Neural insights reveal the secrets of movement

summary: Researchers have made progress in understanding how stick insects control their leg muscles while walking, challenging previous assumptions about motor neuron activation. Their study reveals that the neurons that activate the depressor muscle in the stick insect leg receive unique rhythmic excitation, unlike other leg muscles.

This finding highlights the role of central pattern generators (CPGs) in the production of rhythmic movements and indicates that their influence on motor neurons is limited to each group of neurons. This research not only advances our understanding of animal locomotion, but also underscores the complexity of neural networks in coordinating walking movements.

Key facts:

1. The study found that depressor motor neurons in stick insects are excited rhythmically, in contrast to the activation pattern of other leg muscles.
2. Central pattern generators (CPGs) have been shown to provide specific activation to different groups of motor neurons, debunking the uniform effect theory.
3. This research advances our knowledge of the neural basis of locomotion, suggesting precise control mechanisms for the initiation and stabilization of walking phases.

source: University of Cologne

In a new study, scientists from the University of Cologne have obtained new insights into the mechanism of rhythmic activation of nerve cells (neurons) in stick insects that control leg muscles during walking.

The researchers showed that the neurons that activate the depressor muscle in the leg are excited rhythmically, unlike those in other leg muscles. Until now, it has been assumed that all so-called motor neurons are activated in the same way by central neural networks.

The study, titled “Synaptic drive of central pattern-generating networks of walking insect leg motoneurons is specific to the motoneuron population,” was published in the journal Current biology.

The research team at UCLA is investigating the neural underpinnings of movement generation in animals, particularly those basic motor activities such as walking.

For this purpose, the team led by Prof. Dr. Ansgar Boschges is analyzing insects, among other arguments, since the requirements of the nervous system regarding the generation and control of walking movements are very similar in the animal kingdom.

In many animals, for example, there are networks in the central nervous system that underlie the generation of rhythmic activity patterns for many forms of movement, whether for rhythmic locomotor activity such as running, swimming, crawling, and flying or for vegetative functions. Like breathing.

These highly specialized networks are referred to as central pattern generators (CPGs). It generates the rhythmic motor activity of muscles for movement by interacting with information received from sensory organs and neurons called proprioceptors; Proprioceptors report movements and inform the central nervous system. In the case of walking, they fall on and in the insect's legs.

The networks do this by activating so-called motor neurons that innervate the muscles. Until now, it was assumed that such motor neurons have the same effect on all the motor neurons they target.

In their new study, Angelina Roth, Dr. Charalambos Mantziaris, and Professor Boschges refute this assumption about the locomotor activity of insects.

In their experiments, the scientists pharmacologically activated CPGs in the central nervous system of the stick insect Carausius Maurosus He investigated its effect on the motor neurons that innervated his leg muscles.

They found that all but one of the leg muscle groups of motor neurons receive an identical drive from the networks: rhythmic inhibitory signals from CPGs.

Only motor neurons, which innervate the depressor gastrocnemius muscle, are controlled by phasic excitatory drive. Interestingly, the depressor gastrocnemius muscle is exactly the insect muscle responsible for generating leg posture during any walking condition – regardless of whether the animal is running up or down horizontally, on the ceiling or on a branch.

“Rhythmic excitation and thus specific activation of this motor neuron population by CPGs could serve to ensure the precise timing of depressor muscle contraction and thus the onset and stabilization of the stance phase,” Professor Boschges explained.

Financing: The study was funded by the German Research Foundation (DFG).

About this neuroscience research news

author: Eva Schiesler
source: University of Cologne
communication: Eva Schiesler – University of Cologne
picture: Image credited to Neuroscience News

Original search: Open access.
“The synaptic drive of the central pattern-generating networks of the leg motoneurons of a walking insect is specific to the motoneuron population“By Ansgar Boschges et al. Current biology

a summary

The synaptic drive of the central pattern-generating networks of the leg motoneurons of a walking insect is specific to the motoneuron population

Highlights

• The synaptic drive of motoneuron stalk CPG networks is assembly-specific
• Motor neurons of the protractor, connective tissue and lever receive phasic inhibitory drive
• Exclusively, depressor motor neurons receive phasic excitatory drive

summary

Rhythmic motor activity, such as flying, swimming or walking, results from the interaction between higher centers in the central nervous system, which initiate, maintain and modulate task-specific motor activity, and central pattern generating neural circuits (CPGs). ) that can generate virtual rhythmic motor outputs and, finally, feedback from sense organs that modulate basic motor activity toward function.

In this context, CPGs provide phasic synaptic drive to motor neurons (MNs), thus supporting the generation of rhythmic activity for movement.

We analyzed the synaptic drive received by leg MNs supplying the three major leg joints from CPGs in pharmacologically activated and desmoplastic preparations of the stick insect (Carausius Maurosus). We have shown that motor CPGs model the tonic activity of five of the six leg MNs via phasic inhibitory synaptic drive.

These are the antagonistic MN assemblies that supply the thoracic-trochanteric joint and the tibiofemoral joint and the levator MN assemblage that supplies the coxa-trochanteric (CTr) joint. In contrast, the rhythmic activity of the depressor MN trough feeding the CTR joint was found to be primarily dependent on phasic excitatory drive.

This difference is likely related to the pivotal role of the depressor muscle in generating leg posture during any walking condition. Thus, our results provide evidence for the existence of qualitatively different mechanisms for generating rhythmic activity between MN populations in the same motor system.