| Vestibular ganglion neurons encode and convey vestibular information from the sensory hair cells of the inner ear organs of balance to the brain stem. To fully appreciate the complexity and functionality of this system, it is important to investigate the physiological characteristics of both hair cells and neurons. The aim of this thesis was to address the role of ionic conductances expressed in the vestibular periphery. First, I examined the developmental acquisition of voltage-dependent conductances in vestibular hair cells, proposing a stereotyped pattern of functional maturation of these cells. The four observed conductances, GNa, GDR, G K,L, and GK1, had different properties that determined their functional role within the hair cell; the latter three contributing to the hair cell receptor potential. Determining how information carried by the graded hair cell receptor potential is transmitted and encoded by vestibular ganglion neurons is critical to an understanding of peripheral vestibular physiology. The second aim of this thesis was to examine the intrinsic properties of vestibular ganglion neurons and to determine the role of K+ conductances in these neurons. Here, I present the first characterization of the whole cell firing properties of postnatal mouse vestibular ganglion neurons. I found that the neurons had diverse firing properties and were inherently tuned to frequencies ≤ 40 Hz, which spans the sensitive range of mammalian vestibular organs. I have also shown that these neurons express at least three distinct K+ conductances, based on their sensitivity to the K + channel antagonists 4-AP, TEA, linopirdine and XE991. These results present evidence for expression of a heterogeneous popopulation of K + channels that shape neuronal firing properties. Utilizing molecular, pharmacological and electrophysiological techniques in both wild type and KCNQ4 knockout mice, I have begun to narrow the list of potential candidates for the K+ channel subunits that make up the physiologically and pharmacologically defined K+ conductances in vestibular ganglion neurons. I hypothesize that together with the broad range of responses that arise within the hair cells and at the afferent terminals, a heterogeneous population of neuronal K+ conductances contributes to the diversity in firing properties of vestibular ganglion neurons. |
