Both classification problems and quantitative structure-activitity relationship (QSAR) analyses of drugs have been better studied by the multi-layer feedforward neural networks with back-propagation learning algorithm (BPNN), than the classical methods in pattern recognition such as linear multiple regression (LMR) or adaptive least square method (ALS), since those problems often involve nonlinear relationships between descriptors and the class (/activity).1,2) BPNN is surely powerful and interesting approach, however, it has the defects such as the problem of local minimum, overfitting etc.3,4) Recently Bayesian regularized neural networks (BRNN), 5,6) has been successfully applied for QSAR studies 7,8) even for massive sample data, 9) but this excellent framework is rather complicated and needs much computation time in general.Kohonen developed the unsupervised learning algorithm that simplified the mapping mechanism of the relatively homogeneous structures found in mammalian brains associated with the processing of sensory data, 10) and showed it possible to generate self-organizing map (SOM) of data. It is an essential characteristic of Kohonen's SOM that has the ability to project high-dimensional data onto two-dimensional visualized map which is suitable for easy analysis while preserving the most significant information. Therefore, SOM is applied to extensive problems that characteristics of complicated data structure in high-dimensional space can be grasped visually from two-dimensional maps, and plays an important role to analyze inherent data structure.The advantage of the SOM, compared with some other projection methods is that the algorithm is very simple, straightforward to implement, and fast to compute. In the field of pharmaceutical sciences, the SOM was applied for searching useful drugs. Anzali at al. generated SOMs as a two-dimensional representation of molecules to analyze the shape and surface properties of those three-dimensional molecules responsible for biological activity. After visual comparison of SOMs, they discovered the benzothiadiazole group as a surrogate for methylendioxyphenyl. 11,12) Tetko et al. used SOMs to compress the so many input CoMFA data in their three-dimensional QSAR studies. 13) In the former study, we obtained the SOM of norbornann derivatives and of carbonyl compounds, and showed that the classification of them into some groups was successfully achieved according to the clustering appeared in the gray map. 14)In this paper we use the SOM as a method to predict missing activity in the QSAR studies of carboquinone and benzodiazepine, somewhat different usage of SOM rather than the standard compression or visualization tool of data. Results of the calculation indicate that SOM is considered to be one of useful methods in QSAR study.The Generation of SOM and the Prediction of an Activity Kohonen's neural network consists of two layers, the first layer is the input layer of n-dimension and the second is the competitive layer where every neuron has ncomponents correspon...

Summary. Thrombocytes of early chick embryos were observed in blood smear and whole embryo preparations stained with PAS. In the blood smear preparations, thrombocytes usually had one large glycogen mass in the cytoplasm until 3 days of incubation, and it became progressively smaller with the advance of embryonal development. While, the application of PAS to whole embryo preparations was shown to be a very useful method for observation of the blood cells in embryos at early stages when their blood could not be collected. Thrombocytes were clearly identified in situ in the embryo by PAS staining even in very early stages when no blood circulation occured. At stage 12, distribution of the thrombocytes coincided with that of blood islands, but was limited within the area opaca. Mitotic figures of the thrombocytes were frequently found in and near the blood islands. This suggests that blood islands are the proliferation sites of the thrombocytes in early chick embryos.The morphology of thrombocytes which are involved in blood coagulation has recently been investigated intensely in the bird by electron microscopy (MAXWELL and TREJO, 1970; DAIMON et al., 1977;DAIMON and UCHIDA, 1978). However, differentiation of the thrombocytes in the developing embryo, especially in the early stages of development , is poorly understood.As the thrombocytes contain much glycogen in their cytoplasm, the PAS technique , which selectively stains polysaccharide, is very advantageous for the identification of thrombocytes from other blood cells under the light microscope.Thrombocytes taken from the 2-day-old embryo, which was the earliest embryo in which blood collection was possible, were already identifiable by PAS staining (OMORI et al., 1979) . Since the chick embryo, and especially the early blastoderm, is extremely thin, it is easy to observe the inner cells directly through the epiblast under a microscope without sectioning (UKESHIMA and FUJIMOTo, 1975).In the present study, thrombocytes of chick embryos prior to initiation of blood circulation were investigated by application of the PAS technique to whole embryo preparations.257