Socioeconomic impact of treatment with biological disease-modifying antirheumatic drugs in Japanese patients with rheumatoid arthritis

OBJECTIVES

We evaluate the socioeconomic impact of treatment with biological and targeted synthetic disease-modifying antirheumatic drugs in Japanese patients with rheumatoid arthritis.

METHODS

We analysed data retrospectively from the prospective observational CorEvitas RA Japan Registry (March 2016-February 2020). Patients were categorised into paid workers (PWs) and home workers (HWs) and further based on drug classes. We assessed medication persistence, treatment outcomes, health care resource utilisation, and socioeconomic impact over 12 months, including direct (drugs and health care resource utilisation) and indirect (loss of productivity) costs.

RESULTS

Overall, 187 PWs and 114 HWs were identified. Over 12 months, medication persistence was high, treatment outcomes improved, and outpatient visits reduced in both groups. Following treatment initiation, direct costs increased, whereas indirect (loss of productivity) costs decreased in both groups. The unadjusted socioeconomic impact [Japanese yen (JPY)] increased across all drug classes in PWs (range: 29,700-151,700) and HWs (range: -28,700 to 83,000). Adjusted change in monthly socioeconomic impact was JPY 29,700-138,900 for PWs and JPY -28,000 to 92,800 for HWs.

CONCLUSIONS

In this study of Japanese patients with rheumatoid arthritis, the socioeconomic burden increased across patient groups and drug classes. The decrease in indirect (loss of productivity) costs partially offset the increase in direct costs.

Abstract CT111: Results of a phase 1 dose escalation study of ERY974, an anti-glypican 3 (GPC3)/CD3 bispecific antibody, in patients with advanced solid tumors

Background: ERY974, a bispecific T cell-redirecting antibody, redirects T cells to tumor cells by engaging the CD3 antigen on T cells and the glypican 3 (GPC3) antigen selectively expressed on tumors. ERY974 demonstrates T cell-dependent cellular cytotoxicity in vitro and transient cytokine elevations in preclinical toxicology studies (Ishiguro et al. 2017). The primary objective of this dose escalation (DE) study was to determine ERY974's maximum tolerated dose in patients with locally advanced or metastatic solid tumors expressing GPC3. Methods: The study included adult patients with advanced or metastatic solid tumors not amenable to standard therapy, histologically confirmed, with measurable disease and a life expectancy ≥ 3 months, including patients with ≤ 1cm and ≤ 1 brain metastasis. Patients with interstitial lung disease, or acute/active chronic infection were excluded. ERY974 was administered IV and dosed weekly. DE was initiated with an accelerated titration design of single patient cohorts followed by three patient cohorts. To mitigate for the toxicity of cytokine release syndrome (CRS), steroid prophylaxis and a flexible study design was implemented which included a two-step intra-patient escalation (regimen A), and a three-step intra-patient escalation (regimen B). Results: 29 patients were enrolled in dose levels ranging from 0.003 μg/kg to 0.81 μg/kg. Treatment-related adverse events that occurred in greater than 20% of patients included CRS and pyrexia. Dose level 0.81 μg/kg (regimen A) was confirmed not tolerable due to DLTs of Grade 3 CRS and Grade 2 CRS in two out of three patients (assessed according to Lee, et al. 2014). The Grade 3 CRS was associated with Grade 3 transaminitis and a Grade 3 elevation of bilirubin. Both CRS events led to dose delay and dose reduction. Increases in IL-6, IL-8 and IL-10 were observed in patients with the CRS. The severity and frequency of CRS in regimen B were similar to those observed in regimen A at the same dose level. One partial response (per modified RECIST criteria) was observed in a patient with esophageal cancer treated with 0.54 μg/kg (regimen B) and having 40% of the tumor tissue staining positive for GPC3 via immunohistochemistry. Stable disease lasting 3 months or longer was observed in four patients. Conclusions: The observed responses and CRS side effects are markers of ERY974 biologic activity. At doses below 0.81 μg/kg (regimen A), ERY974 was generally well tolerated with a manageable toxicity profile, including ERY-induced CRS which was manageable with steroid administration and anti-IL6R therapy. Further research is required to determine if combined prophylactic anti-IL6R and steroid therapy is a more effective strategy for managing CRS. References: 1. Ishiguro, Takahiro, et al. Science translational medicine, 2017, 9.410: eaal4291. 2. Lee, Daniel W., et al. Blood, 2014, 124.2: 188-195.

Citation Format: Howard Safran, Mihaela Druta, Michael Morse, Filipa Lynce, Sofya Pintova, Khaldoun Almhanna, Daniel Weiss, Athos Gianella-Borradori, Yoshitaka Ogita, Roland Morley, Mikiko Nakamura, Junnosuke Matsushima, Takahiro Ishiguro. Results of a phase 1 dose escalation study of ERY974, an anti-glypican 3 (GPC3)/CD3 bispecific antibody, in patients with advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT111.

A phase I dose escalation (DE) and cohort expansion (CE) study of ERY974, an anti-glypican 3 (GPC3)/CD3 bispecific antibody, in patients with advanced solid tumors

TPS3112

Background: Bispecific antibodies to facilitate T-cell directed cytotoxicity (TDCC) is a proven therapy strategy in cancer. ERY974 is a humanized IgG4 bispecific antibody designed to simultaneously bind to cytotoxic T-cell CD3 receptors and GPC3 (a glycoprotein expressed on cell surface of several tumors) to elicit T-cell activation and TDCC. The objectives of this multi-country, phase 1 study of ERY974 is to determine the maximum tolerated dose (MTD) and to perform a preliminary assessment of anti-tumor activity in patients with solid tumors expressing GPC3. Methods: ERY974 is dosed IV weekly. All patients receive premedication with dexamethasone (DEX) prior to 1st and 2nd ERY974 dose. DE uses an accelerated titration design (ATD), then a modified continual reassessment method (mCRM) described by one-parameter logistic model, to determine MTD, where DLT occurrence rate is 0.25. Combining ATD and mCRM is to permit rapid dose escalation whilst minimizing patient numbers exposed to sub-therapeutic doses, and to accurately determine MTD. Once grade 2 (G2) cytokine release syndrome (CRS) is observed, DEX is increased. If ≥G2 CRS is again observed, then at all subsequent doses the 1st dose of ERY974 is fixed at the last dose level when < G2 CRS was not seen, DE proceeds with the 2nd dose. ATD commences with n = 1, increasing to n = 3 once drug-related ≥G2 toxicity is seen. mCRM starts after 1st dose limiting toxicity (DLT), with the modifications of at least 3 patients required to dose escalate and up to 1.5x increment to minimize risk of toxicity. CE has 3 arms: GPC3+ gastric/gastroesophageal junction adenocarcinoma; GPC3+ squamous esophageal cancer; and other GPC3+ tumors. A 2-stage design is used to allow CE to stop early for futility. Subjects are adults with histologically confirmed, measurable malignant solid tumors and/or metastatic disease not amenable to standard therapy, and life expectancy ≥3 months. Patients with > 1cm or > 1 brain metastasis, current/previous interstitial lung disease, and acute/chronic infection are excluded. 3 cohorts have been completed without DLT. Cohort 4 began in January 2017. Clinical trial information: NCT02748837.

Chromosomal localization of a gene responsible for vestibulocochlear defects of BUS/Idr mice: identification as an allele of waltzer

Mice of the bustling mutant strain BUS/Idr have vestibulocochlear defects. bus/bus homozygotes, but not heterozygotes, are hyperactive and display an abnormal behavior such as circling, head bobbing and head tilting. To characterize BUS mice further, the auditory brain-stem response of the mutant was examined. In +/bus heterozygotes as well as control animals, the auditory brain-stem response was developmentally first recorded as early as 11 days of age and heterozygous and normal adults showed typical auditory brain-stem responses with five peaks in a threshold of 40-45 dB SPL. In contrast, bus/bus homozygotes showed no auditory brain-stem response at any age in response to stimuli up to 130 dB SPL, indicating that they are deaf throughout life. Linkage analysis revealed that the responsible gene, originally designated as bus, maps on chromosome 10, 1.09+/-0.9 cM distal to D10Mit127 and D10Mit59, and 0.72+/-0.51 cM proximal to three markers, D10Mit48, D10Mit112 and D10Mit258, at a site indistinguishable from that of the Albany waltzer, v(A/b). The results of allelism tests between BUS and Albany waltzer indicated that bus is allelic with v(Alb). From these data, we propose here that the bus mutation could represent another allele of waltzer, now designated v(bus).

Proposal of a new method for narrowing and moving the stimulated region of cochlear implants: animal experiment and numerical analysis

We have proposed the tripolar electrode stimulation method (TESM) for narrowing the stimulation region and continuously moving the stimulation site for cochlear implants. The TESM stimulates the auditory nerve array using three adjacent electrodes which are selected among the electrodes of an electrode array within the lymphatic fluid. Current is emitted from each of the two lateral electrodes and received by the central electrode. The current received by the central electrode is made equal to the sum of the currents emitted from the lateral electrodes. In this paper, we evaluate whether or not TESM works according to a theory which is based on numerical analysis using an electrical equivalent circuit model of the auditory nerve fibers. In this simulation, the sums of the excited model fibers are compared to the compound action potentials (CAP's) which we obtained through animal experiments. To identify the main parameter while maintaining the amplitude of the CAP (the sum of the fired fibers), we assumed the presence of some parameters from the radial current density profile. In the case of the width value among the parameters being kept constant, the amplitude of the CAP was almost constant; thus, the number of the fired fibers was also almost constant. The width value equals the distance between the points at which the profile of the radial current density of the electrode array and the line of the radial threshold current density of the electrode array intersect. It is possible to determine the measure of the stimulation region or site by controlling the width value and the ratios of the currents emitted from the lateral electrodes. As a result, we succeeded in narrowing the stimulation region by controlling the sum of the currents emitted from the two lateral electrodes. Also we succeeded in continuously moving the stimulation site by modifying the currents emitted from the two lateral electrodes.

Improved word perception in tinnitus patients following electrical stimulation of the ear: a preliminary report

The present study showed that there were close relationships between tinnitus relief and improved word perception by means of a grammatically correct but non-sense Japanese word perception test. Fourteen out of 20 patients reported tinnitus relief and improvement in hearing. Nine out of the 14 patients were thought to be significantly improved in word perception. Improved word perception was observed in 7 out of 10 patients whose ears tested were opposite to ears treated while in 2 out of 10 patients whose ears tested were the same as ears treated. Improved word perception was observed in 5 patients at one segment, 2 patients at two segments and 2 patients at three segments. Improved word perception was observed in one patient at the first segment, 5 patients at the second segment, 5 patients at the third segment and 5 patients at the fourth segment. There were no significant differences in hearing level nor age in patients with and without relief of tinnitus.

Improved word perception following electrical stimulation of the ear in hearing-impaired patients without tinnitus

Improved word perception in hearing-impaired patients following electrical stimulation of ears was shown by means of a grammatically correct but non-sense Japanese 4-segment sentence perception test. Improved word perception was reported in 15 out of 20 patients without tinnitus following electrical stimulation of ears. In 11 out of 15 patients, the number of incorrect words significantly decreased, showing that electrical stimulation of ears improved word perception. Improved word perception was observed in 5 out of 8 patients whose tested ears were contralateral to treated ears while in 8 out of 12 patients whose tested ears were the same as treated ears. The present study suggests that electrical stimulation of ears improves word perception in hearing-impaired patients without tinnitus.

Preliminary study of improved perception of words with the same sound but different intonation in tinnitus patients following electrical stimulation of the ear

The present study aimed to explain how tinnitus relief following electrical promontory stimulation affects detection of changes in pitch frequency. To determine the effects of tinnitus relief on the auditory system. Japanese words with the same sound but different intonation were used to verify the effects of tinnitus relief on pitch detection in tinnitus patients Eight out of 11 patients experienced relief of tinnitus following treatment. The averaged number of the ratio in 8 patients with relief of tinnitus, 0.58, was significantly higher (p < 0.02) than that in 3 patients without relief, 0.15. In comparison with averaged hearing level, there was no significant difference in averaged hearing level between 8 patients with relief of tinnitus (52.4 dBSL; SD: 11.4) and 3 without relief of tinnitus (58.0 dBSL; SD: 14.7) (p > 0.68). No significant difference in age between patients with and without relief of tinnitus was observed.

Evaluation of the tripolar electrode stimulation method by numerical analysis and animal experiments for cochlear implants

We have proposed the Tripolar Electrode Stimulation Method (TESM) which may enable us to narrow the stimulation region and to move continuously the stimulation site for the cochlear implants. We evaluated whether or not TESM works according to a theory based on numerical analysis using the auditory nerve fiber model. In this simulation, the sum of the excited model fibers were compared with the compound actions potentials obtained from animal experiments. As a result, this experiment showed that TESM could narrow a stimulation region by controlling the sum of the currents emitted from the electrodes on both sides, and continuously move a stimulation site by changing the ratio of the currents emitted from the electrodes on both sides.

Simple in-office closure of small intractable tympanic membrane perforations after myringoplasty

Perforations produced following myringoplasty are very difficult to close by ordinary cautery or patching even if they are small. Therefore we decided to close these intractable perforations with a skin graft from the cartilaginous ear canal. Our method is an in-office operation under local anesthesia. After the removal of epithelium from around the perforation a skin graft was placed by the over-lay method. A total of 11 patients were treated, of which 81.8% (9/11) demonstrated successful closure in the initial surgery and two re-perforations were successfully closed by a second and third operation, respectively. The technique used in this surgery is relatively easy and appropriate for in-office operations. The method's advantages include decreased invasiveness with minimal anesthesia and no requirement for ear canal packing or fixatives, and cosmetic benefit. This method also can be applied to perforations caused by chronic otitis media, traumatic perforations, and perforations after inserting tubes.

An experience of the usage of electrical tinnitus suppressor

An electrical tinnitus suppressor based on the use of an extracochlear stimulator has been developed at Hokkaido University, Sapporo, Japan, and was implanted in 2 male and 2 female patients. Tinnitus improved in all patients because the auditory nerve was able to be stimulated at home whenever patients wanted treatment. Additional benefits reported after electrical stimulation of the cochlea included sound sleep, relaxation in all cases, and improved hearing acuity in Cases 1, 2, and 4. Minimal temporary complications, including habituation and ear drum perforation, were observed.

Surgical results of tympanoplasty with hokudai-shaped partial and total ossicular replacement prostheses

The surgical results of tympanoplasty using a ceramic partial ossicular replacement prosthesis (PORP) or a ceramic total ossicular replacement prosthesis (TORP) were analyzed. The present study included 25 ears in 22 patients who underwent tympanoplasty between December 1986 and September 1994 and were followed up for more than 6 months postoperatively. Because the ceramic prosthesis was extruded from 2 of the 25 ears, the surgical results in the other 23 ears were analyzed, Surgical results were assessed according to a criterion that permits comparison with data from around the world. The criterion considers a postoperative airbone gap within 20 dB as a success. According to this criterion, the success rate was 90.9% for PORP, 50.0% for TORP, and 69.6% in total. These results are comparable with those found at other centers.

Proposal of a new auditory nerve stimulation method for cochlear prosthesis

The stimulation electrodes of cochlear implants are covered by a lymph liquid with high electrical conductivity, which causes the transmitted information to be reduced by channel interaction. Even if this problem were solved, the stimulation regions may be discrete; therefore, there may be regions in which the electrode array cannot stimulate selectively. To solve these problems, we proposed a new auditory nerve stimulation method which we call the tripolar electrode stimulation method for cochlear implants. Our method stimulates using 3 adjacent electrodes selected from among the electrodes of the electrode array. The center electrode receives the currents emitted from the electrodes on both sides. We conducted animal experiments using this method. On the basis of the results we obtained, we concluded that our method may succeed in narrowing the stimulation region and continuously moving the stimulation site.

Thyroplasty type I with ceramic shim

To prevent side effects from a silicone shim in Isshiki thyroplasty type I, we used a ceramic shim in 10 patients with unilateral recurrent laryngeal nerve paralysis. No published reports have described the use of ceramic in this type of surgery. According to the degree of glottic insufficiency, ceramic shims of various heights were inserted into the fenestration made in the thyroid ala. All patients experienced subjective improvement of voice postoperatively. Laryngoscopies in most cases showed that glottic insufficiency improved postoperatively. In the postoperative examination, the maximum phonation time improved an average of 3.7 s, and the mean flow rate improved an average of 331 ml/s. We have analyzed the relationship of these improvements to the degree of glottic insufficiency and have compared our results with those of other investigators.

A portable digital speech-rate converter for hearing impairment

A real-time hand-sized portable device that slows speech speed without changing the pitch is proposed for hearing impairment. By using this device, people can listen to fast speech at a comfortable speed. A combination of solid-state memory recording and real-time digital signal processing with a single chip processor enables this unique function. A simplified pitchsynchronous, time-scale-modification algorithm is proposed to minimize the complexity of the DSP operation. Unlike the traditional algorithm, this dynamic-processing algorithm reduces distortion even when the expansion rate is only just above 1. Seven out of 10 elderly hearing-impaired listeners showed improvement in a sentence recognition test when using speech-rate conversion with the largest expansion rate, although no improvement was observed in a word recognition test. Some subjects who showed large improvement had limited auditory temporal resolution, but the correlation was not significant. The results suggest that, unlike conventional hearing aids, this device can be used to overcome the deterioration of auditory ability by improving the transfer of information from short-term (echoic) memory into a more stable memory trace in the human auditory system.

Cochlear pathology following chronic electrical stimulation of the auditory nerve: II. Deafened kittens

The present study examines the effects of long-term electrical stimulation of the auditory nerve on cochlear histopathology and spiral ganglion cell survival in young sensorineural deafened cats. Eight kittens were deafened using kanamycin and ethacrynic acid, and implanted with bipolar or monopolar scala tympani electrodes. Following recovery from surgery the animals were unilaterally stimulated using charge balanced biphasic current pulses for 450-1730 hours over implant periods of up to four months. Charge densities varied from 0.6-0.9 microC.cm-2 geom. per phase for monopolar electrodes to 12-26 microC.cm-2 geom. per phase for the bipolar electrodes. Electrically-evoked auditory brainstem responses (EABRs) were periodically monitored during stimulation to confirm that the stimulus levels were above threshold, and to monitor any change in the response of the auditory nerve. Following completion of the stimulation program cochleae were prepared for histological examination. EABRs exhibited relatively stable thresholds for both stimulated and implanted, unstimulated control cochleae for the stimulus duration. While the growth in response amplitude as a function of stimulus current remained stable for the bipolar control and monopolar stimulated cochleae, the five cochleae chronically stimulated using bipolar electrodes exhibited a moderate to large increase in response amplitude. These increases were associated with a more widespread fibrous tissue response which may have altered the current distribution within these cochleae. Implanted control cochleae exhibited significantly less tissue response within the scala tympani. Importantly, we observed no statistically significant difference in the spiral ganglion cell density associated with chronic electrical stimulation when compared with unstimulated control cochleae. While the present study supports the safe application of cochlear implants in young profoundly deafened children, it does not corroborate previous studies that have reported electrical stimulation providing a trophic effect on degenerating auditory nerve fibres.

[A tinnitus case with an implanted electrical tinnitus suppressor]

An electrical tinnitus suppressor, which was developed at Hokkaido University, was implanted in a female tinnitus patient. She had suffered from bilateral chronic otitis media and her bilateral hearing was seriously impaired. The electrical tinnitus suppressor consists of a stimulator, a coil inside the plastic hearing aid case and an implanted coil in the mastoid. The auditory nerve is stimulated at home twice. Using the system, her hearing ability and emotion improved in addition to tinnitus suppression. Her hearing level and tinnitus also improved in the ear contralateral to the stimulated side.

[Electroconduction system for implantable tinnitus suppressor]

The purpose of this study was to introduce the electroconduction system for an implantable tinnitus suppressor. This system is a modification of the extracochlear implant system, which was developed at Hokkaido University. This system consists of a stimulator and two coils. One of the coils is implanted inside the temporal bone and its size, including the current limiter, is 9 mm long, 6.4 mm wide and 6 mm thick. Another is contained in the plastic case which is used for hearing aids. The efficacy of conduction depends on the wave frequency. The most effective frequency was about 30 kHz. The maximum current required to relieve tinnitus is 100 microA when using this system. The heat emitted from the coil inside the case is so minimal at an intensity of 100 microA as to be negligible systemically. The electromagnetic coupling system works well for more than 4 months in saline.

Neural responses to electrical stimulation of the cochlea in guinea pigs

A special bridge circuit was constructed to compensate stimulus artifact to determine the effects of an alternating current (AC) in the range of 3 to 20 kHz and direct current (DC) stimulation on the activity of cochlear nerve fibers. When AC and DC stimulation of the same fiber were compared, a greater current intensity was required to change the spike rate with AC stimulation than DC stimulation. While positive DC stimulation reduced activity, negative DC stimulation increased the spike rate. AC stimuli excited fibers in a manner similar to that observed with negative DC stimulation. Thresholds increased with stimulus frequency, suggesting that the effects of AC stimulation on the discharge rate are independent of the CF (characteristic frequency) of a fiber. The effects of short-time AC and DC stimulation on cochlear fiber activity lasted only during the stimulation, and the spontaneous activity did not significantly differ before and after electrical stimulation.

Thyroplasty type I with ceramic shim

To improve hoarseness or misswallowing caused by unilateral recurrent laryngeal nerve paralysis, medialization of paralyzed vocal cord has frequently been performed. This method includes such techniques as injection method, insertion method, and arytenoid adduction, each presenting its merits and demerits. The insertion method which can be done while monitoring the patient's voice seems advantageous in that the technique is easy to perform and generally guarantees the voice improvement. Among insertion methods, Isshiki thyroplasty type I is the one most representative as well as popularized. However, since a silicone shim is inserted in this operation, it may be accompanied by the risks of carcinogenicity, foreign body reaction, and induction of collagen disease of silicone. Therefore we planned to use a ceramic as a safe substitute instead of silicone. There has been no article reporting the use of ceramic in this type of surgery. We used a fibrin glue to fix the ceramic shim and for hemostasis, which was found very useful. Hitherto, 2 cases of unilateral recurrent laryngeal nerve paralysis underwent Isshiki thyroplasty type I using ceramic shim with satisfactory results.

[Intracochlear electrical stimulation of the auditory nerve in deaf kittens--brainstem response audiometric and histopathologic studies]

The effects of long-term electrical stimulation of the auditory nerve on the morphology of the cochlear nucleus were investigated in young pharmacologically deafened kittens. Comparing the amplitude of EABR with the soma area, there was a strong positive correlation between the amplitude of EABR and the soma area of neurons within the anterior ventral cochlear nucleus on the stimulated side. However, there was no correlation between the amplitude of EABR and the soma area of neurons within the unstimulated anterior ventral cochlear nucleus. In addition, there was no correlation between the amplitude of EABR and the survival rate of spiral ganglion cells. This showed that EABR may be affected not only by the survival rate of the spiral ganglion cell, but also by the development of the central auditory nervous system in kittens, which were deafened under the development of the central auditory nervous system.

[A comparison of time resolution among auditory, tactile and promontory electrical stimulation--superiority of cochlear implants as human communication aids]

Our previous reports showed that second formant information, using a speech coding method, could be transmitted through an electrode on the promontory. However, second formant information can also be transmitted by tactile stimulation. Therefore, to find out whether electrical stimulation of the auditory nerve would be superior to tactile stimulation for our speech coding method, the time resolutions of the two modes of stimulation were compared. The results showed that the time resolution of electrical promontory stimulation was three times better than the time resolution of tactile stimulation of the finger. This indicates that electrical stimulation of the auditory nerve is much better for our speech coding method than tactile stimulation of the finger.

Recording eye movement during stepping in place with a CCD (charge-coupled device) imagesensor

A new system for recording eye movements using a charge-coupled device (CCD) imagesensor in a video camera, in which less than 0.5 degree of horizontal and vertical eye movements can be recorded, was applied in 7 subjects. Eye movements were recorded while they stepped in place. We observed 5 normal subjects, a patient with horizontal and vertical oscillopsia during walking, and one with a chronic limp. In the normal adults, the amplitude of vertical eye movement was less than 0.5 degree, and the horizontal eye movement was less than 2 degrees. The mean amplitude of horizontal and vertical eye movements in the subject who limped was larger than that of normal subjects. The patient who complained of vertical oscillopsia during walking showed the largest amplitude of vertical eye movement among any subject tested. The vertical oscillopsia in the patient was due to the largest amplitude of vertical eye movement. This system for recording eye movements will be useful in analyzing the mechanism of gaze fixation during walking.

[Effects of intravenous injection of salicylate on the spontaneous discharge rate of the cochlear nerve]

This study was aimed to elucidate the effects of salicylate on the cochlear nerve by recording the spontaneous activity in guinea pigs. After guinea pigs were given salicylate (200 mg/kg) intravenously, the transient reduction in cochlear spontaneous activity and the elevation over the subsequent 10-20 minutes were observed in three of four fibers recorded for more than 30 minutes. The mean spontaneous discharge rate of 102 fibers after administration of salicylate (200 mg/kg) was not significantly higher than the control values from 30 to 120 minutes after salicylate administration, while that rate of 112 fibers after administration of salicylate (400 mg/kg) was significantly higher. The observed changes in spontaneous activity due to salicylate administration may represent the evidence of a tinnituslike phenomenon in guinea pigs.

Cochlear pathology following chronic electrical stimulation using non charge balanced stimuli

During the course of a chronic intracochlear electrical stimulation study using charge balanced biphasic current pulses, one animal inadvertently received a short period of direct current (DC) stimulation at a level of approximately 1 microA. Subsequent, the animal was chronically stimulated using a poorly charge balanced waveform that produced a DC level of approximately 2 microA. Extensive pathological changes were observed within the cochlea. These changes included widespread spiral ganglion cell loss and new bone growth that extended throughout all turns of the cochlea. Significant changes in the morphology of the electrically evoked auditory brainstem response (EABR) were associated with these pathological changes. EABRs recorded prior to the DC stimulation exhibited a normal waveform morphology. However, responses recorded during the course of the DC stimulation were dominated by a short latency response believed to be vestibular in origin. The response thresholds were also significantly higher than levels recorded before the DC stimulation. In contrast, the contralateral cochlea, stimulated using charge balanced stimuli, showed no evidence of adverse pathological changes. Furthermore, EABRs evoked from this cochlea remained stable throughout the chronic stimulation period. Although preliminary, the present results illustrate the adverse nature of poorly charge balanced electrical stimuli. These results have important implications for both the design of neural prostheses and the use of DC stimuli to suppress tinnitus in patients.

Glycolipids in rat cochlea

In recent years, the functions of glycolipids have been intensively studied. Before the research of the roles of glycolipids in the inner ear, it seemed to be necessary to demonstrate the composition of glycolipids at first. Therefore, rat cochlea has been examined for glycolipid composition in the present study. Glycolipids extracted from 200 cochlea samples were separated into neutral and acidic glycolipid fractions. Each fraction was analyzed by thin-layer chromatography. The neutral glycolipid was almost exclusively galactosylceramide (cerebroside) with trace amounts of globoside and unidentified glycolipids. In acidic glycolipids, sulfated galactosylceramide (cerebroside sulfate) was most abundant. Of the gangliosides (sialic acid-containing glycolipids), ganglioside GM3 (51.8%) was the predominant component, and GM2 (6.0%), GM1 (8.8%), GD3 (10.7%), GD1a (8.7%), GD1b (5.9%), and GT1b (3.6%) were also detected. In addition to these, rat cochlea also contained several, minor, unidentified gangliosides. This pattern of the cochlear acidic glycolipids is very similar to that of the renal acidic glycolipids. This finding seems to be very interesting when considering that the toxic side effects of aminoglycosides occur only in the kidney and the inner ear.

Rapidly progressive sensorineural hearing loss (rapid deafness)

28 ears of 28 patients, aged 15 to 60 years, whose sensorineural hearing loss had developed over a period of a few hours to 3 days, were defined as having rapidly progressing sensorineural hearing loss (rapid deafness), in comparison with so-called sudden deafness with instantaneous onset. For other criteria, their hearing loss was idiopathic and the rate of hearing loss was confirmed by reliable means. The rate was greatest within the first 1-3 days. Of the 28 patients, 12 (43%) recovered completely, while another 12 improved markedly. The prognosis in rapid deafness was relatively good, but the recovery time was longer than in spontaneously healing sudden deafness. Sensorineural hearing loss in contralateral ears more often preceded rapid deafness (9 cases, 32%). No clear-cut difference could be found between rapid deafness and sudden deafness.

[Origin of N1 wave of the cochlear nerve action potential recorded at the bony wall of the cochlea]

As an objective audiometry, the cochlear nerve action potential (AP) evoked by tone stimulation has been clinically utilized. But the origin of AP wave is still obscure. In order to know the origin of the N1 wave of AP, the author intended to compare the AP waves (AP(W)) recorded at the bony wall of the cochlea with action potentials of the individual spiral ganglion cell (spikes) and group of the spiral ganglion cells (AP(R)) in the Rosenthal canal of the guinea pig. Spikes and AP(R) were recorded by glass pipettes filled with 2M NaCl. The results showed that waves of AP(R) demonstrated a wide monophasic negative wave in contrast to diphasic AP(W) wave. The Input-Output Curves (I.O.C.) of the AP(W) and AP(R) were compared in order to ascertain whether both APs were derived from the cochlear nerve or not. The I.O.C. of latency, onset, amplitude, offset and width of both AP(R) and AP(W) N1 waves showed a same pattern with high correlation coefficient. So it was confirmed that both AP(R) and AP(W) N1 waves were the direct and indirect cochlear nerve action potential respectively. The thresholds of both AP(W) and AP(R) at the characteristic frequency of a single ganglion cell showed a high correlation. The time of onset and latency of AP(R) were longer than those of AP(W). Based on anatomy and electrophysiology, it is concluded that AP(W) N1 wave originates from the action potential generated at the habenula perforata, where spikes are first produced. The curves of the AP(R) were flat in respect of frequency-threshold relationship. The threshold was the lowest in the spiral ganglion cell followed by AP(R) and AP(W).

Vestibular responses and branching of interstitiospinal neurons

1. Interstitiospinal neurons were activated by antidromic stimulation of the ventromedial funiculus of the spinal cord at C1 and C4 in cerebellectomized cats under chloralose anesthesia. 46% of these neurons responded only at C1 (N cells) and the remaining 54% responded at C4 also (D cells). There is no topographical difference in the location of N and D cells. Conduction velocities of N cells were significantly slower than those of D cells. 2. Stimulation of the contralateral whole vestibular nerve evoked firing of 31% of both N and D cells; some responded early enough to suggest disynaptic connections, many responded late. Stimulation of the ipsilateral whole vestibular nerve evoked firing of several cells, one spontaneously discharging D cell was inhibited. 3. Stimulation of the contralateral individual semicircular canal nerves evoked firing of 33% of N cells and 13% of D cells. Most of these responses were late. N cells responded not only to the vertical canals but also to the horizontal canal, whereas D cells responded to the horizontal canal, but seldom to the vertical ones. Most canal responding neurons received specific input, only two N cells received convergent input from both the anterior and horizontal canals. Stimulation of the ipsilateral canals did not evoke excitation of any cells tested; one D cell was inhibited by stimulation of the horizontal canal nerve. 4. Stimulation of the rostral medial vestibular nucleus evoked characteristic negative field potentials centered in the contralateral interstitial nucleus of Cajal (INC). Approximately 60% of both N and D cells received excitation from the contralateral vestibular nuclei. About 17% of these responding neurons received monosynaptic excitation, most frequently from the rostral medial nucleus. Stimulation of the ipsilateral vestibular nuclei evoked firing of 12% of both N and D cells. 5. Twenty-nine neurons were fired antidromically by weak stimuli applied to the ipsilateral vestibular nuclei. Twenty-seven of the 29 were activated only from C1 and were found in the INC (10 cells) and in the reticular formation dorsal to the INC (19 cells). Measurement of the spread of the effect of stimulus current and comparison of latencies to stimulation of the vestibular nuclei and C1 indicated that these neurons have axon collaterals going to the ipsilateral vestibular nuclei. Only one of them received excitation from the contralateral posterior canal, others did not respond to the labyrinth. Some were activated by stimulation of the vestibular nuclei.

Trunk-ocular reflex in the rabbit

The trunk-ocular reflex of the rabbit was investigated by recording EMGs of right lateral rectus and splenius muscles. The skull and the chest of the rabbit were restrained and the lower part of the trunk was flexed laterally around the axis at the TH10--11 intervertebral joint. Two kinds of eye movements, small with short latencies and large with longer latencies, were induced counter to the direction of the lateral flexion. The latency of the former was 158 msec (range: 64--200 msec) and that of the latter was 255 msec (range: 180--380 msec).