Monitoring of functional changes after transient ischemia in gerbil cochlea

Ischemia and reperfusion are involved in numerous sensorineural pathologies. A model of reversible cochlear ischemia has been designed in Mongolian gerbil. Selective labyrinthine ischemia of variable duration (4-10 min) was achieved through a posterior transcranial approach. Ischemia and reperfusion were controlled with the help of laser Doppler velocimetry. Functional changes were monitored every 1-10 s throughout experiments, using cochlear potentials and otoacoustic emissions. After interruption of blood flow, all signals rapidly began to decay. In contrast to cochlear potentials, otoacoustic emissions always exhibited a plateau before reaching noise floor only after approximately 4-5 min. Upon ischemia release, cochlear blood flow recovered instantly and completely and cochlear potentials rapidly improved in most cases, in contrast to otoacoustic emissions that underwent a delayed decay after immediate partial recovery. The phase and group latency of otoacoustic emissions exhibited only small changes throughout ischemia and reperfusion, suggesting adaptive rather than damaging mechanisms. Cochlear function returned to normal after 5 min 30 s ischemia but longer complete ischemia sometimes led to irreversible damage despite the systematic presence of some recovery just after ischemia release. This behavior suggests that reperfusion in itself can be deleterious to a sensorineural organ and this model can be useful for identifying the noxious mechanisms of ischemia and reperfusion.