Extracellular potassium and calcium ion concentration, field potential (Fp), local EEG and cortical impedance were measured continuously in the cortex and hippocampus of the pentobarbital anesthetized gerbils subjected to 5-minute ischemia produced by bilateral carotid occlusion. Extracellular potassium ([K+]e) and extracellular calcium ([Ca++]e) showed a triphasic change during ischemia followed by a biphasic change after recirculation. The EEG became flat within about 20 seconds. There was a sharp increase in the [K+]e and a sharp decrease in the [Ca++]e, which coincided with the sharp increase in the Fp around one and a half minutes. The impedance increased simultaneously with a large amplitude change of EEG. The [Ca++]e continued to decrease for another 1-2 minutes before returning to the normal values after recirculation whereas the [K+]e began to decrease immediately. The extracellular space (ECS) did not change until depolarization. The rise of the [K+]e and [Ca++]e in the pre-depolarization phase was not explained by the shrinkage of the ECS. The possible explanation for the change of the [Ca++]e in ischemia was discussed.

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Contact microradiographic study and histological study were performed to investigate the sequential changes in the bone marrow after a large dose of vinblastine or colchicine administration. Rats were injected intravenously with various dose of vinblastine or colchicine. The following dynamic histological changes were noted in the bone marrow in the vinblastine 2.0 µmol/kg and colchicine 2.5 µmol/kg-injected groups: Necrosis of the bone marrow cells waS observed in the early stage and the necrotic bone marrow cells were replaced by many fibroblast-like cells. After that, the fibroblast-like cells disappeared and the network-like calcified tissue replaced the region where the fibroblast-like cells existed previously. The osteoblasts were lined on the surface of the ectopic calcified tissue and then the osteoblasts were replaced by the typical osteoclasts. In consequence of this dynamic alternation of the cells, the ectopic calcified tissue decreased and the normal bone marrow cells increased in the bone marrow cavity. The ectopic calcification could hardly be observed in the area where the fibroblast like cells had not appeared. These findings suggested that the markedly proliferated fibroblast-like cells in the marrow cavity after the administration of vinblastine or colchicine may differentiate to osteoblasts and that the osteoclasts may be derived from the bone marrow cells which had already recovered from the toxic effect of the drugs. The mechanism of the dynamic histological changes in the bone marrow remains to be investigated.

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The purpose of this study was to carry out the histomorphometric assay on the mandibular condylar tissue of the growing rats Male rats of the Wistar strain at the age of 3, 4, 6, 8 and 10 weeks were used. All rats were injected intravenously with tetracycline and calcein, respectively. They were killed 12 hours after calcein injection. Before embedding in acrylic resin, 3 reference points were marked directly on each condyle to establish the reference plane for the histomorphometry on the ground section. After preparing the ground section, the growth rate of the condyle was obtained by measuring the distance of the two different fluorescent labeling lines. Furthermore, the age-related changes of the relative distribution of the bone, calcified cartilage and prebone (uncalcified bone matrix) were measured under a light microscope by using a grid on the eyepiece reticle. The number of osteoblasts and osteoclasts were also calculated in the same specimen. The following results were obtained: (1 ) The thickness of the cartilaginous layer and the growth rate of the endochondral bone formation decreased with age. (2) The relative ratio of the bone area in the subchondral tissue increased constantly with age

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We have isolated a DNA fragment containing exon I of rat cellular proto-oncogene of K-ras and sequenced the exon I. The obtained sequence was compared with that of the corresponding region in viral oncogene of Kirsten strain of murine sarcoma virus (Ki-MSV). The results showed that the exon I sequences of cellular K -ras genes in rat and human cells could encode the same amino acid sequence, while the viral K -ras gene could code for two different amino acids corresponding to the 12th and 37th positions from the N-terminus of K -ras gene product. The amino acid substitutions found between viral and cellular K- ras genes are discussed in relation to the transforming ability of Ki-MSV.

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