Axonal Tracing

Question 1

Neuronal tracing methods give ?

Answer 1

detailed descriptions of neuron projections in the brain

and allow thes projections to mapped giving info on function and identification

Question 2

Anterograde tracing

Answer 2

establishes where neurons send their axons

Question 3

retrograde tracing

Answer 3

establishes from which neurons axons originate

Question 4

Cytoskeleton polymers

Answer 4

microtubules - alpha/beta tubulin , beta III tubulin in neurons. 25nm

microfliaments - actin monomers 3-5nm

intermeidate filaments - form neurofilaments 10nm

Question 5

Cytoskeleton polmer functions

Answer 5

Microtubules - 25nm diameter hollow tubes interspersed between neurofilaments
occur in individual units or in groups or 2-3.
•Formed by the polymerization of a dimer of two globular proteins; alpha and beta tubulin
• Microtubules form the mitotic spindle during cell division.
• Axon transport.

Intermediate Filaments -10 nm diameter
• Neurofilaments occur individually, scattered or loosely aggregated in small bundles
• bundles of neurofilaments = neurofibrils
• Extend as parallel fibers through cell body into dendrites (forming main component
of cytoskeleton – cytokeratin family, hence very stable).
• Clinical correlate: Alzheimers disease is linked with changes in intermediate
filaments

Microfilaments - 3 -5 nm diameter. Actin monomers.
• Form a dense supportive network underneath plasma membrane.
• Formation of new cell processes and retraction of older ones.
• Cell movement & signal transduction systems use actin
cytoskeleton as scaffold

Question 6

Fast anterograde transport

Answer 6

away from cell body
transport vesicles containg NT
mediated by kinesin motor protein and microtubules
200-400mm/day

Question 7

Slow anterograde transport

Answer 7

bulk movement of cytoplasm (1-5 mm/day).
• Transport of cytoskeletal elements, neurofilaments,
mitochondria and other organelles.

Question 8

Fast retrograde transport

Answer 8

Returns used materials from the axon terminal to cell body
for recycling (100-200 mm/day).
• Transports nerve growth factor and neurotropic viruses and
toxins (herpes simplex, polioviruses, and tetanus toxin).
• Mediated by microtubules and dynein motor protein.

Question 9

Microtubule orientation

Answer 9

same orientation in axons

mixed in dendrites

Question 10

Silver impregnation method

frank & heimer method

Answer 10

damaged neurons

Argyrophilic-Silver affinity= Damaged neuron

Question 11

Marchi method

Answer 11

damaged myelin
first he tissue specimen is first fixed in a solution of potassium bichromate (Müller’s fluid), which prevents normal myelin
sheets from being stained with osmic acid; osmic acid is then applied as a definitive black stain for abnormal
nerve fibers

Question 12

Wallerian degeneration (Anterograde)

Answer 12

Process that results when a nerve fibre is cut orcrushed, in which the part of the axon separated from the neuron’s cell body degenerates.

Occurs toward the distal end of the axon.
 Takes place in both the PNS and the CNS.
 Characterized by successive fragmentation and disappearance of axons and myelin
sheaths and by secondary proliferation of Schwann cells.

Question 13

Retrograde degeneration what happens to the neuron ?

Answer 13

Chromatolysis: The dissolution of the Nissl bodies in the cell body of a neuron (E).
Also occurs in wallerian degeneration if injury is close to cell body

Swelling of the cell body

Flattening and displacement of the nucleus to the periphery

Question 14

Transneuronal degeneration what happens to neuron ?

Answer 14

The death of neurons resulting from the disruption of

input from or output to other nearby neurons

Question 15

Antrograde tracing methods

Answer 15

frank & hemier
marchi
autoradiogrpahy with radiolabelled aa
anterograde tracers

Question 16

Reterograde tarcing methods

Answer 16

nissl reaction
retrogarde tracer
toxins and virus
fluroescent

Question 17

Di I, Dioctadecyl-Tetramethylindocarbocyanine

Answer 17

red orange fluroscent dye that is weakly fluroscent until incorporated into membrane
used to long term staining of neurons
Lipophilic membrane targeted fluorescent dyes.
Stain that diffuses laterally to stain the entire cell.
Several derivatives with different excitation and
emission wavelengths

Question 18

Wheat germ agluttin -HRP

Answer 18

bind to oligosaccharides & endocytosis

Question 19

cholera toxin B-HRP

Answer 19

bind to specific lectin or toxin receptors

Question 20

Colloidal Gold-labelled tracers

Answer 20

WGA-GOLD and CTB-GOLD

retrograde
pressure injection only not suitable fro cut nerves

detection by sliver intensification, a photographic method whereby growing shells of metallic silver are
deposited over colloidal gold particles

Question 21

HRP detection

Answer 21

soluble chromogen oxidised to detectable product by action of HRP on its substrate hydrogen peroxidase

Question 22

Unconjugated cholera toxin B

Answer 22

detected by immunhistochem (Cholera B antibodies)
admin by iontoporesis, pressure injection
long lasting

Major advantage is labelling of distal
dendrites and axon in addition to soma and proximal dendrite

Question 23

Phytohaemagglutinin –leucoagglutinin (PHA-L)

Answer 23

extract of red kidney bean
antergrade tracing - fast axonal transport
administered by iontophoresis
detected immunocytochemically
reveals fine details of axonal projections

Question 24

Biocytin

Answer 24

anterograde tracing 
combo of lysine and biotin 
detection using EM & LM using advin biotin methods 
degraded fast 
admin pressure injection

Question 25

Transneuronal tracers

Answer 25

herpes simplex
• Based on ability of virus to invade and replicate in neurons and
subsequently infect synaptically connected neurons.
• Pass transneuronally and replicate in synaptically linked populations.
• Signal increase with time.
• Detected by immunocytochemistry or by tritiatedthymidine autoradiography