Department of Biological, Geological and Environmental Sciences, University of Bologna, 40126 Bologna, Italy.
Department of Biological, Geological and Environmental Sciences, University of Bologna, 40126 Bologna, Italy.
Aquat Toxicol. 2019 Jan;206:14-23. doi: 10.1016/j.aquatox.2018.10.011. Epub 2018 Oct 23.
The olfactory epithelium of fish includes three main types of olfactory sensory neurons (OSNs). Whereas ciliated (cOSNs) and microvillous olfactory sensory neurons (mOSNs) are common to all vertebrates, a third, smaller group, the crypt cells, is exclusive for fish. Dissolved pollutants reach OSNs, thus resulting in impairment of the olfactory function with possible neurobehavioral damages, and nickel represents a diffuse olfactory toxicant. We studied the effects of three sublethal Ni concentrations on the different OSN populations of zebrafish that is a widely used biological model. We applied image analysis with cell count and quantification of histochemically-detected markers of the different types of OSNs. The present study shows clear evidence of a differential responses of OSN populations to treatments. Densitometric values for G, a marker of cOSNs, decreased compared to control and showed a concentration-dependent effect in the ventral half of the olfactory rosette. The densitometric analysis of TRPC2, a marker of mOSNs, revealed a statistically significant reduction compared to control, smaller than the decrease for G and without concentration-dependent effects. After exposure, olfactory epithelium stained with anti-calretinin, a marker of c- and mOSNs, revealed a decrease in thickness while the sensory area appeared unchanged. The thickness reduction together with increased densitometric values for HuC/D, a marker of mature and immature neurons, suggests that the decrements in G and TRPC2 immunostaining may depend on cell death. However, reductions in the number of apical processes and of antigen expression could be a further explanation. We hypothesize that cOSNs are more sensitive than mOSNs to Ni exposure. Difference between subpopulations of OSNs or differences in water flux throughout the olfactory cavity could account for the greater susceptibility of the OSNs located in the ventral half of the olfactory rosette. Cell count of anti-TrkA immunopositive cells reveals that Ni exposure does not affect crypt cells. The results of this immunohistochemical study are not in line with those obtained by electro-olfactogram.
鱼类的嗅上皮包括三种主要类型的嗅觉感觉神经元（OSN）。纤毛（cOSN）和微绒毛嗅觉感觉神经元（mOSN）是所有脊椎动物共有的，而第三类较小的群体，即crypt 细胞，是鱼类所特有的。溶解的污染物到达 OSN，从而导致嗅觉功能受损，可能导致神经行为损伤，而镍是一种广泛存在的嗅觉毒性物质。我们研究了三种亚致死镍浓度对广泛应用于生物学模型的斑马鱼不同 OSN 群体的影响。我们应用细胞计数的图像分析和不同类型 OSN 的组织化学检测标记物的定量。本研究清楚地证明了 OSN 群体对处理的反应存在差异。与对照组相比，G（cOSN 的标记物）的密度值降低，并在嗅球的腹侧半部分表现出浓度依赖性效应。TRPC2（mOSN 的标记物）的密度分析显示与对照组相比有统计学意义的降低，小于 G 的降低，且没有浓度依赖性效应。暴露后，用抗 calretinin（c 和 mOSN 的标记物）对嗅上皮进行染色，发现厚度减小，而感觉区保持不变。厚度减小和 HuC/D（成熟和未成熟神经元的标记物）的密度值增加表明，G 和 TRPC2 免疫染色的减少可能依赖于细胞死亡。然而，顶极过程和抗原表达的减少可能是进一步的解释。我们假设 cOSN 对镍暴露比 mOSN 更敏感。OSN 亚群之间的差异或嗅腔中水流的差异可能是导致嗅球腹侧半部分 OSN 更易受影响的原因。抗 TrkA 免疫阳性细胞的细胞计数表明，镍暴露不会影响 crypt 细胞。这项免疫组织化学研究的结果与电嗅图的结果不一致。
