This grant is for a pilot study for one year on auditory receptor cells. Inside the ear, in the structure called the cochlea, are the receptor cells for hearing, called hair cells. These specialized cells respond to the vibrations in membranes of the inner ear, and send signals to the auditory nerve. Recently these cells have been found to change their structure when stimulated by certain kinds of chemical or electrical stimulation, when isolated in vitro. It has been known for some time that there is a particular class of nerves, called efferents, that send information from the brain out to receptor organs. The activity of these efferents often modulates the sensitivity of these receptor cells. In the cochlea, it now appears that modulation may be done by triggering the structural changes in the receptors, which in turn could change the vibrating characteristics of the inner ear. This project will attempt to measure whether these small changes in receptor cells in fact occur in the ear itself. A computer assisted method will be combined with measurements of the microstructure of the cochlea; use of three-dimensional whole-mounts of the cochlea will allow measurements not possible with sectioning techniques. The possibility of the active mechanical process will be tested by introducing a fluid with unusually high potassium salt concentration into the ear; such solutions trigger the structural change in the isolated cells. The lengths of the hair cells and their components will be measured in cochleae from normal and experimental animals. Additional stimuli, such as electrical stimuli or efferent nerve stimulation, may also be tried. If these results show that hair cells in the intact cochlea respond by structural changes, it will be extremely important evidence for active processes modulating the activity in this sensory organ. Such active processes could be very important not only in normal hearing, but in noise-induced damage, and in certain diseased states of the ear.
