Addiction Could Be Tied to Lack of Plasticity in Brain Region
There are many mysteries surrounding the disease of addiction, and one of the main ones is this: Why do some drug users become addicts and others don’t? The research teams of Pier Vincenzo Piazza and Olivier Manzoni, at the Neurocentre Magendie in Bordeaux, set out to find answers to this question, and discovered that an impairment of synaptic plasticity in a key structure of the brain could lead to addiction.
This is the first time researchers have discovered a correlation between synaptic plasticity and the transition to addiction. The research appears in the journal Science.
Many species of animals voluntarily use drugs, but it was formerly argued that addiction was specific to the human species. However, in 2004, Pier Vincenzo Piazza’s research team showed that rats can also exhibit signs of addiction, as some of them will self-administer cocaine. Also notable is that, like humans, only some rats develop addiction.
Chronic drug use causes many changes to the brain, but the researchers wanted to find out which of these changes is responsible for addiction. The researchers hoped that their study would help develop new methods of addiction treatment.
By comparing addicted and non-addicted animals at various times during their history of drug use, the researchers showed that the addicted animals showed a permanent loss of a form of plasticity called long-term depression (LTD). This refers to the synapses’ ability to reduce their activity under the effect of certain stimuli, such as drugs. LTD plays an important role in developing new memories and demonstrating flexible behavior.
After using cocaine for a short period of time, LTD wasn’t modified. After longer use, however, a significant LTD deficit was apparent in all of the drug-using rats. Because this form of plasticity allows new learning to occur, drug-using behavior becomes more and more rigid, leading to compulsive behavior. Most of the drug-using rats were able to produce the biological adaptations that counteract the effects of the drug, rebuilding their level of LTD.
But in some rats, the lack of plasticity left them unable to return to a normal LTD. This permanent absence of plasticity could explain why for some, drug-seeking behavior becomes resistant to environmental constraints, such as difficulty obtaining drugs, negative consequences of drug use, and more. Over time, the person loses control over their drug use and addiction emerges.
Pier Vincenzo Piazza said that this study shows that the key to improved addiction treatment lies in the brains of non-addicted users. He added that understanding the biological mechanisms that lead to addiction can help researchers combat the loss of plasticity that leads to addiction in some people.
Source: Science Daily, Addiction: A Loss of Plasticity of the Brain?, June 25, 2010
