Direction of transmission




Viruses can be transmitted in one of two directions. First, one must understand the underlying mechanism of axoplasmic transport. Within the axon are long slender protein complexes called microtubules. They act as a cytoskeleton to help the cell maintain its shape. These can also act as highways within the axon and facilitate transport of neurotransmitter-filled vesicles and enzymes back and forth between the cell body, or soma and the axon terminal, or synapse. Transport can proceed in either direction: anterograde (from soma to synapse), or retrograde (from synapse to soma). Neurons naturally transport proteins, neurotransmitters, and other macromolecules via these cellular pathways. Neuronal tracers, including viruses, take advantage of these transport mechanisms to distribute a tracer throughout a cell. Researchers can use this to study synaptic circuitry.

Anterograde transportedit

Anterograde tracing is the use of a tracer that moves from soma to synapse. Anterograde transport uses a protein called kinesin to move viruses along the axon in the anterograde direction.

Retrograde transportedit

Retrograde tracing is the use of a tracer that moves from synapse to soma. Retrograde transport uses a protein called dynein to move viruses along the axon in the retrograde direction. It is important to note that different tracers show characteristic affinities for dynein and kinesin, and so will spread at different rates.

Dual transportedit

At times, it is desirable to trace neurons upstream and downstream to determine both the inputs and the outputs of neural circuitry. This uses a combination of the above mechanisms.

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