[Effect of hypoxia at 5% oxygen on global electrophysiological responses from normal awake guinea pigs]

All experiments were conducted on awake guinea pigs warranting a normal physiological function of the circulatory system. Global electrophysiological responses from the round window of cochlea were monitored: cochlear microphonic (CM), summating potential (SP) and auditory compound action potential (AP). The results showed that hypoxia induced a threshold elevation at all frequencies thus affecting the whole cochlea, and also very large diminutions of AP at high intensity level exclusively in response to a high frequency, and very large increases of SP at 2 kHz and 8 kHz. After hypoxia, which lasted thirty minutes, a considerable recovery occurred, and at the end of the session recovery reached around eighty percent. Alterations of cochlea action potential in response to high intensity stimuli were dissociated from threshold changes. We speculate that threshold elevation could be associated with over-all energetic (ATP) decrease leading to diminution of endolymphatic resting potential. Action potential changes at high intensity and at cochlear base could reflect neurotransmission (afferent, efferent or sympathetic) disturbance.