Substantia Nigra Pars Reticulata Regulates the Prefrontal Cortex via the Ventromedial Thalamus

Area of Science:

• Neuroscience
• Systems Neuroscience
• Cortical Circuits

Background:

• The ventromedial thalamus (VM) projects to layer 1 (L1) of the medial prefrontal cortex (mPFC), impacting executive functions and arousal.
• Thalamocortical (TC) cells within the VM process cortical inputs crucial for persistent activity generation.
• Limited knowledge exists regarding subcortical input connectivity to VM TC cells and their routing to mPFC circuits.

Purpose of the Study:

• To investigate subcortico-thalamo-cortical circuits involving the VM and their influence on the mPFC.
• To characterize the subcortical inputs to VM TC cells and their functional impact.
• To elucidate the pathway through which these subcortical inputs modulate inhibitory networks in the mPFC.

Main Methods:

• Anatomical tracing techniques were employed to map connectivity.
• Electrophysiology and optogenetics were used to assess neuronal activity and synaptic transmission.
• Intersectional approaches were utilized to trace specific circuit pathways.

Main Results:

• The substantia nigra pars reticulata (SNr) was identified as the primary subcortical input to VM TC cells.
• SNr inputs form strong GABA_A receptor-mediated inhibitory connections onto VM TC cells, suppressing their firing.
• SNr inputs are relayed via VM TC cells to activate inhibitory interneurons in L1 of the mPFC.

Conclusions:

• Subcortical inputs, specifically from the SNr, significantly influence higher-order thalamic circuits.
• The VM acts as a critical relay for subcortical signals to the frontal cortex, modulating mPFC inhibitory networks.
• This pathway highlights a distinct mechanism of subcortical modulation of cortical function compared to motor systems.