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Biomedical subjects

D T Yew

Publications and source records attributed to D T Yew.

At least 55 records · Page 3Linked to original sources
PubMed1994

An immunohistochemical study of the c-fos protooncogene in the developing human retina.

The localization and distribution of the protooncogene c-fos were studied immunohistochemically in the retina of human fetuses ranging in age from 15 to 40 weeks of gestation. The highest levels of immunoreactivity were observed in the retinae of younger fetuses, decreasing in intensity with increasing age. At 15 weeks of gestation intense immunoreactivity was observed in the inner nuclear layer while the photoreceptor cells exhibited moderate staining. At 26 weeks of gestation, immunoreactivity in the inner nuclear layer was reduced. The ganglion cells, amacrine cells and photoreceptor cells showed moderate immunopositivity throughout the 26-40 weeks period. The role of c-fos in development is discussed in the light of its other known functions.

Embryonic and Fetal Development↗
PubMed1994

Distribution of neuropeptide Y in the developing human spinal cord.

The distribution of neuropeptide Y at different levels of the spinal cord of 23 human fetuses aged from 10-41 weeks of gestation was studied using immunocytochemical staining. Neuropeptide Y-immunoreactive neurons were identified at all levels of the spinal cord examined as early as 10 weeks of gestation. These cells were localized in the superficial layers (laminae I and II of Rexed) of the dorsal gray matter. As the age of the fetuses increased, their cell number increased and the region containing positive neurons extended from the superficial to deep layers (laminae III and VI). Immunoreactive fibers started to appear in fetuses at 10 weeks of gestation. They were found not only in the gray and white matters, but also in the pia mater lining the spinal cord. As the fetuses aged, the neuropeptide Y-immunoreactive fibers became mostly concentrated in the intermediate zones of the thoracic and sacral segments corresponding to the developing autonomic centers. Our results suggest that neuropeptide Y may play a role in the early development of the autonomic system.

Embryonic and Fetal Development↗
PubMed1994

Immunohistochemical localization of neuropeptide Y and somatostatin in human fetal retina.

The localization of neuropeptide Y and somatostatin in the retina of six prenatal human specimens was determined by the utilization of light microscopic immunoperoxidase and immunofluorescence methods. The age of the prenatal fetuses ranged from 15 to 40 weeks of gestation. At 15 weeks, round or pear-shaped neuropeptide Y-immunopositive cells were observed in the inner nuclear layer and somatostatin immunoreactivity was only detected in the ganglion cell layer. Positive neuropeptide Y ganglion cells were observed by 17 weeks of gestation and by 28 weeks neuropeptide Y-immunopositive cells were demonstrated in the ganglion cell layer and inner nuclear layer. At 26-28 weeks, neuropeptide Y-immunopositive cells exhibited approximately the same shape as at 15 weeks of gestation, but the appearance of one or two processes was detected extending from the somata. By 38-40 weeks of gestation, neuropeptide Y-immunopositive cells were detected in the ganglion cell layer, inner nuclear layer and an immunopositive fibrous configuration in the inner plexiform layer. During this same period (38-40 weeks), somatostatin-positive cells were located in the ganglion cell layer, inner nuclear layer and the inner segments layers. Due to the difficulty of obtaining fetal materials, the exact time of initiation in the expression of neuropeptide Y and somatostatin is presently hard to delineate; however, it is safe to state that the peptides appear early in development.

Eye Proteins↗
PubMed1994

Bilateral retinal responses during the acute phase (4-14 days) after traumatization of a single eye in the mouse.

The infiltration of T lymphocytes and macrophages was examined in the retinae of traumatized and non-traumatized contra-lateral eyes of mice. Traumatization was produced by channeling a small hole in the limbic region of a single eye in each animal while it was under Nembutal anesthesia and a small piece of iron wire was inserted into the eye. After the T lymphocytes and macrophages were made apparent by immuno-histochemistry, they were counted on sectioned strips of the peripheral retinae 250 micrometer in length in both traumatized and non-traumatized eyes. During the first two weeks after the induced disturbance, both the retinae of the traumatized and non-traumatized eyes showed infiltration of T lymphocytes and macrophages. Although this increase in T lymphocyte infiltration was observed in both damaged eye and the undamaged one, the former displayed an enhanced increase. The contrary was noticed for macrophages infiltrating the undamaged eye. A bilateral response was therefore evident through the cellular infiltration in the traumatized and un-traumatized eyes. Morphometrical observations also revealed nuclear size changes in the retina during this acute phase of traumatization.

Acute Disease↗
PubMed1993

An immunohistochemical study of neuropeptide Y positive sites in the developing human hippocampal formation.

Neuropeptide Y (NPY)-positive sites were evaluated by immunohistochemistry in the hippocampal formation of human fetuses aged from 15 to 41 weeks of gestation. Immunopositive cells and fibers were identified in the hippocampus as early as 15 weeks of gestation. These cells were localized in the polymorphic and pyramidal layers and their numbers increased with the age of the fetuses. NPY-positive cells were observed to be closely apposed to blood vessels and some NPY fibers, present mainly in the polymorphic layer, would infiltrate the alveus.

Binding Sites↗
PubMed1993

Habenulo-interpeduncular descending pathways and their relationship to enkephalin- and somatostatin-immunoreactive neurons in the interpeduncular nucleus of human fetuses.

The interpeduncular nucleus of six human fetuses aged 15 (one specimen), 26 (one specimen), 38 (one specimen) and 40 (three specimens) gestation weeks was studied by immunohistochemistry for enkephalin and somatostatin localization and immunohistochemistry coupled with silver staining. Enkephalin-positive and somatostatin-positive cells were detected, the former initially at 15 weeks gestation and the latter at 26 weeks gestation. They appeared to receive long afferents from the habenular region and projected short efferents to adjacent cells devoid of enkephalin and somatostatin positivity. We postulate that these enkephalin- and somatostatin-positive neurons function as modulatory interneurons in the habenulo-interpeduncular and related pathways.

Enkephalins↗
PubMed1992

Acetylcholinesterase-containing neurons, substance P and enkephalin fibers in the ventral horns of developing human embryos and fetuses.

The presence of the acetylcholinesterase neurons and substance P-like and enkephalin-like fibers in the various nuclear columns of the ventral horns of the spinal cords was studied in the developing human by acetylcholinesterase histochemistry and substance P and enkephalin immunohistochemistry. Acetylcholinesterase-positive neurons initially appeared in the lateral neuronal columns and eventually were also observed in the medial columns as well as the median columns at various levels of the spinal cord by 10 weeks' gestation. Acetylcholinesterase-positive neurons in the lower sacral levels were not detected until 11-12 weeks' gestation. Diffused substance P- and enkephalin-like fibers were demonstrated as early as 10 weeks' gestation but did not align with any particular nuclear column until after 15 weeks' gestation. These fibers further increased in length and adopted reticular branching patterns and many of these tended to surround the cell bodies of the nuclear columns. Possible interaction of acetylcholinesterase neurons and substance P and enkephalin fibers would commence by 15 weeks' gestation.

Acetylcholinesterase↗
PubMed1992

Immunohistochemical localization of enkephalin and substance P in the nucleus caudalis of the spinal trigeminal V in the medulla oblongata of the human fetus.

The distribution of enkephalin-positive neurons, substance P-positive and enkephalin-positive fibers was studied in the nucleus caudalis of the trigeminal spinal V in the medulla oblongata regions of developing humans (12 weeks gestation to 40 weeks gestation). Enkephalin-positive neurons were identified in all the subnuclei of the nucleus caudalis as early as 12 weeks of gestation and increased in number as the fetus aged. Substance P-positive neurons were absent in this area throughout development. On the other hand, substance P-positive and enkephalin-positive fibers were present in all the subnuclei, again commencing as early as 12 weeks of gestation. These fibers tended to be linked to each other in the different subnuclei and to the reticular formation in this area and to increase significantly in quantity by the latter quarter of pregnancy. These results show the early presence of these neurons and fibers in the first trimester of development.

Abortion, Spontaneous↗
PubMed1991

Immunohistochemical and ultrastructural studies of the various nuclei of the trigeminal complex in the human newborn.

The various nuclei of the trigeminal complex were studied by immunohistochemical (enkephalin localization) and ultrastructural means in the brainstems of eight newborn human babies that died within 24 h after birth. Positive enkephalin neurons were detected in the chief sensory and spinal trigeminal nuclei as well as in some fibers of the trigeminal nerve. Ultrastructurally, two morphologically distinct types of neuron were observed, respectively, in the motor nucleus, the spinal nucleus and the mesencephalic nucleus of the trigeminal complex, whereas three morphologically distinct types of neuron were observed in the chief sensory nucleus. "Glomerulus" formation was a frequently observed feature in the chief sensory nucleus. In the spinal nucleus, rolls of synaptic terminals stacking up one on top of another and synapsing onto the final synaptic element were very much in evidence. Axosomatic, axodendritic, dendrodendritic and dendroaxonic synapses were demonstrated in all the different nuclear areas of the trigeminal complex but axoaxonic synapses were absent in the mesencephalic nucleus. Some of the findings in the present human study were similar to those reported in the rats and cats.

Enkephalins↗
PubMed1991

Immunohistochemical localization of substance P, enkephalin and serotonin in the developing human retina.

The localization of substance P (SP), enkephalin (ENK) and serotonin (5-HT) in the retinae of 12 human embryos/fetuses ranging in age from 6-30 weeks was determined immunohistochemically using the PAP method. At the 6 week stage [crown rump length (CRL) unknown due to incomplete specimen], the developing retina consisted of a single undifferentiated cell mass from which immunoreactive cells were absent. By 90 mm CRL (10th week of gestation), the retina was composed of an outer neuroblastic layer, an inner plexiform layer and an innermost layer of ganglion cells. At this stage, SP, ENK and 5-HT positive cells were detected solely in the outer neuroblastic layer. By 140 mm CRL (17 weeks), the retina consisted of cell layers similar in number and type to those of the adult retina. In specimens 140-216 mm CRL (gestation ages 17-24 weeks), SP, ENK and 5-HT neurons were present in the outer nuclear, inner nuclear and inner plexiform layers. In addition, 5-HT positive neurons and fibers were evident in the outer plexiform layer. By 285-295 mm CRL (26-30 weeks), neurons in the ganglion cell layer and the fovea were also SP and ENK positive. In earlier specimens, the cell bodies alone were immunopositive and not until 142 mm CRL (17 weeks) were positive processes observed. Finally, the presence of SP, ENK and 5-HT immunopositive structures occurred in a sequence from outer to inner layers of the developing human retina.

Embryo, Mammalian↗
PubMed1991

Retinal changes in a mutant form of goldfish with megalophthalmia.

The retinal changes of a mutant strain of goldfish with megalophthalmia were studied by histology, electron microscopy and biochemistry. Changes in the morphology of the pigment epithelium, decrease in number of photoreceptors, thinning out of retinal layers and the existence of spaces in the retina were all features as the eyes grew in size. Invasion of macrophages was also evident in the retina. A decrease in leucine uptake per milligram of retina was also detected as the eye grew beyond 0.8 millilitre in volume. These changes, although related to volume changes (i.e., growth) of the eyes, were found to have little relationship with increase of intraocular pressure as intraocular pressures in the growing eyes of the mutant strain did not change much. Goldfish from a control strain with similar eye volumes and sizes (ages) were used for comparison and similar changes as in the mutant were not apparent.

Animals↗
PubMed1990

Development and localization of enkephalin and substance P in the nucleus of tractus solitarius in the medulla oblongata of human fetuses.

The presence of enkephalin and substance P-positive neurons and fibers were studied by immunohistochemistry (peroxidase-antiperoxidase or avidin-biotin-peroxidase complex methods) in 26 human fetuses ranging from 11 weeks of gestation to 40 weeks of gestation. Enkephalin-positive neurons were localized in the commissural, medial and intermediate subnuclei as early as 11-12 weeks' gestation. Positive enkephalin fibers were localized around 12 weeks' gestation and in many subnuclei, notably the medial, commissural, intermediate, ventrolateral, ventral and dorsolateral subnuclei. Substance P-positive neurons were localized in the commissural and medial subnuclei around gestation age 13 weeks. Positive substance P fibers appeared even earlier, around 11 weeks of gestation in many subnuclei, notably the medial, intermediate, ventral, ventrolateral and dorsolateral subnuclei. Increase in both enkephalin- and substance P-positive fibers was evident in the later stages of development (e.g. around 26 weeks of gestation). The importance of the early appearance of enkephalin and substance P neurons and fibers of the pain pathways in the major subnuclei connecting with the cardiovascular, gastrointestinal and respiratory functions in the human has to be stressed.

Embryonic and Fetal Development↗
PubMed1990

Localization of acetylcholinesterase positive neurons and substance P and enkephalin positive fibers by histochemistry and immunohistochemistry in the sympathetic intermediate zone of the developing human spinal cord.

Localization of acetylcholinesterase positive neurons and substance P and enkephalin fibers were studied by histochemistry and immunohistochemistry in the intermediate sympathetic zone of the spinal cords of 39 human embryos/fetuses from gestation ages five to 40 weeks. Acetylcholinesterase positive neurons were observed in the nucleus intermediolateralis pars principalis as early as the fifth week of gestation. By the ninth to 13th weeks of gestation, positive neurons were also seen in the nuclei intermedialis pars funicularis, intercalatus spinalis and intercalatus pars paraependymalis. Increase in amount of these positive acetylcholinesterase neurons was demonstrated till term. Substance P and enkephalin fibers were initially observed by the eighth gestation week in the intermediolaterlis pars principalis nucleus and positive fibers were then detected in the nucleus intermedialis pars funicularis as well as the nucleus intercalatus spinalis by the 14th week of gestation. By the 26th week of gestation, all the major nuclei intermediolateralis par principalis, intermedialis pars funicularis, intercalatus spinalis and intercalatus pars paraependymalis has substance P and enkephalin fibers. Initial demonstration of acetylcholinesterase positive neurons appeared to be at an earlier stage than that of our substance P and enkephalin positive fibers.

Acetylcholinesterase↗
PubMed1990

Bilateral retinal responses after traumatic injury of one eye in mice. A histopathologic and immunohistochemical study.

Iron wires (0.3 mm in diameter and 1.2 mm in length) were lodged in the left eyes of albino mice. 4 weeks after the experiment, the left and right eyes were sectioned and observed by light microscopy for any histopathology. Immunohistochemical techniques were also employed to identify macrophages and T cells. In the first case, both left (wire-lodged) and right eyes of experimental animals demonstrated pathological changes. The left eyes showed degeneration of photoreceptors and infiltration of lymphocytes at the vicinity of the pigment epithelium. The right eyes also showed degeneration of the pigment epithelium with infiltration of macrophages and lymphocytes around these areas. Immunohistochemistry revealed the presence of macrophages (44%), helper/inducer T cells (37%) and cytotoxic/suppressor T cells (19%) in the pigment epithelia and retinae of both eyes. Our results indicate that, following traumatic injury of one eye, not only the lesioned eye undergoes degeneration, but the other nonlesioned eye is affected as well, and immunologic cells are involved.

Animals↗
PubMed1990

Uptake of labelled proline in the degenerating retina of goldfish.

A goldfish model with degenerating retina was utilized. Degeneration of inner nuclear layer and ganglion cell layers began prior to degeneration of outer nuclear layer. In these models, the photoreceptors still showed uptake of labelled proline. This indicated that the metabolic activities of the first order neuron was independent to its neuronal linkage with other neurons.

Animals↗
PubMed1990

Responses of astrocytes in culture after low dose laser irradiation.

The effect of Helium-Neon low dose laser on astrocytes was investigated in cultures of isolated astrocytes from albino neonatal rats. The laser appeared to inhibit the growth of astrocytes as exemplified by the smaller sizes of the cells and the decreased leucine uptake in each cell after treatment. Temporary decrease in the number of mitoses was also observed, but this trend was reversed soon after. Electron microscopic studies revealed an increase in buddings from cell bodies and processes (branches) after irradiation.

Animals↗
PubMed1989

Scanning electron microscopy of the development of layer I of the human visual cortex (area 17).

The development of layer I of the human visual cortex was studied. Tissues were obtained from 14 aborted and stillborn human fetuses, ranging in age from 13 to 32 fetal weeks. The middle third of the rostrocaudal area 17 above the left calcarine sulcus was selected for observation. The sections were cut perpendicular to the pial surface of the cortex. The specimens were processed for scanning electron microscopy. At 13-16 weeks the Cajal-Retzius neurons were the predominant neuronal elements of layer I, with a small amount of fibers present. In addition, it was found that at 13 weeks the folding plasma membranes of the glial cells formed primary myelin sheaths which wrapped around the nerve cell bodies and processes. Axosomatic and axodendritic contacts were present in the cortices of the fetuses. The nerve fibers of layer I increased progressively with age. However, at 17 weeks, some degenerating apical dendrites were occasionally found. These degenerating dendrites appeared fragmented and beaded. At 21-23 weeks, layer I was well developed with all its essential components present. However, the upper half of the cortical plate was still undifferentiated at this age. At 26-32 weeks, layer I had a prominent plexiform lamina. This lamina was poor in neurons and rich in fibers. In summary, during layer I ontogenesis, there were the following major changes: (1) a change from higher to lower neuronal density: (2) changes in morphology of neurons; (3) initial appearance of synapses early in development; (4) early onset of glial wrapping; (5) presence of degenerating fibers during ontogenesis, and (6) increase in fiber proportion as fetus aged.

Humans↗