Researchers at Karolinska Institutet in Sweden have made a breakthrough in understanding the molecular logic behind the assembly of spinal circuits that control the speed of locomotion in adult zebrafish. The study, published in Nature Neuroscience, used single-cell RNA sequencing to link the molecular diversity of motoneurons and interneurons with their modular circuit organization responsible for changes in locomotor speed. The researchers found that each neuronal population comprises three specific subtypes defined by key molecular features and correspond to neurons underlying locomotion at slow, intermediate, and fast speeds. This discovery provides important insights into the molecular mechanisms for neuronal and circuit diversity and has implications for understanding motor actions in general.
The study also revealed molecular signatures that define each of the three circuit speed modules. These findings help to uncover the molecular underpinnings for neuronal diversity and how they relate to the function of locomotor circuits in adult zebrafish. The categorization of muscle units into slow, intermediate, and fast types is universal to all vertebrates, but the molecular underpinnings of motoneuron diversity and their premotor circuits have remained unclear until now. The study fills this critical gap in knowledge and represents a significant advancement in the field. It is of broad interest to researchers studying motor control and brain circuit organization.
To conduct the study, the researchers used single-cell RNA sequencing, along with electrophysiology, anatomical, and behavioral analysis in adult zebrafish. This combination of techniques provided both experimental and genetic accessibility, allowing the researchers to reveal the molecular and functional features that define motoneuron and interneuron subtypes, as well as their modular circuit organization responsible for controlling locomotion speed. The study also suggests that the different speed circuit modules may be driven from the brainstem through distinct command streams, which could explain the flexibility and maneuverability of locomotor movements in different tasks and contexts.
Overall, this research sheds new light on the molecular mechanisms underlying locomotor speed control and provides a foundation for further studies on motor actions and circuit organization in vertebrates.
