The giant freshwater prawn, Macrobrachium rosenbergii, is an economically important crustacean species which has also been extensively used as a model in neuroscience research. The crustacean central nervous system is a highly complex structure, especially the brain. However, little information is available on the brain structure, especially the three-dimensional organization. In this study, we demonstrated the three-dimensional structure and histology of the brain of M. rosenbergii together with the distribution of serotonin (5-HT) in the brain and ovary as well as its effects on ovarian steroidogenesis. The brain of M. rosenbergii consists of three parts: protocerebrum, deutocerebrum and tritocerebrum. Histologically, protocerebrum comprises of neuronal clusters 6–8 and prominent anterior and posterior medial protocerebral neuropils (AMPN/PMPN). The protocerebrum is connected posteriorly to the deutocerebrum which consists of neuronal clusters 9–13, medial antenna I neuropil, a paired lateral antenna I neuropils and olfactory neuropils (ON). Tritocerebrum comprises of neuronal clusters 14–17 with prominent pairs of antenna II (AnN), tegumentary and columnar neuropils (CN). All neuronal clusters are paired structures except numbers 7, 13 and 17 which are single clusters located at the median zone. These neuronal clusters and neuropils are clearly shown in three-dimensional structure of the brain. 5-HT immunoreactivity (-ir) was mostly detected in the medium-sized neurons and neuronal fibers of clusters 6/7, 8, 9, 10 and 14/15 and in many neuropils of the brain including anterior/posterior medial protocerebral neuropils (AMPN/PMPN), protocerebral tract, protocerebral bridge, central body, olfactory neuropil (ON), antennal II neuropil (Ann) and columnar neuropil (CN). In the ovary, the 5-HT-ir was light in the oocyte step 1(Oc₁) and very intense in Oc₂–Oc₄. Using an in vitro assay of an explant of mature ovary, it was shown that 5-HT was able to enhance ovarian estradiol-17β (E₂) and progesterone (P₄) secretions. We suggest that 5-HT is specifically localized in specific brain areas and ovary of this prawn and it plays a pivotal role in ovarian maturation via the induction of female sex steroid secretions, in turn these steroids may enhance vitellogenesis resulting in oocyte growth and maturation.

中文翻译：

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脑的三维组织和5-羟色胺在脑和卵巢中的分布，及其对巨型淡水虾罗氏沼虾卵巢类固醇生成的影响。

巨型淡水虾罗氏沼虾（Macrobrachium rosenbergii）是经济上重要的甲壳类动物，也已广泛用作神经科学研究的模型。甲壳类中枢神经系统是高度复杂的结构，尤其是大脑。但是，关于大脑结构，尤其是三维组织的信息很少。在这项研究中，我们证明了罗氏沼虾的脑三维结构和组织学，以及5-羟色胺（5-HT）在脑和卵巢中的分布及其对卵巢类固醇生成的影响。罗氏沼虾的大脑由三部分组成：前脑，中脑和三脑。在组织学上，前脑由神经元簇6-8和突出的前，后内侧前脑神经枕（AMPN / PMPN）组成。原始大脑后部连接到氘代大脑，后者由神经元簇9-13，内侧触角I神经柱，成对的外侧触角I神经柱和嗅觉神经柱（ON）组成。三角脑由神经元簇14-17组成，其中有突出的触角对II（AnN），外皮和柱状神经柱（CN）。除数字7、13和17是位于中间区域的单个集群外，所有神经元集群都是成对的结构。这些神经元簇和神经绒毛清楚地显示在大脑的三维结构中。5-HT免疫反应性（-ir）主要在簇6 / 7、8、9、10和14/15的中型神经元和神经元纤维以及包括前/后内侧脑前神经在内的许多大脑神经纤维中检测到（-ir）（ AMPN / PMPN），前脑束，前脑桥，中心体，嗅觉神经neuro（ON），触角II神经pil（Ann）和柱状神经pil（CN）。在卵巢中，5-HT-ir在卵母细胞步骤1（Oc₁），并且在Oc ₂ -Oc _4中非常强烈。使用体外检测成熟卵巢的外植体，结果表明5-HT能够增强卵巢雌二醇17β（E ₂）和孕酮（P ₄）的分泌。我们建议5-HT专门定位在该虾的特定大脑区域和卵巢中，并通过诱导雌性类固醇分泌在卵巢成熟中起关键作用，进而这些类固醇可能会增强卵黄发生，从而导致卵母细胞生长和成熟。