Takashi Mito

Embryonic development and postnatal changes in free D-aspartate and D-serine in the human prefrontal cortex

Abstract: We have analyzed free chiral amino acids (aspartate and serine) in the human frontal cortex at different ontogenic stages (from 14 weeks of gestation to 101 years of age) by HPLC with fluorometric detection after derivatization with N‐tert‐butyl‐oxycarbonyl‐l‐cysteine and o‐phthaldialdehyde. Exceptionally high levels of free d‐aspartate and d‐serine were demonstrated in the fetal cortex at gestational week 14. The ratios of d‐aspartate and of d‐serine to the total corresponding amino acids were also high, at 0.63 and 0.27, respectively. The concentration of d‐aspartate dramatically decreased to a trace level by gestational week 41 and then remained very low during all postnatal stages. In contrast, the frontal tip contained persistently high levels of d‐serine throughout embryonic and postnatal life, whereas the d‐amino acid content in adolescents and aged individuals was about half of that in the fetuses. Because d‐aspartate and d‐serine are known to have selective actions at the NMDA‐type excitatory amino acid receptor, the present data suggest that these d‐amino acids might play a pivotal role in cerebral development and functions that are related to the NMDA receptor.

Pathogenesis of periventricular white matter hemorrhages in preterm infants

Periventricular white matter hemorrhage (PWMH) was frequently found in very low-birth weight infants with perinatal asphyxia or respiratory distress. Primary PWMH with or without intraventricular rupture was found at the deep arterial borderzones of the frontal or occipital lobes. The ischemic tissue damage induced by hypoperfusion may be a predisposing factor for PWMH. However, the high incidence of visceral intravascular thrombi and the fan-shaped appearance of hemorrhage suggested venous hemorrhagic infarction. Venous thrombosis with coagulopathy may be an important factor for the pathogenesis of PWMH.

Development of myelination in the human fetal and infant cerebrum: A myelin basic protein immunohistochemical study

The early development of myelination was studied by means of myelin basic protein (MBP) and luxol fast blue (LFB) stainings of large sections of the cerebral hemispheres. Myelination first occurs in the globus pallidus, pallidothalamic fibers of the posterior internal capsule and the thalamus at 25 weeks, which may be related to the cellular maturation in the globus pallidus and thalamus. Then myelination is observed in the striatum, and precentral and postcentral gyri at 35 weeks, and the anterior internal capsule and optic radiation at 37 weeks. Immunoreactivity with MBP is observed earlier and more strongly in the early myelination period than that with LFB. Thus, MBP may play an important role in myelination and its delay. The macroscopic positivity as to MBP as well as LFB staining may be related to the development of high signal intensity observed in a T1-weighted magnetic resonance imaging, which was observed 1 to 3 months after the first microscopic appearance of myelin.

Developmental Changes of S-100 Protein and Glial Fibrillary Acidic Protein in the Brain in Down Syndrome

The location of the gene for the beta subunit of S-100 protein on chromosome 21 suggests that expression may be increased in trisomy 21. Astrocytes from Down syndrome and control patients were examined by immunohistochemistry for the expression of S-100 protein. Adjacent sections were reacted with antisera to glial fibrillary acidic protein to ascertain the presence or absence of astrogliosis. The developmental change in expression of S-100 protein was determined in patients ranging in age from 34 gestational weeks to 57 years. In control patients the number of S-100 protein-immunoreactive cells increased during early infancy to reach a plateau; the number stayed at this level until adulthood and then gradually declined. In Down syndrome, the pattern was similar, except that the number of S-100 protein-positive cells in the hippocampus was greater than in controls, especially during early infancy and at older ages. In the patients examined in early infancy there was no evidence of astrogliosis. However, in older patients with Down syndrome the increased number of immunoreactive cells with antisera to both S-100 protein and glial fibrillary acidic protein indicates the presence of gliosis related to occurrence of senile plaques and neurofibrillary tangles. The increased immunoreactivity of S-100 protein in early life suggests that in trisomy 21 the expression of the gene for the beta subunit may be enhanced. The significance of increased S-100 protein in relation to neural maturation in Down syndrome is unknown.

Endotoxin, cerebral blood flow, amino acids and brain damage in young rabbits

The effects of bacterial endotoxin (lipopolysaccharide; LPS) on the cerebral blood flow (CBF), amino acid levels and brain histology were studied in young rabbits. The CBF was slightly decreased in the cerebral cortex and markedly decreased in the cerebral white matter at 60 and 120 min after LPS administration. Histological examination revealed only slightly pyknotic neurons around small vessels at 24 hours, and multifocal necrosis in the deep cerebral cortex and white matter at 72 hours. Some amino acids were increased in the plasma and brain regions at 24 hours after LPS administration, most of which were essential amino acids. GABA in the cerebral white matter was decreased at 24 hours. At 72 hours, most non-essential and glucogenic amino acids were decreased. These results suggest that the brain histological changes are related mainly to hypoperfusion and vascular damage in the brain. The amino acid changes may also be related to inappropriate amino acid metabolism associated with brain cell damage.

Relationship between periventricular hemorrhage, leukomalacia and brainstem lesions in prematurely born infants.

The brain pathology in very prematurely born infants with intraventricular hemorrhage (IVH) was studied particularly as to the severity and site of the complicated brain lesions responsible for the prognosis. A high frequency of leukomalacia, pontosubicular necrosis and/or olivocerebellar neuronal loss was found in the cases of IVH, and these non-hemorrhagic brain lesions showed an increasing frequency with the grade of IVH. However, there was marked reduction of IVH, periventricular leukomalacia and, in particular, brainstem lesions in prematurely born cases of sudden infant death. These IVH and associated conditions have different pathogenesis, but factors responsible for their occurrence may be present together in each case.

Progress of myelination in the human fetal spinal nerve roots, spinal cord and brainstem with myelin basic protein immunohistochemistry

The early progress of myelination was studied, by means of myelin basic protein (MBP) immunohistochemistry and luxol-fast-blue (LFB) staining, in the spinal cord, spinal nerve roots and brainstem of 66 fetuses and neonates. The degree of myelination was classified from 1 (slight) to 4 (mature). MBP immunoreactivity exhibited slight LFB positivity. Myelination first occurred in the medial longitudinal fasciculus at 20 weeks of age, reaching degree 4 at 34 weeks, but began at 23-24 weeks in the other sites. Myelination of spinal nerve roots progressed with gestation and attained degree 4 at 35-36 weeks. The cuneate fasciculus also reached degree 4 at 34-36 weeks, but corticospinal tracts and solitary tracts, which exhibited long myelinating phases, were slow and incomplete at 40 weeks. This normal development of MBP and LFB myelination can be used for the assessment of delayed myelination in fetal and neonatal diseases.

Vascular dysplasia in down Syndrome: A possible relationship to moyamoya disease

The brain of a child with Down syndrome (DS) and vascular abnormalities is described. Neuropathological examination showed a large cerebral infarction. In the circle of Willis there was hypoplasia of the left middle and posterior communicating cerebral arteries, and microscopically there was thickening of intima and focal disruption of internal elastica in some areas of the circle of Willis. Several reports suggest that the incidence of moyamoya disease is higher in children with DS than in other children. The high incidence of congenital heart disease in DS suggests an abnormality of vascular development that may manifest intracranially as a structural vascular defect, creating a vulnerability to unknown factors important in the pathogenesis of the moyamoya abnormality.

Immunohistochemical study of the vasculature in the developing brain

In this study, the developmental proliferation of human brain vessels, from the fetal to the adult stage, was analyzed by immunohistochemical methods using antitype IV collagen, antilaminin, and antifibronectin antibodies. Examination of the frontal lobe indicates that these antibodies bind to the vessels, both arteries and veins. During cortical angiogenesis, the density and diameter of vessels increase rapidly from about 26 weeks gestation and peak at 35 weeks; after 35 weeks, the density and diameter of vessels are the same as those in adult brain. The white matter demonstrates no major changes in vessel density, although the pattern of the changes in vessel diameter resembles that of the cortex. Small immunopositive spots suggesting neovascularization reveal the same developmental tendency as the density of vessels in the cortex and white matter; therefore, it appears that neovascularization in the fetal brain during development is more rapid than cortical expansion and is equal to the growth of white matter. Neovascularization may be closely related to normal brain development and may play an undefined role in perinatal cerebrovascular insults.

Development of ferritin-positive cells in cerebrum of human brain

The distribution and development of ferritin-containing cells were studied immunohistochemically in the cerebrum at ages ranging from human fetuses to adults. The predominant cell type labeled with antiserum to ferritin was the oligodendrocyte. In frontal and occipital lobes, positive cells appeared at 25 weeks gestation in subcortical and periventricular white matter, and increased earlier in the white matter than in the cortex. They also appeared at 25 weeks gestation and increased continuously in infancy in the putamen and globus pallidus, as well as in the frontal and occipital lobes. This development of ferritin-positive glia may be related to the process of myelination and maturation of oligodendrocyte.