Neuronal tract tracing methods

Question 1

Local circuit neurons

Answer 1

Short axons that end locally, use intracellular labelling dyes not tract tracing

Question 2

Projection neurones

Answer 2

Those with axons that travel a significant distancefrom the cell body. Tract tracing is used to identify; source of tract, destination, route taken by axons, synaptic input/output, neurotransmitter.

Question 3

Retrograde tracing

Answer 3

From axon terminal to cell body.

Question 4

Anterograde tracing

Answer 4

From cell body to axon terminal

Question 5

HRP

Answer 5

Mostly retrograde transport, very soluble, small molecule, stable but insensitive ( not often used now). Detected with enzyme histochemistry

Question 6

Cholera toxin b subunit (CTb)

Answer 6

Non toxic, very sensitive, binds to ganglioside on surface of neurons, retrlgrade and anterograde, detected by immunocytochemistry

Question 7

Fluorogold

Answer 7

Very sensitive,naturally fluorescent, retrograde tracer

Question 8

Phaseolus leucoagglutinin (PHAL)

Answer 8

Glutinates white blood cells, v sensitive anterograde tracer ( apparently complete axon labelling), detected with immunocytochemistry

Question 9

Double labelled neurones

Answer 9

2 different tracers used to identify cells that projecg to more than one target. I.e one to the thalamus (blue) , one to the pons (red) , double labelled neurons that project to both will be purple.

Question 10

Trans-synaptic tracing

Answer 10

Some tracers can cross synapses to label neurons that are presynaptic to the projection cell

Question 11

Monosynaptic retrograde tracing

Answer 11

Uses attenuated virus which is lacking essential coat protein so cannot replicate. Co-inject with helper virus that expresses coat protein but cannot cross synapses. Virus travels retrogradely but can only cross one synapse and protein expressing helper virus cannot cross synapse.