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Biomedical subjects

David V Pow

Publications and source records attributed to David V Pow.

11 recordsLinked to original sources
PubMed2003

Identification of cholinoceptive glycinergic neurons in the mammalian retina.

The light-evoked release of acetylcholine (ACh) affects the responses of many retinal ganglion cells, in part via nicotinic acetylcholine receptors (nAChRs). nAChRs that contain beta2alpha3 neuronal nicotinic acetylcholine receptors have been identified and localized in the rabbit retina; these nAChRs are recognized by the monoclonal antibody mAb210. We have examined the expression of beta2alpha3 nAChRs by glycinergic amacrine cells in the rabbit retina and have identified different subpopulations of nicotinic cholinoceptive glycinergic cells using double and triple immunohistochemistry with quantitative analysis. Here we demonstrate that about 70% of the cholinoceptive amacrine cells in rabbit retina are glycinergic cells. At least three nonoverlapping subpopulations of mAb210 glycine-immunoreactive cells can be distinguished with antibodies against calretinin, calbindin, and gamma-aminobutyric acid (GABA)(A) receptors. The cholinergic cells in rabbit retina are thought to synapse only on other cholinergic cells and ganglion cells. Thus, the expression of beta2alpha3 nAChRs on diverse populations of glycinergic cells is puzzling. To explore this finding, the subcellular localization of beta2alpha3 was studied at the electron microscopic level. mAb210 immunoreactivity was localized on the dendrites of amacrines and ganglion cells throughout the inner plexiform layer, and much of the labeling was not associated with recognizable synapses. Thus, our findings indicate that ACh in the mammalian retina may modulate glycinergic circuits via extrasynaptic beta2alpha3 nAChRs.

Amino Acid Transport Systems, Neutral↗
PubMed2003

Thiamine deficiency results in downregulation of the GLAST glutamate transporter in cultured astrocytes.

Pyrithiamine-induced thiamine deficiency (TD) is a well-established model of Wernicke's encephalopathy in which a glutamate-mediated excitotoxic mechanism may play an important role in determining selective vulnerability. In order to examine this possibility, cultured astrocytes were exposed to TD and effects on glutamate transport and metabolic function were studied. TD led to decreases in cellular levels of thiamine and thiamine diphosphate (TDP) after 24 h of treatment and decreased activities of the TDP-dependent enzymes alpha-ketoglutarate dehydrogenase and transketolase after 4 and 7 days, respectively. TD treatment for 10 days led to a reversible decrease in the uptake of [(3)H]-D-aspartate, a nonmetabolizable analogue of glutamate. Kinetic analysis revealed that the uptake inhibition was caused by a 47% decrease in the V(max) for uptake of [(3)H]-D-aspartate, with no change in the K(m) value. Immunoblotting showed that this decrease in uptake was due to an 81% downregulation of the astrocyte-specific GLAST glutamate transporter. Loss of uptake activity and GLAST protein were blocked by treatment with the protein kinase C inhibitor H7, while exposure to DCG IV, a group II metabotropic glutamate receptor (mGluR) agonist, resulted in improvement of [(3)H]-D-aspartate uptake and a partial reversal of transporter downregulation. These results are consistent with our recent in vivo findings of a loss of astrocytic glutamate transporters in TD and provide evidence that TD conditions may increase phosphorylation of GLAST, contributing to its downregulation. In addition, manipulation of group II mGluR activity may provide an important strategy in the treatment of this disorder.

Acid Anhydride Hydrolases↗
PubMed2003

Neuronal migration and glial remodeling in degenerating retinas of aged rats and in nonneovascular AMD.

PURPOSE: To demonstrate structural and immunocytochemical changes associated with light-induced degeneration in albino rat retinas and human AMD retinas. METHODS: Retinas from Wistar rats aged 3, 6, or 10 months were examined by immunocytochemistry, with antibodies to neuronal and glial markers. Results were compared with human nonneovascular AMD retinas. RESULTS: In aging rat retinas, many photoreceptors were lost in response to normal ambient light exposure. Photoreceptor loss was preceded by loss of RPE cells. Müller cells extended processes through gaps in Bruch's membrane, into the choroid. immunolabeling for gamma-aminobutyric acid (GABA), the glycine transporter Glyt-1, and the rod bipolar cell marker PKC revealed the presence of numerous neuronal somata and processes that appeared to have migrated into the choroidal region. Processes of presumptive ganglion cells remodeled and stratified in the choroid, where strong labeling for synaptic vesicle antigens was present. Myelination of retinal ganglion cell axons was also observed, especially in the peripheral retina. In AMD retinas, glial rearrangement and displacement of neurons suggestive of their migration were also observed. CONCLUSIONS: In response to loss of RPE and photoreceptor cells, adult retinal neurons migrate out of the retina along remodeled processes of Müller cells. The presence of synaptic vesicle antigens suggests the formation of new synapses between migrating neurons. The myelination is probably due to the ingress of Schwann cells from the sclera. The presence of some similar changes in human AMD retinas suggests that these findings are of broad significance for determining the likely events in transplantation of neurons in the human retina and elsewhere.

Amino Acid Transport Systems, Neutral↗
PubMed2003

Decrease in glial glutamate transporter variants and excitatory amino acid receptor down-regulation in a murine model of ALS-PDC.

Glutamate transporter proteins appear crucial to controlling levels of glutamate in the central nervous system (CNS). Abnormal and/or decreased levels of various transporters have been observed in amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD) and in other neurological disorders. We have assessed glutamate transporter (GLT-1/EAAT2) levels in mice fed washed cycad flour containing a suspected neurotoxin that induces features resembling the Guamanian disorder, ALS-PDC. Down-regulation of glutamate transporter subtypes was detected by immunohistology using antibodies specific for two glial glutamate transporter splice variants (GLT-1alpha and GLT-1B). Immunohistology showed a "patchy" loss of antibody label with the patches centered on blood vessels. Computer densitometry showed significantly decreased GLT-1alpha levels in the spinal cord and primary somatosensory cortex of cycad-fed mice. GLT-1B levels were significantly decreased in the spinal cord, in the motor, somatosensory, and piriform cortices, and in the striatum. Western blots showed a 40% decrease in frontal motor cortex and lumbar spinal cord of cycad-fed mice that appeared to be phosphorylation-dependent. Receptor-binding assays showed decreased NMDA and AMPA receptor levels and increased GABAA receptor levels in cycad-fed mice cortex. These receptor data are consistent with an increased level of extracellular glutamate. The generalized decrease in GLT-1, decreased excitatory amino acid receptor levels, and increased GABAA receptor levels may reflect an early glutamate-mediated excitotoxicity following cycad exposure. Deciphering the series of events leading to neurodegeneration in cycad-fed animals may provide clues leading to therapeutic approaches to halt the early stages of disease progression.

Amyotrophic Lateral Sclerosis↗
PubMed2002

Light and electron microscopic analysis of aquaporin 1-like-immunoreactive amacrine cells in the rat retina.

Aquaporin 1 (AQP1; also known as CHIP, a channel-forming integral membrane protein of 28 kDa) is the first protein to be shown to function as a water channel and has been recently shown to be present in the rat retina. We previously showed (Kim et al. [1998] Neurosci Lett 244:52-54) that AQP1-like immunoreactivity is present in a certain population of amacrine cells in the rat retina. This study was conducted to characterize these cells in more detail. With immunocytochemistry using specific antisera against AQP1, whole-mount preparations and 50-microm-thick vibratome sections were examined by light and electron microscopy. These cells were a class of amacrine cells, which had symmetric bistratified dendritic trees ramified in stratum 2 and in the border of strata 3 and 4 of the inner plexiform layer (IPL). Their dendritic field diameters ranged from 90 to 230 microm. Double labeling with antisera against AQP1 and gamma-aminobutyric acid or glycine demonstrated that these AQP1-like-immunoreactive amacrine cells were immunoreactive for glycine. Their most frequent synaptic input was from other amacrine cell processes in both sublaminae a and b of the IPL, followed by a few cone bipolar cells. Their primary targets were other amacrine cells and ganglion cells in both sublaminae a and b of the IPL. In addition, synaptic output onto bipolar cells was rarely observed in sublamina b of the IPL. Thus, the AQP1 antibody labels a class of glycinergic amacrine cells with small to medium-sized dendritic fields in the rat retina.

Amacrine Cells↗
PubMed2002

Distribution of two splice variants of the glutamate transporter GLT-1 in the developing rat retina.

The distributions of a carboxyl terminal splice variant of the glutamate transporter GLT-1, referred to as GLT-1B, and the carboxyl terminus of the originally described variant of GLT-1, referred to hereafter as GLT-1 alpha, were examined using specific antisera. GLT-1B was present in the retina at very early developmental stages. Labelling was demonstrable at embryonic day 14, and strong labelling was evident by embryonic day 18. Such labelling was initially restricted to populations of cone photoreceptors, the processes of which extended through the entire thickness of the retina and appeared to make contact with the retinal ganglion cells. During postnatal development the GLT-1B-positive photoreceptor processes retracted to form the outer plexiform layer, and around postnatal day 7, GLT-1B-immunoreactive bipolar cells appeared. The pattern of labelling of bipolar cell processes within the inner plexiform layer changed during postnatal development. Two strata of strongly immunoreactive terminals were initially evident in the inner plexiform layer, but by adulthood these two bands were no longer evident and labelling was restricted to the somata and processes (but not synaptic terminals) of the bipolar cells, as well as the somata, processes, and terminals of cone photoreceptors. By contrast, GLT-1 alpha appeared late in postnatal development and was restricted mainly to a population of amacrine cells, although transient labelling was also associated with punctate elements in the outer plexiform layer, which may represent photoreceptor terminals.

Aging↗
PubMed2002

Distribution of two splice variants of the glutamate transporter GLT1 in the retinas of humans, monkeys, rabbits, rats, cats, and chickens.

Antibodies have been generated against two carboxyl-terminal splice variants of the glutamate transporter GLT1, namely, the originally described version of GLT1 and GLT1-B, and labelling has been examined in multiple species, including chickens and humans. Although strong specific labelling was observed in each species, divergent patterns of expression were noted. Moreover, each antibody was sensitive to the phosphorylation state of the appropriate protein, because chemical removal of phosphates using alkaline phosphatase revealed a broader range of labelled elements in most cases. In general, GLT1-B was present in cone photoreceptors and in rod and cone bipolar cells in the retinas of rabbits, rats, and cats. In the cone-dominated retinas of chickens and in marmosets, GLT1-B was associated only with cone photoreceptors, whereas, in macaque and human retinas, GLT1-B was associated with bipolar cells and terminals of photoreceptors. In some species, such as cats, GLT-B was also present in horizontal cells. By contrast, GLT1 distribution varied. GLT1 was associated with amacrine cells in chickens, rats, cats, and rabbits and with bipolar cells in marmosets and macaques. In the rat retina, rod photoreceptor terminals also contained GLT1, but this was evident only in enzymatically dephosphorylated tissues. We conclude that the two variants of GLT1 are present in all species examined but are differentially distributed in a species-specific manner. Moreover, each cell type generally expresses only one splice variant of GLT1.

Amacrine Cells↗
PubMed2002

Aberrant expression of the glutamate transporter excitatory amino acid transporter 1 (EAAT1) in Alzheimer's disease.

Glutamate-mediated toxicity has been implicated in the neurodegeneration observed in Alzheimer's disease. In particular, glutamate transport dysfunction may increase susceptibility to glutamate toxicity, thereby contributing to neuronal cell injury and death. In this study, we examined the cellular localization of the glial glutamate transporter excitatory amino acid transporter 1 (EAAT1) in the cerebral cortex of control, Alzheimer's disease, and non-Alzheimer dementia cases. We found that EAAT1 was strongly expressed in a subset of cortical pyramidal neurons in dementia cases showing Alzheimer-type pathology. In addition, tau (which is a marker of neurofibrillary pathology) colocalized to those same pyramidal cells that expressed EAAT1. These findings suggest that EAAT1 changes are related to tau expression (and hence neurofibrillary tangle formation) in dementia cases showing Alzheimer-type pathology. This study implicates aberrant glutamate transporter expression as a mechanism involved in neurodegeneration in Alzheimer's disease.

Aged↗
PubMed2002

Localization of taurine transporters, taurine, and (3)H taurine accumulation in the rat retina, pituitary, and brain.

The nervous system contains an abundance of taurine, a neuroactive sulfonic acid. Antibodies were generated against two cloned high-affinity taurine transporters, referred to in this study as TAUT-1 and TAUT-2. The distribution of such was compared with the distribution of taurine in the rat brain, pituitary, and retina. The cellular pattern of [(3)H] taurine uptake in brain slices, pituitary slices, and retinas was examined by autoradiography. TAUT-2 was predominantly associated with glial cells, including the Bergmann glial cells of the cerebellum and astrocytes in brain areas such as hippocampus. Low-level labeling for TAUT-2 was also observed in some neurones such as CA1 pyramidal cells. TAUT-1 distribution was more limited; in the posterior pituitary TAUT-1 was associated with the pituicytes but was absent from glial cells in the intermediate and anterior lobes. Conversely, in the brain TAUT-1 was associated with cerebellar Purkinje cells and, in the retina, with photoreceptors and bipolar cells. Our data suggest that intracellular taurine levels in glial cells and neurons may be regulated in part by specific high-affinity taurine transporters. The heterogeneous distribution of taurine and its transporters in the brain does not reconcile well with the possibility that taurine acts solely as a ubiquitous osmolyte in nervous tissues.

Amino Acid Transport Systems, Neutral↗
PubMed2002

Distribution of two splice variants of the glutamate transporter GLT-1 in rat brain and pituitary.

We have performed immunocytochemistry on rat brains using a highly specific antiserum directed against the originally described form of the glutamate transporter GLT-1 (referred to hereafter as GLT-1alpha), and another against a C-terminal splice variant of this protein, GLT-1B. Both forms of GLT-1 were abundant in rat brain, especially in regions such as the hippocampus and cerebral cortex, and macroscopic examination of sections suggested that both forms were generally regionally coexistent. However, disparities were evident; GLT-1alpha was present in the intermediate lobe of the pituitary gland, whereas GLT-1B was absent. Similar marked disparities were also noted in the external capsule, where GLT1A labeling was abundant but GLT-1B was only occasionally encountered. Conversely, GLT-1B was more extensively distributed, relative to GLT-1alpha, in areas such as the deep cerebellar nuclei. In most regions, such as the olfactory bulbs, both splice variants were present but differences were evident in their distribution. In cerebral cortex, patches were evident where GLT-1B was absent, whereas no such patches were evident for GLT-1alpha. At high resolution, other discrepancies were evident; double-labeling of areas such as hippocampus indicated that the two splice variants may either be differentially expressed by closely apposed glial elements or that the two splice variants may be differentially targeted to distinct membrane domains of individual glial cells.

Alternative Splicing↗