Publications (3)7.61 Total impact
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Article: Optical stimulation of auditory neurons: effects of acute and chronic deafening.
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ABSTRACT: In developing neural prostheses, particular success has been realized with cochlear implants. These devices bypass damaged hair cells in the auditory system and electrically stimulate the auditory nerve directly. In contemporary cochlear implants, however, the injected electric current spreads widely along the scala tympani and across turns. Consequently, stimulation of spatially discrete spiral ganglion cell populations is difficult. In contrast to electrical stimulation, it has been shown that extremely spatially selective stimulation is possible using infrared radiation (e.g. [Izzo, A.D., Su, H.S., Pathria, J., Walsh Jr., J.T., Whitlon, D.S., Richter, C.-P., 2007a. Selectivity of neural stimulation in the auditory system: a comparison of optic and electric stimuli. J. Biomed. Opt. 12, 1-7]). Here, we explore the correlation between surviving spiral ganglion cells, following acute and chronic deafness induced by neomycin application into the middle ear, and neural stimulation using optical radiation and electrical current. In vivo experiments were conducted in gerbils. Before the animals were deafened, acoustic thresholds were obtained and neurons were stimulated with optical radiation at various pulse durations, radiation exposures, and pulse repetition rates. In one group of animals, measurements were made immediately after deafening, while the other group was tested at least four weeks after deafening. Deafness was confirmed by measuring acoustically evoked compound action potentials. Optically and electrically evoked compound action potentials and auditory brainstem responses were determined for different radiation exposures and for different electrical current amplitudes, respectively. After completion of the experiments, the animals were euthanized and the cochleae were harvested for histology. Acoustically evoked compound action potential thresholds were elevated by more than 40 dB after neomycin application in acutely deaf and more than 60 dB in chronically deaf animals. Compound action potential thresholds, which were determined with optical radiation pulses, were not significantly elevated in acutely deaf animals. However, in chronically deaf animals optically evoked CAP thresholds were elevated. Changes correlated with the number of surviving spiral ganglion cells and the optical parameters that were used for stimulation.Hearing Research 02/2008; 242(1-2):42-51. · 2.70 Impact Factor -
Article: Otoprotective effects of dexamethasone in the management of pneumococcal meningitis: an animal study.
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ABSTRACT: To determine whether treating pneumococcal meningitis with a combined antibiotic and steroid regime will prevent cochlear damage, a common pneumococcal meningitis side effect. Prospective animal study. Gerbils were randomly assigned to three experimental groups. Animals in group 1 received intrathecal saline injections. Animals in groups 2 and 3 received intrathecal injections of Streptococcus pneumoniae to induce meningitis. Group 2 was treated for 7 days with intraperitoneal penicillin injections (48,000 units). Animals from group 3 received intraperitoneal dexamethasone (0.5 mg/kg) injections for 4 days in addition to 7 days of intraperitoneal penicillin. Three months after the meningitis was induced, the animals' cochlear functions were determined using auditory brainstem responses (ABRs). After measuring cochlear function, the animals were sacrificed for cochlear histopathology. Spiral ganglion cell densities at Rosenthal's canal were determined. ABR thresholds were significantly elevated in animals from group 2 when compared with the animals in groups 1 and 3 (P < .05). ABR thresholds for animals from group 3 and group 1 were similar (P > .05). Damage of cochlear structures was detected in animals from group 2. The degree of the damage varied: one animal in group 2 had no identifiable hair cells and pillar cells and showed damage of the tectorial membrane. Spiral ganglion density in the basal turn was significantly less in animals from group 2 when compared with controls (P < .05). Although spiral ganglion cell density was less in the dexamethasone-treated group (group 3) when compared with group 1 (control group), but greater than observed in animals treated with antibiotics only (group 2), the differences were statistically not significant (P > .5). Nuclear diameters of the spiral ganglion cells decreased on average from 7.24 +/- 0.48 microm (group 1) to 6.28 +/- 0.76 microm (group 3, animals that received dexamethasone) to 5.57 +/- 0.82 microm (group 2, animals that received antibiotics only). Differences were significant (P < .05). Differences in stria vascularis thickness were not significant among the animals. Dexamethasone has a protective effect on the cochlea when given together with antibiotics in the treatment of pneumococcal meningitis.The Laryngoscope 07/2007; 117(7):1209-15. · 1.75 Impact Factor -
Article: Selectivity of neural stimulation in the auditory system: a comparison of optic and electric stimuli.
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ABSTRACT: Pulsed, mid-infrared lasers were recently investigated as a method to stimulate neural activity. There are significant benefits of optically stimulating nerves over electrically stimulating, in particular the application of more spatially confined neural stimulation. We report results from experiments in which the gerbil auditory system was stimulated by optical radiation, acoustic tones, or electric current. Immunohistochemical staining for the protein c-FOS revealed the spread of excitation. We demonstrate a spatially selective activation of neurons using a laser; only neurons in the direct optical path are stimulated. This pattern of c-FOS labeling is in contrast to that after electrical stimulation. Electrical stimulation leads to a large, more spatially extended population of labeled, activated neurons. In the auditory system, optical stimulation of nerves could have a significant impact on the performance of cochlear implants, which can be limited by the electric current spread.Journal of Biomedical Optics 12(2):021008. · 3.16 Impact Factor
