Bipolar disorder unexpectedly linked to brain's reward system

Bipolar disorder has long been tied to dysfunction in the cerebral cortex, but scientists have now identified another, unexpected, area of the brain which could be involved in the development of the disease. Such a discovery could pave the way for the creation of new, more effective treatments.

Bipolar disorder is a mental health condition characterised by alternating periods of elation (mania) and depression. It is also fairly common – about one in 100 people in the UK will be diagnosed at some point in their lives – and is highly heritable.

While most studies have looked at genetic factors and how they are expressed in patients' brain cortex, new research published in Molecular Psychiatry is the first to identify the striatum as an area that could assist with effective treatment.

A subcortical part of the forebrain and a critical component of the reward system – the striatum is as a key area for the development of bipolar disorder.

Interconnected genes

The research team analysed the brain tissues of 35 bipolar and non-bipolar subjects, post-mortem. The found out that 14 genes were differentially expressed in tissue samples from the two groups. The scientists then identified a module of interconnected genes – rich in genetic variations associated with bipolar disorder – which was strongly expressed in the striatum.

The finding is unexpected as it is the first time the striatum has been linked to genetic factors involved in bipolar disorder. "This is the first real study of gene expression in the striatum for bipolar disorder," said lead author Ron Davis, from The Scripps Research Institute in Florida. "We now have a snapshot of the genes and proteins expressed in that region."

First author Rodrigo Pacifico said: "Our finding of a link between bipolar disorder and the striatum at the molecular level complements studies that implicate the same brain region in bipolar disorder at the anatomical level, including functional imaging studies that show altered activity in the striatum of bipolar subjects during tasks that involve balancing reward and risk."

This discovery is also interesting because it creates the foundations for the development of new drugs. Currently, the recommended treatment for bipolar disorder involves a combination of medications and psychotherapy. But finding what works best for a particular individual can sometimes be challenging, as some patients are non-adherent to the drugs.

This study points to several pathways as potential targets for treatment, and scientists will now conduct further research on the topic in the hope of developing alternative therapeutic options for patients.