Neuromorphometric features and dimensional analysis of the vestibular end organ in the little brown bat (Myotis lucifugus)

Abstract

Neuromorphometric parameters of the vestibular system were determined from serial sections of temporal bones from four little brown bats. Well-developed eminentiae cruciatae project from the cristae ampullares of the anterior and posterior membranous ampullae. A total of 4,500 bipolar ganglion cells were enumerated within the vestibular ganglion. The widths of the cell somas varied from 2.5 to 20 micrometers, with 70% of them having widths between 5.0 and 12.5 micrometers. Two maxima were observed in a curve of ganglion cell density as a function of the length of the ganglion. The first maximum indicated a density of 4,800 cells per mm2 at a length 0.20 from the apex of the ganglion (in the pars dorsalis); the second, a density of 4,750 cells per mm2 at 0.38 mm (in the pars ventralis). The morphometric parameters studied were the radii of curvature of the semicircular ducts, the cross-sectional diameters of the semicircular canals and ducts, the dimensions of the cristae ampullares and their membranous ampullae, and dimensions pertaining to the statoconial organs. Surface areas (measured from graphic projections) were determined as 0.098 mm2 and 0.016 mm2 and hair cell count 500 and 1,300 cells for the saccular and utricular maculae, respectively. The radii of curvature of the three semicircular ducts, R, were dissimilar, with the anterior duct having the largest radius (R = 0.91 mm) and the posterior duct the smallest one (R = 0.69 mm). The average cross-sectional diameters of the anterior, lateral, and posterior ducts were measured as 0.11 mm, 0.14 mm, and 0.13 mm, respectively. Some of the morphological parameters were used to ascertain information regarding the dynamics of semicircular--canal function. In particular, the coefficients theta and II in the torsion pendulum model (Steinhausen, '31; Egmond et al., '49), and the time constants xi L congruent to II/delta and xi S congruent to theta/II of the torsion pendulum model were estimated for the little brown bat from these parameters. Where appropriate, comparisons were made to time constants obtained for other species.

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

“…The anterior canal is larger than the others in both studies, consistent with the relationship found in other species including pigeon (Landolt et al, 1975), bat (Ramprashad et al, 1980), guinea pig, squirrel and rhesus monkey (Blanks et al, 1985), and man (Curthoys et al, 1977). In pigeon, the gain of anterior canal afferents has been shown to be higher than those of other canals (Dickman, 1996) and in cat, the sensitivity of the canals has been shown to correlate to their radius of curvature, with the most sensitive anterior canal being the largest and the least sensitive horizontal canal the smallest (Blanks et al, 1975b;Curthoys et al, 1977).…”

Semicircular canals and agility: the influence of size and shape measures

“…Generally, amongst mammals, the anterior canal is larger than the posterior and lateral canals. This has been demonstrated in rats (Cummins, 1925), mice (Calabrese & Hullar, 2006), chinchillas (Hullar & Williams, 2006), little brown bats (Ramprashad et al 1980), rhesus and squirrel monkeys (Blanks et al 1985), as well as guinea pigs, cats and humans (Curthoys et al 1977). This relationship is also seen in most of the wide range of mammals studied by Ramprashad et al (1984) and the large number of primates examined by Spoor & Zonneveld (1998) although the anterior and posterior canals are often very close in size and, in some cases, the radius of the posterior canal exceeds that of the anterior canal (e.g.…”

The primate semicircular canal system and locomotion

“…The mammalian sample included, in particular, the canals of groups of arboreal and terrestrial eutherian and metatherian mammals with body masses in the primate range. Previously published measurements of some species that were compatible with those taken in the current study were added (12,(16)(17)(18)(19)(27)(28)(29)(30). Wild-shot specimens were used whenever possible, and the petrosal region of each was scanned by using medical or high-resolution computed tomography (CT) at a sufficiently high resolution for accurately measuring the canals.…”