MONITORING OF FUNCTIONAL-CHANGES AFTER TRANSIENT ISCHEMIA IN GERBIL COCHLEA

Ischemia and reperfusion are involved in numerous sensorineural pathol ogies. A model of reversible cochlear ischemia has been designed in Mo ngolian gerbil. Selective labyrinthine ischemia of variable duration ( 4-10 min) was achieved through a posterior transcranial approach. Isch emia and reperfusion were controlled with the help of laser Doppler ve locimetry. Functional changes were monitored every 1-10 s throughout e xperiments, using cochlear potentials and otoacoustic emissions. After interruption of blood flow, all signals rapidly began to decay. In co ntrast to cochlear potentials, otoacoustic emissions always exhibited a plateau before reaching noise floor only after approximate to 4-5 mi n. 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 otoacousti c emissions exhibited only small changes throughout ischemia and reper fusion, suggesting adaptive rather than damaging mechanisms. Cochlear function returned to normal after 5 min 30 s ischemia but longer compl ete ischemia sometimes led to irreversible damage despite the systemat ic presence of some recovery just after ischemia release. This behavio r suggests that reperfusion in itself can be deleterious to a sensorin eural organ and this model can be useful for identifying the noxious m echanisms of ischemia and reperfusion. (C) 1997 Elsevier Science B.V.