Researchers at Linköping University have developed a new type of pipette that can deliver ions to individual neurons without affecting the sensitive extracellular milieu. Controlling the concentration of different ions can provide important insights into how individual braincells are affected, and how cells work together. The pipette could also be used for treatments. Their study has been published in the journal Small.
"In the long term, this technology could be used to treat neurological diseases such as epilepsy with extremely high precision," says Daniel Simon, professor at Linköping University, LiU.
The human brain consists of about 85 to 100 billion neurons. It also has roughly the same amount of brain cells that support neuron function with, for example, nutrition, oxygen and healing. These cells are called glial cells and can be divided into many subgroups. Between the cells there is a fluid-filled space called the extracellular milieu.
The difference between the milieu inside the cells and that outside is important for cell function and one important aspect is the transport of different types of ions between the two milieus. For example, neurons are activated when the concentration of potassium ions changes.
It is known that a change in the whole extracellular milieu affects neuron activity and thereby brain activity. However, it has so far not been known how local changes in ion concentration affect individual neurons and glial cells.
Previous attempts to change the extracellular milieu have primarily involved pumping in some form of liquid. But this means that the delicate biochemical balance is disturbed, making it difficult to know whether it is the substances in the fluid, the changed pressure or the extracellular fluid swirling around that leads to the activity.
To get around the problem, researchers at the Laboratory of Organic Electronics, LOE, at LiU developed a micropipette measuring only 2 micrometres (m) in diameter. For comparison, human hair measures 50 and a neuron about 10 micrometres in diameter.
Using this so-called iontonic micropipette, the researchers can add only ions, such as potassium and sodium, to the extracellular milieu to see how this affects the neurons. Glial cell, specifically astrocyte, activity is also measured.
"Glial cells are the cells that make up the other – chemical – half of the brain, which we don't know much about because there has been no way to precisely activate those cells, as they don't respond to electrical stimulation. But both neurons and glial cells can be stimulated chemically," says Theresia Arbring Sjöström, assistant professor at LOE.
The experiments were conducted on slices of hippocampus brain tissue from mice.
"The neurons didn't respond as quickly to the change in ion concentration as we had initially expected. However, the astrocytes responded directly and very dynamically. Only when these were "saturated" were the nerve cells activated. This highlighted the fine-tuned dynamics between different types of cells in the brain in a way that other technologies haven't managed to do," says Theresia Arbring Sjöström.
Somewhat simplified, you can say that the pipette is manufactured by heating up a glass tube and pulling it to the breaking point. This produces a very thin and tapered tip. This type of micropipette is usually used in neuroscience to create and measure electrical activity in the brain. The LiU researchers' iontronic micropipette has a tip filled with a specially adapted ion-exchange membrane, which makes it possible to create activity by chemical means. Other than that, it looks identical to the traditional micropipette, and is controlled in a similar way.
"The advantage is that tens of thousands of people around the world are familiar with this tool and know how to handle it. Hopefully this will make it useful sooner," says Daniel Simon.
The next step is to continue studying chemical signalling in both healthy and diseased brain tissue using the micropipette. The researchers also want to develop the delivery of medical drugs and study its effect against neurological diseases such as epilepsy.
