What makes some individuals more vulnerable to addiction than others? One factor that has been largely unexplored is how early childhood experiences may impact brain circuits involved in decision making.
Adverse childhood experiences, such as poverty, are known to negatively impact children and adolescents, though the relationship between those experiences and brain circuits is not clear.
To investigate this connection, Stephen Boehm, professor in the Department of Psychology at IUPUI, and his team is using rodents that experience the stresses of overcrowding, insufficient food and low-level lead exposure to see if these stresses influence later substance use. By placing rodents in these conditions early in life and later giving the rodents the opportunity to consume alcohol, opioids, or THC (the psychoactive component of marijuana), then comparing the behaviors and brains of these rodents to rodents who have not been exposed to these stressors, Boehm hopes to increase our understanding about how challenging early childhood environments may alter brain development in a way that influences the risk of substance use disorders.
Several features make Boehm’s project groundbreaking. First, by using rodents, the research team is able to directly examine a cause-and-effect relationship, which would not be possible with human subjects.
The researchers can selectively place some rodents in each of the stressful conditions while maintaining separate "control" groups that are not exposed. Because such experiments would be neither feasible nor ethical with humans, studies of human subjects cannot isolate the influence of any one aspect of a person’s history in this way. The researchers will observe whether rodents that are exposed to each of the challenging conditions behave differently from the control groups when they are given access to alcohol, morphine or THC.
The study's second innovation is its approach to lead exposure. While previous research has suggested a link between high levels of lead exposure and addiction risk, Boehm's study is the first to assess the effect of lower levels of lead that are currently considered to be safe.
Such low-level exposure is common in Indiana, particularly in areas that have shifted from industrial to residential use. The lead exposure levels of the rodents in the study will imitate that of hundreds of thousands of Indiana residents. Similarly, the overcrowding and insufficient food experiments reflect real-world conditions for substantial numbers of Hoosiers who grow up sharing minimal space with many people and/or without reliable access to nutritious food.
Finally, the study provides a new opportunity to observe how these stressful conditions might affect brain development because the brains of the rodent subjects — which are structurally similar to those of humans — can be directly examined following Boehm's experiments.
Comparing the brains of the rodents in the experimental groups with those of the control groups can provide insight into how these childhood conditions might change parts of the brain known to be associated with addiction. This information could potentially be used to guide interventions addressing substance use disorders through therapies directly targeting these portions of the brain.
Although the study is still in its beginning stages, there are very early indications of a link between low-level lead exposure and addiction. In Boehm's preliminary work, the researchers observed that rodents that were exposed to "safe" levels of lead tended to consume far more morphine than rodents that were not exposed to any lead.
Although it is too soon to draw conclusions, this early evidence suggests there is a connection worthy of further investigation.
