Brain Chemistry Anomalies Found in Bipolar Disorder
October 08, 2004
Individuals with bipolar disorder have an average of 30% more of a vital class of signal-sending brain cells, according to new data. This discovery strengthens the hypothesis that the disorder has inescapable genetic and biologic origins, and may clarify why it runs in families.
This finding is the first neurochemical difference to be discovered between asymptomatic bipolar and nonbipolar individuals. To put it simply, these patients brains are wired differently, in a way that we might expect to predispose them to bouts of mania and depression, noted Jon-Kar Zubieta, M.D., Ph.D., assistant professor of psychiatry and radiology at the University of Michigan Health System (U-Mich; Ann Arbor, MI).
Individuals with bipolar disorder have wild mood swings. The milder, type II kind causes depression alternating with frenzy; whereas the more debilitating type I disorder produces frenzied, even psychotic events and severe depression.
Dr. Zubieta and coworkers made the findings on 16 patients with type I bipolar disorder utilizing positron emission tomography (PET) scanning. The PET scans demonstrated the metabolism of the brain chemicals serotonin, dopamine, and norepinephrine. These chemicals are called monoamines and transmit signals between neurons.
These new results point to a distinct difference in the density of monoamine-releasing cells in the brains of bipolar individuals even when they are not having symptoms. Positioning the PET scanner on regions of the brain where monoamine-releasing cells are concentrated, the scientists looked for the faint signal of a weak radioactive tracer, DTBZ, which they had injected into the blood stream of the 16 study participants without bipolar disorder.
The researchers discovered by looking at the intensity of the DTBZ signal in all the patients brains, bipolar patients averaged 31% more binding sites in the thalamus, and 28% more in the ventral brain stem. In the thalamus, bipolar women in fact had levels near those of healthy comparison individuals, but bipolar men had a 42% higher binding rate, suggesting that there may be certain biologic causes for the clinical differences in the course of the illness in women and men.
Combining the results of functional tests, the researchers discovered that the more monamine cells the patients had, the lower their scores on verbal learning and executive function tests. This finding suggests that the altered brain chemistry due to the excess monoamine cells may directly affect the patients' social and cognitive function.