D.T. Yew

Nitric oxide synthase neurons in different areas of normal aged and Alzheimer's brains

This study investigated the distribution of nitric oxide synthase-containing neurons in the cerebral cortex of individuals with Alzheimers disease, and compared them with age-matched controls. Paraffin-embedded sections of the frontal (area 10), occipital (area 17) and entorhinal cortices (area 28), and hippocampal formation obtained from 13 autopsy cases were used in the study. Neurons expressing nitric oxide synthase messenger RNA and protein were identified, respectively, by in situ hybridization and immunohistochemistry. Optical densities of nitric oxide synthase-positive neurons were assessed in 50 randomly selected fields of each of the above regions of the cortices, in each case by microscopic photometry. In the frontal cortex of the Alzheimer group, while a decrease in the number of nitric oxide synthase-positive neurons was evident, the nitric oxide synthase neurons, on the other hand, showed an increased optical density in layers II-IV when compared with those of normal ageing. In the occipital cortices, no significant differences in optical density were recorded between the normal ageing and Alzheimer specimens. In the entorhinal cortex, the optical densities of nitric oxide synthase neurons were again similar between the Alzheimer and age-matched control groups. In the hippocampar formation itself, there was an increase of nitric oxide synthase staining in the Alzheimer patients. These results show that (i) nitric oxide synthase neurons are abundant in the human cortex, (ii) the distribution of nitric oxide synthase neurons differs between different cortical regions, and (iii) there are differences between normal ageing and Alzheimer patients in the frontal cortex and the hippocampus.

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.

Tyrosine hydroxylase- and dopamine-β-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.

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.

Further Studies on the Effect of Low-Dose Laser Irradiation on Cultured Retinal Pigment Cells of the Chick

The effect of low-intensity laser irradiation on pigment cells cultured by chorioallantoic method was studied. Laser irradiation influenced the cell shapes and sizes of the pigment cells. Metabolically, this treatment increased thymidine uptake and incorporation but reduced those of leucine. The phagocytic activity as measured by latex particles uptake was not affected. It was concluded that the biological effect of laser irradiation on cell cultures depends on the dose applied, the individual tissue and other factors.

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.

Further studies on the morphology of the owl's retina.

The retina of the owl was studied by the wet-mount method and the PAS technique. The presence of hyperboloids and paraboloids and three types of oil droplets was indicated.

Dermotoxicity of the mosquito repellent related to rabbit ears

A commercial brand of mosquito repellent which contains dimethyl phthalate and diethyltoluamide was found causing various forms of dermatitis in rabbit ears.

The effect of laser on the developing rodent retinas

The effect of laser on the developing retinas of the rodents was studied. The visual cell layers and “the inner nuclear layers were involved.

Responses of the Retinal Pigment Epithelium of the Mouse after Acute Loss of Blood

Albino mice were bled through the hearts by cardiac puncture and 1/2, 1/3 and 1/4 mls of blood were taken out from 3 groups of animals. respectively. Half of the experimental animals were reinfused with 5% dextrose 1 h after bleeding. All were killed either 2, 5, 9, 24, 48 or 72 h after bleeding, and the phagosome numbers per 5 pigment cells counted and compared with control retinae. A severe decrease was evident after bleeding and the decrease leveled off 48 h afterwards. Reinfusion with dextrose had a positive beneficial effect.