[Influences of explosion on hearing threshold and acetylcholinesterase activity in inner ears]

Fifty-seven guinea pigs weighting 200-400 g with normal Preyer's reflexes were randomly divided into five groups, one for control and the others studied 8, 48 hours and 7, 30 days after explosion. Cortical response threshold measurement and AchE histochemical observations were made. Histochemical sections were prepared as follows: under anesthesia, blood was washed out with Ringer's solution, then the animals were perfused with ice-cold neutral formol-calcium solution for 10 minutes. Temporal bones were removed and fixed in the same fixative for 24 hours. Fixed specimens were decalcified in 10% EDTA solution at 15 degrees C for one week. Tissue blocks were sectioned serially at 20 microns in a cryostat. Horizontal sections were obtained. Sections were then incubated in a substrate solution prepared according to Tsuji (1983) at 4 degrees C for 50 minutes, washed with 3 changes of distilled water and mounted in 25% gelatin. Inhibitory tests were carried out to non-specified chE or Pseudo-chE activity by using iso-OMPA during incubation. Control sections were incubated without the substrate. The results showed that explosion reduced the AchE activity of the cochlea and elevated cortical response threshold. Both showed a negative correlation. The significance of the results obtained had been discussed.