Yoshiro Kameyama

Developmental brain abnormalities accompanied with the retarded production of S-100β protein in genetic polydactyly mice

The homozygotes of a mouse strain with genetic polydactyly (Polydactyly Nagoya, Pdn) exhibit various brain malformations including exencephaly in about 20%. In the present report, the brains of homozygotes (Pdn/Pdn) which were not exencephalic were examined morphologically and biochemically. Homozygous newborn brains showed hydrocephaly, some gyri on the cerebral hemisphere, absence of the corpus callosum, absence of the commissura anterior, absence of the fornix and commissura fornicis, protuberance of the cortical tissue from the brain surface, and abnormal architecture of the hippocampus. An irregular mass of olfactory nerve was observed on the cribriform plate, and the olfactory bulb was deficient. From these findings, we considered Pdn/Pdn as a kind of arhinencephalic mouse. Nervous tissue-related proteins, S-100 alpha, S-100 beta, creatine kinase B (CK-B), neuron-specific gamma-enolase, guanosine triphosphate binding proteins (Go alpha, Gi2 alpha and G beta) were immunoassayed in the cerebrum of Pdn/Pdn embryos and newborns. Among the protein analysed, only S-100 beta of Pdn/Pdn showed a significantly lower level than that of +/+ cerebrum during the observation period. The newborn brains were examined immunohistochemically using S-100 alpha, S-100 beta, CK-B, Go alpha and NSE antibodies. We could find no differences in the staining patterns among the Pdn/Pdn, Pdn/+ and +/+ brains.

Impaired development of lens fibers in genetic microphthalmia, eye lens obsolescence, elo, of the mouse.

An autosomal dominant microphthalmia (Eye lens obsolescnece, Elo) in the mouse was examined for early pathological changes in the developing lens. The first change was detected on day 12 of gestation, i.e. elongation of the central lens fibers at the basal cytoplasm was impaired. Necrotic cells were found among the central fiber cells, these cells never reached full maturation length and progressively degenerated thereafter. As a consequence, the lens in the late fetal stage was small and deformed. Initial cytological changes of this mutant were the appearance of numerous lysosomal bodies and the destruction of mitochondria at the basal cytoplasm of the lens fibers, and nuclei with dilated perinuclear cisterna. Swelling of lens fibers, known as the earliest catalytic changes, was not observed in this mutant. The impairment of fiber elongation concomitant with the destruction of mitochondria at the basal cytoplasms was characteristic of this mutant. A possible cause for the lens maldevelopment in this mutant was discussed.

Developmental disturbance of rat cerebral cortex following prenatal low-dose γ-irradiation: A quantitative study

Pregnant rats were exposed to a single whole-body gamma-irradiation on Day 15 of gestation at a dose of 0.27, 0.48, 1.00, or 1.46 Gy. They were allowed to give birth and the offspring were killed at 6 or 12 weeks of age for microscopic and electron microscopic examinations of the cerebrum. Their body weight, brain weight, cortical thickness, and numerical densities of whole cells and synapses in somatosensory cortex were examined. Growth of the dendritic arborization of layer V pyramidal cells was also examined quantitatively with Golgi-Cox specimens. A significant dose-related reduction in brain weight was found in all irradiated groups. Neither gross malformation nor abnormality of cortical architecture was observed in the groups exposed to 0.27 Gy. A significant change was found in thickness of cortex in the groups exposed to 0.48 Gy or more. Cell packing density increased significantly in the group exposed to 1.00 Gy. Significant reduction in the number of intersections of dendrites with the zonal boundaries were found in the groups exposed to 0.27 Gy or more. There was no difference in the numerical density of synapses in layer I between the control and irradiated groups. These results suggested that doses as low as 0.27 Gy could cause a morphologically discernible change in the mammalian cerebrum.

Pathogenesis of Ochratoxin A‐ and Concanavalin A‐Induced Exencephalies in Mice

Abstract Early morphogenetic changes of exencephaly induced by ochratoxin A (OA) were compared with those induced by concanavalin A (Con A) in mice in order to examine possible differences in the pathogenesis of neural tube defect. OA and Con A were administered to pregnant mice on day 7 of gestation, and the process of neural tube closure of embryos was observed at different times from 6 to 72 hours after treatment by SEM and light microscopy. In OA‐treated embryos, the cranial neural folds in the fore‐ and midbrains did not elevate and remained in the biconvex shape. The cellular changes were found in the neuroepithelium and surface ectoderm. Neural crest cells, which appeared at the lateral edges of the neural folds, were also involved in degeneration. In Con A‐treated embryos, the neural folds in the mid‐ and hindbrains elevated to assume the V shape, but remained wide open. The main cellular change was a degeneration of the primary mesenchyme underlying the neuroepithelium, resulting in a paucity of the supporting mesenchymal tissue.

Organ culture and immunohistochemistry of the genetically malformed lens, in eye lens obsolescence, Elo, of the mouse.

The central lens fibers of genetically microphthalmic mice (Eye lens obsolescence, Elo) continue to necrose from the early stage of lens development, whereas morphological defects are not observed in the lens epithelium, equatorial zone of the lens and the other ocular tissues. We attempted to determine whether or not this occurrence in the lens of Elo mice was related to extraocular factors such as nutrition and secondly if a possible mal-synthesis of γ-crystallin could be involved. The first problem was investigated using organ cultures of the eye rudiments excised from day 10 and day 11 embryos. The typical Elo lens developed on the artificial nutrients, indicating that pathogenesis of the Elo is independent of the extraocular environment. The second problem was investigated using immunohistochemistry. The synthesis of γ-crystallin in the lens of the Elo and the normal was similar, thereby suggesting that the necrotic process in the lens fibers of the Elo is not due to defects in γ-crystallin synthesis.

Prevention of Genetic Polydactyly in Polydactyly Nagoya (Pdn) Mice in Vitro by Surgical Treatment of Foot Plate during Embryogenesis

Abstract Pdn/Pdn fetuses show preaxial Polydactyly of duplicated or triplicated metacarpal/metatarsal type in the fore‐ and hindlimbs. Pdn/+ fetuses show one extra digit of distal phalangeal type preaxially in the hindlimb and deformity of distal phalanx of the 1st digit in the forelimb. Normal patterns of physiological cell death in the preaxial apical ectodermal ridge (AER) and the deep preaxial mesoderm (fpp) were disrupted in Pdn/Pdn embryos. It was supposed that delayed involution of preaxial AER might have caused the abolishment of fpp, which in turn could have induced polydactyly in Pdn/Pdn.

Effects of TRH on acquisition and extinction of shuttlebox-avoidance behavior in Fischer344 rats

Thyrotropin-releasing hormone (TRH) was injected intraperitoneally into male Fischer344 rats in doses ranging between 1 mg/kg and 20 mg/kg to assess the effects on the acquisition and extinction of shuttlebox-avoidance behavior. Administration of 20 mg/kg TRH resulted in a rapid acquisition of avoidance behavior in early training trials. This enhancement did not involve changes in the occurrence of anticipatory responses to an inevitable shock but was correlated with an increase of concurrent intertrial-responses. Thus, the behavioral changes observed would be a reflection of TRH-induced changes on motor activity. TRH treatment did not alter the resistance to extinction of the avoidance response. This finding is corroborated by the fact that rats given the TRH treatment withheld the well-learned response to a warning signal, when this response was selectively punished after initial acquisition stage.

Avoidance Learning Deficits in Prenatally Gamma-Ray Irradiated Rats

Abstract Pregnant female rats of the Fischer344 (F344/Du Crj) strain were exposed to gamma‐ray radiation of 1.46Gy on day 15 of gestation (vaginal plug = day 0). When male offspring of control and irradiated dams matured, they were trained with various avoidance conditioning paradigms. In the avoidance acquisition paradigm in which one of the tone‐on and lights‐off signals was presented with predetermined random sequences, the irradiated group had lower overall rates of active avoidance responding than controls. In the go/no‐go (active‐passive) discrimination avoidance paradigm after rats learned only active avoidance responses to these two different signals, irradiated rats established stable active avoidance rates under the go (tone‐on) signal, while they decreased gradually the rate of passive avoidance responding to the no‐go (lights‐off) signal as the amount of discrimination training increased. In the standard avoidance acquisition paradigm in which only the lights‐off signal was used, the irradiated group also was inferior in active avoidance learning to controls. However, the irradiated group showed a high level of anticipatory responding, which was maintained in avoidance conditioning paradigms even though no shock‐avoidance contingency was operating. These results indicated that poor associative ability for the warning signal and the shock might result in the active avoidance learning deficits in irradiated rats, and that active responding was more persistent and passive responding declined due to response excitation within a shock paradigm over the subsequent further training.

Abnormal Cerebral Vascularity in Mice with Histogenetic Disorders of the Cerebral Cortex and Postnatal Manifestation of Hydrocephalus

Abstract Pregnant mice were exposed to 60Co gamma‐irradiation on day 13 of gestation, and the offspring after birth were examined in histological sections and microvascular specimens with India ink, in order to know the pathological changes leading to postnatal manifestation of hydrocephalus. The cerebrospinal fluid pressure was also measured.

Developmental abnormalities of mouse cerebellum induced by intracisternal injection of ochratoxin A in neonatal period

Ochratoxin A, one of the food-contaminating mycotoxins, is known to impair brain development in mammals. Slc:ICR mice were treated intracisternally with a single dose of 5 micrograms ochratoxin A on day 0, 1, 2, 4, 5, or 7 after birth, in order to examine the direct effects of ochratoxin A on cerebellar development. The mice in each group were killed at 30 days of age, and the brains examined by light microscopy. Body and total brain weights were reduced (7 to 15%) in the treated groups. Cerebellar weight was also significantly reduced (18 to 27%) in all treated groups. In mice treated on day 0, 1, or 2, the layered structure of the vermis was well preserved, but some animals treated on day 4, 5, or 7 had cerebella with disarranged cortical structure. The number of folia decreased and the foliation index showed a significant decrease in the groups treated on days 0, 1, and 2.