Heterogeneous electrotonic coupling and synchronization of rhythmic bursting activity in mouse Hb9 interneurons

Area of Science:

• Neuroscience
• Spinal Cord Physiology
• Neuronal Networks

Background:

• Mammalian spinal cord networks generate rhythmic locomotor activity through poorly understood mechanisms.
• Hb9 interneurons are a small, localized population of conditionally bursting interneurons in the mouse spinal cord.

Purpose of the Study:

• To investigate the intrinsic properties and network interactions of Hb9 interneurons in generating rhythmic activity.
• To elucidate the role of Hb9 interneurons in mammalian locomotor networks.

Main Methods:

• Applied potassium channel blockers to increase neuronal excitability.
• Utilized 2-photon calcium imaging and whole-cell patch-clamp recordings in spinal cord slices and preparations.
• Investigated effects of tetrodotoxin and carbenoxolone on neuronal activity and calcium transients.

Main Results:

• Postnatal Hb9 interneurons exhibited bursts of action potentials with voltage-independent spikelets upon increased excitability.
• Calcium transients in clustered Hb9 interneurons were synchronous and insensitive to fast synaptic transmission blockade but blocked by carbenoxolone.
• Hb9 interneurons showed common chemical synaptic inputs but no direct electrotonic coupling, though they were coupled to non-Hb9 interneurons.
• Hb9 interneuron bursting was synchronous with rhythmic ventral root output in the absence of fast chemical transmission.

Conclusions:

• Hb9 interneurons are endogenous bursters and rhythmically active within an electrotonically coupled network.
• This network property enables the generation of diverse and stable rhythms essential for locomotion.