Need to balance guides development of limb-body coordination

October 08, 2019

The need to feel balanced drives the development of coordination between body and limbs as zebrafish larvae learn to swim, a new study finds.

Published online October 8 in eLife, the study found that the developing fish rely on their vestibular organs - the equivalent of the human inner ear - as their sense of balance oversees improvements in coordination needed to remain horizontal. A level posture is preferred across evolution, say the study authors, as it helps animals to move, find food, and evade predators.

Led by researchers from NYU School of Medicine, the work focused on zebrafish larvae, which undergo their development while swimming in the water, venturing into their environment much earlier after fertilization (3-30 days) than a human fetus, which continues to develop in the womb. This external development enabled researchers to watch larvae for changes in movement patterns that depend on brain circuits similar to those that enable human balance.

"The relationship between balance and movement is broken in rare diseases like Developmental Coordination Disorder, and in ataxias, the movement problems that occur in patients with multiple sclerosis and in those who have had a stroke," says lead study investigator David Schoppik, PhD, assistant professor in the Department of Neuroscience and Physiology at NYU School of Medicine.

"Our hope is that the work in fish guides the future development of therapies for disorders caused by the brain's mishandling of balance cues as it coordinates muscle groups," says Schoppik.

Balance Basics

Past studies have argued that fins evolved into the forelimbs of land animals, and that zebrafish pectoral fins may provide a useful model for the role of forelimbs in coordinated movement. Maturing humans learn to swing their arms and flex trunk muscles as they walk, which reduces angular momentum (the tendency to pitch forward). However, the sensations that guide the development of this coordination are poorly understood.

One clue observed across evolution is that animals prefer to remain horizontal to satisfy a sense of balance and orientation to the world. On land, animals judge their orientation relative to gravity using many senses, including the feeling of how hard their feet are pressing on the ground, say the authors. The related biomechanics are more complex on land than underwater where, thanks to buoyancy, animals are more dependent on a single factor - their vestibular sense - to guide improvements in coordination, researchers say.

The new study found that zebrafish larvae used upward-orienting body rotations together with lift-producing pectoral fin motions to climb in water. Researchers also observed that fish larvae became better able with age to remain level as they climbed by matching larger fin actions with smaller body movements. Younger fish were more likely to careen upward nose-first like rockets.

The research team also found that zebrafish engineered to lack function in their utricular otoliths - the fish version of the balance system - did not get better with age at coordinating trunk and fin movements to achieve postural stability.

The study results also address the cerebellum, long established as a center for the coordination muscle movements (motor coordination). The new work showed that zebrafish with disabled cerebellar function, instead of using lift-generating pectoral fins only while climbing, also use them as they try to dive. Cerebellar Purkinje cells in particular blocked pro-movement signals to rule out pectoral fin movements when they would clash with body movements.

"Our work shows that the fish brain uses information about balance to generate the right combination of muscle contractions to effectively swim," says study co-author David Ehrlich, PhD, a post-doctoral scholar in Schoppik's lab. "Now that we know these fish are capable of elegant coordination, we can measure brain activity to understand how and where coordinated movements are composed."
The study was funded by National Institute on Deafness and Communications Disorders grant DC017489 and the Hearing Health Foundation.

NYU Langone Health / NYU School of Medicine

Related Zebrafish Articles from Brightsurf:

Zebrafish embryos help prove what happens to nanoparticles in the blood
What happens to the nanoparticles when they are injected into the bloodstream, for example, to destroy solid tumours?

Social experiences impact zebrafish from an early age
Study in zebrafish demonstrates that early social experiences have an effect on the behaviour of the fish even at an age when they are still not considered ''social''.

How zebrafish maintain efficient and fair foraging behaviours
New insight on how zebrafish achieve near-optimal foraging efficiency and fairness among groups has been published today in the open-access journal eLife.

How the zebrafish got its stripes
Animal patterns are a source of endless fascination, and now researchers at the University Bath have worked out how zebrafish develop their stripes.

Extraordinary regeneration of neurons in zebrafish
Biologists from the University of Bayreuth have discovered a uniquely rapid form of regeneration in injured neurons and their function in the central nervous system of zebrafish.

Zebrafish teach researchers more about atrial fibrillation
Genetic research in zebrafish at the University of Copenhagen has surprised the researchers behind the study.

How decisions unfold in a zebrafish brain
Researchers were able to track the activity of each neuron in the entire brain of zebrafish larvae and reconstruct the unfolding of neuronal events as the animals repeatedly made 'left or right' choices in a behavioral experiment.

'Census' in the zebrafish's brain
Dresden scientists have succeeded in determining the number and type of newly formed neurons in zebrafish; practically conducting a 'census' in their brains.

Zebrafish 'avatars' can help decide who should receive radiotherapy treatment
To date, there is no method for clearly determining whether radiotherapy will be an effective treatment for individual cancer patients.

Special cells contribute to regenerate the heart in Zebrafish
It is already known that zebrafish can flexibly regenerate their hearts after injury.

Read More: Zebrafish News and Zebrafish Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to