Kunio Doi

Distribution of N-methyl-D-aspartate receptors (NMDARs) in the developing rat brain

The N-methyl-D-aspartate receptor (NMDAR), which is one of the glutamate receptors, is considered to have a close relationship to synaptic plasticity in the developing brain. In addition, it is known that the excessive stimulation of NMDARs can trigger neuronal apoptosis. In this study, we examined the distribution of NMDAR subunits [anti-NR1, NR2(A-C)] in the developing rat brain immunohistochemically. As a result, NR1, an essential subunit for the formation of a functional NMDAR complex, was mildly expressed in the restricted areas such as the temporal region of the cerebral cortex and the hippocampus in the fetal brain at Embryonal Days 18 and 20. On the other hand, in neonates, NR1 was expressed widely throughout the whole brain. The distributions of NR2A and NR2C showed temporal and spatial similarities to that of NR1, while the expression of NR2B showed differences in the intensity and distribution. A progressive change in subunit expression seen prenatally and postnatally could contribute to variation of NMDARs and synaptic plasticity during the developing period.

Apoptosis in mouse fetuses from dams exposed to T-2 toxin at different days of gestation

T-2 toxin (2 mg/kg b.w.) was orally inoculated to pregnant mice at gestational day (GD) 8.5, 9.5, 10.5, 11.5, 12.5, 13.5, 14.5, 15.5 and GD 16.5, respectively, and the fetuses were examined 24 hours later. The number and region of pyknotic or karyorrhectic cells varied according to inoculation date. In the GD 13.5-subgroup, a moderate to high number of pyknotic or karyorrhectic neuronal cells were observed in the central nervous system, peri-ventricular zone to subventricular zone, and pyknosis or karyorrhexis were also observed in a small number of chondroblasts and chondrocytes. In the GD 16.5-subgroup, a moderate to high number of pyknotic or karyorrhectic cells were observed in the thymus and renal subcapsular parenchyma. The nuclei of these pyknotic or karyorrhectic cells were strongly stained by the terminal deoxy nucleotidyl transferase (TdT)-mediated dUTP-digoxigenin nick end labeling method widely used for the in situ detection of apoptotic nuclei. In addition, a few fetuses from dams which were given T-2 toxin at GD 13.5 or GD 14.5 and killed at GD 17.5 showed skeletal abnormalities such as wavy ribs and short scapula. From the present findings and the well known fact that T-2 toxin readily crosses the rat placenta, it seems that T-2 toxin-induced apoptosis in the developing mouse fetuses might be a direct effect of T-2 toxin on fetuses.

Gene expression profiles in pregnant rats treated with T-2 toxin

Pregnant rats on day 13 of gestation were treated orally with T-2 toxin at a single dose of 2 mg/kg and sacrificed at 24 hours after treatment. Histopathologically, apoptosis was increased in the liver, placenta and fetal liver. Microarray analysis was performed to examine the gene expression in the liver, placenta, and fetal liver. The results of microarray analysis showed that the changes in the expression of apoptosis genes, metabolic enzymes and oxidative stress-related genes were detected in these tissues. Suppression of phase I and II enzymes-related genes expression in the liver, and suppression of phase II enzymes-related genes expression in the placenta and fetal liver were observed. Semiquantitive RT-PCR analysis also showed the same results as those of microarray analysis. From the results of microarray analysis and histopathological examination, T-2 toxin seems to induce oxidative stress in these tissues, following the changes in metabolism-related genes expression. These changes may alter the intracellular environments resulting in the induction of apoptosis. Further studies on the gene expression profiles at the earlier time point are necessary to clarify the detailed mechanisms of T-2 toxin-induced toxicity in pregnant rats.

5-Azacytidine (5AzC)-induced histopathological changes in the central nervous system of rat fetuses.

5-Azacytidine (5AzC) is a cytidine analogue which possesses nitrogen atom instead of carbon atom at the position 5 of the pyrimidine ring. In this study, detailed histopathological changes were sequentially examined in the rat fetal brain obtained from dams treated with 5AzC (10 mg/kg) on day 13 of gestation (GD13). At 6 hours after treatment (HAT), a prominent accumulation of neuroepithelial cells showing pleomorphic mitotic figures were observed in the telencephalic wall. The mitosis-index peaked at 6 HAT, and decreased thereafter. Neuroepithelial cells positive for nick end labeling (TUNEL) method, which is widely used for the detection of apoptotic cells, prominently increased at 9 HAT, and the TUNEL-index peaked at 12 HAT. TUNEL-positive cells showed ultrastructural characteristics of apoptosis. At 24 HAT, the formation of rosette-like structures was observed in the fetal brain. From the results of the present study, it was evident that abnormal mitosis and neuronal apoptosis were induced in the rat fetal brain following 5AzC-administration to dams on GD13. In addition, it is suggested that 5AzC-induced apoptosis might occur mainly in the post mitotic phase of cell cycle.

Abnormal neuronal and glial argyrophilic fibrillary structures in the brain of an aged albino cynomolgus monkey (Macaca fascicularis)

Abstract An aged albino male cynomolgus monkey (Macaca fascicularis) more than 35 years old died after showing neurological signs including gait disturbance, trembling, drowsing tendency and a decrease in activity. Neuropathological examination revealed glial fibrillary tangles (GFTs) mainly distributed in the putamen, caudate nucleus, thalamic nuclei, substantia nigra, red nucleus, globus pallidus, trapezoid body, pyramid, pons and medulla oblongata of the brain, and neurofibrillary tangles (NFTs) in the thalamic nuclei. These structures were positively stained by the modified Gallyas-Braak (GB) method and immunostained for tau. The tau-positive argyrophilic GFTs were morphologically classified into four types, as in human cases, i.e., tufts of abnormal fibers (TAFs), thorn-shaped astrocytes (TSAs), glial coiled bodies (GCBs) and argyrophilic threads (ATs) depending on their GB profiles, and GCBs were the major structures in this case. Some of these structures were also immunoreactive for α-synuclein. The glial cells possessing the structures were negative for glial fibrillary acidic protein, a marker for astrocytes, indicating that the argyrophilic GFTs were present in oligodendroglia. In addition, marked neuronal loss and ubiquitin-positive spheroid bodies were observed in the substantia nigra and globus pallidus. According to the characteristic distribution of the argyrophilic structures in neurons and glial cells as well as clinical signs, the monkey might have suffered from a neurodegenerative disease such as progressive supranuclear palsy (PSP). This is the first report of the occurrence of a neurodegenerative disease in a nonhuman animal.

Lectin histochemistry in the aged dog brain.

Abstract Formalin-fixed and paraffin-embedded canine brains were examined histochemically using 15 selected lectins. Concanavalin A (Con A), Lens culinaris agglutinin, Lycopersicon esculentum agglutinin (LEL) and Limulus polyphemus agglutinin (LPA) labeled neurons in an age-dependent manner. These and some other lectins [Dolichos biflorus agglutinin (DBA), Vicia villosa agglutinin (VVA), Ricinus communis agglutinin 120 (RCA-I), Bandeiraea simplicifolia agglutinin (BSL-I), and Phaseolus vulagaris agglutinin-L (PHA-L)] also age-dependently labeled glial cells. These results indicate that monosaccharide composition and biochemical metabolism in brain cells change with age and that these lectins may be useful as histochemical markers for investigating senile changes in the canine brain. However, no significant correlation was found between ApopTag-positive and lectin-positive cells. Amyloid plaques were positive for Con A, DBA, Glycine maximus agglutinin (SBA), LEL, PHA-L, Limax flavus agglutinin (LFA) and VVA. Among these lectins, VVA, SBA and LFA intensely stained amyloid both in blood vessel walls and senile plaque cores. Therefore, the sugar residues recognized by these lectins likely play specific roles in β-amyloid deposition in the aged dog brain.

5-Azacytidine induces toxicity in PC12 cells by apoptosis

5-Azacytidine (5 Az)is a potent inhibitor of DNA methylation, and it may allow inactive genes to become expressed. In a previous study, we demonstrated that 5 Az administered to the dam induced apoptosis in the brains of fetal mice. In this study, the 5 Az-induced apoptosis was further characterized in differentiated PC 12 cells as a model for neuronal apoptosis. Cell death, determined by the activity of released lactate dehydrogenase (LDH) into the medium, occurred from 24 to 48 hrs after 5 Az treatment. Toxicity for differentiated PC 12 cells was observed on treatment with more than 10(-1) micrograms/ml of 5 Az, and it reached the maximal level at 10 micrograms/ml. Cycloheximide, an inhibitor of protein synthesis, prevented 5 Az toxicity, suggesting that this cell death required protein synthesis which could be related to the activation of a dormant gene(s). Electrophoresis of DNA from 5 Az-treated cells evoked ladder formation, indicating the cleavage of DNA into nucleosomes. Scanning electron microscopy demonstrated bleb formation, the so-called apoptotic bodies on the cell surface. The biochemical and morphological findings indicated that 5 Az-induced cell death occurred in the form of apoptosis. 5 Az-induced cell death was prevented by treatment with cAMP but not by treatment with high K+ or deoxycytidine. These results suggest that a cAMP-sensitive mechanism is involved in 5 Az-induced cell death. PC 12 cells should be of value in elucidating the molecular mechanism of 5 Az-induced neuronal apoptosis.

NMDA-induced apoptosis in the developing rat brain

The N-methyl-D-aspartate receptor (NMDAR), which is one of the glutamate receptors, is considered to have a close relation to synaptic plasticity in the developing brain. In addition, it is also known that the excessive stimulation of NMDARs can trigger neuronal apoptosis. In this study, we examined the expression of neuronal apoptosis in the developing rat brain after the administration of NMDA to pregnant dams or neonates (embryonal days 18 to postnatal days 14). In the NMDA-treated group, the significant increase in nuclei of apoptotic neuronal cells occurred in the dose-dependent manner in the lateral-ventral regions of the fetal cerebral cortex, reaching maximum values at 24 hours after treatment. On the other hand, the induction of apoptosis did not occur in the neonatal brain.