Evans J A, Chamberlain S C, Battelle B A
J Comp Neurol. 1983 Oct 1;219(4):369-83. doi: 10.1002/cne.902190402.
The biogenic amine octopamine is synthesized from both tyrosine and tyramine in the lateral, median, and ventral eyes of Limulus. The autoradiographic studies presented here were designed to locate the sites of octopamine synthesis in the ventral and lateral eyes. We found that efferent fibers, which project to ventral and lateral eyes from the central nervous system, became intensely and selectively labeled during in vitro incubations with 3H-tyramine. In the ventral eye, more than 95% of the efferent fibers were labeled. Results of biochemical analyses suggested that most of the radioactive substance within these efferent fibers was newly synthesized octopamine. The selective labeling of efferent fibers during incubation with 3H-tyramine was used as an anatomical tool to study the number and distribution of efferent fibers within the ventral eye. Light microscopic (LM) reconstructions of the distribution of label in serial longitudinal sections through ventral optic nerves together with electron microscopic (EM) autoradiographic analyses revealed between 70 and 200 efferent axons. The results of these studies and of reconstructions of efferent innervation to photoreceptor somata suggest that each ventral photoreceptor cell or each small cluster of cells is innervated by a separate efferent fiber. Both LM reconstructions and EM analyses showed that efferent fibers ramify extensively and specifically in and near the internal rhabdom of ventral photoreceptor cells. In EM autoradiographs of lateral eyes incubated with 3H- tyramine, the silver grains that were located over ommatidia were concentrated exclusively over efferent fibers. All of these efferent fibers, which lay near rhabdoms and in partitions between retinular cells, were labeled. The results of our present studies support our hypothesis that octopamine is a neurotransmitter in Limulus retinal efferent fibers. This amine may modulate the biochemistry and physiology of ventral photoreceptor cells and may mediate many of the known effects of circadian efferent innervation to the lateral eye.
生物胺章鱼胺在鲎的侧眼、中眼和腹眼中由酪氨酸和酪胺合成。本文所呈现的放射自显影研究旨在确定章鱼胺在腹眼和侧眼中的合成位点。我们发现，从中枢神经系统投射至腹眼和侧眼的传出纤维，在与³H - 酪胺进行体外孵育时会被强烈且选择性地标记。在腹眼中，超过95%的传出纤维被标记。生化分析结果表明，这些传出纤维内的大部分放射性物质是新合成的章鱼胺。在与³H - 酪胺孵育期间对传出纤维的选择性标记被用作一种解剖学工具，以研究腹眼内传出纤维的数量和分布。通过对腹侧视神经连续纵向切片中标记分布的光学显微镜（LM）重建以及电子显微镜（EM）放射自显影分析显示，传出轴突有70至200条。这些研究结果以及对光感受器胞体传出神经支配的重建表明，每个腹侧光感受器细胞或每一小群细胞都由一条单独的传出纤维支配。LM重建和EM分析均表明，传出纤维在腹侧光感受器细胞内小网膜及其附近广泛且特异性地分支。在用³H - 酪胺孵育的侧眼的EM放射自显影片中，位于小眼上的银颗粒仅集中在传出纤维上。所有这些位于小网膜附近和视网膜细胞之间分隔处的传出纤维都被标记。我们目前的研究结果支持了我们的假设，即章鱼胺是鲎视网膜传出纤维中的一种神经递质。这种胺可能调节腹侧光感受器细胞的生物化学和生理学，并可能介导昼夜节律传出神经支配对侧眼的许多已知效应。
