BACKGROUND For marine snails, olfaction represents a crucial sensory modality for long-distance reception, as auditory and visual information is limited. The posterior tentacle of Aplysia, the rhinophore, is a chemosensory organ and several behavioural studies showed that the rhinophores can detect pheromones, initiate orientation and locomotion toward food. However the functional neuroanatomy of the rhinophore is not yet clear. Here we apply serotonin-immunohistochemistry and fluorescent markers in combination with confocal microscopy as well as optical recording techniques to elucidate the structure and function of the rhinophore of the sea slug Aplysia punctata. RESULTS With anatomical techniques an overview of the neuroanatomical organization of the rhinophore is presented. Labelling with propidium iodide revealed one layer of cell nuclei in the sensory epithelium and densely packed cell nuclei beneath the groove of the rhinophore, which extends to about two third of the total length of the rhinophore. Serotonin immunoreactivity was found within the olfactory glomeruli underneath the epithelium as well as in the rhinophore ganglion. Retrograde tracing from the rhinophore ganglion with 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide (DiA) demonstrated the connection of glomeruli with the ganglion. Around 36 glomeruli (mean diameter 49 microm) were counted in a single rhinophore. Fluorimetric measurements of intracellular Ca2+ levels using Fura-2 AM loading revealed Ca2+-responses within the rhinophore ganglion to stimulation with amino acids. Bath application of different amino acids revealed differential responses at different positions within the rhinophore ganglion. CONCLUSION Our neuroanatomical study revealed the number and position of glomeruli in the rhinophore and the rhinophore ganglion as processing stage of sensory information. Serotonin-immunoreactive processes were found extensively within the rhinophore, but was not detected within any peripheral cell body. Amino acids were used as olfactory stimuli in optical recordings and induced sensory responses in the rhinophore ganglion. The complexity of changes in intracellular Ca2+-levels indicates, that processing of odour information takes place within the rhinophore ganglion. Our neuroanatomical and functional studies of the rhinophore open up a new avenue to analyze the olfactory system in Aplysia.

中文翻译：

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Aplysia punctata鼻犀的功能神经解剖学。

背景技术对于海洋蜗牛，嗅觉代表了对于长距离接收的关键感觉方式，因为听觉和视觉信息受到限制。海藻的后触手是一种化学感应器官，一些行为研究表明，该犀牛可以检测信息素，启动食物的定位和运动。然而，犀牛的功能性神经解剖学尚不清楚。在这里，我们应用5-羟色胺免疫组织化学和荧光标记物与共聚焦显微镜以及光学记录技术相结合，阐明海参Aplysia punctata的犀牛的结构和功能。结果借助解剖学技术，对犀牛的神经解剖学组织进行了概述。用碘化丙啶标记表明，在感觉上皮细胞中有一层细胞核，而在荧光团的凹槽下方则是密集堆积的细胞核，延伸到整个荧光团长度的三分之二。血清素的免疫反应性在上皮下面的嗅球和鼻咽神经节中发现。从犀牛神经节的逆行示踪与4-（4-（二十六烷基氨基）苯乙烯基）-N-甲基碘化碘（DiA）证明肾小球与神经节的联系。在单个犀牛中计数了约36个肾小球（平均直径49微米）。使用Fura-2 AM加载液对细胞内Ca2 +水平进行荧光测定，结果表明，鼻基神经节内的Ca2 +对氨基酸刺激的反应。浸浴不同氨基酸后，在犀牛神经节内的不同位置显示出不同的反应。结论我们的神经解剖学研究揭示了作为信息处理阶段的犀牛和犀牛神经节中肾小球的数量和位置。5-羟色胺免疫反应过程广泛存在于犀牛体内，但未在任何外周细胞体内检出。氨基酸在光学记录中用作嗅觉刺激，并在犀牛神经节中诱导感觉反应。细胞内Ca2 +水平变化的复杂性表明，气味信息的处理发生在犀牛神经节内。我们对犀牛的神经解剖学和功能研究开辟了一条新的途径来分析海藻中的嗅觉系统。