These findings suggest that racial differences exist for certain measures of globe and orbital position, i.e., projection, IPD, and PFW. Racial background should be considered when evaluating orbital anatomy.

The cytoplasmic amino terminus of HCN1, the primary full-length HCN isoform expressed in trout saccular hair cells, was found by yeast two-hybrid protocols to bind the cytoplasmic carboxyl-terminal domain of a protocadherin 15a-like protein. HCN1 was immunolocalized to discrete sites on saccular hair cell stereocilia, consistent with gradated distribution expected for tip link sites of protocadherin 15a. HCN1 message was also detected in cDNA libraries of rat cochlear inner and outer hair cells, and HCN1 protein was immunolocalized to cochlear hair cell stereocilia. As predicted by the trout hair cell model, the amino terminus of rat organ of Corti HCN1 was found by yeast two-hybrid analysis to bind the carboxyl terminus of protocadherin 15 CD3, a tip link protein implicated in mechanosensory transduction. Specific binding between HCN1 and protocadherin 15 CD3 was confirmed with pull-down assays and surface plasmon resonance analysis, both predicting dependence on Ca HCN12 is the primary full-length HCN isoform underlying I h (hyperpolarization-activated, cyclic nucleotide-gated, nonselective cation channel current) in a model hair cell preparation from the trout sacccule (1). cAMP-gated I h , possibly in addition to the mechanosensory-transduction current, sets the membrane potential for a subpopulation of saccular hair cells (2, 3). The membrane potential in the saccular hair cell subpopulation is sufficiently depolarized to activate voltage-gated calcium channels, permitting influx of calcium and secretion of hair cell transmitter (2). Given that saccular hair cells expressing I K1 in addition to I h are more hyperpolarized, not supporting activation of the voltage-gated calcium channels, we predicted that spontaneous release of transmitter from the subpopulation of hair cells would constitute hair cell-generated spontaneous activity for the saccule (1). However, little has been previously reported on the morphological localization of the HCN1 isoform in hair cells or possible links to structural proteins that mechanistically would localize HCN1 in hair cells (for preliminary report, see Ref. 4). In general, little is known about proteinprotein interactions for the HCN isoforms that would modulate I h and/or the associated instantaneous current (5).Protocadherin 15 is a proposed tip link protein involved in connecting shorter stereocilia to adjacent taller stereocilia in the stereociliary array of inner ear hair cells, facilitating the opening of the mechanosensory transduction channel in response to auditory and vestibular stimuli. The active tip link protein in Danio rerio is protocadherin 15a (6), characterized by splice variants in its carboxyl terminus. In the mammal, protocadherin 15 CD3 is hypothesized to be a tip link protein at insertion sites in the tips of the shorter stereocilia of the stereociliary array (7,8). EXPERIMENTAL PROCEDURES Acquisition of a Model Hair Cell Preparation from the Trout Saccule and an Organ of Corti Subfraction from theRat Cochlea-Hair cell layers were isolated from the t...

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Effects of pulse width on discrimination of simultaneous changes in frequency and level of electrical pulse trains were studied in a monkey subject with a cochlear implant. At test-stimulus levels where performance was minimum, frequency difference limens were larger for longer-duration pulses than that for shorter-duration pulses. Several factors may have contributed to these differences.