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R Altschuler

Publications and source records attributed to R Altschuler.

5 recordsLinked to original sources
PubMed1998

Guinea pig auditory neurons are protected by glial cell line-derived growth factor from degeneration after noise trauma.

For patients with profound hearing loss, cochlear implants have become the treatment of choice. These devices provide auditory information through direct electrical stimulation of the auditory nerve. Prosthesis function depends on survival and electrical excitability of the cochlear neurons. Degeneration of the auditory nerve occurs after lesions of its peripheral target field (organ of Corti), specifically, including loss of inner hair cells (IHCs). There is now evidence that local treatment of the cochlea with neurotrophins may enhance survival of auditory neurons after aminoglycoside-induced deafness. Glial cell line-derived neurotrophic factor (GDNF) has recently been shown to be an important survival factor in other regions of the nervous system. By in situ hybridization, we now show that IHCs of the neonatal and mature rat cochlea synthesize GDNF and that GDNF-receptor alpha, but not c-Ret, is expressed in the rat spiral ganglion. We also show that GDNF is a potent survival-promoting factor for rat cochlear neurons in vitro. Finally, we examined GDNF efficacy to enhance cochlear-nerve survival after IHC lesions in vivo. We found that chronic intracochlear infusion of GDNF greatly enhances survival of guinea pig cochlear neurons after noise-induced IHC lesions. Our results demonstrate that GDNF is likely to be an endogeneous survival factor in the normal mammalian cochlea and it could have application as a pharmacological treatment to prevent secondary auditory nerve degeneration following organ of Corti damage.

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PubMed1996

Thyroid hormone receptor beta is essential for development of auditory function.

Congenital thyroid disorders are often associated with profound deafness, indicating a requirement for thyroid hormone (T3) and its receptors in the development of hearing. Two T3 receptor genes, Tr alpha and Tr beta are differentially expressed, although in overlapping patterns, during development. Thus, the extent to which they mediate unique or redundant functions is unclear. We demonstrate that Tr beta-deficient (Thrb-/-) mice exhibit a permanent deficit in auditory function across a wide range of frequencies, although they show no other overt neurological defects. The auditory-evoked brainstem response (ABR) in Thrb-/- mice, although greatly diminished, displayed normal waveforms, which suggested that the primary defect resides in the cochlea. Although hypothyroidism causes cochlear malformation, there was no evidence of this in Thrb-/- mice. These findings suggest that Tr beta controls the maturation of auditory function but not morphogenesis of the cochlea. Thrb-/- mice provide a model for the human endocrine disorder of resistance to thyroid hormone (RTH), which is typically associated with dominant mutations in Tr beta. However, deafness is generally absent in RTH, indicating that dominant and recessive mutations in Tr beta have different consequences on the auditory system. Our results identify Tr beta as an essential transcription factor for auditory development and indicate that distinct Tr genes serve certain unique functions.

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PubMed1991

Inner ear damage from toy cap pistols and fire-crackers.

Groups of guinea pigs comprising 7 animals in each group were exposed to 10, 50 or 100 exposures to fire-crackers or 10, 50 or 100 exposures to toy cap pistol shots. An additional group of 7 animals comprised the control material. The exposures were performed with 15-s intervals at 0.25 m distance for the toy cap pistol shots and at 0.8 m for the fire-crackers. The peak sound level at the ear was 155 dBC for both impulsive sounds. After a 3-week survival period the animals were anesthetized and decapitated. The cochleas were examined histologically in surface preparations and read double-blind. One animal in each group exposed to 10 fire-crackers and 10 toy cap pistol shots showed sensory cell loss. With 50 or 100 toy cap pistol shots or fire-cracker exposures, 24 out of 28 animals showed pronounced sensory cell loss. The present results clearly indicate the risk for noise-induced hearing loss in children playing with toy cap guns and fire-crackers.

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PubMedDate not supplied

Electrokinetic shape changes of cochlear outer hair cells.

Rapid mechanical changes have been associated with electrical activity in a variety of non-muscle excitable cells. Recently, mechanical changes have been reported in cochlear hair cells. Here we describe electrically evoked mechanical changes in isolated cochlear outer hair cells (OHCs) with characteristics which suggest that direct electrokinetic phenomena are implicated in the response. OHCs make up one of two mechanosensitive hair cell populations in the mammalian cochlea; their role may be to modulate the micromechanical properties of the hearing organ through mechanical feedback mechanisms. In the experiments described here, we applied sinusoidally modulated electrical potentials across isolated OHCs; this produced oscillatory elongation and shortening of the cells and oscillatory displacements of intracellular organelles. The movements were a function of the direction and strength of the electrical field, were inversely related to the ionic concentration of the medium, and occurred in the presence of metabolic uncouplers. The cylindrical shape of the OHCs and the presence of a system of membranes within the cytoplasm--laminated cisternae--may provide the anatomical substrate for electrokinetic phenomena such as electro-osmosis.

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