Biomedical subjects

D V Pow

Publications and source records attributed to D V Pow.

63 records · Page 4Linked to original sources

PubMedDate not supplied

Are neuronal transporters relevant in retinal glutamate homeostasis?

Exposure of isolated retinas to 30 microM D-aspartate, which is a substrate for all high affinity glutamate transporters, for 30 min, resulted in the accumulation of such D-aspartate into Müller glial cells but not glutamatergic neurons as evinced by immunocytochemistry for D-aspartate. Further incubation of such loaded retinas in physiological media, in the absence of D-aspartate, resulted in the slow release of accumulated D-aspartate from the Müller cells and its accumulation into populations of photoreceptors and bipolar cells. This result indicates that after initial transport into Müller cells, reversal of direction of transport of D-aspartate, and thus by inference glutamate, by GLAST, readily occurs. D-aspartate released by Müller cells was strongly accumulated into cone photoreceptors which are known to express GLT-1, and into rod photoreceptors which we demonstrate here to express the retina specific glutamate transporter EAAT5 (excitatory amino transporter 5). Populations of glutamatergic bipolar cells, which express GLT-1 also exhibited avid uptake of D-aspartate. We conclude that the Müller cell glutamate transporter GLAST is responsible for most of the initial glutamate clearance in the retina after its release from neurones. However, some glutamate is also returned from Müller cells, to neurons expressing GLT-1 and EAAT5, albeit at a slow rate. These data suggest that the role of neuronal glutamate transporters in the retina may be to facilitate a slow process of recycling glutamate back from Müller cells to neurons after its initial clearance from perisynaptic regions by GLAST.

ATP-Binding Cassette Transporters↗

PubMedDate not supplied

Immunocytochemical evidence for an axonal localization of GABA in the optic nerves of rabbits, rats, and cats.

We have examined, by light-microscopic immunocytochemistry, the distribution of GABA in the optic nerves of adult rabbits, rats, and cats. Within the optic nerves, immunoreactivity for GABA was restricted to a small subset of axons; some axons were strongly labelled, others weakly labelled, whilst most axons were unlabelled. Glia and other non-neuronal elements were always unlabelled. Our ability to detect GABA in optic nerve axons of adult mammals contrasts with previous reports that indicate a lack of GABA immunoreactivity in such axons. We suggest that this discrepancy may be due to the sensitivity of our immunocytochemical techniques which enable us to detect low concentrations of GABA.

Animals↗

PubMedDate not supplied

Early appearance and transient expression of putative amino acid neurotransmitters and related molecules in the developing rabbit retina: an immunocytochemical study.

We have studied, by immunocytochemistry, the ontogeny of GABA, glycine, glutamate, glutamine, and taurine-containing cells in the rabbit retina. Amacrine cells show GABA immunoreactivity by embryonic day 25 (E25) and throughout postnatal life. By contrast, ganglion cells and horizontal cells are only transiently GABA-immunoreactive (-IR); few appear GABA-IR by the third postnatal week. At maturity, glycine is present in amacrine cells and in some bipolar cells. During development, putative ganglion cells transiently contained glycine between E25 and postnatal day 3 (P3), whereas immunolabelling in presumed amacrine cells and bipolar cells persists after birth. Ganglion cells, bipolar cells, photoreceptors, and some amacrine cells are glutamate-IR in the adult retina. Glutamate immunoreactivity first appears in the somata and processes of cytoblastic cells by E20 and is prominent by E25. Surprisingly, ganglion cells are not strongly glutamate-IR until just before eye-opening, at postnatal day 10 (P10), coincident with the appearance of glutamine in their somata and in Müller glial cells. Bipolar cells are glutamate-IR before they or Müller cells contain high levels of glutamine (at P10). Glutamate immunoreactivity in photoreceptors is progressively restricted to the inner segments by eye-opening. At no stage are presumed horizontal cells glutamate-IR or glutamine-IR, but some amacrine cells show glutamate- and glutamine-IR by P10. Taurine is localized to photoreceptors and Müller glial in the adult retina. Some cytoblasts are taurine-IR at E20; with ensuing development, taurine labelling becomes restricted primarily to Müller cells and photoreceptors; some putative bipolar cells may also be labelled. However, for a few days around birth, cells resembling horizontal cells, also show taurine immunoreactivity. The early appearance and often transient expression of these amino acids in retinal cells suggests that these neuroactive molecules may be involved in the structural and functional development of the retina.

Animals↗

PubMedDate not supplied

The DAPI-3 amacrine cells of the rabbit retina.

In the rabbit retina, the nuclear dye, 4,6,diamidino-2-phenylindole (DAPI), selectively labels a third type of amacrine cell, in addition to the previously characterized type a and type b cholinergic amacrine cells. In this study, these "DAPI-3" amacrine cells have been characterized with respect to their somatic distribution, dendritic morphology, and neurotransmitter content by combining intracellular injection of biotinylated tracers with wholemount immunocytochemistry. There are about 100,000 DAPI-3 amacrine cells in total, accounting for 2% of all amacrine cells in the rabbit retina, and their cell density ranges from about 130 cells/mm2 in far-peripheral retina to 770 cells/mm2 in the visual streak. The thin varicose dendrites of the DAPI-3 amacrine cells form a convoluted dendritic tree that is symmetrically bistratified in S1/S2 and S4 of the inner plexiform layer. Tracer coupling shows that the DAPI-3 amacrine cells have a fivefold dendritic-field overlap in each sublamina, with the gaps in the arborization of each cell being occupied by dendrites from neighboring cells. The DAPI-3 amacrine cells consistently show the strongest glycine immunoreactivity in the rabbit retina and they also accumulate exogenous [3H]-glycine to a high level. By contrast, the AII amacrine cells, which are the best characterized glycinergic cells in the retina, are amongst the most weakly labelled of the glycine-immunopositive amacrine cells. The DAPI-3 amacrine cells costratify narrowly with the cholinergic amacrine cells and the On-Off direction-selective ganglion cells, suggesting that they may play an important role in movement detection.

Animals↗

PubMedDate not supplied

Analysis of the distribution of glycine and GABA in amacrine cells of the developing rabbit retina: a comparison with the ontogeny of a functional GABA transport system in retinal neurons.

The objectives of this study were to (1) determine whether the glycinergic and GABAergic amacrine cells in the developing rabbit retina were neurochemically distinct at birth, (2) determine if the ratio of GABAergic to glycinergic amacrine cells was constant during development, (3) determine whether the capacity to take up a GABA analogue was restricted to GABAergic neurons, and (4) whether initiation of GABA transport into GABAergic neurons preceded the presence of a content of GABA in these neurons. We have used a novel strategy to immunolocalize a non-endogenous GABA analogue, gamma-vinyl GABA, which is taken up into neurons by a GABA transporter. Examination of serial semithin resin-embedded sections of neonatal rabbit retinae that had been immunolabelled for glycine, GABA or gamma-vinyl GABA revealed that at 1 day postnatum, 60% of amacrine cells contain glycine but not GABA and did not accumulate gamma-vinyl GABA, which is similar to the percentage of glycinergic amacrine cells in the adult retina. The vast majority of the remaining amacrine cells contained GABA and many also transported gamma-vinyl GABA; however, a significant number of GABA-containing cells failed to accumulate gamma-vinyl GABA suggesting that possession of a content of GABA did not have to be preceded by, or be concomitant with, the presence of a GABA transport system. By 10 days postnatum, over 99% of GABA-containing amacrine cells also transported gamma-vinyl GABA indicating their functional maturity. Analysis of the horizontal cells revealed no evidence for uptake of gamma-vinyl GABA, but another GABA analogue, diaminobutyric acid, which is a substrate both for the neuron-associated GABA transporter and the glial GABA transporter, was accumulated into some horizontal cells at 21 days postnatum, a time point when these cells also contain endogenous GABA. We conclude that amacrine cells are committed to being GABAergic or glycinergic at, or prior to birth, and that in some amacrine cells, expression of a content of GABA may occur prior to the capacity to transport GABA. Conversely, in some ganglion cells transport of gamma-vinyl GABA may precede a content of GABA.

Aging↗

PubMedDate not supplied

Expression of glycine and the glycine transporter glyt-1 in the developing rat retina.

Previous studies show that glycine transporter-1 (glyt-1) is a consistent membrane marker of adult retinal neurons that are likely to release glycine at their synaptic terminals (Pow, 1998; Vaney et al., 1998; Pow & Hendrickson, 1999). The current study investigated when glyt-1 immunoreactivity appeared in the postnatal rat retina, and whether all glycine-containing neurons also labelled for glyt-1. Ganglion cells, horizontal cells, and photoreceptors showed transient labelling. Many cells in the ganglion cell layer are immunoreactive for both glycine and glyt-1 at postnatal day (Pd) 1 but both are minimal by Pd5. Transient immunoreactivity for both glyt-1 and glycine was observed in presumptive horizontal cells between Pd5 and Pd10. At Pd1 many cells in the outer part of the retina which resembled immature photoreceptors were heavily labelled for glycine, but did not express glyt-1; these disappeared at older ages. These findings suggest diverse mechanisms and transient roles for glycine in the developing rat retina. In the adult rat retina, a subpopulation of amacrine cells are prominently immunoreactive for both glycine and glyt-1. These cells labelled for glycine at Pd1, but did not express significant levels of glyt-1 until Pd5. Processes from these amacrine cells did not reach the inner half of the inner plexiform layer until Pd10-14. Bipolar cells became glycine-IR between Pd10 and Pd14, but consistently lacked any glyt-1 immunoreactivity. This temporal pattern of labelling strongly indicates that bipolar cells label for glycine when gap junctions become functional between glycine/glyt-1 immunoreactive amacrine cells and cone bipolar cells.

Amino Acid Transport Systems, Neutral↗

PubMedDate not supplied

Distribution of the glycine transporter glyt-1 in mammalian and nonmammalian retinae.

We have examined the distribution of the glycine transporter glyt-1 in retinae of macaques, cats, rabbits, rats, and chickens. In all species, all glycine-containing amacrine cells expressed immunoreactivity for glyt-1, though the intensity of immunoreactivity for glyt-1 did not appear to directly correlate with the intensity of immunoreactivity for glycine in individual cells. A small subpopulation of glycine-immunoreactive displaced amacrine cells or ganglion cells also expressed glyt-1 in retinae from macaques, cats, chickens, and rats but not in retinae from rabbits. In addition, in all species examined, some displaced amacrine cells also contained glycine but did not express glyt-1. In monkeys, cats, and rats, populations of cells which we interpret as being glycine-containing interplexiform cells expressed glyt-1: these cells lacked a content of glutamate, suggesting they are not bipolar cells. The glycine-containing bipolar cells did not express glyt-1, suggesting that these cells probably acquired their content of glycine by other means such as via gap junctional connections with glycine-containing amacrine cells.

Amino Acid Transport Systems, Neutral↗

PubMedDate not supplied

Neuronal composition and morphology in layer IV of two vibrissal barrel subfields of rat cortex.

The technique of intracellular injection in fixed, flattened slices was used to study neuronal composition and morphology in the postero-medial barrel subfield (PMBSF) and the antero-lateral barrel subfield (ALBSF) in layer IV of rat cortex. The PMBSF and the ALBSF contain the cortical representation of the mystacial and rostral snout vibrissae respectively. Neuronal composition differed between the PMBSF and the ALBSF. Modified pyramidal cells were the most numerous neuronal type in the PMBSF (73.1%), whereas spiny multipolar (stellate) neurons were the most numerous type in the ALBSF (40.9%). Tangential dendritic field areas of modified pyramidal cells and spiny multipolar cells in the barrels of the two barrel subfields were compared. Dendritic field areas of spiny multipolar neurons located in the barrels of the PMBSF and the ALBSF were similar (mean +/- SD; 2.44 +/- 1.83 x 10(4) and 2.88 +/- 1.47 x 10(4) microns2 respectively). Likewise, there was no significant difference in 'basal' dendritic field area of modified pyramidal neurons located in the barrels of the two different barrel subfields (4.63 +/- 1.96 x 10(4) and 4.45 +/- 1.81 x 10(4) microns2 for PMBSF and ALBSF respectively). The mean cross-sectional area of PMBSF barrels (20.5 +/- 5.69 x 10(4) microns2) in which neurons were injected was approximately seven times larger than that of the ALBSF (2.94 +/- 1.46 x 10(4) microns2). Thus, on average, the dendritic territories of these two neuronal classes sample a larger proportion of the cross-sectional area of the barrels in the ALBSF than in the PMBSF. We conclude that the close relationship between basal dendritic field area of supragranular pyramidal neurons and module size, reported in studies of other sensory areas, is not evident in all barrel subfields of the rat.

Animals↗

PubMedDate not supplied

Expression of glycine and the glycine transporter Glyt-1 in the developing rat retina.

Previous studies show that glycine transporter-1 (glyt-1) is a consistent membrane marker of adult retinal neurons that are likely to release glycine at their synaptic terminals (Pow, 1998; Vaney et al., 1998; Pow & Hendrickson, 1999). The current study investigated when glyt-1 immunoreactivity appeared in the postnatal rat retina, and whether all glycine-containing neurons also labelled for glyt-1. Ganglion cells, horizontal cells, and photoreceptors showed transient labelling. Many cells in the ganglion cell layer are immunoreactive for both glycine and glyt-1 at postnatal day (Pd) 1 but both are minimal by Pd5. Transient immunoreactivity for both glyt-1 and glycine was observed in presumptive horizontal cells between Pd5 and Pd10. At Pd1 many cells in the outer part of the retina which resembled immature photoreceptors were heavily labelled for glycine, but did not express glyt-1 these disappeared at older ages. These findings suggest diverse mechanisms and transient roles for glycine in the developing rat retina. In the adult rat retina, a subpopulation of amacrine cells are prominently immunoreactive for both glycine and glyt-1. These cells labelled for glycine at Pd1, but did not express significant levels of glyt-1 until Pd5. Processes from these amacrine cells did not reach the inner half of the inner plexiform layer until Pd10-14. Bipolar cells became glycine-IR between Pd10 and Pd14, but consistently lacked any glyt-1 immunoreactivity. This temporal pattern of labelling strongly indicates that bipolar cells label for glycine when gap junctions become functional between glycine/glyt-1 immunoreactive amacrine cells and cone bipolar cells.

Amino Acid Transport Systems, Neutral↗