Lithium and Brain Growth

There’s an interesting story about the way that lithium was found to be helpful to some people with bipolar disorder. It was thought that there was a link between bipolar disorder and gout, and gout is caused by an accumulation of uric acid in some joints. It just so happens that lithium is very good at getting guinea pigs to pass any excess uric acid in their urine. So in 1949 a medical scientist in Australia called John Cade tried lithium in bipolar disorder. It worked, but not because of any effect on uric acid: the lithium/uric acid connection only works in guinea pigs. But now, all these years later, it turns out that there may actually be a link between bipolar disorder and uric acid after all: uric acid levels often rise in people who are insulin resistant, and insulin resistance is a common feature of bipolar disorder.

The last few years have seen the growth of an impressive body of evidence about the effects of lithium on the brain. Lithium modulates the way in which many neurotransmitters act in the brain. That raised interesting questions, because many of the chemical transmitters do not only send messages between neurons, they may also stimulate the growth of cell processes and perhaps neurons themselves. Then it was discovered that lithium protects neurons by increasing the levels of a neuroprotective protein called Bcl-2. Then it was found to help stimulate the production of new neurons (neurogenesis) in the hippocampus.

A major breakthrough came in 2000, with the demonstration that lithium increases the amount of gray matter in the human brain, probably by stimulating the production of a growth promoter called brain-derived neurotrophic factor. Gray matter is composed primarily of neurons, so this suggested that lithium was either stimulating the growth of new neurons, or causing the migration of neural stem cells, or alternatively somehow preventing the death of neurons.

Within less than two years it was confirmed that treatment with lithium increased the amount of gray matter in the brains of people with bipolar disorder.

The findings remained controversial for two reasons: first was the seeming impossibility of stimulating the production of new gray matter. That is no longer such a problem: there is more and more evidence that the adult brain can indeed produce new neurons.
The second problem was technology: the measurements were open to
different interpretations.

Now neuroscientists at UCLA, using brain scans collected by collaborators at the University of Pittsburgh School of Medicine have shown that lithium does indeed increase the amount of gray matter in the brains of patients with bipolar disorder. But what is far more important is that the effects are seen in precise regions of the brain that are thought to be implicated in bipolar disorder.

The research is published in the July issue of the journal Biological Psychiatry.

Carrie Bearden, a clinical neuropsychologist and assistant professor of psychiatry at UCLA, and Paul Thompson, who is associate professor of neurology at the UCLA Laboratory of NeuroImaging, used a novel method of three-dimensional magnetic resonance imaging (MRI) to map the entire surface of the brain in people diagnosed with bipolar disorder. Everyone interested in the brain has been amazed by the quality of the images coming from the UCLA lab over the last six or seven years. (Graphics from the study, including the one above, are available online here.)

When the researchers compared the brains of bipolar patients on lithium with those of people without the disorder and those of bipolar patients not on lithium, they found that the volume of gray matter in the brains of those on lithium was as much as 15 percent higher in the cingulate and paralimbic regions of the brain, that are critical for attention, motivation and emotional control. There was no change in the amount of white matter, telling us that these effects are unlikely to be either artifacts or swelling of the brain.

These are extraordinary findings that may help explain how lithium works. If lithium increases the amount of gray matter in specific regions of the brain, this may suggest that existing gray matter in these regions may be underused or dysfunctional in people with bipolar disorder.

Conventional MRI studies in bipolar disorder measured the total volume of the brain, but these new imaging techniques employ high-resolution MRI and cortical pattern-matching methods to map gray matter differences that are so precise that they can pick up subtle differences in brain structure and this is the first time that researchers have been able to look at specific regions of the brain in people with bipolar disorder, and examine the effects of treatment.

The researchers at UCLA analyzed MRI scans of 28 adults with bipolar disorder, 20 of whom were lithium-treated, and 28 healthy control subjects collected by collaborators at the University of Pittsburgh. The analysis involved detailed spatial analyses of the distribution of gray matter by measuring local volumes of gray matter at thousands of locations in the brain.

This is superb research, and one of the signs of good research is that it raises yet more questions:

• We do not know whether these effects on gray matter persist once the medicine is stopped.
• Neither do we know whether the same effect might occur in other illnesses in which there is loss of gray matter. It may just be that lithium corrects an abnormality that is specific to bipolar disorder. That being said, there is recent evidence that lithium may be neuroprotective in a mouse model of Alzheimer’s disease.
• We also do not know if these brain changes correlate with clinical improvement.
• Lithium can have a lot of side effects, so we shall also need to factor that into the equation.
• We also need to know whether other medicines – or any other kind of therapy – might produce similar effects: there are already several medicines that have been shown to do something similar in some animals.

It’s still a bit too early to suggest putting lithium in the water supply…