods of these oscillations did not correspond to either the best frequency (BF) of these units or the periodicities of the stimuli. They were interpreted as multiples of a neuronal time constant, tau 1 = 0.4 ms, probably a minimal synaptic delay. These units were tuned to AM-signals with particular combinations of the modulation frequency, fm, and the carrier frequency, fc. The corresponding periods tau m and tau c were related to the intrinsic oscillation by a periodicity equation: m X tau m + n X tau c = 1 X tau 1, where a few small integers for m, n and 1 were adequate to describe all observed properties of a unit. Variation of fm or fc shifted the phase delays of the coupled spike activities proportional to m X tau m or n X tau c, respectively. These effects were explained by coincidence of neuronal activity phase coupled to fc, with intrinsic oscillations triggered by the fm-cycles. The coincidence condition at the level of the recorded units was given by the periodicity equation. Psychophysical experiments using AM-signals indicated that the described mechanisms, together with the same neuronal time constant, tau 1, are adequate to explain pitch perception in humans.

Animals↗
PubMed1983

Linear phoneme boundaries for German synthetic two-formant vowels.

The phonetic boundaries of variable, synthetic two-formant vowels were studied in psychophysical tests. In the F1 versus F2 formant plane, vowel boundaries appeared to be straight and all but one were parallel to the formant axes. Discrimination of two of the eight German vowels examined relied within certain boundaries upon information of the frequency of the first formant (F1) independent of that of the second (F2) or vice versa. Two vertical F1 boundaries were common to six vowels and one horizontal F2 boundary was common to five vowels. Interpreted in the light of recent neurophysiological data these findings point to the existence of mechanisms of vowel recognition with independent assessment of the two formants.

Communication Devices for People with Disabilities↗
PubMed1981

Neuronal discrimination of natural and synthetic vowels in field L of trained mynah birds.

The discrimination of single neurons for vowels and vowel components was analyzed in the telencephalic field L which is a layered and tonotopically organized primary auditory projection area in the bird's neostriatum. Among 250 units, 132 (53%) were responsive to at least one out of nine vowels from one German speaker. The distribution of responsiveness to n (one to nine) vowels showed that a maximum of 33 out of the 132 neurons preferred n = one vowel. The mechanisms of vowel selectivity were analyzed with five synthetic vowels composed of two formants F1 and F2 which could be presented separately. Most of the selective units also responded to F1 or F2 of the preferred vowel alone. The suppression of the vowels could be explained by formants which fell into inhibitory ranges of that unit, independently demonstrated by the pure tone response. Other units had several excitatory bands which coincided with the formants of the preferred vowel. In some cases a certain amplitude ratio of F1 versus F2 gave the strongest response. Several qualitative models of excitatory-inhibitory interaction of inputs to field L neurons are presented which explain the described selectivities. It is interesting that the distribution of vowel-selective units relates to the most superficial and most basal layer of field L where units selective for species-specific calls have previously been located in a gallinaceous bird.

Animals↗
PubMed1981

Neuronal mechanisms for pitch analysis in the time domain.

Many units in the auditory midbrain nucleus (MLD) of the Guinea fowl are found to be tuned to amplitude modulated tones (AM). For a given response maximum the relationship of the period tau m of the modulation frequency fm and the period tau c of the carrier frequency fc may be given by an empirical equation: m . tau m + n . tau c = 1 . tau l, where m, n and l are small integers typical for a unit. tau l is a time constant of 0.4 ms. The temporal pattern of the neuronal response support these findings. The averages of spike trains oscillate with periods multiple to tau l. These oscillations are elicited by stimulus onsets and zero crossings of fm and may by coupled strongly to fm depending on fc. Variation of fm or fc shifts the mean delay of the phase coupled activity proportional to m . tau m and n . tau c, respectively. These effects may be explained with activity phase coupled to fc which coincides at the level of the recorded units with oscillations coupled to fm. This is expressed by the above given periodicity equation. Psychophysical results with AM-stimuli indicate that the mechanisms described and the periodicity equation are adequate for the explanation of the analysis of periodicity pitch in humans. Hence the period corresponding to pitch is defined by tau p = n . tau c-1 . tau l, where n and 1 are integers and tau l = 0.4 ms. Plots of tau p as a function of tau c reveal steps at 0.4 ms intervals indicating that the neuronal time constant is the same in both species.

Animals↗
PubMed1979

Functional organization of some auditory nuclei in the guinea fowl demonstrated by the 2-deoxyglucose technique.

The auditory pathway of the Guinea Fowl was labeled with [C14]2-deoxy-D-glucose after stimulation with pure tones, harmonic tones and species-specific calls. In addition to other auditory nuclei, which showed more or less uniform labeling with the present technique, the n. mesencephalicus lateralis dorsalis (MLD) of the midbrain, as well as field L and parts of the hyperstriatum ventrale in the telencephalon, showed a stripe-pattern of labeling after stimulation with a pure tone. The position and orientation of the tone-activated striped areas in field L, observed after stimulation with different tones, correspond to isofrequency contours obtained with microelectrode recordings. The labeling of the three congruent tonotopically organized layers of field L (L1, L2, and L3) was not uniform along the anterior-posterior axis of the field. Harmonic tones produced multiple reactive stripes each of which corresponded to the stripe characteristic of a particular harmonic presented as a pure tone. The species-specific Iambus-call labeled the tonotopic area of field L that corresponds to the frequency band with the highest energy of the call. The hyperstriatum ventrale generally showed a weaker pattern of labeling that, however, resembled the labeling in field L.

Animal Communication↗
PubMedDate not supplied

Electroreception and electrolocation in platypus.

Electroreceptors with sensitivity in the microvolt range, which mainly function to detect live prey, are well known in phylogenetically old fishes and some amphibians. In African mormyriform and South American gymnotiform fishes this sense has evolved to an active system using an electric organ as a source for impedance measurement of the environment and for communication. Electroreception in higher vertebrates has not previously been reported. Here we establish that the platypus, the Australian nocturnal diving monotreme, can locate and avoid objects on the basis of d.c. fields. High-frequency sensitivity to a.c. could allow the detection of muscle activity of animals, such as crustaceans, which are preyed on by the platypus. Recordings of cortical evoked potentials showed that the bill of the platypus, previously considered to be exclusively mechanoreceptive, is also an electroreceptive organ with behavioural and electrophysiological sensitivity of approximately 50 microV cm-1. Several lines of evidence suggest that electroreception has evolved independently in this monotreme.

Animals↗
PubMedDate not supplied

Experimental model of hepatic venoocclusive disease (VOD) caused by dactinomycin--preliminary report about hepatoprotective effect of amifostine.

UNLABELLED: The purpose of the study was elaboration of the experimental model of hepatic venoocclusive disease (VOD) induced by dactinomycin and investigation of possible hepatoprotective effects of amifostine and heparin individually or in combination with dexamethasone. 198 Wistar strain male rats were used in the trial in two series of experiments. In the first series the experimental model of VOD induced by dactinomycin was elaborated on the group of 18 animals (divided into 3 groups receiving intraperitoneally isotonic salt solution, dactinomycin or nitrosamine). Nitrosamine--a well-known agent causing VOD--was used as positive control. Open biopsies of the liver and blood collections were repeated in order to determine liver enzymes' concentrations. Histopathological examinations demonstrated that dactinomycin caused liver lesion corresponding with VOD picture. Second series of animals was divided into 6 groups receiving the following drugs: I--0.9% NaCl solution, II--dactinomycin (ACT), III--ACT + fraxiparine s.c., IV--ACT + fraxiparine + dexamethasone, V--ACT + amifostine. Five animals from each group were sacrificed on the 3rd and 7th day after each cycle of drug administration. Blood was drawn in order to determine the following: AspAT, AlAT, Falk, GGTP and LDH. Intravital wedge biopsies under anesthesia with the use of inactin were also performed. Liver samples were stained with the use of H&E, p. a. S and Gomory's techniques. We did not find significant differences in liver enzymes' levels between the groups. Pathological changes corresponding with VOD picture of different intensification were found in liver samples from all the rats receiving ACT. Changes became more and more intensive after consecutive cycles. Lesion of central veins' and liver sinusoids' endothelium dominated. Fraxiparine administered individually or in combination with dexamethasone did not prevent the lesion. Administration of amifostine before ACT decreased pathomorphological changes in liver. Dactinomycin caused homogenous subclinical liver lesion corresponding with VOD. It may also occur in children receiving ACT in the course of nephroblastoma's treatment. But probably the changes are too subtle to manifest themselves clinically with exception of patients particularly sensitive (for example after previous radiotherapy). Lack of differences observed in liver enzymes' levels between the groups supports the explanation. Markers of lesion of liver vessels' endothelium should be looked for to make more specific diagnostics of VOD possible. Hepatoprotective properties of amifostine need further studies. CONCLUSIONS: 1. It is possible to create the experimental model of VOD induced by dactinomycin administration. 2. Amifostine seems to act hepatoprotectively to liver lesions caused by dactinomycin.

Alanine Transaminase↗