New sensors for fMRI

A functional magnetic resonance imaging tool capable of detecting levels of neurotransmitters could help scientists understand more about neurodegenerative conditions like Parkinson’s disease.

Functional magnetic resonance imaging (fMRI) is one of the best ways to study brain activity indirectly. It measures blood flow by tracking haemoglobin – when bound to oxygen its magnetic properties change and can be detected by MRI. However, it only identifies areas that are active during a particular task – what this activity is or which neurons are involved remains unknown.

Measuring the concentrations of neurotransmitters is considered a more direct way to gauge neural activity so researchers from MIT designed a sensor capable of detecting dopamine – a neurotransmitter involved in learning and movement control.

“This new tool connects molecular phenomena in the nervous system with the whole-brain imaging techniques, allowing us to probe very precise processes and relate them to the overall function of the brain and of the organism,” said Alan Jasanoff, associate professor of biological engineering at MIT and senior author.

Working with chemical engineers from Caltech, researchers built new sensors based on the protein cytochrome P450 – a paramagnetic enzyme found in most organisms which becomes weakly magnet when exposed to a magnetic field.

Using a technique called error-prone PCR – a faulty version of PCR – researchers collected a number of mutated forms of the gene each of which was placed into an E. coli bacterium to produce the mutated protein. These were tested for their ability to bind to dopamine, and the best candidates mutated again to improve its performance.

In studies with rats, the sensor can effectively detect dopamine in the brain but, in its current form, it must be injected into the brain and imaging is limited to the site of injection.