IMMUNOHISTOCHEMICAL LOCALIZATION OF S-100 PROTEIN IN THE SACCULE OF THE RAINBOW-TROUT (SALMO-GAIRDNERII R)

The distribution of S-100-like immunoreactivity in the trout saccule ( a presumed organ of hearing in fish) has been determined by means of i mmunohistochemistry. Within the sensory epithelium of the saccular mac ula, hair cells and myelinated saccular nerve fibers were found to be immunoreactive. Hair-cell immunoreactivity was relatively uniform thro ughout the macula except at the extreme periphery (rostral, caudal, ve ntral and dorsal), where staining was either decreased or absent. The immunoreactivity associated with myelinated nerve fibers was greatest at the peripheral edges of the nerve processes, a position correspondi ng to the location of Schwann cells. However, the nerve processes them selves (within and subjacent to the sensory epithelium), as well as ce ll bodies within the saccular nerve, were also immunoreactive. Thus, t he immunoreactivity of the saccular nerve observed above the basal lam ina can be attributed to the saccular nerve processes as well as to ne rve-associated Schwann cells. Overall, the immunoreactivity displayed by hair cells was less intense than that associated with myelinated sa ccular nerve, as evidenced by a disappearance of signal in hair cells first, upon serial dilution of antibody. No S-100-like immunoreactivit y was observed in supporting cells within the sensory epithelium or in epithelial cells in non-sensory regions. A concentration of S-100-lik e immunoreactivity in hair cells and saccular nerve is suggestive of t he presence of S-100 calcium-binding protein-mediated activities in th ese cell types.