At UHN, we strive to deliver Compassionate Care & Caring. Learn more about the services and supports that are available to you throughout your journey.
Our UHN programs and services are among the most advanced in the world. We have grouped our physicians,
staff, services and resources into 10 medical programs to meet the needs of our patients and help us make
the most of our resources.
At the heart of everything we do at UHN are our Healthcare Professionals. Refer a patient to one of our 12 medical programs. Learn more about the resources and opportunities available for professional growth.
University Health Network has grown to be one of the largest research and teaching hospital networks in Canada - pioneers in improving the lives of patients. Our long history of health professions education at Toronto General, Toronto Western, Princess Margaret and Toronto Rehab hospitals has consistently advanced the science of education.
University Health Network is a health care and medical research organization in
Toronto, Ontario, Canada. The scope of research and complexity of cases at UHN has made us a national and international
source for discovery, education and patient care.
Being touched by illness affects us in different ways. Many people want to give back to the community
and help others. At UHN, we welcome your contribution and offer different ways you can help so you can find one that suits you.
The Newsroom is the source for media looking for information about UHN or trying to connect with one
of our experts for an interview. It's also the place to find UHN media policies and catch up on our news stories, videos, media releases,
podcasts and more.
Researchers at UHN's Krembil Brain Institute have shown that stimulating a specialized type of brain cell – known as astrocytes – can correct chemical imbalances associated with disorders such as migraine and epilepsy.
When the brain is active, concentrations of charged molecules called ions change, allowing for messages to be transmitted. A particular ion – potassium – accumulates outside these cells in high concentrations after brain activity. Astrocytes, a type of support cell that helps to regulate signal transmission, normally help to take up excess potassium.
This cleanup process is important to maintain the delicate equilibrium of chemicals in the brain and maintain normal brain activity. However, when astrocytes malfunction, potassium builds up in the extracellular space.
"Abnormally high potassium levels are associated with several conditions, such as migraine, epilepsy and stroke," explains Dr. Peter Carlen, a Senior Scientist at the Krembil Brain Institute and senior author of the study. "We explored whether we could stimulate these cells to increase the absorption of potassium and prevent the adverse effects of abnormal brain activity."
In an experimental model, the researchers used genetic approaches to introduce a light-sensitive protein into astrocytes. This then enabled the team to selectively stimulate astrocytes by applying light. When stimulated, the cells became hyperpolarized – meaning that the charge cell became even more negative than normal (i.e., they exhibited a more negative resting potential).
"A negative resting potential is key to astrocyte function," says Dr. Carlen. "The negative charge enables the cell to attract potassium ions, which are positively charged."
The researchers then looked at how stimulating astrocytes – while either activating or not activating neurons – affected potassium concentrations. They found that, regardless of whether neurons were active or resting, stimulating astrocytes increased their ability to take up potassium from the extracellular space.
"We found that there was a limit to how much we could drive astrocytes to take up potassium – stronger stimulation did not necessarily translate into greater absorption," explains Azin Ebrahim Amini, first author of this study. "This finding suggests that other regulatory mechanisms might be involved in normalizing ion concentrations following brain activity."
These findings provide an important insight: stimulating astrocytes can help regulate ion concentrations and promote healthy brain activity. The results also point to astrocytes as a potential therapeutic target for patients suffering from debilitating conditions associated with abnormally high potassium levels – including neurotrauma, migraine, strokes and seizures.
This work was supported by the Canadian Institutes of Health Research and the UHN Foundation. B Stefanovic holds a Tier 1 Canada Research Chair in Neuroimaging and is a professor at the department of Medical Biophysics at the University of Toronto.