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W K Stell

Publications and source records attributed to W K Stell.

At least 73 records · Page 4Linked to original sources
PubMed1975

Goldfish retina: functional polarization of cone horizontal cell dendrites and synapses.

In serial electron micrographs we observed that dendrites of goldfish cone horizontal cells are either central or lateral in ribbon synaptic triads, depending on cone and horizontal cell type. The chromatic properties of cone horizontal cell responses may be explained if the cone horizontal cells act as interneurons, receiving from cones through their central processes but acting on cones through their lateral processes.

Animals↗
PubMed1975

Color-specific interconnections of cones and horizontal cells in the retina of the goldfish.

In Golgi preparations of goldfish retina we have observed three types of horizontal cell which receive exclusively from cones and one which receives exclusively from rods. The cone horizontal cells were designated H1, H2 and H3, in order of increasing dendritic spread, increasing separation from the outer synaptic layer, decreasing size of perikaryon, and decreasing density of cone contacts. Slender appendages with knobby terminal enlargements project horizontal cells by alalyzing serial 1 mum sections with the light microscope. The probable inputs, in terms of visual pigments in the cones which contact them, are: H1, red+green+blue; H2, green+blue; H3, blue. Analysis of previously published work suggests (1) that H1 cells generate monophasic or L-type responses, H2 cells generate biphasic or C1-type responses, and H3 cells generate triphasic or C2-type responses; (2) that H1 cells receive direct functional input at least from red-sensitive cones, H2 cells from green-sensitive cones, and H3 cells from blue-sensitive cones, and (3) that H1 constitute pathways from cones to H2 cells, and H2 cells, and H2 cells constitute pathways from cones and H1 cells to H3 cells. The precise location and route of the transfers, from H1 to H2 and from H2 to H3, are not yet known.

Animals↗
PubMed1975

Horizontal cell axons and axon terminals in goldfish retina.

Retinas of ordinary and black moor varieties of goldfish (Carassius auratus) were prepared by the Golgi method, mounted flat or sectioned vertically, and studied in the light microscope. Three types of horizontal cells whose dendrites contact only cones, and one type whose dendrites contact only rods, were observed. The cone horizontal cells (Cajal's "external horizontal cells") all have slender axons which descend gradually to the inner nuclear layer and terminate there in long, fusiform expansions (Cajal's "internal horizontal cells"). The thin and thick portions of the axons, as well as the perikarya of the horizontal cells, bear small numbers of straight, horizontally-directed, knobby filamentous appendages which may be sites of synaptic contact. The cone horizontal cell axons in goldfish, unlike those in higher vertebrates, do not terminate in contact with synaptic endings of photoreceptor cells, but in proximity to cells and processes deep in the inner nuclear layer. Axons have not yet been demonstrated on rod horizontal cells in goldfish.

Animals↗
PubMed1968

A role for the sodium pump in photoreception in Limulus.

The membranes of photoreceptor cells in Limulus have an electrogenic sodium pump which contributes directly to membrane potential and whose activity is changed by light. These light-induced changes in pump activity underlie the receptor potential.

Adenosine Triphosphatases↗
PubMedDate not supplied

Apomorphine blocks form-deprivation myopia in chickens by a dopamine D2-receptor mechanism acting in retina or pigmented epithelium.

Studies of form-deprivation myopia (FDM) in animal models have shown that postnatal ocular growth is regulated by the quality of patterned images on the retina. One of the major challenges in myopia research is to identify the biochemical mechanisms which translate retinal visual responses into signals that regulate scleral growth. Dopamine (DA) has been implicated in this process, since retinal DA levels decline in FDM and subconjunctival injections of apomorphine (Apo, a nonspecific DA agonist) prevent FDM in a dose-dependent way (Stone et al., 1989). To gain insight into where and how DA ligands act to regulate ocular elongation, we compared the action and distribution of DA receptor ligands injected intravitreally vs. subconjunctivally in young chicks. Ocular length was measured by A-scan ultrasound. We found that daily intravitreal injections of Apo block FDM at a 50% effective dose (ED50) of 5 pg per day, or a peak concentration in the vitreous humor of 108 pM, compared to an ED50 of 2.5 ng for subconjunctival injections as reported by Stone et al. (1989, 1990). [3H]-spiperone, a D2-receptor antagonist, reached average maximum retinal concentrations of 160 pM and 260 pM, during the first hour after intravitreal and subconjunctival administration, respectively, at the ED50 dose. In contrast, the maximum spiperone concentrations in the retinal pigment epithelium (RPE) were 30 pM and 410 pM, respectively, after intravitreal or subconjunctival ED50 doses. Spiperone concentrations in sclera after ED50 doses to the two sites differed by 4 x 10(4) (0.4 pM vs. 1.7 nM, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Endogenous opiates in the chick retina and their role in form-deprivation myopia.

In this study, the possible role of the retinal enkephalin system in form-deprivation myopia (FDM) in the chick eye was investigated. Daily intravitreal injection of the nonspecific opiate antagonist naloxone blocked development of FDM in a dose-dependent manner, while injection of the opiate agonist morphine had no effect at any dose tested. The ED50 for naloxone (calculated maximum concentration in the vitreous) was found to be in the low picomolar range. The results using receptor-subtype-specific drugs were contradictory. Drugs specific for mu and delta receptors had no effect on FDM. The kappa-specific antagonist nor-binaltorphimine (nor-BNI) reduced FDM by about 50% at maximum daily retinal doses ranging between 4 x 10(-10) and 4 x 10(-7) M, while the kappa-specific agonist U50488 blocked FDM in a dose-dependent manner with an ED50 between 5 x 10(-8) and 5 x 10(-7) M. Met-enkephalin immunoreactivity (ME-IR) was localized immunocytochemically to a subset of amacrine cells (ENSLI cells) and their neurites in the inner plexiform layer (IPL). As reported previously, ENSLI cells from untreated chick retinas showed a cyclical pattern of immunoreactivity, with increased immunoreactivity in the light compared to the dark. Form-deprivation did not appear to change this pattern. Amounts of preproenkephalin mRNA from normal or form-deprived eyes were approximately the same under all conditions. Daily injection of naloxone, however, did increase ME-IR in the dark. These results suggest that naloxone may affect release of enkephalin from the ENSLI cells. The results as presented are inconclusive with regards to the role of the enkephalin system in FDM. While the kappa receptor may participate, there is no conclusive evidence here for a direct effect of opiate receptors. The effect of naloxone on form-deprived eyes may be due to its effect on release of peptides from the ENSLI cells.

Analgesics, Opioid↗
PubMedDate not supplied

Spatial, temporal, and intensive determinants of dopamine release in the chick retina.

The retinal dopaminergic system is a global regulator of retinal function. Apart from the fact that the rates of dopamine synthesis and release are increased by increasing illumination, the visual image parameters that influence dopaminergic function are mostly unknown. Roles for spatial and temporal frequency and image contrast are suggested by the effects of form-deprivation with a diffusing goggle. Form-deprivation reduces the rates of dopamine synthesis and release, and induces myopia, which is prevented by dopamine agonists. Our purpose here was to identify visual stimulus parameters that activate dopaminergic amacrine cells and elicit dopamine release. White Leghorn cockerels 4-7 days old were exposed to 2 h of form-deprivation, reduced light intensity, or stimuli of varied temporal or spatial frequency. Activation of dopaminergic neurons, labeled for tyrosine hydroxylase (TH), was assessed with immunocytochemistry for c-Fos, and dopamine release was measured by HPLC analysis of dopamine metabolite accumulation in the vitreous body. Form-deprivation did not reduce TH+ cell activation or vitreal dopamine metabolite accumulation any more than did neutral-density filters of approximately equal transmittance. TH+ cell activation and vitreal metabolite accumulation were not affected significantly by exposure to 2, 5, 10, 15, or 20 Hz stroboscopic stimulation on a dark background, or by sine-wave gratings of 0.089, 0.44, 0.89, 1.04, or 3.13 cycles/deg compared to a uniform gray target of equal mean luminance. These data indicate that the retinal dopaminergic system does not respond readily to short-term changes in visual stimulus parameters, other than light intensity, under the conditions of these experiments.

Amacrine Cells↗
PubMedDate not supplied

Association amacrine cells of Ramón y Cajal: rediscovery and reinterpretation.

In 1895, by means of the Golgi method, Santiago Ramón y Cajal discovered a cell having a unique morphology in the avian retina. This cell had its cell body in the amacrine cell level of the inner nuclear layer, only a few rudimentary dendrites at the outermost level of the inner plexiform layer (IPL), and a long axon coursing horizontally and terminating in the IPL. Despite having defined amacrine cells as cells without axons, Cajal named this cell type "association amacrine cell" (AAC). This discovery was not confirmed by other investigators for nearly a century. Very recently, however, isthmo-optic target cells (IOTCs), which receive the terminals of centrifugal fibers emanating from the isthmo-optic nucleus, have been identified as one type of AAC. As summarized and discussed in this review, the morphology of the AACs as described by Cajal has been completely confirmed. However, since these cells appear to be classical polarized, monoaxonal neurons and lack the dendritic interactions that are typical of amacrine cells, they should be regarded as a distinct type of retinal interneuron and not as amacrine cells.

Animals↗