Midbrain circuits that set locomotor speed and gait selection.

Area of Science:

• Neuroscience
• Animal Behavior
• Motor Control

Background:

• Locomotion is essential for animal survival and behavior.
• Brainstem structures control locomotion, but specific neuronal substrates remain unclear.
• Different behaviors (e.g., exploration, escape) require distinct speeds and gaits.

Purpose of the Study:

• To elucidate the neuronal mechanisms underlying speed and gait selection in locomotion.
• To identify specific midbrain nuclei and neuron types involved in controlling locomotor behaviors.
• To differentiate the roles of distinct neuronal populations in context-dependent movement.

Main Methods:

• In vivo electrophysiology in mice.
• Optogenetic manipulation of neuronal activity.
• Analysis of neuronal connectivity and activation dynamics.
• Behavioral assays for locomotion, including speed and gait analysis.

Main Results:

• Glutamatergic excitatory neurons (GlutNs) in the cuneiform nucleus (CnF) and pedunculopontine nucleus (PPN) control locomotion.
• GlutNs in both CnF and PPN contribute to slow, alternating-gait locomotion.
• CnF GlutNs uniquely control high-speed, synchronous-gait locomotion.
• Distinct activation dynamics and connectivity patterns of PPN and CnF GlutNs support exploratory and escape behaviors, respectively.

Conclusions:

• Two midbrain nuclei, CnF and PPN, house distinct GlutN populations that control locomotion.
• These GlutN populations act in concert to select context-dependent locomotor behaviors like exploration and escape.
• The findings reveal a neural circuit for adaptive motor control based on behavioral needs.