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Morphology and development of nucleus subpre-tectalis /interstito-pretectalis-subpretectalis (SP/IPS), its cytoarchitecture, distribution of some neuron peptides, and morphology of its cells which projected to Rt, were studied by DiI retrogradely labeling, axonal trace with WGA-HRP, Nissl staining, and immunohistochemistry method. The results showed that n. SP/IPS is round or ellipse. By WGA-HRP labeling, the average long diameter, short diameter and area of n. SP/IPS are 410.3±57.4μm, 331.3±30.2μm and 1.23±0.23 × 10~5μm~2 respectively. After Nissl staining, the average long diameter, its short diameter and area are 728.6±138.72μm, 490.7±115.27μm and 2.93±0.72 × 10~5μm~2 respectively. It indicated that only a part of its cells project to Rt. Observation on the development showed that the average diameters and areas in E11, E14, E17 and E20 were 581.39± 117.83μm and 2.04 ± 0.56 × 10~5μm~2, 597.92 ± 116.27μm and 2.06±0.61 × 10~5μm~2, 679.29±123.26μm and 2.17 ± 0.68×10~5μm~2, 759.60±135.82μm and 3.31 ±0.71 × 10~5μm~2, respectively. The soma and dendrites of the neurons in this nucleus were successfully labeled by DiI retrograde labeling method. According to the amount of its primary dendrites, the labeled cells can be divided into two types, type1 cell and type2 cell. Based on the amount of the secondary dendrites, these cells were further divided into simple and complex cells respectively. The average long diameter, short diameter and area of typel cells were 26.72μm, 19.04μm and 442.28μm~2 respectively. Those of type 2 cells were 32.55μm, 21.75μm and 653.11μm~2 respectively, and they are obvious larger than those of type 1 cells. In the Nissl staining samples, Nissl body and the nucleolus in the neurons could be clearly seen. The cells showed round, oval, triangular, and polygonal etc. The average area, long diameter and short diameter were 91.3±28.92μm~2, 14.5±3.27μm and 8.15±1.86μm respectively. According to their diameter, the cells were divided into large cells( φ >15μm), medium cells (φ10~15μm) and small cells (φ< 10μm). The amount of medium cells was most that of the large cells was fewest. The percentage of large, medium and small cells was 4.51%, 67.96% and 27.53% respectively. Using immunohistochemistry method, the immunoreactionpositive cells of VIP, SP, and NPY in n. SP/IPS were all observed. VIP immunoreaction positive cells and fibers were most, could be seen in the ventral and medial of n. SP/IPS. Substance P and NPY immunoreaction positive cells were mainly seen in P3, the former could be seen in the ventral of n. SP/IPS, and the latter were seen in the middle and lateral of n. SP/IPS. VIP positive cells could be seen in the nucleus of Ell, E14, E17 and E20. They were mainly seen in the medial, some presented in the ventral occasionally.
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