Researchers unlock mechanism of inner-ear synapses to improve treatment for balance disorders

After 15 years of research, a research team has unraveled the mechanism of the synapses responsible for processing signals related to balance and head movements.

Neuroscientists, physicists and engineers from various institutions jointly published their findings in the Proceedings of the National Academy of Sciences, a January news release from Rice University said. The paper sheds light on the workings of "vestibular hair cell-calyx synapses" found in the innermost ear organs that sense head position and movements.

One key point is that fast synaptic activity is what helps us stay on our feet.

The team included Rice University bioengineer Rob Raphael; the University of Chicago's Ruth Anne Eatock; the University of Illinois Chicago's Anna Lysakowski; current Rice graduate student Aravind Chenrayan Govindaraju; and former Rice graduate student Imran Quraishi, now an assistant professor at Yale University; the release said. The members set out to gain an understanding of why those synapses operate at an incredibly fast pace.

Synapses are the junction points where neurons transmit information so the message gets from brain to body. Most synapses in the human body rely on quantal transmission, which takes at least 0.5 millisecond to send information. The vestibular hair cell-calyx synapses operate much faster. 

In those synapses, a signal-receiving neuron envelops the end of its partner hair cell with a large cup-shaped structure called a calyx, separated by a minuscule gap measuring only a few billionths of a meter. Lysakowski referred to the vestibular calyx as a "wonder of nature" due to its unique structure and the energy invested in its formation. 

The scientists used computational modeling based on the anatomy and physiology of the synapse and simulated impulses, the release said. They then tracked the flow of potassium ions through ion channels to accurately predict changes in potassium levels and electrical potential within the synaptic cleft. This enabled them to explain the speed of nonquantal transmission, among other things.

The team's computational model provides key insights into the interplay between different ion channels, the calyx structure, and changes in the potassium and electric potential within the synaptic cleft. It also opens the door for further exploration of information processing that occurs in vestibular synapses as well as studying the interactions between quantal and nonquantal transmission. 

The research findings hold significant promise for the treatment of vertigo and balance disorders, as researchers will be better able to develop therapies that target the underlying causes of those conditions, the release said. Balance disorders affect approximately 1 in 3 Americans over 40 years of age, so this new approach to finding solutions for the problems could be substantial.

The researchers similarly project that their model could aid in the development of vestibular implants, devices that can restore balance. The model may also prove valuable in studying electrical transmission in other areas of the nervous system.

The research received support from the National Institutes of Health, the Hearing Health Foundation and a seed grant from Rice University's ENRICH program.