Dendritic arbors on the saccule and lagena in the ear of the goldfish, Carassius auratus

Abstract

The ear of the goldfish ( Carassius auratus) contains three otolithic endorgans: the saccule, lagena, and utricle. The saccule has an auditory function in most teleost fishes for whom data are available, and there is evidence that the lagena is also an auditory endorgan in the goldfish. This study was conducted to compare the innervation of the saccule and the lagena to one another and to previously published data from goldfish and other species. We placed cobaltous-lysine in saccular and lagenar nerves in vivo and permitted uptake over 18–24 h. A total of 59 saccular and 59 lagenar dendritic arbors were labeled in 10 fishes. Our data indicate that arbors on the saccule and lagena have similar morphologies, but differ in relative size. Saccular arbors tend to be smaller than lagenar arbors, with median arbor widths of 50 μm on the saccule and 74 μm on the lagena. Fiber diameters on the two endorgans are similar. A regional analysis of the saccule indicated that a wide range of arbor sizes are found along the rostral-caudal axis, with larger arbors more common caudally. Our data do not support the presence of two distinct categories of saccular afferents with non-overlapping distributions. Moderate arbor widths (50–99 μm) were most common in all regions of the lagena. Maximum arbor width and hair cell density do not appear to be correlated with one another on either the saccule or the lagena. Comparisons with published data from goldfish and oscar revealed similarities and differences that may be attributable to variations in label uptake or transport as well as potential species differences.