The effects of L-carnitine on presbyacusis in the rat model.

Reactive oxygen metabolites are products of oxidative metabolism that are continuously generated in vivo, and are known to produce serious cellular, tissue and genomic damage. l-carnitine is an endogenous amine that has been shown to have an effect on the synthesis of reactive oxygen metabolites. Twenty Wistar rats, 24 months of age, were randomly assigned to two groups as control and l-carnitine treatment groups. One millilitre of distilled water was administered to control rats and 50 mg/kg l-carnitine to rats of l-carnitine treatment groups by intragastric gavage once a day for 30 days. At the end of 30 days, all groups underwent auditory brainstem response testing after administration of intraperitoneal urethane anaesthesia. l-carnitine treatment reduced III, V latencies and I-III, III-V and I-V interpeak latencies (IPL) significantly compared with the control group. l-carnitine treatment improved age-related deterioration in auditory pathways and hence may be a new alternative for the treatment of presbyacusis.

Effects of cadmium on the hearing system.

The functional resemblance between kidney proximal tubular and inner ear epithelial cells which has often been pointed out in the literature led us to hypothesize that nephrotoxic agents that cause renal tubular injury might also impair the function of inner ear cells. As one of the most toxic environmental nephrotoxic agents is cadmium, we aimed to study its effects on hearing experimentally in rats. In this study, increased blood and renal cortical cadmium levels were associated with high cadmium accumulation in ear ossicles and labyrinth in rats exposed to cadmium. The changes in auditory brainstem response (ABR) and otoacoustic emission in 2-month-old male rats exposed to drinking water containing 5 and 15 ppm CdCl2 for 30 days showed that cadmium-induced nephrotoxicity was associated with signs of defective hearing at a concentration of 15 ppm CdCl2 but that 5 ppm CdCl2 caused hearing loss without affecting kidney function. The mean latency of ABR wave 1, which indicates the function of the cochlea, was 1.335 +/- 0.31 ms in the control group and 1.641 +/- 0.052 and 1.74 +/- 0.88 ms in the rats subjected to 5 and 15 ppm CdCl2, respectively (p < 0.001). In the cadmium-treated groups short interpeak wave I-III latencies (p < 0.01) indicated cochlear dysfunction and this was also supported by the distortion product otoacoustic emission results (p < 0.001). Non-significant changes in wave III and V latencies were accepted as evidence of unaltered function of the other parts of the auditory system. These results suggest that hair cells are more sensitive to cadmium than kidney tubule cells and that the cochlear component of hearing is more vulnerable to cadmium toxicity than other parts of the auditory system.

The canal of the posterior ampullar nerve: an important anatomic landmark in the posterior fossa transmeatal approach.

The canal of the posterior ampullar nerve is located between the inferior part of the internal acoustic meatus and ampulla of the posterior semicircular canal. It permits a more accurate localisation of the underlying labyrinth in inner-ear surgery. An anatomical and radiological study was undertaken to determine the importance the relationship between the canal and the labyrinth. Ten dry and 10 cadaveric temporal bone dissections, together with 20 high resolution CT scans of the same temporal bones were studied in an attempt to describe the anatomy of the canal of the posterior ampullar nerve. The length of the canal of the posterior ampullar nerve, the length of internal acoustic meatus, and distances from porus acusticus to the singular foramen and the transverse crest, and from the singular foramen to the vestibule and transverse crest, and from operculum to the sigmoid sinus and to the porus acusticus were measured. During the transmeatal posterior cranial fossa approach using the canal of the posterior ampullar nerve as a landmark enables more bone to be safely removed from the internal acoustic meatus thus preserving hearing.