Orientation Selective Ganglion Cell
Orientation Selective Ganglion Cells (OSGCs) are ganglion cells that respond to the alignment orientation of stimuli as opposed to the direction of movement of the stimuli. The cell-bodies of ganglion cells are located on the vitreal side of the inner plexiform layer of the retina. Occasionally displaced cell-bodies of ganglion cells are found in the inner margin of the inner nuclear layer. The majority of these ganglion cells are located in the visual streak region of the retina (Levick 1967). In a study by Levick and Thibos in 1982 it was found that 70% of ganglion cells in the cat retina are orientation selective ganglion cells. Orientation selective ganglion cells are categorized into ON-center and OFF-center cells. The responses recorded from both ON-center and OFF-center orientation selective ganglion cells have shown that there is an initial hyperpolarization at light onset regardless of the orientation of the stimulus(Bloomfield 1994). The receptive fields of these cells consist of a center, excitatory region surrounded by inhibitory sections (Bloomfield 1994). The initial hyperpolarizations recorded are thought to have been caused by the field peripheral to the center (Bloomfield 1994).
ON-center orientation selective ganglion cells have a preferred orientation that results in an initial hyperpolarization followed by a large depolarization and increased spiking when a slit of light is introduced to the receptive field of the cell (Bloomfield 1994). As the orientation of the slit was moved away from the preferred orientation, the initial hyperpolarization remained the same, while the depolarization decreased (Bloomfield 1994). At 90 degrees from the preferred orientation there was an initial hyperpolarization followed by sustained hyperpolarization (Bloomfield 1994). OFF-center orientation selective ganglion cells respond with an initial hyperpolarization followed by sustained hyperpolarization and then depolarization when the light is removed from the center (Bloomfield 1994). When the slit of light was placed at the null angle (90 degrees from the preferred orientation) there was no longer a depolarization when the light was removed, but rather a declining hyperpolarization was found (Bloomfield 1994).
Contents
Physiology
The axons of ganglion cells that are located in the retina are not myelinated. The axons of ganglion cells that are outside the retina are myelinated. AMPA and NMDA receptors have been found to play a significant role in signal integration in ganglion cells found in rabbit retinas (Marc, 1999). Different types of ganglion cell types have been found to 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 AMPA receptors in the ganglion cells (Marc, 2002).
Anatomy
Among the types of ganglion cells present in the ganglion cell layer, orientation selective ganglion cells have relatively small cell-bodies (Amthor, 1989) and have an elongated shape.
ON-center orientation selective ganglion cells have asymmetric dendritic arbors and have a wavy appearance (Bloomfield 1994). OFF-center orientation selective ganglion cells have cell-bodies that are shaped like elipsoids and have two main dendrites extending from either side of the cell body (Bloomfield 1994). 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 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 (Amthor, 1996).
Molecules
Orientation selective ganglion cells may synthesize the neurotransmitter GABA and have been found to have GABA signals that are very similar to those found in amacrine cells (Marc, 2002). Compared to the other types of ganglion cells that have been identified, orientation selective ganglion cells have a relativity high GABA content (Marc, 2002). The neurotransmitter glutamate has also been found to be used for neural transmission by these ganglion cells (Marc, 2002). The molecules aspartate and glutamine have also been found to be present in orientation selective ganglion cells (Marc, 2002).
