Out of kilter neurotransmitters could indicate OCD

People with obsessive-compulsive disorder have imbalances between two brain chemicals, Cambridge researchers have found, saying the correlational findings might improve OCD therapy.

Glutamate and gamma-aminobutyric acid (or GABA) are important neurotransmitters that assist in brain function, with glutamate acting as the most abundant excitatory chemical in the brain.

It triggers an electrical signal in brain cells, whereas GABA is an inhibitory neurotransmitter, which prevents neurons from firing such signals.

Research using magnetic resonance spectroscopy – a form of imaging similar to MRI – to measure neurotransmitter levels in 61 people, identified that those with OCD have elevated glutamate and lowered GABA in the anterior cingulate cortex and supplementary motor area of the brain.

The anterior cingulate cortex contributes to several decision-making and mood functions.

As well as brain scans, study participants were also asked to undergo computer-based assessments and questionnaires with researchers testing for other obsessive-compulsive habits and tendencies.

Some of those without diagnosed OCD who showed low-level signs of repetitive behaviour also showed the glutamine-GABA imbalance in their supplementary motor area scans, although to a lesser extent.

These findings, says the study’s senior author Professor Trevor Robins from Cambridge’s psychology department, provide valuable information for improving OCD therapy, with spiked glutamine levels in these regions potentially acting as biomarkers for the disorder.

“Understanding obsessive-compulsive disorder is a central question for psychiatry,” Robins says.

“We have now shown definitive changes in these key neurotransmitters in OCD sufferers: excess glutamate and reduced GABA is disrupting the neural circuitry in key regions of the OCD brain.”

“Our findings are a major piece of the puzzle for understanding the mechanisms behind OCD. The results suggest new strategies for medication in OCD based on available drugs that regulate glutamate.”

Robins and his colleagues acknowledge their findings are correlational, and that monitoring the effects of medication on regulating glutamate and GABA would provide a more rigorous test of the imbalances observed in their study groups.

Currently, there are few interventions for people with OCD. While anti-depressants like selective serotonin reuptake inhibitors (SSRIs) can be prescribed, more severe cases may require advanced therapies such as deep-brain stimulation. Non-invasive treatments have been trialled involving magnetic stimulation through the scalp.

OCD is a debilitating medical condition that can have severe impacts on quality of life. Those living with the disorder experience unwanted and intrusive obsessions or repetitive behaviours.

“Some treatments already target glutamate imbalance in a roundabout way, but now we have the evidence for why certain approaches seem to have some beneficial effects,” says the study’s lead author Dr Marjan Biria.

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