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Biomedical subjects

M D McGinn

Publications and source records attributed to M D McGinn.

14 recordsLinked to original sources
PubMed1992

Incidence of otitis media in CBA/J and CBA/CaJ mice.

The inbred CBA/J mouse has become a standard experimental animal for auditory study because of its lifelong good hearing. In a newly established mouse breeding colony that housed CBA/J and CBA/CaJ mice to reared as auditory subjects, otitis media frequently afflicted CBA/J mice, reaching an incidence of 90% in animals greater than 400 days of age. Otitis media was not found in CBA/CaJ mice. Three attempts to establish a colony that was free of otitis were unsuccessful. Although the primary pathogen was not clearly established, Pasteurella pneumotropica was isolated from infected bullae. Partial control of otitis media followed the introduction of tetracycline prophylaxis. The CBA/CaJ mice may be suitable replacements for CBA/J mice in studies that require inbred mice with good hearing, since their auditory thresholds did not differ significantly from those of otitis-free CBA/J mice.

Animals↗
PubMed1992

The mouse as a model for human audition. A review of the literature.

The mouse has several distinct advantages as an experimental model for human audition. Mice and humans express a similar presbyacusic and ototraumatic pattern. Several genetic mouse models also exist for conditions resembling human auditory disorders, such as otosclerosis. This paper reviews the strains of inbred mice (e.g. the CBA/J) which have recently been used as models for the normal human auditory system, describing their deficiencies. It is suggested that the F1 offspring of CBA/CaJ and AU/SsJ inbred mice would have advantages over existing models.

Acoustic Stimulation↗
PubMed1992

Auditory brainstem function of the F1 offspring of the cross of CBA/CaJ and AU/SsJ inbred mice.

Inbred strains of laboratory mice have several distinct advantages as models for examining conditions that influence the human auditory system, but the CBA/J mouse which has most often been used as a normal model has recently been found to have several disadvantages. This paper is the first report of the auditory brainstem responses (ABRs) of the F1 offspring of CBA/CaJ and AU/SsJ parents. At midlife, high-frequency ABR thresholds are lower in the F1 than in either parental genotype. Tuning curves obtained by forward masking of the ABR also display heterosis, i.e. they are narrower in the F1 than in either parental strain.

Animals↗
PubMed1991

Cochlear bone erosion: effects on cochlear hair cells. A scanning electron microscopy study.

Cochleae from gerbils with normal middle ears were compared with cochleae from gerbils with experimentally induced cholesteatomas that were in contact with the cochlear wall (stage III cholesteatomas). Cochleae from gerbils with stage III cholesteatomas were further divided into two groups: one without erosion of cochlear bone, and one with cholesteatoma-induced bone erosion but without cochlear fistulae. The cochleae with bone erosion showed significant loss of outer hair cells in the middle and apical turns, but not in the basal turn. The cochleae with stage III cholesteatomas but without bone erosion did not differ from normal controls. These results suggest that an ototoxic agent, involved in the process of bone erosion, acts through the bony cochlear wall.

Animals↗
PubMed1990

Acoustic isolation reduces degeneration of the ventral cochlear nuclei in Mongolian gerbils.

The role of auditory experience in the development of spongiform degeneration in the cochlear nuclei of Mongolian gerbils was studied by comparing results of animals exposed to either high or low levels of ambient noise. Gerbils reared in a typical vivarium experienced higher levels of ambient noise than animals reared in acoustic isolation chambers. Animals reared in the colony room showed a much greater number density and area density of spongiform lesions in the CN than did gerbils reared in acoustic isolation. The differences in the number and extent of spongiform lesions between the two groups of gerbils appeared to reflect their differences in exposure to ambient noise. These differences in lesion number and extent were most pronounced in the tonotopic regions of the PVCN which correspond to the greatest differences in the spectral characteristics of the ambient noise to which the animals were exposed. These results were compared with results previously obtained from gerbils with loss of hearing experimentally induced by a conductive block or by sensorineural damage. The lesion numbers and extent reflected the auditory experience of each group; in descending order, colony-reared, isolate, conductive-block, sensorineural loss. These results strongly support the hypothesis that this gerbilline encephalopathy is directly related to auditory functional activity.

Animals↗
PubMed1990

Effects of profound sensorineural loss on gerbilline auditory encephalopathy.

To investigate the role of acoustic stimulation in the development of spongiform degeneration in the cochlear nuclei of Mongolian gerbils, the right cochlea in 8 juvenile gerbils was chemically treated by placing sodium chloride (NaCl) crystals on the cochlear round window membrane. Sixty days after NaCl treatment there was extensive damage to the strial, sensorineural and supporting cells of the treated inner ear. The cochlear damage was accompanied by a dramatic decrease in the number and the extent of the spongioid lesions in the ipsilateral cochlear nuclei compared to the contralateral (control) cochlear nuclei. These results lend further support to the hypothesis that the progress of this disorder is related to auditory function.

Animals↗
PubMed1989

Characteristics of auditory brainstem responses in ground squirrels.

Auditory brainstem responses (ABRs) were characterized at 37 degrees C in ground squirrels (Citellus lateralis) which were implanted with recording screws to record ABRs, and a thermistor to record brain temperature. After two weeks ground squirrels were reanesthetized and tone pips and clicks were delivered through a TDH-49 headphone. Recorded ABRs were found to vary in a predictable manner as a function of stimulus frequency and intensity. At intensities above 50 dB SPL, ABRs could be recorded over the range tested (2-32 kHz). An 8 kHz tone pip was the best frequency for recording ABRs at the lowest stimulus intensities. Latencies decreased as stimulus frequencies increased from 4 kHz to 32 kHz.

Acoustic Stimulation↗
PubMed1989

Auditory brainstem responses in ground squirrels arousing from hibernation.

Auditory brainstem responses (ABRs) were recorded in ground squirrels (Citellus lateralis) arousing from hibernation. Squirrels implanted with recording screws to record ABRs, and a thermistor to record brain temperature, were placed in a cold room at 9 degrees C on a 2L:22D light-dark cycle. Hibernating animals were moved from the cold room and ABRs recorded during arousal. The responses showed a gradual development of all brainstem peaks. At low temperatures there were very long latencies to the peaks. The amplitudes of the peaks increased (with fluctuations) as brain temperature increased. The data indicate that neural generators on the brainstem auditory pathway were all activated early in arousal. These results do not support the hypothesis that successive peaks appear and grow in amplitude only after previous peaks are fully developed.

Acoustic Stimulation↗
PubMed1987

Auditory experience affects degeneration of the ventral cochlear nucleus in Mongolian gerbils.

Gerbils exhibit a unique encephalopathy characterized by spongioform lesions in the neuropil of the cochlear nucleus and that others have recently described. The present results suggest that the course of this degenerative disorder is affected by acoustic experience. In gerbils in which acoustic stimulation was limited postnatally, the number and the extent of these lesions was dramatically reduced. Monaural deprivation reduced lesion number and extent only in the ipsilateral cochlear nucleus; binaural deprivation affected both cochlear nuclei. The lesions were most evident in certain portions of the cochlear nucleus, the caudal anterior ventral cochlear nucleus and the posterior ventral cochlear nucleus, sparing the rostral pole of the anterior ventral cochlear nucleus. In the affected regions the lesions were topologically restricted to the low and middle frequency regions. The apparent tonotopic distribution of lesions was associated with frequent exposure to low and middle frequency ambient noise.

Acoustic Stimulation↗
PubMed1986

Bone resorption induced by middle-ear implants.

The pressure produced by expanding aural cholesteatomas has been implicated as a causal factor in the induction of osteoclastic resorption of adjoining bone. This concept is supported by observations of osteoclastic bone resorption produced by expansive tympanic implants. We induced osteoclastic bone resorption in gerbils with tympanic implants of autologous and homologous cartilage, silicone rubber, and Teflon, which exerted pressure only by forces of gravity and surface tension. We estimated that the pressure exerted by these implants ranged from 2.1 X 10(-3) to 8.0 X 10(-3) dynes/sq cm (1.6 to 6.0 mm Hg). These pressures are within the range of pressures known to be exerted by cholesteatomas.

Animals↗
PubMed1975

Acute versus chronic acoustic deprivation: effects on auditory evoked potentials and seizures in mice.

C57BL/6J mice are not typically susceptible to audiogenic seizures, but temporary conductive hearing loss (via earplugging) can induce susceptibility in these subjects. The present study observed that a 40-dB hearing loss, beginning at 17 days postpartum, requires 2 days before it induces susceptibility to audiogenic seizures. When this hearing loss occurred only between 17 and 21 days postpartum, seizures were maximally severe 1-2 days after earplug removal. The peak-to-peak amplitudes of the auditory evoked potential (AEP) were also maximal at this same time. But mice deprived of acoustic input between ages 42-46 days exhibited equally large or even larger AEP amplitudes, while not exhibiting susceptibility to audiogenic seizures. Animals at this older age were shown to be capable of convulsing, in that chronic conductive loss from 17-42 days maintained susceptibility to audiogenic seizures. The acoustic deprivation produced both behavioral (audiogenic seizures) and neural (augmented AEP amplitudes) supersensensitivity to sound, but the former requires a critical period, whereas the latter does not. Some degree of residual hearing loss persisted at all ages for approximately 2 days after removal of the earplugs.

Age Factors↗
PubMedDate not supplied

Pressure-induced bone resorption in the middle ear.

Osteoclastic activity is seen in areas of bone resorption which are the result of experimental and human cholesteatoma. Many factors may induce osteoclasts, including transmitted pressure. The purpose of this study was to determine if transmitted pressure, in the absence of cholesteatoma, could cause localized bone resorption in the middle ear. Surgical grade silicone was implanted into the middle ear of gerbils without cholesteatoma. Bone resorption was observed only in areas where the implants exerted pressure on bone. It was estimated that pressures of 50 to 120 mm Hg (6.7 X 10(4) to 16 X 10(4) dynes/cm2) resulted in the induction of osteoclastic bone resorption.

Animals↗