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Biomedical subjects

G R Bock

Publications and source records attributed to G R Bock.

At least 19 recordsLinked to original sources
PubMed1988

EEC hearing impairment programme: collaboration in Europe, 1974-1988.

The Commission of the European Communities funds a 'concerted action' programme in the area of hearing impairment. The programme does not fund research directly, but is intended to provide funds for coordination of research in different countries. Previous projects funded by the programme include a comprehensive study of the prevalence of childhood deafness in the European Community, and meetings on cochlear implants, human temporal bone histopathology, diagnostic techniques and hearing impairment in children. The programme is currently concerned with new technologies for communication in the hearing impaired and activities in 1988 will include workshops on signal processing hearing aids and early diagnosis in children.

Child↗
PubMed1987

Strial dysfunction in mice with cochleo-saccular abnormalities.

Most viable dominant spotting (Wv/Wv) mutant mice, which show cochleo-saccular degeneration, were found to have an endocochlear potential (EP) around zero together with a structurally abnormal stria vascularis. Inner hair cells were well preserved, but outer hair cells in the basal half of the cochlea were degenerating, possibly as a result of primary strial dysfunction. Thresholds for the detection of a compound action potential were raised to around 100 dB SPL in the mutants with no EP, and there was little if any cochlear microphonic at the round window. Of the 20 Wv/Wv mice studied, five partially escaped the effects of the mutation and had measurable positive potentials (15-86 mV) in scala media in the basal turn; responses in these animals were intermediate between control responses and those of mutants with no EP. These findings confirm that the pathological processes in this mutant, with cochleo-saccular abnormalities, are fundamentally different from the pathological processes in animals with neuroepithelial abnormalities reported previously [see Steel and Bock (1983) Arch. Otolaryngol. 109, 22-29, for references].

Animals↗
PubMed1987

Mixed conductive and sensorineural hearing loss in LP/J mice.

Air and bone conduction thresholds for the detection of a compound action potential response were measured in mice of the LP/J inbred strain, which has been proposed as a possible model for human otosclerosis. Thresholds were compared with control data from CBA/Ca mice. Evidence of a mixed sensorineural and conductive hearing loss was obtained in LP/J mice. Few signs of hair cell degeneration or middle-ear bony lesions were found in 20-day old mice, although they generally showed raised thresholds to both air and bone conducted stimuli. The reason for the observed sensorineural component of the hearing loss at this age is not clear, since endocochlear potentials were normal in mice of this strain. By 225 days of age, hair cell loss was extensive and there was clearly excess bone growth in all middle-ear specimens studied, particularly on the incus and the cochlear wall facing the middle ear. Microbiological analysis of LP/J specimens revealed no evidence of a middle-ear infection specific to these mice which might explain the pathology.

Action Potentials↗
PubMed1985

Combined electrophysiological and autoradiographic delimitation of retrocochlear dysfunction in a mouse mutant.

The hereditary retrocochlear dysfunction in the quivering (qv) mouse was investigated with autoradiography and single unit recordings. Whilst the cochlea appears to function normally, earlier studies had indicated some single unit dysfunction detectable at the level of the cochlear nucleus (CN) and abnormality of auditory evoked potentials recorded at the inferior colliculus (IC). The present study investigated the possibility of progressive deterioration of function at successive higher levels in the auditory system. The 2-deoxyglucose technique illustrated auditory activity in the CN of quivering mice similar to that seen in normally-hearing control animals. There was only a slight increment in metabolic activity detectable at the level of the IC. Electrophysiology demonstrated that this minimal IC activity was the result of abnormally raised thresholds associated with all single units recorded, rather than of activity in a few normally responding cells. There was no evidence from autoradiography for any enhanced auditorily evoked metabolic activity in either the superior olivary complex or the lateral lemniscus. This study suggests that the retrocochlear dysfunction in quivering mice is due to a specific abnormality at a low stage in the auditory pathway rather than being non-specific and cumulative over stages.

Animals↗
PubMed1985

Distortion product otoacoustic emissions in hearing-impaired mutant mice.

The acoustic intermodulation distortion product (2f1-f2) was recorded in the ear canal of two different types of normally hearing mice and in four different types of hearing-impaired mutant mice. In the normally hearing animals, primary tones at levels of 60- to 100-dB SPL evoked distortion product emissions (DP's) at 20-50 dB below the primary levels. In the hearing-impaired mutants the level was dependent on the particular type of auditory dysfunction associated with the mutation. In both the deafness and the viable dominant spotting mutants, where either the whole organ of Corti or the stria vascularis is affected by the mutation, no DP's could be detected. The quivering mutant has a central auditory dysfunction associated with the nuclei of the superior olivary complex and the lateral lemniscus, with apparently normal cochlear function. DP's at levels and thresholds similar to those in normally hearing animals were recorded in quivering mice. The Bronx Waltzer mutant has a full complement of outer hair cells but only about of 20%-25% inner hair cells. DP's of small amplitude were recorded but the thresholds were raised by about 30 dB. The data suggest that the 2f1-f2 emission can be used as a noninvasive monitor of cochlear function.

Acoustic Stimulation↗
PubMed1985

Genetic factors affecting hearing development.

Both genetic background and single gene mutations may affect the development of the auditory system. A classification system is presented for those single gene mutations causing hearing impairment. The new feature of this classification is the inclusion of a category for hereditary deafness of central origin. The other categories involve peripheral abnormalities and are: morphogenetic defects, in which the overall structure of the labyrinth is deformed; neuroepithelial degeneration, in which the primary defect appears to occur in the organ of Corti; and cochleo-saccular degeneration, where the stria vascularis is abnormal and Reissner's membrane collapses, leading to further degeneration.

Animals↗
PubMed1985

Electrical stimulation of the auditory system in animals profoundly deaf from birth.

Animals homozygous for the recessive deafness gene (dn/dn) have been used to study central responses to modiolar or round window electrical stimulation. Inferior colliculus evoked responses to contralateral constant current pulses are larger in mutants than in controls. In mutants, responses are largest in animals aged 5-7 months, compared with animals aged 42-50 days or 13.5-19 months. The spiral ganglion cell density is normal in the youngest group, but decreases significantly in older animals. Electrical stimulation of the round window is less effective than modiolar stimulation. Single unit recordings suggest that the larger evoked responses in deafness mice are produced by stronger discharges in neurones, rather than greater synchrony of discharge. The deafness mutation appears to provide a useful animal model for studying electrical stimulation of a central pathway which has never received stimulus-related input.

Age Factors↗
PubMed1985

The effects of paracetamol on frusemide ototoxicity.

Paracetamol (acetaminophen) is currently one of the most widely used drugs. In large doses, paracetamol is both nephrotoxic and hepatotoxic, and this toxicity may arise through the production of free radicals. Recently, there has been a revival of interest in the hypothesis that aminoglycoside antibiotics are ototoxic because they facilitate free-radical production. Aminoglycosides interact strongly with loop diuretics, producing enhanced ototoxicity. The object of the present study was to determine whether paracetamol would also interact with a loop diuretic. Pigmented guinea pigs received a dose of 500 or 1000 mg/kg paracetamol via an intragastric cannula. Compound action potentials (CAP) were recorded every 10 min for 2 h. Paracetamol alone had no effect on CAP thresholds, but significantly enhanced the CAP decrement induced by frusemide given intraperitoneally 1 h after paracetamol. This enhancement was larger in animals receiving 1000 mg/kg paracetamol. Repetition of these drug doses in recovery experiments indicated that all threshold shifts recovered within 7 days.

Acetaminophen↗
PubMed1979

Frequency selectivity in bird and man: a comparison among critical ratios, critical bands and psychophysical tuning curves.

The relative frequency selectivity of the internal auditory filters, as measured by critical bands or critical ratios, and psychophysical tuning curves, was compared in an avian species (parakeet) and human listeners. The results indicate that the critical band predicts the frequency selectivity of psychophysical tuning curves and vice versa. These findings suggest that there are similar mechanisms which contribute to the frequency selectivity measured by these two procedures and that these mechanisms operate in both the human and avian ear.

Adult↗
PubMed1979

Supra-normal susceptibility to acoustic trauma of the rat pup cochlea.

1 Young and adult rats were exposed to a continuous 120 dB SPL white noise for 30 min. 2 Animals exposed before the 40th postnatal day showed drastic and permanent threshold shifts (PTS) at high frequencies (between 6 and 20 kHz). 3 After 60 days of age, only temporary threshold shifts (TTS) were noticed, which lasted 7 days. 4 Thus the sensory structures of the rat cochlea showed a supra-normal susceptibility to acoustic trauma, during and just after their anatomical differentiation. 5 These results support previous data obtained on hamsters and guinea-pigs and are discussed in terms of anatomo-functional relationships.

Aging↗
PubMed1978

Frequency selectivity in the parakeet (Melopsittacus undulatus) studied with psychophysical tuning curves.

Seven parakeets were trained to avoid shock during pure-tone stimulation. A modified method of limits was used to measure detection thresholds of the pure tones. The intensity of masker tones, at numerous frequencies, was varied in order to measure the masked threshold of a probe-tone signal set at a fixed frequency and intensity. Masking curves were obtained for three probe tones (.63, 1.6, and 2.5 kHz) at each of five sensation levels (10, 20, 30, 40, and 50 dB). The masking curves from this procedure are frequently referred to as "psychophysical tuning curves" and provide an indication of frequency selectivity. The results are compared with analogous data in other species and suggest that frequency analysis in the parakeet ear is somewhat less accurate than in the mammalian ear.

Acoustic Stimulation↗
PubMed1978

Frequency selectivity in the parakeet (Melopsittacus undulatus) studied with narrow-band noise masking.

Narrow-band noise masking was studied in the parakeet (Melopsittacus undulatus) using a modified method of limits and an instrumental avoidance-conditioning procedure. Masked thresholds were obtained from five subjects at 10 frequencies between 0.5 and 5.0 kHz for each of four sensation levels (26, 46, 66, and 86 db) of a 1/3-octave band noise masker centered at 1.6 kHz. The amount of masking was found to be linearly related to noise level, and the shape of the masking curve was symmetrical on both sides of the center frequency of the masker. In all cases, the greatest threshold shift occurred at the center frequency of the masker. The relative symmetry of the parakeet narrow-band masking curves contrasts with masking results reported in mammals.

Acoustic Stimulation↗