A transgenic mouse line for rabies virus-mediated trans-synaptic tracing in the postnatal developing brain

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Understanding neural circuits requires mapping neuronal connections.
• Rabies virus (RV)-mediated trans-synaptic tracing visualizes presynaptic neurons.
• Adeno-associated virus (AAV) is traditionally used for RV tracing but has limitations in developmental studies due to slow gene expression.

Purpose of the Study:

• To develop a new transgenic mouse line for efficient RV-mediated trans-synaptic tracing, particularly for developmental studies.
• To overcome the limitations of AAV-based gene expression timing in studying neural circuit development.

Main Methods:

• Generated a Cre-dependent transgenic mouse line (Ai162-nCTG) expressing nuclear mCherry, TVA receptor, and rabies glycoprotein.
• Crossed Ai162-nCTG with vasopressin-Cre mice for proof-of-principle.
• Injected RV into the paraventricular hypothalamic nucleus and compared with AAV-based tracing.
• Performed trans-synaptic tracing in juvenile (postnatal day 7 and 30) and adult mice.

Main Results:

• mCherry expression in Ai162-nCTG mice was specific to vasopressin neurons in the paraventricular hypothalamic nucleus.
• RV tracing using the Ai162-nCTG line successfully mapped presynaptic inputs to vasopressin neurons.
• The Ai162-nCTG method enabled tracing in juvenile mice (P7, P30), unlike the slower AAV approach.
• Presynaptic input distribution to paraventricular vasopressin neurons remained stable from juvenile to adult stages.

Conclusions:

• The Ai162-nCTG transgenic mouse line provides a valuable tool for rabies virus-mediated trans-synaptic tracing, especially in developmental neuroscience.
• This new method overcomes the temporal limitations of AAV, facilitating the study of neural circuit development.
• Paraventricular vasopressin neuron connectivity is largely established before weaning and remains stable into adulthood.