Hair cell distribution and orientation in goldfish otolith organs

Abstract

Structurally diverse sensory regions occur in the otolith organs of the goldfish inner ear. Scanning electron microscopy reveals regional distinctions based on three criteria. (1) Hair cells have different sizes of apical bundles, based on thickness. In all three maculae, two central regions have hair cells with bundles significantly thicker than those in surrounding regions. (2) Hair cell population density varies, with regional aggregations present. The central regions with thick bundles have two to three times the density of surrounding regions with thin bundles, and contain 40-80% of the total hair cell number in each macula. (3) Hair cell orientation maps show that each macula has two oppositely oriented cell populations that can be separated completely, not by a zone of interspersion, but apparently by a single unbroken line. The lagena is like the utricle in having hair cells with the kinocilium on the side of the cell toward the opposition line, but in the saccule the kinocilia face away from the line, and the small macula neglecta consists of two completely separate, oppositely oriented patches. The opposition line does not divide each macula simply down its midline; instead, the line divides the regions with thich bundles into nearly equal opposing areas, except for a remarkably abrupt large loop in the line in the anterior part of the saccule. The regional structural diversity in these organs may relate to localized functional diversity of responses to tilt, vibration and sound.

Afferent Innervation of the Utricular Macula in Pigeons

“…With average dimensions of 1.5 ϫ 1.2 mm, the pigeon utricular macula appears to be comparably larger than that of several other animals studied including frogs (Baird and Schuff 1994), turtles (Fontilla and Peterson 2000), chinchillas ), guinea pigs (Werner 1933), and three species of fish (Chang et al 1992;Platt 1975;Popper and Northcutt 1983). If one compares across animal classes, several morphological features are present in the pigeon utricular macula that may represent general adaptations refined through parallel evolutionary paths for motion detection in terrestrial/aerial environments.…”

“…Except for hair cells located on either side of the reversal line, the morphological polarizations of neighboring utricular hair cells all have similar directional orientations (Baird and Lewis 1986;Jørgensen and Andersen 1970;Lindeman 1969;Platt 1975;Rosenhall 1970;Wersäll et al 1966). Thus as afferents develop terminal fields, branching fibers directed either parallel or perpendicular to the reversal line would ensure innervation of hair cells with similar morphological polarizations (Fig.…”

“…For example, similar to frog and fish utricular maculae, the pigeon striola eccentrically traverses the lateral portion of the epithelium with a narrow lateral extrastriola region Schuff 1994, Chang et al 1992;Platt 1975;Popper and Northcutt 1983), whereas in mammals, the striola is more centrally located ). In the bird utriclar macula, the reversal line of opposing polarizations extends along the outer margin of much of the macula, similar to fish and amphibians (Baird and Schuff 1994;Lewis and Li 1975;Platt 1975;Wersäll et al 1965). Although most of the polarizations were perpendicular for the lateral and anterior macular regions, the antiparallel polarizations of the medial macula reversal line appear unique to birds and to our knowledge have not been previously observed.…”

“…The striola typically runs longitudinally through the neuroepithelium; however, its exact shape and position differs among species. In fish (Platt 1975;Popper and Northcutt 1983), amphibians (Baird and Schuff 1994), and birds (Jørgensen and Andersen 1973), the utricular striola is eccentrically placed near the lateral border of the macula, whereas in mammals (Flock 1964;Fernandez et al 1990), it lies more medially toward the center of the macula. In chinchillas, a utricular striola was described that comprised 10% of the surface epithelium and divided the rest of the macula into a medial extrastriola (40%) and a lateral extrastriola (50%) ).…”

Development of the zebrafish inner ear

“…The utricular macula develops a long thin extension, the lacinia, whereas the whole saccular macula becomes very elongated. Hair cell densities and polarity patterns have been mapped for each sensory patch in the adult ear (Platt, 1977;Bang et al, 2001). Hair cells probably continue to be produced into adulthood, as in the goldfish (Lanford et al, 1996).…”