Planar Relations of Semicircular Canals in Awake, Resting Turtles, <i>Pseudemys script</i><i>a</i>

Abstract

As part of a project aimed at elucidating mechanisms of vestibulocollic control in the red-eared turtle Pseudemys scripta, we have calculated the planar relations of its semicircular canals using principal-components analysis. This information is prerequisite to understanding the pattern of canal activation that is set up by head movement of any spatial form. In addition, we have developed a method for monitoring canal orientation in an awake, behaving animal, and we have used this technique to assess canal position in resting turtles. Our results indicate that ipsilateral canals in Pseudemys are not mutually orthogonal, nor are complementary canals precisely coplanar, although they approach this idealized condition more closely than do the canals of several other vertebrates for which quantitative data exist. One significant departure from the perfectly orthogonal configuration is that both verical canals are rotated slightly toward the frontal plane; thus, Pseudemys should be somewhat more sensitive to head roll than to head rotation in other planes. Radiographic analyses of awake, resting turtles indicate that the anterior interparietal suture is held aligned with the earth horizontal and midsagittal plane. The horizontal canal is pitched up (open anterior) 3–4° relative to the earth horizontal.

Planar Relationships of the Semicircular Canals in Two Strains of Mice

“…The C57Bl/6J and CBA/CaJ mice also show a deviation from parallel between contralateral, synergistic pairs of canals. A range of 7.84--11.81-was observed in both of the strains of mice, which coincides with observations in other studies: 4.81--14.91-in turtle (Brichta et al 1988), 12.49--14.49-in cat (Blanks et al 1972, and 3.3--20.0-in pigeons (Dickman 1996). Other studies show greater ranges of deviations from parallel: 11.1--33.2-in toadfish (Ghanem et al 1998) and15.32--26.78-in rabbit (Mazza andWinterson 1984).…”

“…This is in the range of other reported species, with the canals of the cat ranging from 0.38-to 4.23- (Blanks et al 1972), turtle from 5.67-to 9.83- (Brichta et al 1988), and albino rat from 0.2-to 12.3-(Cummins 1924). The C57Bl/6J and CBA/CaJ mice also show a deviation from parallel between contralateral, synergistic pairs of canals.…”

“…Other studies show greater ranges of deviations from parallel: 11.1--33.2-in toadfish (Ghanem et al 1998) and15.32--26.78-in rabbit (Mazza andWinterson 1984). In some species, such as turtle (Brichta et al 1988) and rabbit (Mazza and Winterson 1984), the orientation of the canals differs so significantly from orthogonal that it has been suggested that the animals are particularly sensitive to rotations in some directions relative to others. However, the deviations from orthogonal reported here in mice are unlikely to be large enough to constitute a strongly preferential sensitivity to movements in particular directions.…”

“…A stereotaxic needle held in a micromanipulator has been used to determine the planar geometry of the semicircular canals in several species, including rhesus and squirrel monkey (Blanks et al 1985;Haque et al 2003), turtle (Brichta et al 1988), rabbit (Ezure and Graf 1984;Mazza and Winterson 1984), guinea pig (Curthoys et al 1975), rat (Blanks and Torigoe 1989), and man (Blanks et al 1975a). This technique, however, is unlikely to be practical or accurate for an animal as small as the mouse.…”

Geometry of the semicircular canals of the chinchilla (Chinchilla laniger)

“…Physiologic study of semicircular canal function requires accurate positioning of the head to bring a particular canal into the plane of rotation. The orientation of the plane in which each canal lies has been determined geometrically from the shape of the labyrinth in many species, including toadfish (Ghanem et al, 1998), turtle (Brichta et al, 1988), pigeon (Dickman, 1996), guinea pig (Curthoys et al, 1975), rabbit (Ezure et al, 1984;Mazza et al, 1984), cat (Blanks et al, 1972;Ezure et al, 1984), monkey (Blanks et al, 1985;Reisine et al, 1988), and human (Blanks et al, 1975a;Spoor et al, 1998;Takagi et al, 1988;Takagi et al, 1989).…”