Difference between revisions of "Orientation Selective Ganglion Cell/ko"

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In a study by Venkataramani and Taylor it was observed that the orientation selectivity of vertical OSGCs is more tuned than the orientation selectivity of horizontal OSGCs. This may suggest that the spatial organization of the receptive fields of vertical and horizontal selective OSGCs are different.
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Venkataramani와 Taylor의 연구에서 수직적 오리엔테이션 선택적 신경절 세포의 오리엔테이션 선택성은 수평적 오리엔테이션 선택적 신경절 세포의 오리엔테이션 선택성에에 비해 보다 잘 조정되어 있는 것이 밝혀졌습니다. 이러한 사실은 수직적 오리엔테이션 선택적 신경절 세포의 수용장과 수평적 오리엔테이션 선택적 신경절 세포의 수용장이 공간적 구성이 다르다는 뜻일지 모릅니다.
  
 
Orientation selective ganglion cells receive synaptic input from amacrine and bipolar cells.<ref name="Venkataramani"></ref> The responses of OSGCs may already be coded by the amacrine cells that synapse onto the ganglion cells. It is likely that these amacrine cells produce complex synaptic inputs.<ref name="Bloomfield"></ref>
 
Orientation selective ganglion cells receive synaptic input from amacrine and bipolar cells.<ref name="Venkataramani"></ref> The responses of OSGCs may already be coded by the amacrine cells that synapse onto the ganglion cells. It is likely that these amacrine cells produce complex synaptic inputs.<ref name="Bloomfield"></ref>

Revision as of 04:04, 8 January 2016

아이와이어에서 재구성된 오리엔테이션 선택적 신경절 세포

오리엔테이션 선택적 신경절 세포(Orientation Selective Ganglion Cells, OSGCs)는 자극의 이동 방향에 반응하는 것에 반해 자극의 오리엔테이션 정렬에 반응하는 신경절 세포입니다. 오리엔테이션 선택적 신경절 세포의 세포체는 망막 내망상체의 유리체쪽으로 위치해 있습니다. 그러나 잘못 놓여진 신경절 세포의 세포체가 내핵층의 안쪽경계에서 종종 발견되기도 합니다. 대부분의 오리엔테이션 선택적 신경절 세포는 망막의 시각띠 부분에 위치합니다. 오리엔테이션 선택적 신경절 세포들은 On-중심 세포와 OFF-중심 세포로 분류할 수 있습니다. 망막의 시각띠 안에는 ON-중심 오리엔테이션 선택적 신경절 세포에 비해 OFF-중심 오리엔테이션 선택적 신경절 세포가 더 많은 것이 관찰된 바 있습니다.Cite error: Invalid <ref> tag; refs with no name must have contentCite error: Invalid <ref> tag; refs with no name must have content


생리(Physiology)

수용장 구조(Receptive Field Structure)

오리엔테이션 선택적 신경절 세포는 타원형으로 수평 또는 수직 오리엔테이션을 선호하는 동심의 수용장을 가지고 있습니다. 1967년 Levick의 연구에서 이들 세포의 오리엔테이션 선택성을 보여주기 위해 사용된 자극은 수용장에 서로 다른 방향으로 놓인 얇은 띠 형태의 빛이었습니다. 신경절 세포가 선호하는 오리엔테이션으로 주어졌을 때 이들 세포들은 이러한 고정된 띠 형태의 빛에 반응을 보였습니다. 이들 세포중 어떤 것들은 빛 띠가 가로 방향으로 주어졌을 때만 반응을 보인 반면 어떤 세포들은 세로 방향으로 주어졌을 때 강한 반응을 보였습니다. 또한 이들 세포들은 빛 띠와 배경간의 강도 대비가 1/5인 경우에 빛 띠에 반응을 한다는 것을 알아냈습니다.

이들 세포들의 타원형의 수용장은 억제 구역을 양 옆에 둔 중심 구역으로 구성되어 있습니다; 중심 구역은 두 개의 억제 구역들을 분리하는 띠입니다. 중심 구역과 양쪽 두 개의 억제 구역에 빛을 쏘면 세포에선 아무 반응도 일어나지 않는데 흥분성 반응과 억제성 반응이 상쇄되기 때문입니다.Cite error: Invalid <ref> tag; refs with no name must have content

중심 수용장은 선호하는 오리엔테이션의 축삭을 따라 길이에서 약 480 마이크로미터이며 반응이 없는 축을 따라서 길이는 약 230 마이크로미터입니다. 반응이 없는 억제 구역은 중심으로 부처 약 135 아이크로미터정도부터 시작됩니다.Cite error: Invalid <ref> tag; refs with no name must have content

수평적으로 선택적인 오리엔트 선택적 신경절 세포의 수용장에 서로 다른 각도로 위치하는 빛 띠.[1]


선호 오리엔테이션에 대한 반응(Response to Preferred Orientation)

이들 세포의 수용장은 억제 구역에 둘러쌓인 흥분 구역인 중심으로 구성되어 있습니다. 폭이 95 마이크로미터이고 길이기 6 미리미터인 빛을 여러가지 각도로 수용장 내에 오리엔테이션 시키고 오리엔테이션 선택적 신경절 세포 내의 전기적 반응을 측정했습니다. ON-중심 및 OFF-중심 오리엔테이션 선택적 신경절 세포로부터 측정된 반응을 보면 자극의 오리엔테이션과는 무관하게 빛을 처음 비추는 순간에 초기 과분극이 있음을 알 수 있습니다.

ON-중심 오리엔테이션 선택적 신경절 세포는, 세포의 수용장에 띠 모양 빛이 비춰질 때, 초기 과분극에 이은 큰 탈분극 과 spiking의 증가를 보이는 선호하는 오리엔테이션이 있습니다. 빛 띠의 오리엔테이션이 선호하는 오리엔테이션으로부터 변화됨에 따라 초기 과분극은 동일하게 유지되는 반면 탈분극은 감소했습니다. 선호하는 오리엔테이션으로부터 90도 변화하였을 때는 초기 과분극에 이어 지속적인 과분극이 나타났습니다.

OFF-중심 오리엔테이션 선택적 신경절 세포는 빛이 중심에서 제거되었을 때 초기 과분극에 이은 지속적 과분극 그리고 이후 탈분극 반응을 나타냈습니다. 빛 띠가 반응이 없는 각도(선호하는 오리엔테이션으로부터 90도)에 놓인 경우 빛이 제거 되었을 때 더 이상 탈분극은 나타나지 않았지만 오히려 다소 감소하는 과분극이 관찰되었습니다.

기록된 초기 과분극은 중심의 주변장에 의한 것으로 생각되었습니다. 빛 띠의 길이가 감소하였고 과분극은 크기 면에서 감소했습니다. 빛 띠가 300 마이크로미터로 감소되었을 때 초기 과분극이 나타났지만 지속적이던 과분극은 탈분극으로 교체되었습니다. 225마이크로미터에서는 과분극 반응은 더 이상 보이지 않았으며 오리엔테이션 선택적 신경절 세포는 이 자극에 대해서는 오리엔테이션에 대한 선호를 보이지 않았습니다. 이 것은 수용장의 주변 구역에 의한 억제가 오리엔테이션 선택성에 필요하다는 것을 뜻합니다.Cite error: Invalid <ref> tag; refs with no name must have content

빛 띠의 길이가 과분극에 대해 갖는 영향을 알아보기 위해 빛 띠의 길이를 감소시켜보았습니다.Cite error: Invalid <ref> tag; refs with no name must have content

수평적 및 수직적으로 선택적 신경절 세포(Horizontally and Vertically Selective Ganglion Cells)

Venkataramani와 Taylor의 연구에서 수직적 오리엔테이션 선택적 신경절 세포의 오리엔테이션 선택성은 수평적 오리엔테이션 선택적 신경절 세포의 오리엔테이션 선택성에에 비해 보다 잘 조정되어 있는 것이 밝혀졌습니다. 이러한 사실은 수직적 오리엔테이션 선택적 신경절 세포의 수용장과 수평적 오리엔테이션 선택적 신경절 세포의 수용장이 공간적 구성이 다르다는 뜻일지 모릅니다.

Orientation selective ganglion cells receive synaptic input from amacrine and bipolar cells.[2] The responses of OSGCs may already be coded by the amacrine cells that synapse onto the ganglion cells. It is likely that these amacrine cells produce complex synaptic inputs.[3]

Orientation selectivity of these ganglion cells depends largely on GABA transmission.[4] It was found that using GABA antagonists reduced the receptor's responses to the preferred orientation.[2] It has been proposed that surround inhibition is necessary to produce orientation selectivity.[5][4]

During excitation at the preferred orientation in vertically selective OSGCs, it was found that there is temporary NMDA receptor activity, sustained AMPA/kainate activity, and sustained disinhibtion (reduced glycinergic input). At the null orientation it was observed that the NMDA receptor activity and the inhbitory components were suppressed. The timing and amplitude of the excitatory and inhibitory responses recorded remained the same. This may suggest that NMDA receptor activity is not responsible for orientation selectivity.[2]

In a previous study by Caldwell, the antagonists picrotoxin and strychnine were introduced to orientation selective ganglion cells. Picrotoxin is a GABA antagonist and strychnine is a glycine antagonist; both are antagonists of inhibitory neurotransmitters. When picrotoxin was introduced to the OSGCs, the cells responded in the same way to a strip of light oriented at the preferred and null directions. With strychnine, the orientation selectivity decreased slightly.[4]

Using a GABA antagonist, it was found that NMDA activity was slightly suppressed, and that the ganglion cells lost their orientation preference. The NMDA activity and disinhibition were no longer selective to orientation in vertically selective OSGCs.

At the preferred orientation in horizontal OSGCs, inhibition (GABA from amacrince cells) is reduced and AMPA/kainate and NMDA activity increases. Unlike vertical OSGCs, glycinergic disinhibition does not play a role in the excitation response, but rather there is only an increase in excitatory inputs.

OFF-center bipolar cells provide direct excitatory synaptic input to orientation selective ganglion cells with the transmission of glutamate to the NMDA and AMPA/kainate receptors. OFF-center amacrine cells inhibit the excitatory input from OFF-bipolar cells to the ganglion cells.[2]

Top: Wiring diagram showing presynaptic innervation from amacrine and bipolar cells onto a vertically selective OSGC. Bottom: Wiring diagram showing synaptic contact from amacrine and bipolar cells onto a horizontally selective OSGC.(VS-GC= vertically selective ganglion cell; HS-GC=horizontally selective ganglion cell; OFF BC= off bipolar cell; AC=amacrine cell)[2]

Anatomy

Among the types of ganglion cells present in the ganglion cell layer, orientation selective ganglion cells have relatively small cell-bodies[6] and have an "elongated" and "polygonal" shape [7].

ON-center orientation selective ganglion cell to the left. OFF-center orientation selective ganglion cell to the right. [6]
Side-view of ON-center orientation selective ganglion cell to the left and side-view of OFF-center orientation selective ganglion cell to the right.[6]

Dendritic Arbors

ON-center orientation selective ganglion cells have asymmetric dendritic arbors and have a wavy appearance. The dendrites of ON-center orientation selective ganglion cells are not elongated in a particular direction that corresponds to their preferred orientation (horizontal or vertical). The dendrites of ON-center orientation ganglion cells were found to extend approximately 163 micrometers along the axis of preferred orientation.

OFF-center orientation selective ganglion cells have cell bodies that are shaped like ellipsoids and have two main dendrites extending from either side of the cell body. The dendrites of OFF-center orientation selective ganglion cells are wavy in appearance, as well, and are longer than the ON-center cell dendrites. The dendrites of OFF-center orientation ganglion cells were found to extend approximately 283 micrometers along the axis of preferred orientation. The dendrites of both types of orientation selective ganglion cells are bistratified[3]. The extent of the dendrites of orientation selective ganglion cells has been found to be closely related to the size of the receptive field centers of OSGCs [8]; however a clear elongation of the dendrites along the preferred axis has not been observed.

The dendritic arbors of horizontal OSGCs are more densely branched than the dendritic arbors of vertical OSGCs.[2]

The receptive field of an orientation selective ganglion cell, with an excitatory center (+) and inhibitory surround (-).[3]

AMPA and NMDA Receptors

AMPA and NMDA receptors have been found to play a significant role in signal integration in ganglion cells found in rabbit retinas.[9] AGB cation was used to evaluate the differences in permeability of the different ganglion cells types when kainate, AMPA, and NMDA receptors were activated.

It was found that different types of ganglion cell types respond differently to glutamate release from bipolar cells, and it is hypothesized that it may be a result of the responsivity of the different types of AMPA receptors in the ganglion cells and also the presence of GluR2 subunits.

The size of the cell and the concentration of GABA in the cell are thought to be unrelated to the responsivity of the AMPA receptors. The responsitivity of AMPA receptors in orientation selective ganglion cells is relatively high. Higher responsivity of these AMPA receptors means that signal integration time is lower for orientation selective ganglion cells.[7]

Molecules

The neurotransmitter glycine is found in very small concentrations in ganglion cells.

Compared to the other types of ganglion cells that have been identified, orientation selective ganglion cells have a relativity high GABA concentration. The neurotransmitter glutamate has also been found to be used for neural transmission by these ganglion cells, which is what differentiates these ganglion cells from amacrine cells. The molecules aspartate and glutamine have also been found to be present in orientation selective ganglion cells.

Orientation selective ganglion cells may synthesize the neurotransmitter GABA and have been found to have GABA concentrations that are very similar to those found in amacrine cells. GABA from amacrine cells may enter these ganglion cells through channels present at gap junctions. The molecule glycine is also thought to pass through these channels from amacrine to ganglion cells.[7]

History

In 1967, Levick was the first to describe the properties of three new types of retinal ganglion cells found in the rabbit retina: orientation selective ganglion cells, local-edge detectors, and uniformity detectors. Before strips of light were oriented at different angles on the receptive fields in this study, it was thought that these ganglion cells had off-center surround concentric receptive fields. Levick described the receptive fields of orientation selective ganglion cells as either being horizontally or vertically selective and mentioned that the receptive fields had incomplete antagonistic surrounds. He proposed that the neurons in the retina process visual information and organize information before it is sent to higher centers in the brain for further processing.

In this study they found that the excitatory regions of the receptive field were difficult to find.[5]

Open Questions/Status

It is thought that amacrine cells help form the orientation selectivity of OSGCs, however, the exact role of amacrine cells still remains unclear [3]. Many questions remain on how the synaptic mechanisms create orientation selectivity in ganglion cells. A complete description of all the different types of ganglion cell types has yet to be formed and further research is needed for this to be accomplished.[7]

References

  1. Levick WR (1967) Receptive fields and trigger feature of ganglion cells in the visual streak of the rabbits retina. J Physiol 188:285-307. http://jp.physoc.org/content/188/3/285.abstract?ijkey=9e2025595bfc5bfe14d04894d4c3dcd7d1b03682&keytype2=tf_ipsecsha
  2. 2.0 2.1 2.2 2.3 2.4 2.5 Venkataramani S, WR Taylor (2010) Orientation Selectivity in Rabbit Retinal Ganglion Mediated by Presynaptic Inhibition. J Neurosci, Nov 17; 30(46):15664-15676. http://www.jneurosci.org/content/30/46/15664.full
  3. 3.0 3.1 3.2 3.3 Bloomfield SA(1994) Orientation-sensitive amacrine and ganglion cells in the rabbit retina. J Neurophysiol 71:1672-1691. http://jn.physiology.org/content/71/5/1672.abstract?ijkey=4cfa4066fd39257147ad90ee1df8864247a4132f&keytype2=tf_ipsecsha
  4. 4.0 4.1 4.2 Caldwell JH, Daw NW, Wyatt HJ (1978) Effects of Picrotoxin and strychnine on rabbit retinal ganglion cells: lateral interactions for cells with more complex receptive fields. J Physiol, 276: 277-298. http://jp.physoc.org/content/276/1/277
  5. Cite error: Invalid <ref> tag; no text was provided for refs named Levick
  6. 6.0 6.1 6.2 Amthor FR, Takahashi ES, Oyster CW (1989) Morphologies of rabbit retinal ganglion cells with concentric receptive fields. Journal of Comparative Neurology 280:72-96. [1]
  7. 7.0 7.1 7.2 7.3 Marc RE, Jones BW (2002) Molecular phenotyping of retinal ganglion cells. J Neurosci, Jan 15;22(2):413-27. http://www.ncbi.nlm.nih.gov/pubmed/11784786
  8. Amthor FR, Grzywacz NM, Merwine DK (1996) Extra-receptive-field motion facilitation in on-off directionally selective ganglion cells of the rabbit retina. Visual Neuroscience 13:303-309. http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=4618320
  9. Marc RE (1999) Mapping glutamatergic drive in the vertebrate retina with a channel-permeant organic cation. J Comp Neurol, 407(1):47-64. http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1096-9861(19990428)407:1%3C47::AID-CNE4%3E3.0.CO;2-0/abstract