Quantum chemical calculations could help scientists locate key neurotransmitters in the brain. The calculations should make the detection of small molecules in vivo much more accurate, claims the French team behind the research.

GABA's theoretical spectrum is similar to its experimental one

GABA (gamma-aminobutyric acid) is a neurotransmitter involved in brain disorders such as epilepsy, schizophrenia, alcoholism and drug addiction. In order to diagnose these disorders or monitor their treatment it is vital to be able to detect GABA in the brain.

Usually GABA is detected in humans using nuclear magnetic resonance spectroscopy (NMR, also known as MRI, magnetic resonance imaging). The problem is that GABA is only present in the brain in very small amounts, and its signal is swamped by those of other molecules. Current detection methods involve filtering the NMR signals to separate out the overlapping spectra, but this relies on knowing precisely where to look for the peaks from GABA.

Monique Aubert-Frécon's team from the University of Lyon has performed calculations to work out how to locate these GABA peaks. Instead of the usual approach of predicting the peaks from experimental measurements, the group used quantum chemical calculations to calculate GABA's electronic structure from first principles. From this they could predict GABA's signature spectrum and how it would change in different magnetic fields. The calculations should make it easier to pick GABA out from the complicated NMR spectrum of the brain, said Aubert-Frécon.

The new approach can provide estimates 'accurate enough to be useful as good starting values for the analysis of experimental NMR data,' said Aubert-Frécon. It should also be applicable to other small molecules, she said.

Clare Boothby