CHICAGO, Oct. 24 (Xinhua) -- A Northwestern University (NU) research team has discovered in a study of zebrafish that there is a very orderly relationship between when spinal inhibitory neurons are born, their participation in different speeds of movement and what part of a motor neuron they innervate.
In the study, the researchers used a number of cutting-edge approaches, including using lasers and fluorescent proteins to light up individual neurons and their connections in the transparent fish. They also used electrophysiology in genetically modified fish to characterize function in intact, behaving animals.
They found that inhibitory neurons born first are active during the fastest movements and are most effective at silencing motor output by innervating motor neuron axons, closest to where activity is generated. Next to develop are interneurons active at intermediate speeds that strongly inhibit motor neuron cell bodies, followed by those active at slow speeds that weakly inhibit dendrites.
Collectively, the arrangement of inhibitory inputs in different structural compartments simplifies the process of ensuring appropriate patterns of motor output at different speeds, since different cell types can provide a stronger or weaker "veto" over motor output depending on when they are active.
"This makes some sense when you consider human development, where our first actions are kicking movements in the womb," said David McLean, an associate professor of neurobiology in the Weinberg College of Arts and Sciences at NU. "Only later do we require and acquire finer motor skills."
"The fact that we see this pattern in the spinal cord, a relatively primitive part of the nervous system, and in fish, a relatively primitive vertebrate, means that nervous systems made use of this compartmental scheme to regulate activity much earlier than we would have expected," he said.
Zebrafish is a model organism whose spinal cord works in a fashion similar to human. Learning more about the undulating movement of the swimming fish will allow scientists to better understand how humans walk.
The study was published Friday by the journal Science. Enditem
