Retinal Interneurons - Ocular Physiology Spring 2025

bipolar and horizontal cells

Photoreceptors synapse with _____ and _____ cells in the outer plexiform layer

glutamate

Receptors on bipolar cells bind output signal of ________

peripherally but not centrally

Convergence of multiple cones onto multiple bipolar cells occurs ____ but not ______

1:1

Foveal cons have a ______ relationship with bipolar cells

retinal ganglion cells and amacrine cells

Bipolar cells synapse with what 2 things in the inner plexiform layer?

1 type, DBC

How many types of rods are there?

10 types

How many types of cones are there?

1) On center or depolarizing bipolar cells (DBC)

2) Off center or hyperpolarizing bipolar cells

What are the 2 major types of cone bipolar cells?

differently

DBCs and HBCs respond (the same/differently) to glutamate from the photoreceptors

hyperpolarize

Hyperpolarizing bipolar cells ______ with light

cation channel closure

Reduced glutamate release from the photoreceptor causes what on the hyperpolarizing bipolar cell?

cation channel opening

Increased glutamate release from the photoreceptor causes what on the hyperpolarizing bipolar cell?

depolarize

Depolarizing bipolar cells _____ with light

cation channel opening of DBCs

Reduced glutamate release from the photoreceptor causes what on the depolarizing bipolar cell?

cation channel closure of DBCs

Increased glutamate release from the photoreceptor causes what on the depolarizing bipolar cell?

AMPA & KA glutamate receptors

Post synaptic terminal of the depolarizing bipolar cell and hyperpolarizing bipolar cell express different receptors. What receptors do hyperpolarizing bipolar cells expres?

ionotrophic

AMPA & KA glutamate receptors are (metabotropic/ionotrophic)

When AMPA and KA are stimulated by glutamate they trigger the opening of cation channels. Cation ion channel will depolarize the cell

What is the mechanism of ionotropic AMPA & KA receptor?

Glutamate release is reduced, HBC cation channels close and the cell becomes hyperpolarized

Upon light stimulation, what happens to the hyperpolarizing bipolar cell?

mGluR6 glutamate receptors

Post synaptic terminal of the depolarizing bipolar cell and hyperpolarizing bipolar cell express different receptors. What receptors do depolarizing bipolar cells express?

metabotropic

mGluR6 glutamate receptors are (metabotropic/ionotrophic)

When mGluR6 is stimulated by glutamate it activates a G protein cascade that triggers the closure of cation channels. Cation channel closure will hyperpolarize the cell

What is the mechanism of metabotrophic mGluR6 receptor?

glutamate release is reduced from the photoreceptor. the depolarizing bipolar cell cation channels will open, and the cell will become depolarized

Upon light stimulation, what happens to the depolarizing bipolar cell?

False -- they respond to light differently

True or False:

HBCs and DBCs respond to light in the same way

glutamate

When bipolar cells (HBCs and DBCs) are depolarized, they release what to retinal ganglion cells?

they reduce glutamate release to ganglion cells

When bipolar cells (HBCs and DBCs) are hyperpolarized, what happens to the glutamate release from these cells?

true

True or False;

Retinal ganglion cells have a basal firing rate (constantly fire action potentials)

increases

Glutamate release from the bipolar cells (increases/decreases) the ganglion cell firing rate

decreases

Reduction of glutamate release from the bipolar cells (increases/decreases) the ganglion cell firing rate

horizontal cells

These cells are found in the outer plexiform layer and interconnect photoreceptor and bipolar cell synapse?

lateral inhibition

What are horizontal cells responsible for?

limit

Horizontal cells (increase/limit) glutamate release from the photoreceptors

-enhances image contrast

-facilitates color discrimination

-assists with light adaption

What do horizontal cells help with in vision?

1) Glutamate release by the photoreceptors depolarize horizontal cells

2) Release of GABA to cone receptors (inhibitory neurotransmitter)

3) Causes hyperpolarization of photoreceptors

4) Reduces photoreceptor glutamate release

What is the Mechanism of GABA use for Lateral Inhibition of Bipolar cells?

Glutamate release by the photoreceptors depolarize horizontal cells

Mechanism of GABA use for Lateral Inhibition of Bipolar Cells

What is the first step in this mechansim?

Release of GABA to cone receptors (inhibitory neurotransmitter)

Mechanism of GABA use for Lateral Inhibition of Bipolar Cells

After Glutamate release by the photoreceptors depolarize horizontal cells, what happens next?

Causes hyperpolarization of photoreceptors

Mechanism of GABA use for Lateral Inhibition of Bipolar Cells

After Release of GABA to cone receptors (inhibitory neurotransmitter), what happens next?

Reduces photoreceptor glutamate release

Mechanism of GABA use for Lateral Inhibition of Bipolar Cells

What is the last step in this mechanism?

amacrine cells

These cells are found in the inner plexiform later and synapse with bipolar and retinal ganglion cells

30 types

Approx how many types of amacrine cells are found in mammals

most - GABAergic

the rest - glycinergic

**both are inhibitory

Most amacrine cells are _____? The rest are ______?

glutamate

Amacrine cells are stimulated by _____ from the bipolar cells

-alter glutamate release of bipolar cells via GABA

-modify the function of other amacrine cells

enhance or diminish the signal to ganglion cells

What is the function of amacrine cells?

spatial and temporal

Amacrine cells function in shaping both the ____ and _____characteristics of receptive fields of bipolar cells and retinal ganglion cells

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

What is the RGC receptive field?

greater

Smaller receptive field = (less/greater) spatial acuity

yes

Do receptive fields in the retina overlap?

depending on whether the stimulus is on or off center

By HBCs and DBCs being distinct, receptive filed can send distinct signals depending on what?

the detection of edges and recognizing contrast

What do receptive fields aid in?

Center Surround Antagonist Receptive Field (CSARF)

Functions to encode spatial information due to distinct types of bipolar cells (HBCs and DBCs) and amacrine/horizontal cell inhibition

-RGC firing rate

-the type of RGC

-Location of photoreceptors that trigger RGC

-location of the RGC axon synapse within the LGN

What is the information that is encoded within an RGC a combination of?