AN IN-VITRO MODEL FOR ACOUSTIC OVERSTIMULATION

Although many studies have been performed on the effects of acoustic o verstimulation on the inner ear, our knowledge about the cellular proc esses underlying reduced hearing sensitivity and auditory cell death i s still limited. In order to further our understanding of cellular pro cesses occurring in conjunction with acoustic trauma, we designed an i n vitro model to study the effects of overstimulation directly on sens ory hair cells isolated From the low-frequency part of the guinea pig cochlea. The isolated outer hair cells were subjected to pressure jets delivered by a glass micropipette positioned close to the cell, in or der to mimic the pressure changes occurring in the intact inner ear du ring sound stimulation. A second micropipette coupled to a piezoresist ive pressure transducer was used as a probe measuring the pressure at precise locations at and around the cell. In a previous study, we foun d that such stimulation gave rise to increases in the intracellular ca lcium concentration. The present study characterizes the stimulus, des cribes the computer-controlled setup used for calibration, and gives e xamples of different modes of overstimulation at the cellular level. T he peak pressure that could be generated using the pressure jet was ar ound 325 Pa, or 144 dB (re 20 mu Pa) at 140 Hz. The pressure jet elici ted large mechanical vibrations of the cell bodies of isolated cells. The vibration mode of the cells often changed over time, implying that the stimulation caused changes of the cellular stiffness. However, mo st cells appeared quite resistant to the high intensity mechanical sti mulation.