Electrical stimulation of the guinea pig cochlea

As a result of practical considerations, histopathologic findings of the temporal bone in humans with cochlear prosthesis implants have been limited. This project attempts to better define safe parameters of electrical stimulation of the inner ear and compare the safe limits of intracochlear vs. extracochlear stimulation sites. Guinea pigs were implanted with single electrodes either on the promontory or in the scala tympani and were stimulated relative to a remote indifferent for 12 hours distributed over a 4-week period. Electrical auditory brainstem evoked responses (EABRs) were tested before and after each of four 3-hour stimulation sessions. Six weeks after implantation, the animals were killed, and their cochleas were examined under the scanning electron microscope. Intracochlear electrodes exhibited thresholds for damage well below one half of that found for most extracochlear stimulation sites. The function-relating damage threshold (in amperes) to frequency of intracochlear stimulation is represented by two straight lines, with an intercept of 1 kHz. The low-frequency limb exhibited a slope of 3 to 4 dB/octave, whereas the high-frequency limb exhibited a slope of 9 to 10 dB/octave. Extracochlear results were too variable to permit speculation. Changes in EABRs were only variably related to histopathologic findings.     

Protective effect of electrical stimulation in the deafened guinea pig cochlea

The effect of chronic intrascalar electrical stimulation on the spiral ganglion cell survival of the ototoxically deafened guinea pig was investigated. Immediately after ototoxic drug administration, unilateral sinusoidal (1 kHz) charge-balanced electrical stimulation on a 50% duty cycle was administered for 2 hours per day, 5 days per week, at intensities from 0 (control) to 400 microAmp via an implanted scala tympani electrode. The relationship of electrically evoked middle latency response (EMLR) to stimulation protocol and cell survival was studied. At 9 weeks post-drug treatment, the animals were killed and temporal bones were prepared for morphometric analysis of spiral ganglion cell density. The subjects showed essentially complete elimination of outer hair sensory cells, with minimal remaining inner hair cells confined to apical turns. Variable loss of spiral ganglion cell populations was observed, which related to electrical stimulation. In animals that received daily unilaterally electrical stimulation, statistically significant increases in survival of spiral ganglion cells were observed in the stimulated ear, compared to the nonstimulated ear-particularly in basal cochlear regions near the electrode. Spiral ganglion cell density was a function of stimulation current intensity level. Moreover, the slope of the amplitude input/output (I/O) function of the EMLR was found to be dependent on stimulating current level. The effect of stimulation on induced survival may be dependent on a number of mechanisms, including metabolic effects of direct activation of "deafferented" spiral ganglion cells. These data support the suggestion that implantation may provide optimal benefits when performed shortly after deafness.     

Experimental in vivo fenestration of guinea pig cochlea using 2.79 Μm laser radiation

Erbium-YSGG laser systems are promising tools in ear, nose and throat (ENT) surgery. The high absorption in biological tissues, resulting in precise tissue ablation with minimal thermal tissue damage, and the possibility to guide the radiation through optical fibres make the 2.79 Μm wavelength a favourite for microsurgery. In order to simulate the fenestration of the human stapes foot plate required for prosthesis implantation when treating otosclerosis, five guinea pig cochleae were irradiated in vivo until perforation was achieved. The laser-induced temperature rise and pressure transients evoke activity in the inner hair cells that was investigated by micro-iontophoresis. Perforation of the cochlea bone (hole diameter of 350 Μm) can be performed with a few laser pulses and high precision with a thermal damage zone of<100 Μm. The bone ablation rate is 10 ± 2 Μm pulse^-1 at a radiant exposure of 12 J cm^-2. The functionality of the afferent inner hair cells in the guinea pig cochlea was verified before and after laser treatment using glutamate receptor agonists AMPA and NMDA. For the above selected laser parameters, the induced 15-min enhanced activity was blockable with the specific reversible AMPA and NMDA antagonists CNQX and AP-7. Micro-iontophoresis confirms the reversibility of cochlea functionality after its perforation with Er-YSGG laser pulses. A limit of radiant exposure around 12 J cm^-2 is found for safe fenestration. It is demonstrated that the Er-YSGG laser is a precise and safe instrument whilst still using adequate laser parameters. On the other hand, this study demonstrates the potential of uncontrollable and unintended induced damage, resulting from vapour channel formation in the perilymph, if a high laser radiant exposure is applied.     

Effects of nerve stimulation on spontaneously active preparations of the guinea pig ureter

The effects of intrinsic nerve stimulation on the spontaneous electrical activity of the smooth muscle cells of the guinea pig ureter still attached to its renal pelvis were investigated using standard intracellular microelectrode techniques. Action potentials discharged spontaneously at a frequency of 3.3 ± 0.2 min⁻¹ (n = 67) and consisted of an initial rapidly rising spike, followed by a variable period (0.2–5 s) of membrane potential oscillation and a quiescent plateau phase which was terminated by an abrupt repolarisation and after-hyperpolarisation to −66 mV. Transmural electrical stimulation (20–50 Hz for 2 s) transiently decreased the frequency of action potential discharge; the half-amplitude duration of the following action potentials, however, was transiently increased to 156 ± 12% of control. Substance P (1 μM applied for 2 min) or neurokinin A (100 nM for 2 min) transiently increased the frequency of action potential discharge to 155 ± 19% and 142 ± 21%, respectively, of control. The excitatory actions of nerve stimulation or agonist application were reduced by the tachykinin antagonist, MEN 10,627 (1–3 μM), while the inhibitory actions of nerve stimulation were enhanced by MEN 10,627 (1 μM) or thiorphan (1 μM). Capsaicin (10 μM for 10–15 min) also evoked a transient increase in the frequency and half-amplitude duration of the ureteric action potentials, in a manner blocked by MEN 10,627 (3 μM), which was followed by a long period of membrane potential quiescence. Human calcitonin gene related peptide (hCGRP) (100 nM applied for 2–5 min) induced a time-dependent decrease in the frequency amplitude and duration of the spontaneous action potentials, in a manner blocked by glibenclamide (1 μM). It was concluded that the nerve-evoked excitatory and inhibitory changes in the parameters of the spontaneous ureteric action potentials arise from the release of the sensory neuropeptides, tachykinins and CGRP, respectively. Received: 22 December 1998 / Accepted: 14 April 1999     

Laser stimulation of the auditory nerve

BACKGROUND AND OBJECTIVES: For centuries, electric current has been used to stimulate neurons. Shortcomings of electrical stimulation include the contact between the stimulating electrode and the tissue, and the non-selective stimulation of the tissue. In contrast to electric stimulation, optical radiation can provide spatially selective neural stimulation without tissue contact. STUDY DESIGN/MATERIALS AND METHODS: Acute in vivo experiments using gerbils were conducted to record optically evoked compound action potentials (CAPs) from the cochlea. RESULTS: Optical radiation evokes CAPs in normal hearing animals and in deafened animals, in which cochleae lack outer and inner hair cells. Stimulation threshold was measured as 0.018+/-0.003 J/cm(2) (mean+/-SE). Laser radiation could be increased by 30-40 dB until drastic changes were seen in cochlear function. Cochlear response amplitudes to optical radiation were stable over extended stimulation times. CONCLUSIONS: We have demonstrated that the auditory nerve can be stimulated by optical radiation. One potential clinical use of this technology would be for cochlear implants.     

Effect of agitation of EDTA with 808-nm diode laser on dentin microhardness

Lasers in Medical Science - The aim of this study is to analyze the effect of agitation of ethylenediaminetetraacetic acid (EDTA) with diode laser at different agitation times on root dentin...     

Low-power 808-nm laser irradiation inhibits cell proliferation of a human-derived glioblastoma cell line in vitro

It has been reported that low-power laser irradiation (LLI) can modulate various biological processes including cell proliferation. Some reports suggest that LLI interferes with the cell cycle and inhibits cell proliferation, while others suggest that LLI has a stimulatory effect. Mechanisms underlying the effects of LLI remain unclear. Since the effects of LLI on cancer cells are not well understood, with the aim of developing an LLI therapy for malignant glioblastoma, we investigated the effects of LLI on the cell proliferation of the human-derived glioblastoma cell line A-172. Glioblastoma cell cultures were irradiated with a diode laser at a wavelength of 808 nm and the effects on cell viability and proliferation were examined. Cell counting at 24 and 48 h after irradiation showed that LLI (at 18, 36 and 54 J/cm²) suppressed proliferation of A-172 cells in a fluence-dependent manner (irradiation for 20, 40 and 60 min). A reduction in the number of viable cells was also demonstrated by a fluorescent marker for viable cells, calcein acetoxymethylester (calcein-AM). The reduction in cell viability was not associated with morphological changes in the cells or with necrotic cell death as demonstrated by propidium iodide staining. LLI also had little effect on cell proliferation as shown by 5-bromo-2′-deoxyuridine staining. We discuss possible mechanisms underlying the suppressive effect of 808-nm LLI on the viability of human-derived glioblastoma A-172 cells.     

Morphologic changes in the guinea pig cochlea following cochleostomy--a preliminary scanning electron microscope study

Fistulization of the membranous labyrinth via a surgically created endolymphatic-perilymphatic shunt (cochleosacculotomy) is currently being advocated as a treatment for endolymphatic hydrops. As a preliminary study to the investigation of the effects of labyrinthine fistulization on the hydropic condition, we sought first to reproduce the cochleosacculotomy procedure in a series of normal animals. Fistulization of the cochlear duct was performed in 15 normal animals using a tungsten wire directed via the round window through the cochlear partition in the region of the organ of Corti. The animals were sacrificed at regular intervals and the cochleas examined for histopathologic changes with the scanning electron microscope. Observations suggest that discrete permanent fistulization of the cochlear duct in the normal guinea pig results in progressive sensory cell degeneration. The implication of these observations and the apparent difference between these results and the experience thus far reported in humans are discussed.     

Effect of glycerol and mannitol on perilymphatic PO2 in guinea pig cochlea

The effects of glycerol and mannitol on partial oxygen pressure (PO2) in perilymph were studied with a polarographic technique in the guinea pig cochlea. Following a transient reduction immediately after the intravenous injection of each drug, the oxygen tension increased to reach a peak 5 to 10 minutes later, and then decreased gradually. The magnitude and duration of the PO2 increases were larger after the administration of glycerol than after that of mannitol. These results corresponded well with the clinical experience that glycerol was more effective than mannitol in improving hearing in Meniere's disease. The increase of PO2 in the cochlea, therefore, is considered to be one of the possible contributory factors for the improvement of hearing in patients with Meniere's disease after glycerol administration.     

窒息豚鼠脑干听觉诱发电位变化窒息时限及其自然转归的实验研究

目的：了解不同窒息时限下豚鼠脑干听觉诱发电位（ＢＡＥＰ）的变化。方法：应用氯胺酮－甲苯噻嗪麻醉豚鼠２６只，随机分为三组，Ⅰ组窒息４分豚鼠８只，Ⅱ组窒息５分豚鼠８只，Ⅲ组窒息５．５分豚鼠１０只；记录窒息前、窒息后、解除窒息后ＢＡＥＰ各波及潜伏期的变化。结果：窒息后０．５分ＢＡＥＰ各波无明显变化，１．５～２分ＢＡＥＰ消失，Ⅰ组解除窒息后１分，Ⅰ、Ⅲ波出现，３分Ｖ波出现，６０分时潜伏期仍未恢复正常。Ⅱ组解除窒息后豚鼠死亡２只，余Ⅰ波１分出现，Ⅲ波３分出现，Ｖ波５分出现，到６０分各波潜伏期均明显延长Ｐ＜０．０５。Ⅲ组豚鼠全部死亡。结论：豚鼠能耐受窒息时限为４分，此时脑干听觉通路受到一定影响。     

Performance of the 808-nm diode laser on equine upper airway tissue is enhanced by intravenous administration of indocyanine green

OBJECTIVE: The objective was to develop a protocol whereby 808-nm diode laser irradiation combined with intravenous (IV) indocyanine green (ICG) could be used in non-contact mode with equal surgical efficacy to the Nd:YAG on equine tissues. BACKGROUND DATA: The 808-nm diode laser, delivering 20-40 W of power, has been produced for veterinary medical applications. This laser's power output is less than that of most neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers. ICG is absorbed at a wavelength of 810 nm, which when concentrated in tissue should be an excellent absorber for the energy produced by the 808-nm diode laser. METHODS: This study compares the depths and widths of thermal penetration achieved with the 808-nm diode laser in equine respiratory tissue after intravenous injection of ICG. ICG was administered at two doses: 1.5 mg/kg and 3 mg/kg. The 808-nm diode laser and Nd:YAG laser were set to deliver 200 J of energy. The depths and widths of thermal penetration obtained were compared. RESULTS: Lesion depth and width tended to be greater in the ICG + 3 mg/kg group than in the ICG + 1.5 mg/kg group. Even so, the 1.5-mg/kg dose substantially increased the efficacy of the diode laser. Plasma ICG concentrations peaked at 5 min post-administration and then dropped markedly; lesion depth decreased after peaking at 7 min post-administration. CONCLUSION: This study demonstrated that the 808-nm diode laser, when augmented with intravenous ICG, will be as effective a surgical tool as the Nd:YAG laser on equine upper airway tissues when applied using a non-contact fiber.     

In vivo studies on amino acid transmitters in the central auditory system of the guinea pig

The extracellular concentrations of endogenous amino acids were measured in vivo in the guinea pig cochlear nucleus during sound stimulation. The purpose was to explore whether certain amino acids might be employed as neurotransmitters by the auditory nerve. A dialysis sampling probe was used to collect a dialysate of the cochlear nucleus. The amino acids were determined fluorometrically after precolumn derivation and high-performance liquid chromatography separation. A short pulse of p-chloromercuryphenylsulfonate (p-CMS) was used to reduce the reuptake of amino acids. The concentration of glutamic and aspartic acid increased twofold to threefold during sound stimulation, while gamma-aminobutyric acid was unaffected. The results support a role for glutamic and/or aspartic acids as neurotransmitters in the auditory nerve.     

Evaluation of a silicon-substrate modiolar eighth nerve implant in a guinea pig

The availability of thin-film multichannel electrodes provides new possibilities for implantation and direct stimulation of the modiolar portion of the auditory nerve. Electrodes in direct contact with the auditory nerve should be functional at lower thresholds and might require fewer remaining neurons for stimulation compared to electrodes in the scala tympani. This strategy would also provide close contact with neural elements subserving a greater frequency range. Implantation of the eighth nerve may also be advantageous in profoundly deaf subjects who lack an implantable scala tympani. In this study we evaluated the effect of surgical implantation and chronic placement of a silicon substrate implant in the modiolar portion of the auditory nerve of the guinea pig. Of six chronically implanted ears, five showed changes limited to the loss of spiral ganglion cells in the canal of Rosenthal, immediately adjacent to the implant. The sixth ear showed more extensive cochlear alteration in a pattern suggestive of vascular injury. In separate acute experiments, implants were placed in the modiolar portion of the auditory nerve and electrophysiologic analysis was performed. Middle latency responses with good morphology were obtained at thresholds below those found with scala tympani implants. Input-output functions exhibited a plateau in response amplitude at stimulus levels below thresholds for seventh or vestibular portion of the eighth nerve. Further modifications of the modiolar portion of the auditory nerve electrode design will include development of an electrode interconnect that will allow chronic implantation with stimulation.     

Pulsed electromagnetic fields reduce knee osteoarthritic lesion progression in the aged Dunkin Hartley guinea pig.

An experimental in vivo study was performed to test if the effect of Pulsed Electromagnetic Fields (PEMFs) on chondrocyte metabolism and adenosine A2a agonist activity could have a chondroprotective effect on the knee of Dunkin Hartley guinea-pigs of 12 months with spontaneously developed osteoarthritis (OA). After a pilot study, 10 animals were randomly divided into two groups: PEMF-treated group (6 h/day for 3 months) and Sham-treated group. Microradiography and histomorphometry were performed on the entire articular surface of knee joints used in evaluating chondropathy severity, cartilage thickness (CT), cartilage surface Fibrillation Index (FI), subchondral bone plate thickness (SBT) and histomorphometric characteristics of trabecular epiphyseal bone. The PEMF-treated animals showed a significant reduction of chondropathy progression in all knee examined areas (p<0.05). CT was significantly higher (p<0.001) in the medial tibia plateaus of the PEMF-treated group when compared to the Sham-treated group. The highest value of FI was observed in the medial tibia plateau of the Sham-treated group (p<0.05). Significant lower values were observed in SBT of PEMF-treated group in comparison to Sham-treated group in all knee examined areas (p<0.05). The present study results show that PEMFs preserve the morphology of articular cartilage and slower the progression of OA lesions in the knee of aged osteoarthritic guinea pigs. The chondroprotective effect of PEMFs was demonstrated not only in the medial tibial plateau but also on the entire articular surface of the knee.