Interleukin-2 (IL-2), one of the chemical mediators produced by helper T cells, activates its target cells via its receptor and induces inflammatory reactions indirectly. In this study, IL-2 was instilled into the round window niche of rats and the electrophysiological effects of inflammation on the inner ear were evaluated by a frequency-specific auditory brainstem response (ABR) technique. ABR threshold curves and intensity-latency (I-L) curves were investigated. In most cases, moderate sensorineural hearing loss (SNHL) was observed in the high-frequency areas (16–31.5 kHz). In the time course investigation of I-L curves, the responses of SNHL type appeared only 1 day after instillation (day 1) gradually becoming more prominent, to become most pronounced on days 5–7. The electrophysiological impairment was reversible within 2 weeks. Differing degrees of responsiveness of effusion production were observed following the instillation of IL-2, varying from pronounced middle ear effusion causing rather severe mixed hearing loss, to complete lack of effusion. Inflammation induced by IL-2 affects cochlear function gradually but reversibly.

Computer-assisted image analysis was used to study the immunoreactivity to NF-L, NF-M and NF-H in human spiral ganglion cells. The concentrations, represented by the relative mean grey of NF-L, NF-M and NF-H, were calculated and compared. The cell-area mean-grey correlations for NF-L, NF-M and NF-H were analysed and calculated, showing that NF-M is more specific to the larger cells (type 1?) and NF-H is more specific for the smaller cells (type 2?), while NF-L is non-specific for cell size. These findings confirm several previous assumptions by providing a quantitative basis. We conclude that image analysis is a useful – even essential – tool for the analysis of immunostained temporal bone sections.

Seven ears of Sprague-Dawley rats were exposed to 20 µl Staphylococcus aureus exotoxin suspension by injection via the tympanic membrane into the round window niche. Another 6 ears were exposed to 20 µl broth as controls. ABR was performed in the interval 2–31.5 kHz immediately before and 1, 2, 5, 7 and 10 days after the exposure. Although threshold changes could be found in the toxin-exposed group but not the control group in the frequency range 10–20 kHz, there were only statistically significant threshold changes – at 31.5 kHz – on the 1st, 2nd, 5th, and 7th days after the exotoxin injection. S. aureus exotoxin has minor transient but reversible effects on the inner ear, causing chiefly high-frequency threshold and latency changes.

Objectives: Streptococcus pneumoniae (pneumococcus) produces various toxic proteins such as pneumolysin, autolysin, neuraminidase, hyaluronidase and pneumococcal surface protein A. To evaluate effects on the sensorineural component of hearing of such an infection in the middle ear a sterile suspension of pneumococcus containing all these toxins was instilled into the round window niche. Material and Methods: Inner ear function was evaluated by a frequency-specific auditory brainstem response (ABR) technique using the rat as experimental animal. Both ABR threshold curves and intensity-latency (I-L) curves were investigated. Results: The electrophysiological effects of pneumococcal toxin on the middle and the inner ear were moderate. Sensorineural hearing loss appeared from 1 day after instillation especially at high frequencies (31.5-20 kHz) and gradually extended into the frequencies 16, 14 and 12 kHz. The threshold impairment was reversible and improved within 2 weeks after exposure. The mean threshold change ranged from 5 to 10 dB at high frequencies. Conclusions: Our experimental results are compatible with previously reported clinical findings. The I-L curve investigation was useful to distinguish the changes due to conductive or sensorineural or mixed type of hearing loss. The I-L curve is more accurate than ABR threshold diagrams to identify minor electrophysiological changes of the cochlea.