Biomedical subjects

M Walger

Publications and source records attributed to M Walger.

41 records · Page 3Linked to original sources

PubMed1985

The influence of moderate-intensity noise on the compound action potential evoked by tone bursts in the guinea pig, Cavia porcellus.

Noise-induced changes in the compound action potential (CAP) evoked by tone bursts in the frequency range 0.5-24 kHz were studied in 15 pigmented guinea pigs by means of chronically implanted electrodes positioned near the round window. The animals were exposed for 120 h to continuous pink noise at the intensities 80, 90 and 100 dB SPL. During the exposure period, all the animals exhibited an exponential rise in CAP threshold, leveling out after 24-72 h (asymptotic threshold shift, ATS). The largest threshold shifts were recorded during exposure to 100 dB SPL, for frequencies in the range 8-12 kHz. In the recovery phase, after the end of noise exposure, the threshold to tones at all frequencies tested fell exponentially, reaching the original level in about 72 h in all cases.

Animals↗

PubMed1985

[Electrophysiologic studies on the course of the adaptation phase following noise stress].

It was the aim of this study to settle the problem whether the post-stimulatory pattern of the extent of excitation (amplitude, latency) registered with the cortical evoked potentials can be verified in the recovery phase via leads from the brain stem region and cochlea. In this context electrophysiological measurements with human and animal material were performed. After a five-minute stimulation with a wide-band noise of various intensity we examined in the post-stimulation phase the specific stimulus pattern of the evoked potentials during an interval of 5 minutes with a resolution of 5 sec. We determined the change in response patterns of evoked potentials. Finally, the relevance of the results with regard to various nuclei of the auditory pathway is compared with corresponding electrophysiological measurements of the cochlear microphonics potentials, the VIII nerve compound action potential, and evoked potentials of different units of the brain stem and brain.

Animals↗

PubMed1985

[Implantation technics for long-term recording of the compound action potentials in the guinea pig, Cavia porcellus. A comparison of methods].

Long-term recordings of the compound action potential of the acoustic nerve of young, pigmented guinea pigs were carried out by two different techniques of implantation. The electrodes were inserted either by way of the mastoid process into the bony recess above the round window or they were introduced into the facial canal via the stylomastoid foramen. Before and after each implantation, special tests (Preyer-reflex, otoscopy, impedance audiometry) were performed for preliminary selection of the animals and to discover postoperative induced disturbances of sound conduction in the middle ear. These tests showed that the proportion of operatively induced middle ear inflammations was reduced from 24 to 10%, if electrodes were implanted into the facial canal.

Acoustic Impedance Tests↗

PubMedDate not supplied

A method for the induction of a cochlea-specific auditory deprivation in the gerbil (Meriones unguiculatus).

The neurophysiological effects of early electrical stimulation on the development and neural plasticity of the central auditory system in prelingually deafened children with cochlear implants are still unknown. Many of these basic questions can be answered systematically only in animal experiments. Meriones unguiculatus is a well-established animal model in hearing research. Deafening is produced by a single intracochlear application of an ototoxic aminoglycoside antibiotic (neomycin sulfate) on the 14th day after birth (DAB), i.e. before the late natural onset of hearing on the 16th DAB. A single application of the antibiotic abolishes auditory brainstem responses (ABR) to clicks completely and reduces sensitivity to low frequency tonebursts by 50 dB SPL. Scanning electron microscopy results show a destruction of the stereocilia of the inner and outer hair cells of the basal and medial cochlear turn and a reduction of those in the apical turn. Our method avoids a systemic application of antibiotics and can be used in studies dealing with the consequences of different forms of auditory deprivation, neuronal compensation processes or with ontogenetic studies and chronic electrostimulation in an animal model.

Acoustic Stimulation↗

PubMedDate not supplied

Effects of prostacyclin on hearing recovery after repetitive noise and on histomorphology of the inner ear in the guinea pig.

A probable relation between prostaglandin formation and the pathophysiology of hearing loss led to the application of the potent vasodilator prostacyclin in the treatment of inner ear disorders. Two drugs may be administered to humans: (1) unstable natural prostacyclin (epoprostenol) with a strong biological potency but with a high first-pass effect, or (2) a prostacyclin analogue (taprostene) with less biological activity, but a longer biological half-life and intravenous application. Therefore, the purpose of this study was to investigate potential differences of both drugs in their effect on the inner ear. The therapeutic potency of both drugs was evaluated in a recently developed animal model consisting in the recovery of hearing after a temporary threshold shift obtained by two noise exposures at 100 dB. In addition, the ultrastructure of the stria vascularis was examined by electron microscopy after the application of the drugs. After administering epoprostenol (12 ng/kg body weight/min) and taprostene (25 ng/kg body weight/min) histomorphological alterations in the stria vascularis did not differ from the controls. In the repetitive low-level noise model, neither drug showed a significant difference in its effect on the recovery of the hearing threshold. The results indicate that in the guinea pig epoprostenol has the same effect on the hearing threshold as the stable analogue taprostene, as shown by auditory brain stem response.

Animals↗