Inhibitory connections between motor neurons modify a centrally generated motor pattern in the leech nervous system

Area of Science:

• Neuroscience
• Animal Behavior
• Motor Control

Background:

• Leeches possess both excitatory and inhibitory motor neurons controlling body wall muscles.
• Inhibitory motor neurons exert central inhibition on excitatory motor neurons innervating the same muscle.
• This inhibition is strong, likely monosynaptic, and relies on graded membrane potential changes.

Purpose of the Study:

• To investigate the role of inhibitory motor neurons in modulating excitatory motor neuron activity during leech swimming.
• To determine if central inhibition by IMNs affects EMNs during rhythmic motor behaviors.

Main Methods:

• Electrophysiological recordings from motor neurons in the leech Hirudo medicinalis.
• Analysis of neuronal activity during fictive swimming (simulated swimming behavior).

Main Results:

• Both excitatory and inhibitory motor neurons are rhythmically active during leech swimming.
• Inhibitory motor neurons were found to phasically inhibit excitatory motor neurons during swimming.
• This phasic inhibition increased the amplitude of membrane potential oscillations and burst intensity in excitatory motor neurons.

Conclusions:

• Phasic inhibition by IMNs is a key mechanism for augmenting EMN activity during leech swimming.
• This interaction enhances motor output, contributing to the generation of swimming behavior.
• The findings highlight the importance of central inhibition in shaping rhythmic motor patterns.