Study On The Characteristics Of Embryonic Stages And Late Embryonic Development Of Cerebral Cortex In Elaphe Dione

Taking Elaphe dione as the research object, this paper investigated the characteristics of different stages of emryonic development and the histological changes of cerebral cortex development, and the AChE activity of cerebral cortex was detected by colorimetry at different developmental stages. At the present time, there are few reports about the staging of embryonic development and neural development of snakes at home. The study will provide references for further research into developmental mechanism of snake neural system and other related experiments.The embryo development of Elaphe dione lasts about 35 days and the whole process can be divided into 16 stages. From the 5th stage cephalic flexure began to appear; The front neural tube regionalized and formed into cerebral vesicle at the 6th period; The embryonic body flexed and turned around, and then cephalic flexure, cervical flexure and dorsal flexure emerged at the 7th stage; The amb-prosencephalon protruded outward and formed optic vesicle, and anterior and posterior neuropore had closed at the 8th stage; Three cerebral vesicle were clearly visible at the 9th stage; Eyeball iris was observed clearly, heart differentiated into artrial and ventricular, and blood cycle initiated with heart beating at the 10th stage; From the 11th to 16th stage, heart was embedded into the body and gradually matured, and other organs were also close to those of adults.The zonation of lateral cortex, dorsal cortex and medial cortex gradually became obvious and each zone got thickened as Elaphe dione's cerebral cortex developed from late stages of embryo (including the 12th, 14th and 16th stage), larvae to adult. Medial cortex was first matured, followed by dorsal cortex and lateral cortex sequentially. The three-layer structure (namely, outer plexiform layer, cell layer and inner plexiform layer) of each zone of cerebral cortex became apparent as developmental process progressed. At the 12th stage, only the inner plexiform layer rich in tightly arranged cells was visible in cerebral cortex; At the 14th stage, the cerebral cortex can be clearly divided into three parts (lateral cortex, dorsal cortex and medial cortex); Cortex structure at the 15th stage was similar to that at the 14th stage. There were few cells in the outer plexiform layer. The outer plexiform layer of lateral cortex and dorsal cortex was relatively thin but the medial cortex thick; From the 16th stage to adult, development of lateral cortex, dorsal cortex and medial cortex gradually matured, outer plexiform layer and inner plexiform layer continued to thicken, cell layer became thinner, and the cell density in each layer decreased.Dorsal cortex cells of Elaphe dione can be divided into four categories: irregular cells, round cells, pyramidal cells and fusiform cells. Among them, irregular cells had the largest quantities, followed by round cells, pyramidal cells and fusifrom cells successively. Cerebral cortex at stage the 12th was mainly composed of irregular cells and round cells and then pyramidal cells gradually increased at the later stages. At different stages of development, the cell types scattered to all levels. There is no obvious pyramidal cell layer. Therefore, the functional specialization of the never system might be lower.The density of synapse, mitochondrium, rough endoplasmic reticulum and Gogi's body in lateral cortex, dorsal cortex and medial cortex increased from the 14th stage to adult. The periods of neuron migration, differentiation, maturation in each zone were different. The number and shape of organelles and synapses also differed. Results showed that cell development in cerebral cortex was characterized by asynchronization.AChE activity in cerebral cortex decreased gradually from the 12th to 15th stages, but then increased from the 16th stage to adult, which may have relations with the neurocyte development at the different developmental stages of cerebral cortex.