Abstract
Zinc sulfate is a known olfactory toxicant, although its specific effects on the olfactory epithelium of zebrafish are unknown. Olfactory organs of adult zebrafish were exposed to zinc sulfate and, after 2, 3, 5, 7, 10 or 14 days, fish were processed for histological, immunohistochemical, ultrastructural, and behavioral analyses. Severe morphological disruption of the olfactory organ was observed two days following zinc sulfate exposure, including fusion of lamellae, epithelial inflammation, and significant loss of anti-calretinin labeling. Scanning electron microscopy revealed the apical surface of the sensory region was absent of ciliated structures, but microvilli were still present. Behavioral analysis showed significant loss of the ability to perceive bile salts and some fish also had no response to amino acids. Over the next several days, olfactory organ morphology, epithelial structure, and anti-calretinin labeling returned to control-like conditions, although the ability to perceive bile salts remained lost until day 14. Thus, exposure to zinc sulfate results in rapid degeneration of the olfactory organ, followed by restoration of morphology and function within two weeks. Zinc sulfate appears to have a greater effect on ciliated olfactory sensory neurons than on microvillous olfactory sensory neurons, suggesting differential effects on sensory neuron subtypes.
Highlights
The peripheral olfactory organs, unlike the peripheral structures of most other sensory systems, are openly exposed to the environment, allowing exposure to a wide variety of toxicants
Irrigation of the olfactory organ with various concentrations of zinc sulfate produced degeneration of olfactory sensory neurons (OSNs), the tissue regenerated within a week
We found that exposure to zinc sulfate does differentially affect olfactory sensory neuron subtypes in adult zebrafish
Summary
The peripheral olfactory organs, unlike the peripheral structures of most other sensory systems, are openly exposed to the environment, allowing exposure to a wide variety of toxicants. Perhaps for this reason, the olfactory system is renowned for its natural neuronal turnover [1] and ability to restore critical functions related to nutrition, protection, and reproduction. Irrigation of the olfactory organ with various concentrations of zinc sulfate produced degeneration of olfactory sensory neurons (OSNs), the tissue regenerated within a week. More significant effects on olfactory organ structure were seen with prolonged exposure to the toxicant, and little regeneration occurred
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