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David I Vaney

Publications and source records attributed to David I Vaney.

8 recordsLinked to original sources
PubMed2006

Local edge detectors: a substrate for fine spatial vision at low temporal frequencies in rabbit retina.

Visual acuity is limited by the size and density of the smallest retinal ganglion cells, which correspond to the midget ganglion cells in primate retina and the beta-ganglion cells in cat retina, both of which have concentric receptive fields that respond at either light-On or light-Off. In contrast, the smallest ganglion cells in the rabbit retina are the local edge detectors (LEDs), which respond to spot illumination at both light-On and light-Off. However, the LEDs do not predominate in the rabbit retina and the question arises, what role do they play in fine spatial vision? We studied the morphology and physiology of LEDs in the isolated rabbit retina and examined how their response properties are shaped by the excitatory and inhibitory inputs. Although the LEDs comprise only approximately 15% of the ganglion cells, neighboring LEDs are separated by 30-40 microm on the visual streak, which is sufficient to account for the grating acuity of the rabbit. The spatial and temporal receptive-field properties of LEDs are generated by distinct inhibitory mechanisms. The strong inhibitory surround acts presynaptically to suppress both the excitation and the inhibition elicited by center stimulation. The temporal properties, characterized by sluggish onset, sustained firing, and low bandwidth, are mediated by the temporal properties of the bipolar cells and by postsynaptic interactions between the excitatory and inhibitory inputs. We propose that the LEDs signal fine spatial detail during visual fixation, when high temporal frequencies are minimal.

Action Potentials↗
PubMed2005

Gap-junction communication between subtypes of direction-selective ganglion cells in the developing retina.

The On-Off direction-selective ganglion cells (DSGCs) in the rabbit retina comprise four distinct subtypes that respond preferentially to image motion in four orthogonal directions; each subtype forms a regular territorial array, which is overlapped by the other three arrays. In this study, ganglion cells in the developing retina were injected with Neurobiotin, a gap-junction-permeable tracer, and the DSGCs were identified by their characteristic type 1 bistratified (BiS1) morphology. The complex patterns of tracer coupling shown by the BiS1 ganglion cells changed systematically during the course of postnatal development. BiS1 cells appear to be coupled together around the time of birth, but, over the next 10 days, BiS1 cells decouple from each other, leading to the mature pattern in which only one subtype is coupled. At about postnatal day 5, before the ganglion cells become visually responsive, each of the BiS1 cells commonly showed tracer coupling both to a regular array of neighboring BiS1 cells, presumably destined to be DSGCs of the same subtype, and to a regular array of overlapping BiS1 cells, presumably destined to be DSGCs of a different subtype. The gap-junction intercellular communication between subtypes of DSGCs with different preferred directions may play an important role in the differentiation of their synaptic connectivity, with respect to either the inputs that DSGCs receive from retinal interneurons or the outputs that DSGCs make to geniculate neurons.

Animals↗
PubMed2004

Type 1 nitrergic (ND1) cells of the rabbit retina: comparison with other axon-bearing amacrine cells.

NADPH diaphorase (NADPHd) histochemistry labels two types of nitrergic amacrine cells in the rabbit retina. Both the large ND1 cells and the small ND2 cells stratify in the middle of the inner plexiform layer, and their overlapping processes produce a dense plexus, which makes it difficult to trace the morphology of single cells. The complete morphology of the ND1 amacrine cells has been revealed by injecting Neurobiotin into large round somata in the inner nuclear layer, which resulted in the labelling of amacrine cells whose proximal morphology and stratification matched those of the ND1 cells stained by NADPHd histochemistry. The Neurobiotin-injected ND1 cells showed strong homologous tracer coupling to surrounding ND1 cells, and double-labelling experiments confirmed that these coupled cells showed NADPHd reactivity. The ND1 amacrine cells branch in stratum 3 of the inner plexiform layer, where they produce a sparsely branched dendritic tree of 400-600 microm diameter in ventral peripheral retina. In addition, each cell gives rise to several fine beaded processes, which arise either from a side branch of the dendritic tree or from the tapering of a distal dendrite. These axon-like processes branch successively within the vicinity of the dendritic field before extending, with little or no further branching, for 3-5 mm from the soma in ventral peripheral retina. Consequently, these cells may span one-third of the visual field of each eye, and their spatial extent appears to be greater than that of most other types of axon-bearing amacrine cells injected with Neurobiotin in this study. The morphology and tracer-coupling pattern of the ND1 cells are compared with those of confirmed type 1 catecholaminergic cells, a presumptive type 2 catecholaminergic cell, the type 1 polyaxonal cells, the long-range amacrine cells, a novel type of axon-bearing cell that also branches in stratum 3, and a type of displaced amacrine cell that may correspond to the type 2 polyaxonal cell.

Amacrine Cells↗
PubMed2003

New directions in retinal research.

Direction-selective retinal ganglion cells (DSGCs) respond to image motion in a "preferred" direction but not the opposite "null" direction. Extracellular spike recordings from rabbit DSGCs suggested that the key mechanism underlying the directional responses is spatially offset inhibition projecting in the null direction. Recent patch-clamp recordings have shown that this inhibition, which acts directly on the DSGC, is already direction selective. Dual recordings established that the inhibition arises from starburst amacrine cells (SBACs) located on the null side of the DSGC but not from those on the preferred side. Thus, for each radially symmetric SBAC, processes pointing in different directions would provide the null-direction inhibition to subtypes of DSGCs with different preferred directions. Ca2+ imaging revealed that the SBAC terminal processes respond more strongly to image motion away from the soma than towards the soma, therefore accounting for the direction selectivity of the inhibitory input to the DSGCs.

Amacrine Cells↗
PubMed2002

Diverse synaptic mechanisms generate direction selectivity in the rabbit retina.

The synaptic conductance of the On-Off direction-selective ganglion cells was measured during visual stimulation to determine whether the direction selectivity is a property of the circuitry presynaptic to the ganglion cells or is generated by postsynaptic interaction of excitatory and inhibitory inputs. Three synaptic asymmetries were identified that contribute to the generation of direction-selective responses: (1) a presynaptic mechanism producing stronger excitation in the preferred direction, (2) a presynaptic mechanism producing stronger inhibition in the opposite direction, and (3) postsynaptic interaction of excitation with spatially offset inhibition. Although the on- and off-responses showed the same directional tuning, the off-response was generated by all three mechanisms, whereas the on-response was generated primarily by the two presynaptic mechanisms. The results indicate that, within a single neuron, different strategies are used within distinct dendritic arbors to accomplish the same neural computation.

Action Potentials↗
PubMed2002

Direction selectivity in the retina.

The neuronal circuitry underlying the generation of direction selectivity in the retina has remained elusive for almost 40 years. Recent studies indicate that direction selectivity may be established within the radial dendrites of 'starburst' amacrine cells and that retinal ganglion cells may acquire their direction selectivity by the appropriate weighting of excitatory and inhibitory inputs from starburst dendrites pointing in different directions. If so, this would require unexpected complexity and subtlety in the synaptic connectivity of these CNS neurons.

Amacrine Cells↗
PubMedDate not supplied

The type 1 polyaxonal amacrine cells of the rabbit retina: a tracer-coupling study.

The type 1 polyaxonal (PA1) cell is a distinct type of axon-bearing amacrine cell whose soma commonly occupies an interstitial position in the inner plexiform layer; the proximal branches of the sparse dendritic tree produce 1-4 axon-like processes, which form an extensive axonal arbor that is concentric with the smaller dendritic tree (Dacey, 1989; Famiglietti, 1992a,b). In this study, intracellular injections of Neurobiotin have revealed the complete dendritic and axonal morphology of the PA1 cells in the rabbit retina, as well as labeling the local array of PA1 cells through homologous tracer coupling. The dendritic-field area of the PA1 cells increased from a minimum of 0.15 mm2 (0.44-mm equivalent diameter) on the visual streak to a maximum of 0.67 mm2 (0.92-mm diameter) in the far periphery; the axonal-field area also showed a 3-fold variation across the retina, ranging from 3.1 mm2 (2.0-mm diameter) to 10.2 mm2 (3.6-mm diameter). The increase in dendritic- and axonal-field size was accompanied by a reduction in cell density, from 60 cells/mm2 in the visual streak to 20 cells/mm2 in the far periphery, so that the PA1 cells showed a 12 times overlap of their dendritic fields across the retina and a 200-300 times overlap of their axonal fields. Consequently, the axonal plexus was much denser than the dendritic plexus, with each square millimeter of retina containing approximately 100 mm of dendrites and approximately 1000 mm of axonal processes. The strong homologous tracer coupling revealed that approximately 45% of the PA1 somata were located in the inner nuclear layer, approximately 50% in the inner plexiform layer, and approximately 5% in the ganglion cell layer. In addition, the Neurobiotin-injected PA1 cells sometimes showed clear heterologous tracer coupling to a regular array of small ganglion cells, which were present at half the density of the PA1 cells. The PA1 cells were also shown to contain elevated levels of gamma-aminobutyric acid (GABA), like other axon-bearing amacrine cells.

Amacrine Cells↗