V2b Neurons Act via Multiple Targets to Produce in Phase Inhibition during Locomotion

Area of Science:

• Neuroscience
• Motor Control
• Spinal Cord Circuits

Background:

• Spinal interneurons are crucial for motor control, but their complex circuitry and long-range connections pose challenges to understanding their function.
• V2b neurons represent a significant inhibitory spinal population with an unknown role in locomotion timing and behavioral specificity.
• Previous studies in zebrafish indicated V2b neurons slow locomotion, but their precise activity patterns and targets remained unclear.

Purpose of the Study:

• To investigate the precise timing and behavioral recruitment of V2b neurons during locomotion in larval zebrafish.
• To map the postsynaptic targets of V2b neurons beyond motor neurons within the spinal cord.
• To elucidate the role of V2b neurons in shaping motor neuron activity across different behaviors.

Main Methods:

• Optogenetic mapping of V2b neuron output along the rostrocaudal axis.
• Electrophysiological recordings of V2b neuron activity during visually and electrically evoked movements.
• Calcium imaging to monitor V2b neuron recruitment during locomotion and sensory stimulation.

Main Results:

• V2b neurons extensively inhibit motor neurons, V2a, V1, and commissural interneurons, with patterned long-range and localized inhibition.
• V2b neuron activity is specifically recruited for forward swims and turns, but not for fast escape behaviors.
• V2b inhibition occurs in phase with the rising edge of motor bursts, distinct from V1 neuron inhibition.

Conclusions:

• V2b neurons are key regulators of axial motor networks, providing leading, in-phase inhibition during locomotion.
• Their diverse targets and specific recruitment patterns suggest a role in modulating rhythmic motor behaviors.
• These findings reveal a distinct functional contribution of V2b neurons to motor control and spinal circuit dynamics.