Biomedical subjects

D T Yew

Publications and source records attributed to D T Yew.

At least 37 records · Page 2Linked to original sources

PubMed1999

Neurotransmitters, peptides, and neural cell adhesion molecules in the cortices of normal elderly humans and Alzheimer patients: a comparison.

Immunocytochemical techniques was used to compare the proportion of neurons expressing various neurotransmitters (tyrosine hydroxylase, choline acetyltransferase and gamma-aminobutyric acid), neuropeptides (Leu-enkephalin and substance P) and neural cell adhesion molecules (NCAM) in the hippocampus, frontal (area 10) and occipital (area 17) cortices of neurologically normal elderly humans to that of age-matched Alzheimer disease (AD) patients. There was no difference in the proportion of GABAergic and cholinergic cells between the normal and AD groups in all three brain regions studied. However, the catecholaminergic cells in the frontal cortex of the AD patients revealed a significant decrease. The catecholaminergic cells present in the cortex were both neurons and astrocytes, as revealed by a double immunostaining of tyrosine hydroxylase and glial fibrillary acid protein (GFAP). Furthermore, the difference in the proportion of cells expressing Substance P and Leu-enkephalin was minimal between the two groups studied. Although there was little difference in the levels of NCAM in the occipital cortex and hippocampus of the two groups, there were significantly fewer positive NCAM neurons in the frontal cortex of AD than normal aging individuals.

Aged↗

PubMed1999

A rabbit model of proliferative vitreoretinopathy induced by injection of astrocytic cultures.

1. The objective of this study was to decipher whether proliferation of astrocytes and invasion of astrocytic processes into the retina could contribute to retinal detachment in a rabbit model. 2. Cultures of astrocytes were injected intravitreally into the eyes of albino rabbits. 3. Two weeks after injection, proliferation of astrocytes on the retinal surfaces was observed. Vascular endothelial growth factor (VEGF) and proliferative cell nuclear antigen (PCNA) were found by immunohistochemistry to be expressed in the center of the astrocytic growth. 4. Using the same immunohistochemical technique to visualize glial fibrillary acidic protein (GFAP), a marker for astrocytes, processes of astrocytes in the growth were observed to penetrate into the host retina. 5. Retinal detachment was then confirmed by ultrasound, histologically, and grossly 2 weeks after injection of astrocytes. 6. Histochemistry on esterase indicated chloroesterase positive cells inside the growth. The secretion of this form of esterase might soften the vitreous and enhanced retinal detachment. 7. Six weeks after injection, VEGF and PCNA decreased in the astrocytic growth but astrocytic processes still attached onto and penetrated the host retina. 8. This study suggests that astrocytes could be a major factor in inducing retinal detachment.

Animals↗

PubMed1998

Apoptosis and Bcl-2 oncoprotein expression in the human fetal central nervous system.

Apoptosis and the apoptosis-regulatory gene bcl-2 have been suggested from animal studies to be important during the development of the central nervous system (CNS), but information on apoptotic activities of the developing human CNS has been scarce. To establish spatial and temporal distributions of apoptotic cells and Bcl-2 oncoprotein expression, we examined sections taken from cerebral cortex, hippocampus and brainstem at weeks 14, 18, 27, and 32 of gestation. Terminal transferase-mediated nick end labelling (TUNEL), histological analyses, and immunocytochemical staining using monoclonal antibodies were employed. Except for layer I of the motor cortex and the molecular layer of the hippocampus, both at week 14 of gestation, TUNEL-positive cells with typical apoptotic appearance and apoptotic indices, ranging from 0.08 to 2.85, were found in all other brain regions examined including visual, sensory, frontal and motor cortices, hippocampus, dorsal raphe, locus coeruleus, and periaqueductal grey of the brainstem. No specific spatial or temporal distribution patterns of apoptotic cells were found in the cortices. However, the apoptotic index of the molecular layer of the hippocampus increased with the gestation age. The periaqueductal grey of the brainstem showed high apoptotic indices (ranging from 0.37 to 2.85) at all the gestation ages studied. An inverse correlation between apoptosis and Bcl-2 oncoprotein expression was found in visual, sensory, and motor cortices but not in the frontal cortex and hippocampus. Apoptosis and Bcl-2 oncoproteins are important for CNS development and, apart from being an apoptosis regulator, Bcl-2 oncoproteins may also have other roles to play during neural development.

Antibodies, Monoclonal↗

PubMed1998

Time-course expression of vascular endothelial growth factor as related to the development of the retinochoroidal vasculature in rats.

Growth factors involved in angiogenesis are critical to both the normal and pathological vascular development in the retina and choroid. In the present experiment, the relationship between the vascular endothelial growth factor (VEGF) expression and the retinochoroidal vasculogenesis in Sprague-Dawley rats was investigated using in situ hybridization and immunohistochemistry. It was found that VEGF was produced mainly by astrocytes and Muller cells in the neural retina, and this was correlated temporally and spatially with the retinal vasculogenesis. In addition, it was observed that, although the VEGF expression in the retinal pigment epithelium (RPE) decreased with increasing age, it persisted from the embryonic stage to adulthood. These findings indicate that the VEGF expression in RPE may play a role in the development of the choroidal vessels as well as in the maintenance of the normal structure and permeability of the choriocapillaris in adults.

Animals↗

PubMed1998

Apoptosis in astrocytomas with different grades of malignancy.

Apoptosis, a form of programmed cell death was studied in astrocytomas with varying stages of malignancy, including low grade astrocytoma, anaplastic astrocytoma and glioblastoma multiforme. Apoptosis was visualized by employing the TUNEL technique and the evaluation of nuclear morphology and this was correlated with a study of bcl 2 expression. A decrease in the percentage of apoptotic cells and bcl 2 expression were evident with increasing malignancy. Furthermore, there was an increase in the proportion of apoptotic cells of the early stage in the more advanced form of astrocytoma. This is a study which demonstrates a possible direct inverse relationship between the severity of apoptosis and the stages of malignancy.

Apoptosis↗

PubMed1997

Differential expression of calretinin, calbindin D28K and parvalbumin in the developing human cerebellum.

Three calcium-binding proteins, calretinin, calbindin D28K and parvalbumin, were immunohistochemically localized in the human cerebellum at different developmental stages. Cells positive for calretinin were not detected during early development of the cerebellum until 21 weeks of gestation at which stage weak staining was found in Purkinje and basket cells of the cortex and in neurons of the dentate nucleus. Both the number of positive cells and the intensity of immunoreactivities were found to increase as the cerebellum became more mature. Calbindin D28K immunoreactivity was, however, detected early in development at 14 weeks of gestation. Positive cells were found in Purkinje, basket, stellate and granule cells of the cerebellar cortex and in neurons of fastigial, globose, emboliform and dentate nuclei. The number of positive cells and the staining intensity for calbindin in both the cerebellar cortex and deep nuclei decreased at more advanced developmental stages. At 21-31 weeks of gestation, positive staining was restricted to Purkinje and basket cells of the cortex. Parvalbumin immunoreactivity was also observed early in development at 14 weeks of gestation. Positivity was found in Purkinje, basket and stellate cells of the cerebellar cortex and in neurons of all the deep nuclei, with the highest number of positive cells in the fastigial nucleus followed by emboliform, globose and dentate nuclei. As the cerebellum became more mature, both the number of positive cells and the staining intensity for parvalbumin decreased in the cortex and deep nuclei. The results of the present study showed that among the three calcium-binding proteins examined, strong immunoreactivities for calbindin D28K and parvalbumin were found inthe human cerebellum early in development at 14 weeks of gestation, but there was a decrease in both the intensity and number of positive cells at more advanced stages. In contrast, calretinin positive cells were not detected until 21 weeks of gestation and the immunoreactivity increased as the cerebellum became more mature. A possible correlation between the developmentally regulated expression of the calcium-binding proteins and expression of different neurotransmitters during development is discussed.

Abortion, Induced↗

PubMed1997

Processing of Alzheimer's amyloid precursor protein during H2O2-induced apoptosis in human neuronal cells.

The processing of Alzheimer's amyloid precursor protein was studied by Western blotting during H2O2 induced apoptosis in cultures of human neuroblastoma cells. A new 5.5 kDa fragment putatively containing intact A beta was detected and found to be highly associated with apoptosis. The results suggest a possible vicious cycle involving H2O2, A beta and apoptosis which may contribute to the neuronal death mechanism in Alzheimer's Disease.

Alzheimer Disease↗

PubMed1997

Terminal dUTP nick end labeling (TUNEL) positive cells in the different regions of the brain in normal aging and Alzheimer patients.

This study investigated terminal dUTP nick-end labeling (TUNEL)-positive cells in the frontal, occipital, and hippocampal cortices of seven normal aging and four Alzheimer's patients. Significant increase in TUNEL-positive cells was observed in the frontal and hippocampal cortices of Alzheimer's patients when compared with controls. In the hippocampal cortex, only area CA4 demonstrated a significant increase of TUNEL-positive cells. Double staining of TUNEL-positive cells for glial fibrillary acidic protein revealed that < 13% of the TUNEL-positive nuclei belonged to astrocytes. The results of this study illustrated a differential pattern of cortical degeneration between normal aging and Alzheimer patients.

Aged↗

PubMed1996

Bilateral biochemical and biophysical retinal changes after unilateral ocular trauma in the mouse.

The bilateral response of the mouse retinae after puncture and insertion of iron wire in one eye was studied by electrophoretic analysis of protein changes and free radicals quantitation at 4, 15 and 42 days after surgery. The effect of cyclosporine was also studied. Several low molecular weight (< 24 kDa) polypeptide subunits were detected in both the traumatized and contralateral eyes of experimental animals. Free radical levels rose in both traumatized and contralateral eyes although the extent was much greater in the former. Both biochemical and biophysical assays showed that treatment with cyclosporine was effective in suppressing the responses in retinal proteins and free radicals only for up to 15 days. These results substantiated our earlier report that unilateral injury to one eye with retention of the foreign body affects both eyes in the mouse.

Animals↗

PubMed1996

Neurotransmitters and peptides in the developing human facial nucleus.

The human facial nucleus can be sub-divided into five structurally discrete regions. Immunohistochemistry was used to locate various neurotransmitters and neuropeptides in the neurons and nerve fibres of the human facial nucleus at 14 and 27 weeks of gestation and in the neonate. Whilst choline acetyltransferase-positive neurons were observed in the facial nucleus at all stages of development, dopamine beta-hydroxylase-positive neurons were only found in the neonate. In addition, afferent nerve fibres positive for choline acetyl-transferase, enkephalin and substance P were observed at all stages of development. In the younger specimens these fibres were evenly distributed; however, in the neonates the fibres were asymmetrically distributed as the different types became concentrated in the various structurally distinct regions of the facial nucleus.

Choline O-Acetyltransferase↗

PubMed1996

Immunohistochemical studies of GABA and parvalbumin in the developing human cerebellum.

The localization of GABA and parvalbumin was studied in the developing cerebellum of human fetuses from 16 to 28 weeks of gestation. The avidin-biotin complex immunohistochemical method combined with silver staining were used to reveal the presence of GABA- and parvalbumin-positive neurons and nerve fibres. As early as the 16th week of gestation, GABA immunopositivity was observed in the cerebellar cortex and the deep nuclei. GABA-positive neurons included Purkinje cells, stellate and basket cells of the cerebellar cortex and neurons in the deep nuclei. The gradient of immunoreactivity increased with the maturing cells, being weak at 16 weeks and becoming markedly pronounced at 28 weeks of gestation. GABA-immunopositive mossy fibres were observed in the granular cell layer at 16 weeks, and by 28 weeks, a robust fibre network was present in the cortex and deep nuclei. Immunohistochemical localization for parvalbumin indicates that weak immunoreactivity was observed in Purkinje cells, stellate and basket cells at 16 weeks of gestation, increasing in intensity with advancing age, notably in the Purkinje cells which had acquired an elaborate arbor of neurites at 28 weeks of gestation. In the deep nuclei, parvalbumin-positive cells and nerve fibres were observed throughout the 16 to 28 week period. These results indicate that GABA- and parvalbumin-positive neurons and fibres appeared as early as 16 weeks of gestation, expressing a high degree of immunoreactivity by the 28 week of fetal age.

Cerebellum↗

PubMed1996

Enkephalin positive sites in the developing human cerebellum.

Enkephalin (ENK) positive sites in the developing human cerebellum (gestation ages 18 weeks to 30 weeks) were studied by immunohistochemistry (ABC method). Positive reactions were registered as early as 20 weeks of gestation and initially in the deep cerebellar nuclei. By 23 weeks some mossy fibers exhibited positivity and by 27 weeks some climbing fibers as well as a few Purkinje basket, golgi and granule cells were also positive. This result indicated that the human cerebellum possesses ENK positive fibers and neurons before birth.

Cerebellar Cortex↗

PubMed1996

Differential expression of the soluble 170 kDa brain protein in the fetal and adult human brain.

The expression of the soluble 170 kDa brain protein (BP170) was studied in the developing human brain. Using immunohistochemical methods, it was possible to demonstrate that BP170 was expressed very strongly in the visual cortex up to approximately 27 weeks of gestation. After this time, the level of expression was reduced so that by adulthood the levels of BP170 were negligible. Similarly, BP170 was expressed in the hippocampus at all stages of development; however, unlike in the visual cortex, this protein was still apparent, albeit at low levels, in the adult. In addition, BP170 was co-expressed with tyrosine hydroxylase which suggests its possible role in the dopamine pathway.

Adult↗

PubMed1995

Differential expression of glial fibrillary acidic protein (GFAP) in the retinae and visual cortices of rats with experimental renal hypertension.

To examine the expression of the GFAP protein in the retina and visual cortex under normal and pathological conditions, hypertension was induced in adult male Sprague-Dawley rats by applying silver clips onto renal arteries and the change in GFAP expression was followed by Western blotting and immunocytochemical staining. One week after operation when the induced hypertension was at the initial stage, GFAP expression in the retina was reduced to half of the sham control. By 4 weeks, when consistent hypertension was developed, a further decrease in the level of GFAP expression in the retina to one third of the sham control was observed. Immunocytochemical staining showed that the number of GFAP-positive cells in the nerve fiber layer of the retina of the hypertensive rat was reduced to less than one third of the sham control. However, similar changes in GFAP expression in the visual cortex of hypertensive rats were not observed. This study represents the first report to date on GFAP expression in the retina and visual cortex and includes discussion of the possible mechanisms through which GFAP expression is mediated.

Animals↗

PubMed1995

Effects of astrocyte implantation into the hemisected adult rat spinal cord.

Morphological and biochemical methods were applied to assess the effects of implanting cultured astrocytes into the hemisected adult rat spinal cord. Astrocytes were purified from neonatal rat cortex and introduced into the lesioned spinal cord either in suspension injection or cultured on gelfoam first. The control groups were rats which had hemisection with injection of culture media or with gelfoam grafted alone. At various time points after surgery (two weeks to two months), the spinal cord was removed and processed for routine light microscopy, immunofluorescence, gel electrophoresis and immunoblotting. As early as two weeks after surgery, a significantly smaller volume of scar tissue was consistently found in the experimental groups. This reduced scarring was also confirmed by immunofluorescence staining and immunoblotting for glial fibrillary acidic protein in the specimens two months after hemisection. Compared to the control groups, the experimental groups also had more intense staining for neurofilaments, which was confirmed by immunoblotting. However, labelling of the astrocytes with Phaseolus vulgaris leucoagglutinin conjugated with fluorescein showed that the astrocytes migrated at a rate of 0.6 mm/day from the original implanted site. The results therefore suggested that the cultured astrocytes probably exerted their effects over a short time period (less than two weeks) around the lesion site. They could have altered the microenvironment and as a result less scar tissue was formed. Hence, there was less barrier to the regrowth of nerve fibres.

Animals↗

PubMed1995

Tyrosine hydroxylase- and dopamine-beta-hydroxylase-positive neurons and fibres in the developing human cerebellum--an immunohistochemical study.

Six human fetuses of gestational ages 16-28 weeks were employed. The immunocytochemical avidin-biotin-peroxidase complex method combined with the silver Bodian technique was used to evaluate the presence of tyrosine hydroxylase and dopamine-beta-hydroxylase neurons and afferent and efferent fibres in the cerebellum during development. Our results illustrated that by 16-18 weeks, immunoreactivity of the Purkinje cells and the granule cells was evident. By 23 weeks, the positive Purkinje cells were tightly packed together and the perinuclear granules began to extend into the processes. The positive cells next to Purkinje cells were the basket cells and stellate cells. By 26-28 weeks, all positive cells increased in number and size. Mossy and climbing fibres appeared early in development (16-18 weeks of gestation) and were seen synapsing with the positive granule cells. At the same time, some parallel fibres were observed. At later stages, the tyrosine hydroxylase- and dopamine-beta-hydroxylase-positive Purkinje cells were surrounded by abundant climbing fibres, while parallel fibres were also evident in the molecular layer. In the deep cerebellar nuclei, positive tyrosine hydroxylase and dopamine-beta-hydroxylase neurons were present by 16-18 weeks of development. Those in the dentate nucleus were more polymorphic but smaller in size. Some afferent fibres were also spotted around 16-18 weeks of gestation and their numbers increased later. Positive efferent fibres were present by 26 weeks. All these observations point to an early presence of tyrosine hydroxylase and dopamine-beta-hydroxylase components in cerebellar development.

Avidin↗

PubMed1995

The c Fos immunoreactivities in the developing and adult rat cerebella.

c Fos immunoreactivities were studied by immunohistochemistry in the developing and adult rat cerebella. c Fos immunoreactivities were observed in purkinje cells early in postnatal development (P26 d) and reached a peak by P40-P60 d, followed by a decline in the 3-month-old adult. The granule cells revealed c Fos immunoreactivities by P26 d but declined until P50 d. Then c Fos immunoreactivities increased in the granule layer by P50-P60 d and decreased again in the adult. The deep nuclei showed c Fos immunoreactivities by P40 d and persisted in the adult. In spite of the difference in the patterns of location in c Fos immunoreactivities from the early postnatal period to adulthood, no decrease in the amount of c Fos immunoreactivity was evident from immunoblotting studies. Thus, it is concluded that c Fos immunoreactivities change from development to adult, but this does not affect the total amount of c Fos protein expression in the cerebellum.

Age Factors↗

PubMed1994

Axonal sprouting in the hemisected adult rat spinal cord.

The morphological and biochemical changes were studied in adult Sprague-Dawley rats after hemisection at the L3 spinal cord level. After survival periods of one, two and three months, fluorescent tracers, FluoroGold or rhodamine B, were implanted into the dorsal white columns of these rats at the positions of the corticospinal tract below the lesion. Following uptake of the tracer, the rats were killed and the motor cortices and spinal cords of both control and hemisected rats were analysed for positively labelled neurons. The highest number of labelled cells were found two months after hemisection. They were present in both sides of the cortices, particularly in the contralateral cortex, and also in the gray matter of the spinal cord above the hemisection. A few rats which were subjected to complete transection of the spinal cord also showed labelling of neurons in the motor cortex two months after lesion. The Protargol silver technique and the [3H]choline uptake study confirmed the presence of nerve fibres traversing the lesion site in the hemisected spinal cord. Furthermore, when the rats that had been hemisected two months earlier were subjected to a second cut at the same site, chromatolytic neurons were observed in the spinal cord as well as in the motor cortices of both sides. The hemisected rats demonstrated limited recovery in limb movement. The evidence of this study clearly shows that sprouting of nerve fibres has occurred in the lesioned adult rat spinal cord.

Animals↗