Neurons are the cells in the brain whose main task is transmitting information. They can do so in two ways: electrical, via pores between cells, or chemical, via release of neurotransmitters. The location of this communication is the synapse, a structure at the end of the branch-like structures of neurons. There are many different neurotransmitters with different effects. Glutamate is the primary activating neurotransmitter in the brain. It modulates the strength of connections between neurons, which is understood to underlie memory formation. However, it also plays a role in several diseases of the brain, such as depression, ADHD and addiction. Overstimulation by glutamate can have toxic effects on neurons. This is thought to be involved in diseases characterized by dementia, such as Alzheimer’s and Parkinson’s. With ageing being the most important population trend in large parts of the world today, these diseases are expected to become even more prevalent, and no curative therapies currently exist. Even though many drugs that are used against these diseases have effects on glutamate receptors, it is unclear to which extent glutamate neurotransmission are changed during disease, or how drugs change them. Besides drugs, it is known that certain dietary compounds, such as cholesterol and omega-3, can influence the glutamate signalling system in the brain. To elucidate some of these (changes in) glutamate levels during health and disease, this project aimed to monitor glutamate release in the synaptic cleft between neurons.
For this, electrodes and electrochemical detection were employed. The advantage of this technique is that electrodes can be easily miniaturized, to allow sensitive measurement of very fast events at the cellular level. Unfortunately, glutamate itself cannot be electrochemically detected directly. The project proposed to overcome this by developing a glutamate biosensor. Biosensors employ a biological recognition element – in this case the enzyme glutamate oxidase – which is immobilized on an electrode and specific for the analyte. The enzyme converts the analyte, while producing an electroactive reporter molecule – in this case hydrogen peroxide. The hydrogen peroxide can then be detected at the electrode. The biosensor is based on a nanoscale electrode, which allows measurement in the synaptic cleft. In the project, a novel immobilization method for enzymes was developed. This method allows the creation of very thin layers of enzyme, allowing the sensors to operate at maximum spatial and temporal resolution. This is necessary to be able to resolve the sub-millisecond dynamics of the glutamate release events at neurons. Within the project, the use of human induced stem cells was established in the host lab. These cells can be differentiated into glutamatergic neurons. A microfluidic device was designed, fabricated and used for the culturing of neurons. This can be used to assist the probing of the very small synaptic cleft structure, as neurons can be grown in a controlled way. The project ran for 11 months in the Andrew Ewing lab at the University of Gothenburg, Sweden.
