Which Comes First – Prescription Painkiller Addiction or Depression?
Researchers are now investigating the “chicken and the egg” relationship between depression and opiate abuse to determine the extent that one condition leads to another. Patients taking prescription painkillers sometimes develop depression. People with depression are more likely to start taking opiates, even when they are not in pain.
A person in a negative emotional state is more likely to take a mind-altering substance, like drugs or alcohol, as a way of “self-medicating.” A chronic negative emotional state makes an individual more prone to abusing drugs on a long-term basis; this is especially true for opiates. Long-lasting negative mindset is also an important feature of major depressive disorder (MDD), which is very common in people who are addicted to opiates.
Depression and opiate abuse are so closely related that neuroscientists suspect the two conditions might be caused by similar brain functions. An international group of scientists studied this question in 2013 and published their results in the Journal of Clinical Investigation. In this study, researchers looked deep inside the brains of lab rats, focusing on the amygdala. This is the part of the brain responsible for emotions, emotional behavior, and motivation.
Humans also have an amygdala. Testing on rats is helpful because this part of the brain works similarly in rats and humans. Previous human imaging studies show that the brains of addicted individuals and people with depression have similar structural and functional problems, especially in the amygdala. This means depression and addiction might come from the same place in the brain.
Testing the association between prescription painkiller and depression
Scientists have performed autopsies to look at the brains of people who had abused heroin or suffered MDD. They focused on the part of the amygdala known as the periamygdaloid cortex (PAC). In these postmortem tests on human brains, researchers discovered heroin abusers and people with MDD each had low levels of prodynorphin (Pdyn), an opium-like hormone that plays a role in how cells communicate with each other. Rats also have Pdyn in their brains but in larger relative quantities than humans. This makes rats excellent subjects for testing the association between prescription painkillers and depression in humans.
In the 2013 study, the team of researchers allowed lab rats to self- administer heroin freely. The scientists looked at the brains of these rats intermittently, using a special DREAM test. Such a test allows researchers to map brain circuitry in living animals. They found that addicted rats had low levels of Pdyn and that low levels of Pdyn affect the entire amygdala. In turn, causing the negative emotions normally associated with depression.
The researchers also found that suppressing Pdyn levels in lab rats caused physiological and behavioral changes. This could mean that suppressed Pdyn levels associated with depression in humans could also cause behavioral changes that make depressed individuals more prone to drug abuse.
Through continued research, scientists hope to understand the close connection between depression and opiate abuse. These discoveries may someday prevent opiate abuse among people with depression, and help the addicted from becoming clinically depressed.
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