Biology 202

2006 First Web Paper

On Serendip

"Drug addiction is most often defined as a chronically relapsing disorder in which the addict experiences uncontrollable compulsion to take drugs, while simultaneously the repertoire of behaviors not related to drug seeking, taking, and recovery, declines dramatically."(1) Recent scientific research has shown significant causal relationships between drug addiction and genetic predisposition as well as between addiction and environmental factors. Both genetics and the environment influence the brain, which in turn effects the behavior of usage. Once an individual begins using psychotropic substances, such as cocaine or heroin, measurable changes in brain chemistry and physiology perpetuate the cycle of addiction. Thus, we have an example of brain affecting behavior, which in turn, affects the brain. This cycle is particularly extreme and insular in the situation of drug addiction where free will and decision making are quickly and severely impaired. In this paper, we will first explore the genetic and environmental theories on drug addiction. We will then investigate how the behavior of drug addiction changes the brain to perpetuate the circle of cause and effect between the brain and behavior.

Genetic Influences on the Behavior of Drug Addiction:
Addiction does not result from a single gene. However, multiple genetic trends have been identified as crucial contributors to the illness of addiction. Alcoholics and cocaine addicts often express the A1 allele of the dopamine receptor gene DRD2 and lack the serotonin receptor gene Htr1b. These genes both fit into the pleasure-response category, but there are numerous ways in which other genes affect an individual's response to drugs, from tolerance of the substance to the severity of withdrawal.(2) One must ask whether these genetic factors exist before the person's first experience with a drug or whether the genes are 'turned on' like a light switch upon first usage.(3) Can these predispositions be observed in other behaviors before the addiction is active? Addiction specialists refer to "addictive behavior" as a category much broader than the limited definition of actual usage, and many of these addictive behaviors can identified in an addict before they ever pick up the drug. Should we assume that those addictive behaviors are purely a direct result of genetic patterns, or can a person learn addictive behavior from their surroundings? Why does not the source of the behavior of drug use affect the prognosis of addiction?

Environmental Influences on the Behavior of Drug Addiction:
While addiction does seem to follow a genetic path in families, even when there is no contact between generations of addicts, a person's environment can contribute to their tendency towards addiction. Community characteristics such as access to education, income level, crime rates, and family dynamic can all affect if and when an individual begins usage. Regardless of these many factors, drug addiction affects all segments of society; the difference between Bel-Air and a Compton ghetto lies merely in the area's drug of choice and the visibility of usage/trafficking. Social risk factors are more difficult to isolate in research studies than specific neurobiological genes, but definitive patterns have emerged within environmental categories.(4) However, even a complete understanding of the relevant risk factors for addiction does not solve the entire equation. Addiction does not only concern the initial usage, but the continued/increased use of a substance and repeated relapse after temporary abstinence. Beyond the roles of genes and the environment in this pattern, a major contributor to continued use, and therefore to addiction, is the change in brain physiology caused by drug use.

Effects of Usage on Brain Physiology:
Pleasure responses in the brain are a type of reward pathway whereby activating dopamine receptors encourages repetition of the responsible behavior.(5) Drug addiction interferes with/over-activates this natural cycle by altering "neural function in such a way as to render the brain circuits mediating various behavioral effects of these drugs more, or less, responsive to those effects."(1) Several neurotransmitter and neuropeptide systems have been shown to disrupt brain circuits mediating mood, affecting the underlying addiction process. Beyond the effects on serotonin and norepinephrine levels, which in turn affect mood and the pleasure-response system, drugs also inhibit an individual's decision-making process, implying an inhibition of free will and a hindrance of the I-function. "The highest levels of human cognition, such as problem solving and complex decision making" are compromised by the addiction through the semi-permanent biochemical changes within the brain that encourage and sustain usage. "Drugs of abuse have a direct influence on the neuronal networks that underlie self-regulation."(6)

These biochemical changes are complicated in adolescent addicts where the physiology of the brain is affected (in addiction to the biochemical signaling pathways) and stunted by early drug use.(7) The frontal cortex, responsible for reasoning, personality, and self-esteem (arguably a component in adolescent drug use), physically matures during the teen years and becomes less oriented toward risk taking behavior during this time.(8) The normal maturation process is replaced by an imbalance between the reward-response pathway, which becomes overactive, and the logic area of the frontal cortex, which is overridden by the drug abuse.

Part of the Normal Development Process?:
Current neurobiological research on drug addiction assumes that addiction interferes with an individual's healthy psychological and mental development and lifestyle. But do the genetic patterns and biochemical changes during addiction necessarily indicate a flaw in the brain's evolutionary development, or do they represent a variation on normal neurochemistry?

Connecting the neuroscience of natural rewards to drug addiction explains the ability of addiction to progressively hijack the brain and prevent decisions that support an individual's survival, such as eating and sleeping. "Indeed, a recurring theme in modern addiction research is the extent to which neuroadaptations responsible for various aspects of the addiction process are similar to those responsible for other forms of neural plasticity studied in cellular models of learning, such as long-term potentiation and long-term depression."(1) Drugs do not replace components in the brain; they only alter them. If a brain's survival mode or natural state of being can be replaced with the pattern of addiction, can not addiction be an inherent part of neurochemical infrastructure?

Current research supports the theory that drug addiction is a result of combined genetic and environmental factors. The findings have led to a better understanding of why people begin and continue using, as well as the most effective forms of treatment.(9) From our current understanding, certain questions remain unanswered: 1.) Why do some people remain drug users/abusers while others fall prey to the illness of drug addiction? and 2.) Is addiction merely a significant standard deviation from 'normal' neurobiological function, or is it an example of evolutionary failure to protect the brain from chemical imbalance? These issues will be addressed in more depth in future web papers.

1)"A Behavioral/Systems Approach to the Neuroscience of Drug Addiction",The Journal of Neuroscience, May 1, 2002
2)"Drugs Alter the Brain's Reward Pathway",Genetics Science Learning Center at The University of Utah
3)"Trigger for Cocaine Addiction Found",Medline Plus
4)NIDA InfoFacts: Nationwide Trends,National Institute on Drug Abuse- The Science of Drug Abuse and Addiction
5)"Marijuana and Its Potential for Addiction",Serendip Web Paper from Neurobiology and Behavior Class, Bryn Mawr College, Spring 2005
6)"Cognitive Neuroscience & Drug Addiction: Primed for Interaction?",A Symposium at the Cognitive Neuroscience Society Meeting, San Fransisco, CA, April 9-11, 2000
7)"More People in Drug Abuse Treatment Began Drug Use Before Age 13",U.S. Dept. of Health and Human Services 2006 Press Release
8)"Genetics is an Important Factor in Addiction",Genetics Science Learning Center at The University of Utah
9)"Wellbutrin plus reward helps cocaine users cut back",Medline Plus


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