Visual subcircuit-specific dysfunction and input-specific mispatterning in the superior colliculus of fragile X mice

Area of Science:

• Neuroscience
• Genetics
• Developmental Biology

Background:

• Sensory processing deficits are common in neurodevelopmental disorders like fragile X syndrome (FXS).
• FXS, caused by FMR1 gene silencing, leads to visual impairments, particularly in motion processing.
• The superior colliculus (SC) is a key midbrain structure for visual circuit development and function.

Purpose of the Study:

• To investigate the function and organization of visual circuits in the SC of a mouse model of FXS (Fmr1^-/y).
• To explore the role of the FMR1 gene in activity-dependent synaptic plasticity within the SC.

Main Methods:

• In vivo extracellular electrophysiology with controlled visual stimuli.
• Analysis of receptive field properties of SC neurons in control and Fmr1^-/y mice.
• Anatomical tracing to assess visual input organization.

Main Results:

• Fmr1^-/y mice exhibited larger SC receptive fields and decreased direction selectivity.
• Axis-selective (AS) neurons in Fmr1^-/y mice showed specific hyperexcitability.
• Retinocollicular and retinogeniculate pathways were normal, but V1 to SC projections were poorly refined.

Conclusions:

• FMR1 is essential for proper visual circuit development and function in the SC.
• Visual dysfunction in FXS is subcircuit-specific, affecting V1 inputs to the SC.
• FMR1 plays distinct developmental roles in different visual subcircuits.