Neuronal Tracing Tools

Neuronal connectivity through various synapses is fundamental to the brain's complex functions. Understanding these brain circuits is a critical focus in neuroscience, driving the need for advanced tools to map them. Traditional tracers like CTB, HRP, PHA-L, and BDAs have been used for this purpose, but they come with limitations: 1) Lack of cell specificity, 2) Inconsistent efficiency, and 3) Inability to trace multi-step synaptic connections.

Genetically engineered recombinant viral vectors have emerged as powerful tools for visualizing neural connectivity due to their ability to efficiently enter cells and deliver a variety of genes. Commonly used neurotropic viruses such as HSV (Herpes simplex virus type 1), VSV (Vesicular stomatitis virus), PRV (pseudorabies virus), and RABV (rabies virus) can cross synapses from one cell to another when provided with the necessary replication proteins. Additionally, SFV (which marks the fine morphology of in-situ neurons) and AAV (used as a helper virus to express exogenous genes or as a monosynaptic tracer, particularly with serotype 1) are also valuable in neuronal tracing.

Ignis Bioscience offers comprehensive services with AAV, PRV, RABV, and HSV to support and advance neuronal tracing studies.

Table 1: Recombinant viral vectors commonly used in neural circuit tracing

Rabies virus (RV)

Rabies virus (RV) is a single-stranded negative-sense RNA virus classified under the Lyssavirus genus in the Rhabdoviridae family. When RV infects the central nervous system, it primarily targets neurons while largely sparing glial cells. Infected neurons generally remain intact without significant damage or lysis for 7-12 days. A replication-deficient recombinant RV, derived from the RV vaccine strain Sad-B19, has been engineered to be less toxic and safer. This version of RV is highly effective in clearly labeling the fine structures of neurons and enables retrograde, monosynaptic tracing of neural circuits through a complementary approach.

Ignis Bioscience provides the RV-CVS and SAD-B19 viral strains. The latest RV-CVS strain features lower neurotoxicity, minimal neural damage, and enhanced labeling efficiency. It allows for extended infection periods of up to one month and can be integrated with techniques like optogenetics, calcium imaging, Cre, and Flp for targeted functional studies of brain networks and gene expression regulation.

For information on compatible helper viruses, please visit the Rabies Virus & HSV Helper pages or reach out to us at support@ignisbio.com.

Pseudorabies virus (PRV)

Pseudorabies virus (PRV) is a double-stranded DNA virus with a genome of approximately 150 kb, encoding proteins for the capsid, tegument, and envelope. The retrograde trans-synaptic variant of PRV, derived from the Bartha vaccine strain, is utilized to investigate neuronal connectivity within the brain and peripheral nervous system. Upon infecting nerve cells, PRV replicates and expresses target genes within the cells. The newly produced viruses then travel to synapses, enabling retrograde trans-synaptic labeling of upstream neurons for further replication and synaptic transmission.

Applications:

Multisynaptic Tracing: From peripheral areas to brain centers, or from higher to lower brain regions.
Peripheral-Central Nervous System Connectivity: Tracking connections between peripheral organs and the central nervous system.
Neural Network Analysis: Examining neural networks in disease or injury models.
Neural Development: Studying changes in neural networks during development

For information on compatible helper viruses, please visit the Rabies Virus & HSV Helper pages or reach out to us at support@ignisbio.com.

Herpes simplex virus (HSV)

Herpes simplex virus (HSV), particularly the H129 strain, is widely used as an anterograde tracer. When modified to include a fluorescent protein, HSV can effectively label connections between different brain regions as well as between the peripheral and central nervous systems.

Thymidine kinase (TK) is a critical enzyme for HSV replication in nerve cells. In the presence of TK, HSV can replicate within the cell, express the target gene, and transport progeny viruses to synapses, where they cross into downstream neurons, enabling multisynaptic tracing. When the TK gene is deleted (HSV-ΔTK), the virus can still infect neurons but cannot replicate. Since only replicating viruses can cross synapses, HSV-ΔTK alone cannot perform synaptic tracing. However, by using an AAV helper virus to first express the TK protein, HSV-ΔTK can be used for anterograde monosynaptic tracing.

Applications:

Multisynaptic Tracing: From the brain center to the periphery, or from lower to higher brain regions.
Peripheral-Central Nervous System Connectivity: Tracking connections between peripheral organs and the central nervous system.
Neural Network Analysis: Examining neural networks in disease or injury models.
Neural Development: Studying changes in neural networks during development.

For information on compatible helper viruses, please visit the Rabies Virus & HSV Helper pages or reach out to us at support@ignisbio.com.

Further questions or requests

If you have any special requests or questions, feel free to email us at support@ignisbio.com. Our team of highly experienced scientists is here to guide you every step of the way.