L20 Retinal Interneurons

What cells to photoreceptors synapse with?

bipolar and horizontal cells in the outer plexiform layer

How are the cone synapses onto bipolar cells different between peripheral retina and central retina?

1. convergence of cones onto multiple bipolar cells occurs peripherally but not centrally

2. foveal cones have a 1:1 relationship with bipolar cells

What cells do bipolar cells synapse on?

retinal ganglion cells and amacrine cells in the inner plexiform layer

What are the cone bipolar cell types?

on-center or depolarizing bipolar cells

off-center or hyper polarizing bipolar cells

How do off-center hyper polarizing cells respond to light?

hyperpolarizing bipolar cells hyper polarize with light

reduced glutamate from photoreceptor causes cation channel closure of HBCs

glutamate from photoreceptors cause cation channel opening of HBCs

How do on-center depolarizing cells respond to light?

depolarizing bipolar cells depolarize with light

reduced glutamate from photoreceptor causes cation channel opening of DBCs

glutamate from photoreceptors cause cation channel closure of DBCs

How are the DBC and HBC post synaptic terminals different?

HBC: synapse has AMPA and KA glutamate receptors that are inotropic and are stimulated why glutamate, this causes opening of cation channels

upon light stimulation glutamate release is reduced, the HBC cation channels close and the cell becomes hyperpolarized

DBC synapse: has mGlur6 receptors which are metabotropic and are stimulated by glutamate

upon light stimulation glutamate release is reduced from photoreceptors, the DBC cation channels open, and the cell becomes depolarized

What layer of the retina contains horizontal cells?

outer plexiform layer

What is the function of horizontal cells?

interconnect photoreceptor and bipolar cell synapses

What cell is responsible for lateral inhibition?

horizontal cells

lateral inhibitoon

feedback mechanism to limit glutamate release from photoreceptors

enhances image contrast

facilitates color discrimination and assists in light adaption

What is the GABA hypothesis for lateral inhibition?

1. glutamate release by photoreceptors depolarize HCs

2. causes release of GABA to cone receptors

3. causes hyper polarization of photoreceptors

4. reduces photoreceptor glutamate release

What layer of the retina contains amacrine cells?

inner plexiform layer

What cells do amacrine cells synapse with?

bipolar and ganglion cells

What neurotransmitter is mostly released by amacrine cells?

GABA

(rest are glycinergic)

How are amacrine cells stimulated?

stimulated by glutamate from bipolar cells

What is the function of amacrine cells?

function to shape both spatial and temporal characteristics of receptive fields of bipolar cells and ganglion cells

RGC receptive field

comprised of the region of photoreceptors and interneurons that are electrically coupled to an individual RGC

How are receptive fields related to spatial acuity?

smaller receptive fields allow for greater spatial acuity

How do bipolar cells aid in the detection of edges and recognizing contrast?

distinct HBC and DBC allow for receptive fields to send distinct signals depending on whether the stimulus is on or off center

center-surround antagonistic receptive field

functions to encode spatial information due to distance types of bipolar cells and amacrine and horizontal cell inhibition

What is the information encoded within the RGCs dependent on?

RGC firing rate

the of RGC

location of photoreceptors that trigger RGC stimulation

location of RGC axon synapse within the LGN