Supplementary Material for: Convergence of Olfactory Inputs within the Central Nervous System of a Cartilaginous and a Bony Fish: An Anatomical Indicator of Olfactory Sensitivity

The volume of the olfactory bulbs (OBs) relative to the brain has been used previously as a proxy for olfactory capabilities in many vertebrate taxa, including fishes. Although this gross approach has predictive power, a more accurate assessment of the number of afferent olfactory inputs and the convergence of this information at the level of the telencephalon is critical to our understanding of the role of olfaction in the behaviour of fishes. In this study, we used transmission electron microscopy to assess the number of first-order axons within the olfactory nerve (ON) and the number of second-order axons in the olfactory peduncle (OP) in established model species within cartilaginous (brownbanded bamboo shark, <i>Chiloscyllium punctatum</i> [CP]) and bony (common goldfish, <i>Carassius auratus</i> [CA]) fishes. The total number of axons varied from a mean of 18.12 ± 7.50 million in the ON to a mean of 0.38 ± 0.21 million in the OP of CP, versus 0.48 ± 0.16 million in the ON and 0.09 ± 0.02 million in the OP of CA. This resulted in a convergence ratio of approximately 50:1 and 5:1, respectively, for these two species. Based on astroglial ensheathing, axon type (unmyelinated [UM] and myelinated [M]) and axon size, we found no differentiated tracts in the OP of CP, whereas a lateral and a medial tract (both of which could be subdivided into two bundles or areas) were identified for CA, as previously described. Linear regression analyses revealed significant differences not only in axon density between species and locations (nerves and peduncles), but also in axon type and axon diameter (<i>p</i> &lt; 0.05). However, UM axon diameter was larger in the OPs than in the nerve in both species (<i>p</i> = 0.005), with no significant differences in UM axon diameter in the ON (<i>p</i> = 0.06) between species. This study provides an in-depth analysis of the neuroanatomical organisation of the ascending olfactory pathway in two fish taxa and a quantitative anatomical comparison of the summation of olfactory information. Our results support the assertion that relative OB volume is a good indicator of the level of olfactory input and thereby a proxy for olfactory capabilities.此前，在包括鱼类在内的诸多脊椎动物类群中，研究人员常以嗅球（olfactory bulbs, OBs）相对于全脑的体积作为嗅觉能力的替代指标。尽管这种宏观评估方法具备一定预测效能，但要准确理解嗅觉在鱼类行为中的作用，更精准地测定传入嗅觉输入的数量，以及该信息在端脑层面的会聚情况，仍是至关重要的。 本研究采用透射电子显微镜，对软骨鱼类的模式物种——点纹斑竹鲨（*Chiloscyllium punctatum* [CP]），以及硬骨鱼类的模式物种——普通金鱼（*Carassius auratus* [CA]）的嗅神经（olfactory nerve, ON）内一级轴突数量，与嗅脚（olfactory peduncle, OP）内二级轴突数量进行了测定。 轴突总数量存在显著差异：点纹斑竹鲨的嗅神经轴突均值为18.12 ± 7.50百万，其嗅脚轴突均值为0.38 ± 0.21百万；而普通金鱼的嗅神经轴突均值为0.48 ± 0.16百万，嗅脚轴突均值为0.09 ± 0.02百万。据此计算，两种鱼类的轴突会聚比分别约为50:1与5:1。 基于星形胶质细胞包被情况、轴突类型（无髓鞘轴突[unmyelinated, UM]与有髓鞘轴突[myelinated, M]）以及轴突尺寸，我们发现点纹斑竹鲨的嗅脚内不存在分化的神经束；而正如此前研究所描述的那样，普通金鱼的嗅脚可分为外侧与内侧神经束，二者均可进一步细分为两个亚束或亚区域。 线性回归分析结果显示，不仅不同物种、不同取样部位（嗅神经与嗅脚）间的轴突密度存在显著差异，轴突类型与轴突直径亦存在显著差异（*p* < 0.05）。不过，两种鱼类的嗅脚内无髓鞘轴突直径均显著大于其嗅神经内的无髓鞘轴突直径（*p* = 0.005），而两种鱼类嗅神经内的无髓鞘轴突直径则无显著差异（*p* = 0.06）。 本研究对两类鱼类的上行嗅觉通路神经解剖结构进行了深入分析，并对嗅觉信息的整合情况开展了定量解剖学比较。研究结果支持“嗅球相对体积可作为嗅觉输入水平的良好指标，进而可作为嗅觉能力的替代评估指标”这一论断。