Exam 5: Wiring of the Visual System

In chick, ephrin-A2 is found in an increasing gradient from anterior to posterior tectum. Researchers virally misexpressed ephrin-A2 in patches throughout the tectum and then visualized the temporal RGC axons that expressed high levels of its receptor EphA3. What result would demonstrate the sufficiency of ephrin-A2 for repulsion?

Based on the competition model, what would be the expected result if the temporal axons could be ablated early in development (before they had grown into the tectum/SC)?

Semaphorin receptors (called plexins) promote growth cone collapse via the small GTPase RhoA. How is this most likely to be accomplished?

A single cortical neuron that receives a score of 4 on the ocular dominance scale (which ranges from 1-7) receives information from: (Select all that apply.)

Receptors of attractive cues in axon guidance and targeting include:

When Sperry and colleagues ablated the dorsal RGCs, the remaining ventral RGCs projected to the dorsal tectum. Conversely, when they ablated the ventral RGCs, the remaining dorsal RGCs projected to the ventral tectum. A. What are some plausible models for dorsoventral patterning suggested by these results? B. Ephrins and Ephs are distributed in dorsoventral gradients in both structures. EphB1 is expressed in the tectum, in a low-dorsal to high-ventral gradient. Ephrin-B1 and ephrin-B2 are expressed in the retina in a high-dorsal to low-ventral gradient. What do these expression patterns suggest about the mechanism used for dorsoventral patterning of RGCs projecting to the tectum? C. A stripe assay was prepared in which stripes of artificially clustered EphB1 receptor extracellular domain were prepared on a polylysine coated coverslip. Based on your model, how would you expect the axons of dorsal retinal explants to behave in this assay?

Arrange the following events into their chronological order during monkey development. A. Consolidation of ocular dominance columns in layer 4 of primary visual cortex B) Eye-specific segregation of RGC axons at the LGN C) Formation of ocular dominance columns in layer 4 of primary visual cortex D) Arrival of RGC axons at the LGN E) Onset of vision

Which of the following are required for retinal lamina-specific dendritic targeting by RGCs?

In the Drosophila melanogaster compound eye:

Both RGCs and LGN neurons are glutamatergic. If their target cells receive isolated action potentials prior to birth:

What is the experimental evidence that reception of information from single whiskers by stellate neurons requires cell-autonomous glutamatergic reception?

Temporal and nasal RGC axons behave very differently in the stripe assay with alternating anterior and posterior tectal membranes, as seen in Figure Q5-4. Figure Q5-4 A. What possible interpretations can be drawn from the selective growth of temporal RGC axons in this assay? B. What possible interpretations can be drawn from the indiscriminate growth of nasal RGC axons in this assay?

Fill in each of the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. The axon growth cone contains two prominent actin structures: _____________ are composed of bundled F-actin, whereas _____________ are a meshwork of branched F-actin. Many axon guidance cues affect the actin cytoskeleton through their receptors and downstream effectors such as the _____________ Rho, Rac, and Cdc42. These molecules are activated by _____________ and inactivated by _____________. For example, in the context of ephrin-A to EphA _____________ signaling, a GEF called ephexin was shown to mediate growth cone _____________ by linking the EphA receptor to RhoA. collapse guanine nucleotide exchange factors (GEFs) filopodia lamellipodia forward reverse G-protein-coupled receptors (GPCRs) small GTPases GTPase activating proteins (GAPs) stabilization

Netrin was first discovered in a biochemical assay for the attraction of vertebral commissural axons to floor plate. In mutants for the worm netrin homologue Unc6, sensory axons failed to project ventrally and motor neurons fail to project dorsally. This result suggested that:

Both ephrins and cholinergic retinal waves appear to be necessary for normal formation of retinotopic maps in the:

Humans have a much greater degree of binocular vision than mice. Which of the following is/are also very likely to be true of humans?

RGC axon segregation into ipsilateral vs. contralateral layers in the LGN:

Monocular deprivation of cats during the critical period (about four through twelve weeks after birth) results in profound and irreversible effects on:

Temporal RGC axons exhibited selectivity in the stripe assay when:

Roger Sperry surgically rotated an amphibian's eye, severed the optic nerve, and allowed the retinal ganglion cells to re-grow into the brain. Based on the animal's movements in the opposite direction from its prey, the RGC axons made connections to the same part of the brain as before. If normal vision had been restored, what would he have concluded?