Exposure to Zinc Sulfate Results in Differential Effects on Olfactory Sensory Neuron Subtypes in Adult Zebrafish

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.

Rearrangement of Actin Microfilaments in the Development of Olfactory Receptor Cells in Fish

“…Unlike the results of existing studies on mice, so far, only GAP-43 has been identified as an iOSN histochemical antigen for fish 32 , 33 . It turns out that calretinin, which is typically present in iOSNs of mice 30 , colours only mature OSNs in fish and may be observed at varying extents in ciliated, microvillar and crypt OSNs 34 – 40 .…”

The Olfactory System of Zebrafish as a Model for the Study of Neurotoxicity and Injury: Implications for Neuroplasticity and Disease

“…The fish olfactory sensory epithelium (OE) is in direct contact with the aquatic environment, and thus it is particularly vulnerable to exposure to waterborne pollutants, chemical toxicants, and direct injury. Damage to the olfactory system can impair olfactory function through various mechanisms affecting its different components: (1) by acting as olfactory signals (i.e., binding directly to ORs and reducing sensing of odorants) [6]; (2) by reducing odor perception and processing (e.g., through OSN injury or death) [19]; and (3) by affecting odor-dependent behaviors (e.g., reducing social behaviors) [95]. The effects of toxicants and injury on olfactory organ morphology can be studied by assessing tissue and cellular alterations through histological, immunohistochemical, and ultrastructural techniques.…”

“…Given that odors mediate behaviors essential for survival, the olfactory system is equipped with wide-ranging neuroplasticity, remodeling, and regeneration mechanisms following damage [3,4,5,18,19,20], thus making it an excellent model to study repair responses following toxicant exposure and injury. In this section, we review results from several studies that have addressed the impact of a variety of toxicants, as well as the morphological and behavioral effects of chemical and physical lesioning on the olfactory system of zebrafish, as well as regeneration and repair mechanisms following damage.…”

“…In zebrafish, it produces substantial damage to the olfactory sensory epithelium with a marked decrease in ciliated OSNs and an associated reduction of detection of bile salts and amino acids, to a lesser extent. Additionally, the anosmia produced by Zn treatment induces a stress response accompanied by anxiety-like behaviors and a reduction in locomotor activity [19,88,133].…”

“…In particular, zebrafish is an ideal model for studying the olfactory system, since its anatomical components are more accessible in this animal than other vertebrates. This makes the zebrafish olfactory system very amenable to experimental manipulations with less invasive techniques, increasing the rate of survival and recovery [10,11,17,18,19]. Another key characteristic of zebrafish is that it presents a high degree of central nervous system (CNS) regeneration, including the olfactory system, following damage [18,20,21,22,23,24,25].…”