[Observation on the protective effect of MK-801 against hearing loss in acoustic trauma]

To observe the protective effects of MK-801, an antagonist of N-methyl-D-aspartate (NMDA) receptor, against temporary (TTS) or permanent threshold shifts (PTS) in acoustic trauma.

Twenty guinea pigs were exposed to octave band noise with a central frequency of 4 kHz, 110 dB SPL for 3 h, and another twenty guinea pigs, to the same band noise at 115 dB SPL for 5 h. The test animals were given MK-801 (0.5 mg/kg, i. p. ) before and immediately after noise exposure; the control animals were treated with saline solution. Auditory brainstem responses (ABRs) of animals were recorded and ultrastructure of inner hair cells and afferent synapses were examined with transmission electron microscopy.

There was no significant difference in temporary threshold shifts immediately after noise exposure to 110 dB noise between the test and control group. The threshold shifts disappeared in one week after exposure in both groups. In 115 dB group, the threshold shifts of the test animals 7 days after exposure were significantly less than those of the control animals ( P >0.05) and 3 weeks after exposure, there was still this difference. The inner hair cell and afferent dendrites of the control animal exposed to 115 dB noise displayed many vacuoles. No vacuoles, however, were found in the inner hair cells or in the afferent dendrites of animals that were exposed to 110 dB noise or the test animals of 115dB group that received MK-801.

MK-801 could partially protects against PTS, but not TTS in acoustic trauma through preventing from vacuole degeneration in inner hair cell and afferent dendrites.