Study On The Development And Neuron Morphology Of SAC In Chick Tectum

Optic tectum of mesencephalon is a very important component in the avian visual andoptical information pathway, being obvious delaminate structure with alternatearrangement of grey matter and white mater. The morphological character anddevelopmental rule of stratum album centrale (SAC) within chick optic tectum in differentembryonic days, the cytoarchitecture and morphology of neurons that projecting to nucleusrotundus in chick SAC were observed and analysed using Nissl staining, Golgi-Coxmethod, and DiI nerve labeling technique to furtherly understand formation mechanism ofvisual and optical information pathway in chick. The results showed that the averagethickness of SAC, its thickness proportion in whole layer of tectum, and the thickness indifferent regions are all different in different developmental periods of embryo. In the E11,E14, E17and E20embryo days, the average thickness of SAC is133.95±9.66μ m,157.38±13.83μ m,162.88±10.05μ m, and163.09±16.98μ m (mean±SD, n=40)respectively. Their thickness proportions in whole layer of tectum is24.42%,28.13%,28.06%, and28.04%respectively. The average thickness of dorsal SAC is129.47±13.83μ m,138.61±7.81μ m,143.44±11.52μ m, and145.68±12.32μ m respectively. Theaverage thickness of lateral SAC is139.05±11.68μ m,147.54±16.17μ m,149.91±12.39μ m,154.27±6.72μ m respectively. The average thickness of dorsal SAC is129.47±13.83μ m,138.61±7.81μ m,143.44±11.52μ m, and145.68±12.32μ m respectively.Whereas the average thickness of ventral SAC is154.84±9.32μ m,169.07±15.84μ m,173.43±11.05μ m,174.57±13.19μm respectively. It indicated that the developmentalspeed of SAC in E11~E17is rapid, in E17~E20is slow. Developmental speed differ indifferent regions of SAC. That in lateral part is faster than those in dorsal and ventral ones,almost finishing embryonic development in E17. Whereas those in dorsal and ventral partfinish development until E20. The shape of soma of SAC neurons is mainly triangular, ovaland polygonal. The dendrite fields, long diameter, short diameter, and area of SAC neuronsis167.79±47.03μ m,17.73±5.32μ m,8.52±1.79μ m and150.39±38.03μ m (mean±SD, n=1500) respectively. The proportion of type SAC I cells which having2~3primarydendrites is,42.45%. That of type SAC II cells which having more than4primarydendrites is57.55%(n=478). Soma size of SAC neurons was analysed according to theprescribing of giant, large, middle and small cells. The giant cells, whose soma area aremore than250μm2, occupy2.33%. The large cells, whose soma area are more100～175μm2, occupy29.27%. The middle cells, whose soma area are100～174μm2,occupy64.13%. The small cells, whose soma area are less than100μm2, occupy4.27%(mean±SD, n=1500). The dendrite fields of SAC cells are50.08μm to470.26μm (167.79±47.03μm, n=1500). According to the size of dendrite fields, they were divide intonarrow dendrite field, middle dendrite field, and wide dendrite field. The narrow ones, being less than100μm, occupy4.93%. The middle ones, being100-200μm, occupy77.33%. The wide ones, being larger than200μm, occupy17.73%(mean±SD, n=1500).After injecting DiI into nucleus rotundus, few labeling cells were also observed in SACapart from the abundant labeling cells in SGC and nucleus SP/IPS. But their number is less.It suggested that a small part of SAC cells project to nucleus rotundus. A number ofnervous fibers labeled with DiI were also seen in SAC. They may be mainly composed ofthe axons that projecting to nucleus rotundus or nucleus SP/IPS from SGC.