Scientists have known that a mood disorder such as depression can increase an individual’s risk for substance abuse.

New research suggests that a converse relationship also exists, that is, substance abuse can increase the risk for a stress-related illness.

In a study using a mouse model, repeated cocaine use increases the severity of depression. From this, researchers identified a pathway that demonstrated the cocaine-induced vulnerability.

Researchers believe the finding may facilitate the development of new treatments for mood disorders associated with substance abuse.

The research is published by Cell Press in the journal Neuron.

“Clinical evidence shows that substance abuse can increase an individual’s risk for a mood disorder,” said senior study author Dr. Eric Nestler from Mount Sinai School of Medicine.

However, researchers wanted to learn why this was so – they surmised that the drug use caused changes in the brain resulting in altered responses to stress.

Dr. Nestler and colleagues examined whether histone H3 lysine 9 dimethylation (H3K9me2), a prominent type of chromosomal modification, might be involved in the effects of repeated cocaine use on vulnerability to depressive-like behaviors.

A reduction in H3K9me2 reflects a decrease in the number of histone methyl groups, with previous human and animal studies suggesting a link between histone methylation and mood disorders.

The researchers found that cocaine increases the susceptibility of mice to stress. And that decreased H3K9me2 in a major reward center in the brain was a central mechanism linking cocaine with the stress vulnerability.

The researchers went on to show that key areas of the brain are susceptible to stress or cocaine and this promotes both depressive and addictive behaviors.

“Together, our results provide fundamentally novel insight into how prior exposure to a drug of abuse enhances vulnerability to depression and other stress-related disorders,” Nestler said.

“Identifying such common regulatory mechanisms may aid in the development of new therapies for addiction and depression.”

Source: Cell Press