Difference between revisions of "On-Off Direction-Selective Ganglion Cell"

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(Anatomy)
(Anatomy)
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[[Image:e2198_reconstruction.png|320px|Reconstructed ganglion and amacrine cells.]]
 
[[Image:e2198_reconstruction.png|320px|Reconstructed ganglion and amacrine cells.]]
 
 
 
 
 
  
 
There are four subtypes, each with a preference for direction.
 
There are four subtypes, each with a preference for direction.

Revision as of 22:27, 3 April 2012

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Image of an On-Off Direction-Selective Ganglion Cell.[1].

Direction selective (DS) cells in the retina are defined as neurons that respond differentially to the direction of a visual stimulus. The term is used to describe a group of neurons that “gives a vigorous discharge of impulses when a stimulus object is moved through its receptive field in one direction.”[2] This direction in which a set of neurons respond most strongly to is their “preferred direction.” In contrast, they do not respond at all to the opposite direction, “null direction.” The preferred direction is not dependent on the stimulus- that is, regardless of the stimulus’ size, shape, or color, the neurons respond when it is moving in their preferred direction, and do not respond if it is moving in the null direction. There are three known types of DS cells in the vertebrate retina of the mouse, ON/OFF DS ganglion cells, ON DS ganglion cells, and OFF DS ganglion cells. Each has a distinctive physiology and anatomy.

This wiki will only apply to ON/OFF DS Ganglion Cells. There are also ON DS Ganglion cells (which respond to the leading edge of a stimulus) and OFF DS Ganglion cells (which respond only to the trailing edge of a stimulus).

Physiology

ON/OFF DS ganglion cells act as local motion detectors. They fire at the onset and offset of a stimulus (a light source). If a stimulus is moving in the direction of the cell’s preference, it will fire at the leading and the trailing edge. Their firing pattern is time-dependent and is supported by the Reichardt- Hassenstain model, which detects spatiotemporal correlation between the two adjacent points.

ON/OFF DS ganglion cells can be divided into 4 subtypes differing in their directional preference, ventral, dorsal, nasal, or temporal. The cells of different subtypes also differ in their dendritic structure and synaptic targets in the brain. The neurons that were identified to prefer ventral motion were also found to have dendritic projections in the ventral direction.

Visual response properties

Cellular biophysics

Anatomy

The anatomy of ON/OFF cells is such that the dendrites extend to two sublaminae of the inner plexiform layer and make synapses with bipolar and amacrine cells. They have four subtypes, each with own preference for direction.

The colored objects in panel a are six DSGCs reconstructed by the researchers. The circles are representations of the cell bodies, and the lines are "skeletons" of the dendrites. Each DSGC is said to be "bistratified," which means that its dendrites branch out in two sublayers ("strata") of the IPL. The total number of strata in the IPL is estimated to be around ten. A view of the bottom of the sandwich (panel b) shows the branching of the DSGC dendrites.

Reconstructed ganglion and amacrine cells.

There are four subtypes, each with a preference for direction.

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Location

Shape

Synapses with bipolar and amacrine cells.

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Connections

TODO: DS ON/OFF ganglion cells receive excitatory input from bipolar cells but also from the previously mentioned starburst cells (Figure 5A), which are also known as cholinergic amacrine cells (Famiglietti, 1983,Masland and Mills, 1979). Besides ACh, starburst amacrine cells (SACs) also release GABA (Brecha et al., 1988,Masland et al., 1984b,Vaney and Young, 1988) and provide DS ganglion cells with inhibition as well (Figure 5A). In addition, the DS ganglion cells receive both GABA and glycinergic inhibition from other amacrine cell types (reviewed in Dacheux et al., 2003).

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Molecules

ON/OFF DS ganglion cells can be divided into 4 subtypes differing in their directional preference, ventral, dorsal, nasal, or temporal. The cells of different subtypes also differ in their dendritic structure and synaptic targets in the brain. The neurons that were identified to prefer ventral motion were also found to have dendritic projections in the ventral direction. Also, the neurons that prefer nasal motion had asymmetric dendritic extensions in the nasal direction. Thus, a strong association between the structural and functional asymmetry in ventral and nasal direction was observed. With a distinct property and preference for each subtype, there was an expectation that they could be selectively labeled by molecular markers. The neurons that were preferentially responsive to vertical motion were indeed shown to be selectively expressed by a specific molecular marker. However, molecular markers for other three subtypes have not been yet found.[3] (NEED TO ADD SPECIFIC MARKER)

History

Levick 1966 rabbit experiments are a good place to start.

TODO: The majority of studies on DS ganglion cells have used the rabbit retina as a model system, reflecting both the wide availability of this laboratory animal and the importance of the classic study by Barlow and Levick (1965). Some of the key findings in the rabbit retina have been confirmed in the turtle retina (Marchiafava 1979; Ariel and Adolph 1985; Rosenberg and Ariel 1991; Kittila and Granda 1994; Smith et al. 1996; Kogo et al. 1998), indicating that similar mechanisms may underlie the generation of direction selectivity in diverse vertebrate retinas. In16 Vaney, He, Taylor and Levick the rabbit retina, there are two distinct types of DS ganglion cells (Barlow et al. 1964). The commonly encountered On-Off DS cells are excited by objects that are lighter or darker than the background and they respond over a wide range of stimulus velocities; the rarer On DS cells are excited by objects that are lighter than the background and they respond optimally to slow movements (Oyster 1968; Wyatt and Daw 1975). Throughout this chapter, references to DS ganglion cells should be taken to mean the On-Off DS cells of the rabbit retina, unless otherwise specified. The numerous physiological and morphological studies on vertebrate DS ganglion cells have been most recently reviewed by Amthor and Grzywacz (1993a), who placed special emphasis on the spatiotemporal characteristics of the excitatory and inhibitory inputs to the On-Off DS cells. Although the actual neuronal circuitry that underlies the generation of direction selectivity in the retina has yet to be elucidated, the diverse models that have been proposed over the last 35 years provide guideposts for future experiments (Barlow and Levick 1965; Torre and Poggio 1978; Ariel and Daw 1982; Koch et al. 1982; Grzywacz and Amthor 1989; Vaney et al. 1989; Oyster 1990; Vaney 1990; Borg-Graham and Grzywacz 1992; Grzywacz et al. 1997; Kittila and Massey 1997). These models are judged primarily by their ability to account for the detailed functional properties of the DS ganglion cells, but this is only one of the requirements. Morphological and biophysical constraints also pose hurdles for candidate mechanisms. For example, it would not be appropriate to require a higher density of a particular neuronal type than is known to exist. Nor would it be sound to postulate highly localised synaptic interactions on dendritic segments where the electrotonic properties indicate more extensive interactions. Finally, the developmental requirements need to be kept in mind: it should be possible to achieve the appropriate specificity in the neuronal connections by such mechanisms as Hebbian-type synaptic modification or the selective expression of marker molecules

Open questions / status / relevance to eyewire

TBD

References

  1. A. Borst and T. Euler, €œSeeing Things in Motion: Models, Circuits, and Mechanisms, Neuron, vol. 71, no. 6. Cell Press, pp. 974-994, 22-Sep-2011. Paywalled.
  2. Barlow, H. B. and Levick, W. R. The Mechanism of Directionally Selective Units in Rabbit's Retina. J. Physiol. (1965), 178, pp.477-504.
  3. Kay, Jeremy N et al. “Retinal ganglion cells with distinct directional preferences differ in molecular identity, structure, and central projections.” Journal of Neuroscience 31.21 (2011) : 7753-7762.

See Also