Researchers and addiction specialists know that drug and alcohol addiction have a biological basis in lasting changes that occur in the brains of people who repeatedly use specific substances over time. However, they don’t know all of the details about how these changes manifest inside the brain. In a study published in May 2014 in the journal Neuron, researchers from three U.S. universities explored the role that a specific brain protein, called FMRP, plays in setting the stage for the development of cocaine addiction. This same protein has a known role in the development of the childhood developmental disorder called autism spectrum disorder.
Addiction and the Brain
Alcohol and all common drugs of abuse have one thing in common: they change the chemical balance in a part of the brain known as the pleasure center and produce an intense sensation called euphoria. Patterns of abuse typically begin when substance users try to recreate a euphoric mental state on demand, or alternatively, when other effects of substance use (e.g., pain relief) are required on demand. When the pleasure center’s chemical levels go through frequent substance-related alteration, the brain can start to treat this repeated alteration as a given and come to rely on the responsible substance. This state of reliance is commonly known as physical dependence or chemical dependence. Physically or chemically dependent people become substance addicts when they do such things as develop a compulsive desire to use more drugs or alcohol, lose the ability to limit drug or alcohol consumption, orient their life’s resources toward substance use and grow increasingly tolerant to the effects of any specific level of drug or alcohol intake.
Autism Spectrum Disorder
People with autism spectrum disorder have developmental problems that include an inability to fully recognize or understand the social cues that form much of the basis for human interaction, an inability to effectively communicate with others in one-on-one or social situations, and involvement in repetitive patterns of behavior that seem useless or pointless to outside observers. Until quite recently, doctors used an independent diagnosis called autism or autistic disorder to identify the most profoundly affected individuals. Lesser-affected individuals qualified for any one of several independent diagnoses, including childhood disintegrative disorder, Asperger syndrome and PDD-NOS (pervasive developmental disorder not otherwise specified). The autism spectrum disorder (ASD) diagnosis incorporates the symptoms of these various conditions under a single heading.
Shared Basis With Cocaine Addiction
In the study published in Neuron, researchers from Harvard Medical School, the University of Minnesota and the University of Texas Southwestern Medical Center looked at the role the brain protein FMRP (short for fragile X mental retardation protein) plays in the onset of cocaine addiction. Under normal circumstances, this protein helps the brain grow, develop and adapt to important changes inside and outside the body. Deficiencies in FMRP are the underlying cause of fragile X syndrome, a condition recognized as one of the primary pathways to the development of autism spectrum disorder.
During the study, the researchers used laboratory experiments on mice to determine how FMRP levels affect the brain’s ability to process the pleasure triggered by cocaine consumption. Specifically, they gave the drug to mice that had unusually low levels of FMRP inside their brains. After observing the effects of cocaine in these animals, they found that the lack of the protein reduces the ability to perceive the rewarding impact of cocaine use, diminishes the ability to associate cocaine intake with a specific setting or environment, and reduces the repetitive muscle movement often found in cocaine users. Based on these findings, the researchers concluded that FMRP plays a critical role in the brain’s typical responses to cocaine exposure. In turn, they also concluded that the actions of normal levels of the protein in human beings help explain the ways in which the brain grows accustomed to the presence of the drug and becomes susceptible to the onset of cocaine addiction.
The authors of the study do not propose a connection between autism spectrum disorder and cocaine addiction. Instead, they note that the two conditions can stem, at least in part, from the actions of a single protein. FMRP plays its part in cocaine addiction when at normal levels inside the brain; conversely, it plays its part in the development of autism when absent or at unusually low levels.