Study of the modulatory CNS regions in the visual circuit Retina-Superior Colliculus-Lateral Posterior nucleus triggering freezing behavior
Ares Sellés Rius
NERF (Neuro-Electronics Research Flanders), Karl Farrow's Laboratory, Belgium

Aim: The goal is to understand the neuronal networks organization from the sensory input to the freezing behavior through the identification of modulatory brain regions that project to the Superior Colliculus.

Introduction: The behavior of an animal can be triggered by signals in its visual environment. Threating visual stimulus evoked innate defense behaviors as freezing behavior. This project is focused in one visual-guided behavioral circuit that links the retina visual information with the Lateral Posterior thalamic nucleus(LP) via Superior Colliculus(SC).

Methods: The experimental approach is based on retrograde viral tracing techniques. Using the stereotaxic surgery, the first injection with a Herpes Simplex Virus expressing TVA receptor and glycoprotein G was done at LP. After 21 days, the second injection was done at the SC with a Rabies Virus coated by EnvA and lacking of glycoprotein G. The combination of these viruses allowed the restriction of the viral tracing to the circuit of interest. Subsequently, the experimental procedure continued perfusing the mouse, slicing the brain and staining it. Finally, the slices were scanned using the fluorescent confocal microscope.

Results: The resulting images presented labeled cells in all brain areas that sent inputs to collicular neurons that are projecting to LP. The main nuclei identified were the Periaqueductal gray, the primary visual cortex and the Substantia nigra, suggesting their modulatory role in freezing responses.

Conclusion: The main areas labeled are sending excitatory projections to SC to reinforce the freezing behavior. Also, Ntsrl-GN209-Cre mice used in combination with flox-HSV for the first injection restricted more the viral tracing, specifically to the Ntsrl+-Wild-field neurons of SC which were already known that project to LP. The results were not completely consistent with the non-flox-HSV injections but the main nuclei named above were also labeled. These results suggest that the flox-HSV is necessary to exclude nonspecific labeling of projections from SC-LGN.

Acknowledgements: The exposed project was done in Karl Farrow's laboratory, at NERF (Neuro-Electronics Research Flanders) in Leuven, Belgium. It was a Bachelor's thesis, supported by both KatholiekeUniversiteit Leuven and University of Barcelona.

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