Rodlet cells and the sensory systems in zebrafish (Danio rerio)

This preliminary work was designed to study, using routine procedures for light and transmission electron microscopy, the presence of rodlet cells (RCs) in or near the sensory systems of 12 adult specimens (4.0 +/- 1.2 cm, LT +/- SD) of zebrafish, Danio rerio Hamilton, 1822. Rodlet cells, characterized by a distinctive cell cortex (range, 0.4-1.5 microm in thickness) and conspicuous inclusions named "rodlets," have a round to ovoid nucleus with irregular outline. Mature RCs are 11.5 +/- 1.2 microm (mean +/- SD) long and 7.8 +/- 1.1 microm (mean +/- SD) wide. These cells are more numerous near neuromasts enclosed by an epithelial roof and/or ossified canal wall. In contrast, very few RCs were noticed near superficial neuromasts. Based on the presence of RCs around the two cranial neuromasts of each fish, a variable number from 1 to 15 rodlet cells was found (10.4 +/- 3.6, mean +/- SD). The RCs were located 1.5 microm (minimal) to 73.3 microm (maximal) from the neuromast (27.9 +/- 17.2, mean +/- SD). Moreover, RCs were found in olfactory epithelium and in proximity to some taste buds. Interestingly, RCs were absent in the inner ear, eye, and brain.