Department of Experimental Zoology, Centre for Ecological Research, Balaton Limnological Institute, 8237, Tihany, Hungary.
Department of Analytical Biochemistry, Institute of Biochemistry and Medical Chemistry, University of Pécs, 7624, Pécs, Hungary.
Brain Struct Funct. 2020 Nov;225(8):2563-2575. doi: 10.1007/s00429-020-02145-z. Epub 2020 Sep 20.
Perception and processing of chemical cues are crucial for aquatic gastropods, for proper elaboration of adaptive behavior. The pond snail, Lymnaea stagnalis, is a model species of invertebrate neurobiology, in which peripheral sensory neurons with different morphology and transmitter content have partly been described, but we have little knowledge regarding their functional morphological organization, including their possible peripheral intercellular connections and networks. Therefore the aim of our study was to characterize the sensory system of the tentacles and the lip, as primary sensory regions, and the anterior foot of Lymnaea with special attention to the transmitter content of the sensory neurons, and their relationship to extrinsic elements of the central nervous system. Numerous bipolar sensory cells were demonstrated in the epithelial layer of the peripheral organs, displaying immunoreactivity to antibodies raised against tyrosine hydroxylase, histamine, glutamate and two molluscan type oligopeptides, FMRFamide and Mytilus inhibitory peptide. A subepithelial plexus was formed by extrinsic serotonin and FMRFamide immunoreactive fibers, whereas in deeper regions axon processess of different origin with various immunoreactivities formed networks, too. HPLC-MS assay confirmed the presence of the low molecular weight signal molecules in the three examined areas. Following double-labeling immunohistochemistry, close arrangements were observed, formed by sensory neurons and extrinsic serotonergic (and FMRFamidergic) fibers at axo-dendritic, axo-somatic and axo-axonic levels. Our results suggest the involvement of a much wider repertoire of signal molecules in peripheral sensory processes of Lymnaea, which can locally be modified by central input, hence influencing directly the responses to environmental cues.
化学线索的感知和处理对水生腹足类动物至关重要，因为它们需要适当的适应性行为。田螺（Lymnaea stagnalis）是无脊椎动物神经生物学的模式物种，其中已经部分描述了具有不同形态和递质含量的周围感觉神经元，但我们对它们的功能形态组织知之甚少，包括它们可能的周围细胞间连接和网络。因此，我们研究的目的是描述触角和唇的感觉系统，作为主要感觉区域，以及田螺的前足，特别关注感觉神经元的递质含量及其与中枢神经系统外在元素的关系。在外周器官的上皮层中证明了许多双极感觉细胞，它们对针对酪氨酸羟化酶、组胺、谷氨酸和两种软体动物型寡肽（FMRFamide 和 Mytilus 抑制肽）的抗体具有免疫反应性。外生的 5-羟色胺和 FMRFamide 免疫反应性纤维形成了一个亚上皮丛，而在更深的区域，具有不同免疫反应性的不同来源的轴突过程也形成了网络。HPLC-MS 测定法证实了这三种检查区域中存在低分子量信号分子。在双标记免疫组织化学之后，观察到由感觉神经元和外生 5-羟色胺（和 FMRFamide 能）纤维形成的紧密排列，在轴突-树突、轴突-体和轴突-轴突水平上。我们的结果表明，在田螺的周围感觉过程中涉及到范围更广的信号分子，这些信号分子可以通过中枢输入进行局部修饰，从而直接影响对环境线索的反应。
