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Biomedical subjects

J M Aran

Publications and source records attributed to J M Aran.

At least 91 records · Page 5Linked to original sources
PubMed1987

Mathematical analysis of VIIIth nerve cap with a linearly-fitted experimental unit response.

The compound action potential (CAP) recorded at the round window has for some time been investigated in order to determine the underlying temporal spike sequence: the firing probability density (FPD) function of the fibres. Charlet de Sauvage et al. [(1980) Hear. Res. 2, 343-346; (1983) J. Acoust. Soc. Am. 73, 616-627] have previously described a close estimate of the far-field unit response (UR) by presenting to the ear a transient electrical stimulation combined with an acoustical masking noise. A linear model of UR, free of noise or extrinsic potentials and based on both experimental data and on the dipole principle of Teas et al. [(1962) J. Acoust. Soc. Am. 34, 1438-1459], was proposed [(1985) Hear. Res. 18, 121-125]. Using the UR model, deconvolutions were performed on CAPs recorded in various conditions of stimulation and of cochlear pathologies in the guinea pig. The principal findings were: (1) a plateau was observed in the amplitude function around 60-70 dB above normal threshold both for click-evoked CAPs and for the corresponding FPDs; (2) FPDs resulting from the deconvolution of high-frequency derived responses showed 2 main peaks with a 0.7 ms interval followed by a second homologous pair with lower amplitude. Convolution computations confirmed the need for the second set with peaks 2 and 3 being only 0.3 ms apart. These findings are interpreted in terms of mechanical excitation pattern.

Animals↗
PubMed1987

Stapedius reflex and cerebellopontine angle tumours.

The stapedius reflex was investigated in 61 patients with cerebellopontine angle tumours, in order to evaluate the reliability of the reflex-decay test in VIIIth nerve disorders. The reflex was completely normal in 11% of the patients. The 2 most frequently observed abnormalities were (1) an absence of the reflex when stimulating the ear on the side of the tumour, and (2) the conjunction of pathological reflex-decay at 0.5 kHz with a unilateral threshold elevation and/or absence of the reflex at other frequencies. The decay test was normal in one-third of the patients with a preserved reflex.

Acoustic Impedance Tests↗
PubMed1987

Ototoxicity of teicoplanin in the guinea pig.

Experiments were performed on guinea pigs to assess the eventual ototoxic side effects of a new glycopeptide antibiotic called teicoplanin. For a better validation, in the same study other animals were treated with tobramycin, a well known ototoxic antibiotic of the aminoglycoside family, and a group of control animals was also constituted. Antibiotic treated animals were injected with the high dose of 90 mg/kg/day during 21 consecutive days. Electrophysiological measures of equilibrium and acoustic functions were taken and morphological evaluations of the cochleas were performed. The results indicate that in these animal experiments teicomycin appears to be clearly toxic for the vestibule and the cochlea.

Animals↗
PubMed1987

[Responses evoked in "steady state" in man by means of a sinusoidal frequency modulation].

The response of the human auditory system to a 40 Hz sinusoidal modulation of the frequency of a tone can be reliably recorded from the human scalp using Fourier analysis. With increasing intensity the amplitude of the response becomes larger and its phase delay shorter. The response amplitude is larger and the phase delay longer for lower carrier frequencies. The response may possibly become useful in the objective evaluation of frequency discrimination.

Adult↗
PubMed1986

GABA immunoreactivity in the primary nuclei of the auditory central nervous system.

Structures containing gamma-amino butyric acid (GABA) were investigated in the guinea pig cochlear nuclei and superior olivary complexes by means of an immunohistochemical procedure using an antibody directed against GABA. Immunoreactivity was observed in cell bodies of the superficial layers of the ventral and dorsal cochlear nuclei, in lateral superior olive, in some neurons of the medial superior olive, in lateral preolivary nuclei and in the lateral nucleus of the trapezoid body. Fibers and profiles exhibiting GABA immunoreactivity were found in almost all regions of the lower auditory pathways. The abundance of GABA in these regions indicates an important role of this inhibitory amino-acid in the auditory brainstem.

Animals↗
PubMed1986

Comparative uptake of gentamicin, netilmicin, and amikacin in the guinea pig cochlea and vestibule.

The kinetics of the entry of three aminoglycosides into inner-ear tissues of the guinea pig after acute and chronic administration were compared: gentamicin toxic to the cochlea and the vestibule, amikacin preferentially cochleotoxic, and netilmicin of low ototoxic liability. During constant intravenous infusion, levels of the three drugs in plasma tended to reach a plateau after 1 h, while levels in perilymph did not reach a plateau within 6 h. The drug concentrations in both vestibular and cochlear tissues quickly reached saturation. Amikacin and gentamicin concentrations were similar in vestibular and cochlear tissues, while netilmicin values were somewhat lower. After 1 week of chronic treatment (100 mg of drug per kg of body weight daily subcutaneously), levels of gentamicin and amikacin in tissue were similar to each other and were not significantly different between cochlear and vestibular tissues. Netilmicin concentrations again were somewhat lower in the tissues, but identical to those of the other drugs in the perilymph. After 3 weeks of treatment, all of the drugs were equally distributed in the inner-ear tissues. Release of the drug from the tissues after the 3-week treatment was faster for amikacin (83% decrease after 20 days) than for netilmicin and gentamicin (approximately 50% decrease). There was no correlation, under any of the experimental conditions, between the drug concentrations and their degrees of toxicity. These results demonstrate that selective aminoglycoside ototoxicity cannot be explained by a preferential uptake or accumulation of drugs in the afflicted tissues or in the perilymph.

Amikacin↗
PubMed1986

Investigation of cochlear mechanisms using combined acoustical and electrical stimulations.

Electrically-evoked VIIIth nerve CAP responses evoked by electrical stimulation and derived by masking with sounds are recorded in the guinea pig, using different masking paradigms (pure tones and high-pass filtered white noise). CAP frequency threshold curves correlate with threshold curves determined by other means, in normal as well as in pathological guinea pigs. Amplitudes of the responses as a function of pure tones frequency and intensity are also measured. Such measurements provide an estimate of the number of fibers activated by the pure tones. These responses can be further analysed using masking with high-pass filtered white noise.

Acoustic Stimulation↗
PubMed1985

Derived evoked potentials for continuous tones using a hybrid electrical-acoustical stimulation.

Averaged VIIIth nerve and brainstem potentials are recorded in normal guinea pigs in response to electrical stimulation of the ear presented once without and once with a simultaneous masking continuous pure tone. The waveform difference yields a well synchronized 'derived signal' which is the response to the electrical stimulation of only the group of fibers masked by the pure tone. Study of very low frequency activation is a new possibility brought by this method which is efficient whatever the sound frequency. Pure tone thresholds obtained are similar to previous measurements. Response amplitudes are likely a measure of the number of fibers stimulated by the sounds.

Acoustic Stimulation↗
PubMed1985

Effects of glycerol on cochlear frequency selectivity in patients with Menière's disease.

During transtympanic electrocochleography, action potential (AP) tuning curves were derived as a measure of cochlear frequency selectivity. In 18 out of 21 patients with symptoms of Menière's disease, a poor frequency selectivity was observed. In 12 subjects the effects on frequency selectivity of oral glycerol were measured, and in 5 patients AP tuning curves indicated an improvement in sharpness of tuning by a factor of 1.5-2.5. These changes started approximately 30 min after oral glycerol administration. In 2 subjects there was a deterioration in AP tuning. In 5 patients no significant changes were observed.

Action Potentials↗
PubMed1984

Some otological differences between pigmented and albino-type guinea pigs.

Cochlear action potential thresholds across frequency (AP audiograms) and AP tuning curves were compared in albino (Dunkin-Hartley) guinea pigs and normal pigmented animals. AP audiograms were very similar; on average the albinos had AP thresholds 2-3 dB lower at 2 kHz and below compared with the pigmented guinea pig. AP tuning curves at 16 kHz were, on average, significantly less sharply tuned in the albino, but similar at 8, 4, and 2 kHz. Although we find only small differences in these measures of normal cochlear function, other evidence in the literature suggests that in auditory research the use of "albino" guinea pigs is best avoided.

Animals↗
PubMed1984

Electrophysiological measures of cochlear function in guinea pigs with long-term endolymphatic hydrops.

Experimental endolymphatic hydrops was induced in guinea pigs by obliteration of the endolymphatic sac and duct. From 3 to 24 months after this operation, cochlear action potential (AP) audiograms and AP tuning curves were measured. The purpose of this study was to establish parallels, if any, between this supposed animal model of Menière's disease and the auditory symptoms of the disease in man. In some animals, low and middle frequency AP threshold elevations were observed whilst higher frequency regions maintained normal sensitivity. Other animals developed flat or very gradually sloping AP audiograms. These patterns are qualitatively similar to those found clinically in Menière's disease. AP tuning curves measured in frequency regions of threshold elevation indicated a deterioration of cochlear frequency selectivity; psychophysical and electrocochleographic studies demonstrate related changes in Menière's patients. One animal exhibited modifications in AP thresholds and tuning as a result of glycerol administration. These observations improve our confidence in the validity of this animal model for further studies of the pathophysiology of Menière's disease.

Action Potentials↗
PubMed1983

Artificial activation and degeneration of the cochlear nerve in guinea pigs.

Degeneration of the cochlear nerve was produced in guinea pigs after treatment with high doses of ototoxic antibiotics completely destroying the cochlear receptor. An effective electric stimulation of the inner ear inducing evoked potentials at the auditory cortex was applied over a period of 3.5 months in half of the animals, while the other half was kept for control. The artificial stimulation had no effect on the sensitivity of the inner ear to electric stimulation and did not modify the extent of degeneration of the cochlear nerve.

Amikacin↗
PubMed1983

Intensity difference thresholds assessed with eighth nerve and auditory cortex potentials: compared values from cochlear and vascular responses.

In normal guinea pigs the eighth nerve compound action potential shows a latency of about 1 ms and the evoked early potential at the auditory cortex occurs after about 10 ms. Determination of auditory sensitivity with both responses using tone-bursts of variable rise/fall time and plateau duration showed they are responses to the onset of the stimulus since the existence of a plateau has no effect. Increases in stimulus rise time diminish the synchrony of both responses, the limits were found to be 2 ms for eighth nerve responses and 10 ms for cortical potentials. Amplitude modulation of continuous tones using these time values evokes clear responses at levels which apparently correspond to intensity difference thresholds measured behaviorally by other authors. Similar measures were performed on saccular acoustic responses, using the model of selective cochlear destruction. Evoked responses could also be observed at levels of amplitude modulation similar to those of normal animals. This fine sensitivity reinforces the idea of a functionality of the saccular acoustic reception.

Action Potentials↗
PubMed1983

Acoustically derived auditory nerve action potential evoked by electrical stimulation: an estimation of the waveform of single unit contribution.

An experimental study of the electrical stimulation of the guinea pig cochlea is made using an electrode on the round window for both stimulation and recording. The neural response is separated from the electrical artifact with a masking procedure combined with a low amplification, "statistical" averaging method [Charlet de Sauvage et al., Hear. Res. 2, 343-346 (1980)]. The high electrical impedance required for recording physiological responses implies the use of a current pulse generator. Monitoring of evoked potentials from the auditory cortex provides evidence that the effects of electrical stimulation (and of masking noise) are of auditory origin. The electrically evoked round window response is of very short latency (less than 0.2 ms). There is a response threshold for both electrical stimulus and masking noise. The response amplitude varies monotonically as a function of masking noise or electrical stimulus intensity. Experiments with high-pass noise masking suggest that the electrical stimulus is mainly acting on basal fibers. The response latency and waveform are independent of electrical stimulus intensity, repetition rate, masker level, or spectrum. Little intersubject variation is noted. Our experiments (reciprocal forward masking by electrical and acoustic stimuli) suggest that a direct, instantaneous electrical stimulation of the fibers occurs. We believe that this response to electrical stimulation represents the mean unit response of the auditory nerve fibers. This approach may be useful in the separate study of cochlear and VIIIth nerve functions and in the analysis (deconvolution) of the acoustically evoked compound AP.

Acoustic Stimulation↗