Eric Yu Pang Cho

Serotonin 5-HT2A and 5-HT6 receptors in the prefrontal cortex of Alzheimer and normal aging patients

BackgroundIt has been hypothesized that alterations of the serotonergic system contribute to neuropsychiatric symptoms in Alzheimer disease (AD). Cellular expressions of the two serotonergic receptors 5-HT2A and 5-HT6 have therefore been determined by immunohistochemistry in the prefrontal cortex of patients with AD (n=6) and normal age-matched controls (n = 7).ResultsIn normal aging patients, 5-HT2A label was mainly observed in large pyramidal cells, but to a lesser extent also in small pyramidal cells and in stellate cells of cortical layers II-VI. In AD, a similar distribution was observed, but density of positive cells was significantly reduced by 33%. In aging control patients, the 5-HT6 receptor was expressed by pyramidal cells and occasional stellate cells, not only of layers II-V, but also of layer I, where a distinct label was observed in neurons and surrounding fibers. 5-HT6 receptor expression in AD patients had the same pattern, but was significantly decreased by 40%.ConclusionOur results indicate that a decline in neurons expressing 5-HT2A, but also 5-HT6 receptors may play a role in the etiopathology of neuropsychiatric symptoms in AD.

Rate of regrowth of damaged retinal ganglion cell axons regenerating in peripheral nerve graft in adult hamsters

The rate of regrowth of ganglion cell axons regenerating into a peripheral nerve graft implanted into the retina of adult hamster was measured, utilizing the method of retrograde labelling by horseradish peroxidase. The fastest regrowing axons were found, after an initial delay of 4.5 days, to extend at about 2 mm/day in the graft. The role of the cell body in controlling the rate of axonal regeneration was briefly discussed.

Characterization of the sprouting response of axon-like processes from retinal ganglion cells after axotomy in adult hamsters: a model using intravitreal implantation of a peripheral nerve

SummaryPeripheral nerves provide a favourable environment for damaged CNS axons to sprout and regenerate. It has also been demonstrated that retinal ganglion cells respond to a peripheral, nerve segment grafted to the retina by emitting axon-like processes from the somatodendritic compartment into the graft. The factors influencing the pattern of sprouting of axotomized retinal ganglion cells were explored in this study by implanting a short segment of peripheral nerve, which did not come into contact with the retina, into the vitreous body of an eye whose optic nerve was concurrently crushed. Silver staining was used to assess the morphology of the retinal ganglion cells which underwent sprouting.Some retinal ganglion cells were induced to sprout axon-like processes; these emerged primarily from dendrites and less frequently from the soma or intraretinal axon. Implantation of a nonviable graft (freezed-thawed) elicited only minimal sprouting. These results suggest that diffusible factors secreted by cells in the graft are a possible stimulus to sprouting in axotomized retinal ganglion cells.Examination of the pattern of dendritic sprouting indicates that sprouting was most intense (in terms of number of sprouts per cell) at early times post-axotomy. Moreover, a differential pattern of development of sprouts arising from individual primary dendrites of the same cell was observed; sprouts tend to arise from all primary dendrites initially but as the post-axotomy time increased, retraction of sprouts from some primary dendrites occurred. Concomitant with this retraction, however, there was an increase in the number of sprouts on those primary dendrites which were still in the active phase of sprouting. Selective stabilization of sprouts by extrinsic factors may account for this phenomenon.Changes in the area and outline (irregularity) of the somata of retinal ganglion cells with sprouts from two weeks to two months after optic nerve crush could be correlated temporally with the intensity of sprouting from the dendritic tree, suggesting that during sprouting, intrinsic mechanisms coordinate the responses of different cellular compartments.In contrast to extensive ectopic sprouting of axotomized retinal ganglion cells in the presence of an intravitreal graft, when a long peripheral nerve segment is grafted to the cut optic nerve, there is extensive axonal regeneration into the graft from retinal ganglion cells, most of which did not exhibit ectopic sprouting. Thus, a hierarchy of sprouting sites within a neuron seems to exist, with the damaged axonal tip being the most favoured site, followed by the dendrites, and then the intraretinal axon. The soma appears to be the least preferred compartment for sprout emission.

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.

De novo formation of axon-like processes from axotomized retinal ganglion cells which exhibit long distance growth in a peripheral nerve graft in adult hamsters

Damaged axons in the central nervous system of the adult mammal can be stimulated to regenerate extensively into a peripheral nerve graft. It was generally believed that the new axonal sprouts which extend into the graft arose from the injured proximal axonal stumps. However, when retinal ganglion cells of the adult hamster were axotomized by crushing the optic nerve and the proximal axonal stump was not in direct apposition to the graft, a new axon-like process could be seen to be emitted from either the cell soma or dendrite and extended in the graft for at least 1-2 cm. This axon-like process was distinct from the original injured axon which could still be seen to course towards the optic disc in the retina. Evidently, even a fully differentiated central nervous system neuron of the adult mammal retains a great degree of morphological plasticity so that if the original axon is discouraged to regrow after injury, other parts of the neurons can act as favourable sites for the sprouting of a new axon-like process.

Anti-tumor action of trichosanthin, a type 1 ribosome-inactivating protein, employed in traditional Chinese medicine: a mini review

Trichosanthin (TCS) as a midterm abortifacient medicine has been used clinically in traditional Chinese medicine for centuries. Additionally, TCS manifests a host of pharmacological properties, for instance, anti-HIV and anti-tumor activities. TCS has been reported to inhibit cell growth of a diversity of cancers, including cervical cancer, choriocarcinoma, and leukemia/lymphoma, etc. This article purported to review the various anti-tumor activities of TCS and the mechanism of apoptosis it induced in these tumor cells. These research progresses provide an insight into cancer research and treatment as well as disclose new pharmacological properties of the ancient but popular Chinese medicine.

Antibodies against neurofilament subunits label retinal ganglion cells but not displaced amacrine cells of hamsters

Although neurofilament (NF) antibodies have been used to visualize ganglion cells and their axons in the retina, it is not known, however, how many ganglion cells contain NF, and how the various NF subunits are distributed in the ganglion cells. Moreover, it is not known whether displaced amacrine cells in the ganglion cell layer are also labelled. In order to see whether NF antibodies can be used as a specific marker for ganglion cells, antibodies raised against the low (NF-L), middle (NF-M) and high (NF-H) molecular weight subunits of NF were employed to stain retinal whole-mounts of adult hamsters after pre-labelling the ganglion cells with Granular Blue. It was found that NF-L and NF-H antibodies labelled 38,777 and 17,750 cells in the ganglion cell layer respectively. By co-localization with GB-labelled cells, 88% of NF-L positive cells and 91% of NF-H positive cells were found to be ganglion cells. In contrast, the NF-M antibody labelled only very few ganglion cells (418 per retina) although robust staining of axonal bundles was observed. Thus, NF antibodies may prove useful in studying this population of ganglion cells.

Morphological changes of retinal ganglion cells regenerating axons along peripheral nerve grafts: a Lucifer Yellow and silver staining study.

The morphology of the retinal ganglion cells (RGCs) with their axons regenerating along a peripheral nerve graft at different post-grafting periods was studied by the intracellular injection of Lucifer yellow (LY) and silver staining methods. Several morphological features which were observed on developing RGCs, but not mature RGCs, have also been observed in the regenerating RGCs studied by the intracellular injection of LY. These morphological features observed on the regenerating RGCs included intraretinal axonal branches and collaterals, spine-like processes on the dendrites and soma, and short processes on the soma. These results suggest that damaged mammalian RGCs may be able to recapitulate certain cellular events which occur during normal development provided the regenerating cells are given the proper stimulus and a favorable environment for regrowth. From the results of both LY injection and silver staining experiments, it was found that the dendrites of the regenerating RGCs were, in general, much simpler than that of control Type I RGCs. However, regenerating RGCs with different degree of dendritic complexity could be observed in all post-grafting periods studied, and the dendritic complexity seems to decrease continuously with the increase in the post-grafting time. These results suggest that the ability to regenerate an axon is not closely related to dendritic responses and the peripheral nerve does not seem to be able to prevent the deterioration and retraction of the dendrites.

Hepatocyte Growth Factor Promotes Long‐Term Survival and Axonal Regeneration of Retinal Ganglion Cells after Optic Nerve Injury: Comparison with CNTF and BDNF

Different trophic factors are known to promote retinal ganglion cell survival and regeneration, but each had their own limitations. We report that hepatocyte growth factor (HGF) confers distinct advantages in supporting ganglion cell survival and axonal regeneration, when compared to two well‐established trophic factors ciliary neurotrophic factor (CNTF) and brain‐derived neurotrophic factor (BDNF).

Sprouting of axon-like processes from axotomized retinal ganglion cells is influenced by the distance of axotomy from the cell body and the mode of transplantation of the peripheral nerve.

It is a well known fact that the proximity of an axonal lesion from the cell body influences the degree of neuronal survival: a lesion close to the cell body leads to more severe cell death and vice versa. On the other hand, experiments involving transplantation of a peripheral nerve (PN) to various central nervous system (CNS) regions to induce axonal regeneration have suggested that axonal regrowth is more vigorous when the grafting is performed closer to the cell body. It is not clear, however, whether it is the distance of the site of axotomy or the location of the trophic source (PN graft) or both from the cell body which dictates the vigorousness of axonal regrowth. Using either a model of transplantation of a PN to the retina or implantation of a short PN into the vitreous body of the eye of the adult hamster, we have demonstrated that sprouting of axon-like processes from retinal ganglion cells (RGCs) depends on the distance of axotomy from the cell body when the PN graft is maintained at a constant distance from the cell body. Moreover, it was found that the distance of axotomy at which sprouting of axon-like processes could be induced was different for the 2 paradigms: with the intravitreal PN model, sprouting was observed even after intracranial ON cut whereas it was absent in the PN grafting-to-retina paradigm. This suggests that extrinsic influence (in this case an intravitreal PN) can overcome to a certain extent the growth-suppressive effects due to a long distance of axotomy.