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Addiction: Genetics And The Brain

Walkthrough of Mouse Party
  • Addiction: Genetics and the Brain

This collection of materials addresses the neurobiology of drug use and abuse at the molecular, cellular, and organism levels.

Addiction involves complex mechanisms that are only partially understood. Yet ongoing research in molecular biology, physiology, and genetics continues to reveal more about the mechanisms that drive drug use and abuse. This work, along with research in the psychosocial factors involved, informs programs for more effectively treating and preventing substance abuse.

Learning Goals

  • Drugs disrupt communication between neurons at the molecular level.
  • Drugs interfere with the brains reward and pain pathways, reinforcing repeated drug use.
  • Repeated drug use alters the physiology of neurons, increasing tolerance and the risk of overdose.
  • There is a genetic component to addiction.
  • Social factors influence drug use, addiction risk, and addiction treatment.

Resources

The resources on this page have been designed with educators in mind. They are meant to support, supplement and extend the concepts explored in the materials on the Learn.Genetics website, designed for students and the public.

Animal Models And Gene Discovery

Animals are particularly valuable research tools because they allow scientists to conduct experiments that they could never perform on humans. Many animals, especially mice, are greatly expanding our understanding of the complex disease of addiction.

Even organisms that lack a complex brain, like the fruit fly and roundworm, share many of the pieces that make up the reward pathway. They have the same neurotransmitters, receptors, and signaling mechanisms as we do. So scientists commonly study a variety of animals to learn about different aspects of human biology, including the reward pathway and addiction.

The genomes of many organisms used in research have been sequenced. So when researchers discover a gene in a model organism that plays a role in addiction, they can then identify the counterpart gene in humans by searching a DNA database for similar sequences. Once they identify the human gene, they can study it.

To the right are several model organisms that have been used in addiction research.

Chimpanzee, Pan troglodytes – 20,000-25,000 genes Just 50 human genes lack a known homologue in chimps. Of the protein-coding genes in the human and chimp genomes, one-third have identical sequences.

Mouse, Mus musculus – 20,000-25,000 genes The average mouse gene is about 85% similar to its human homologue.

Zebrafish, Danio rerio – 25,000 genes Scientists routinely transfer human genes into zebrafish and study their functions.

Anatomy Of A Neuron / Anatomy Of A Synapse

In part 1, students label a diagram of a neuron with structure and function . In part 2, they describe what is happening in a labeled diagram of a synapse .

Use as worksheets for students to fill in as they explore the multimedia sources linked below. They may be used as a formative or summative assessment.

  • The parts of a neuron work together to receive and send signals.
  • Using neurotransmitters, neurons communicate with one another at a junction called the synapse.

15 minutes

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Constellation Of Protective Factors

In this poster-building activity, students place themselves at the center of a constellation. They surround themselves with the protective factors that they have and ones that they want to develop .

Have students work individually

  • Protective factors decrease the likelihood of risk-taking behaviors, including drug misuse.
  • Individuals have the ability to increase their protective factors.

30 minutes

Large pieces of paper or poster board , glue, scissors

Copies of cut-outs

Note: The protective factors listed in this PDF are generalized from a number of sources and appear to be broadly accepted. You may wish to:

  • Use factors that are consistent with other addiction prevention curricula that your students might be familiar with.
  • Use factors from the resources listed in the Risk Continuum pdf file, below.
  • Ask your students to brainstorm about protective factors. Discuss them as a class, and make a list for students to draw from.

Risk and protective factors do not necessarily cause or prevent disease themselves. Some are causative, and others are markers that are associated with healthy or disease states.

Mouse Models For Addiction

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Researchers soon learned that, by selectively breeding rats or mice with certain addiction traits, they could generate lines of animals with very specific addiction profiles. They bred mice with differences in drug preference, sensitivity, tolerance, dependence, and withdrawal symptoms.

Today, researchers are still studying some of these animal lines and strains. For example, Dr. Scott Rogers is studying different strains of mice that vary in their addiction potential for alcohol. After identifying the genes correlated to this vulnerability in mice, researchers hope to identify homologous genes in humans that render a person more or less susceptible to alcohol addiction.

When humans have a gene in common with another organism, scientists call the counterpart gene a homologue or a homologous gene.

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Of Mice And Men: How Similar Are We

The limbic system in both rats and humans controls instincts, feeding, fighting, fleeing, and sexual behavior. But rodents and humans share more than just the reward pathway. In fact, the entire set-up of the brain is nearly identical. And both use the same neurotransmitters and receptors, the same proteins for synaptic vesicle release and recycling, and similar signaling mechanisms.

These functions are controlled by genes, so it makes sense that humans and rodents are similar genetically. But if we share genes, then what makes humans and rodents so different? Many of the differences come from slight differences in genes DNA sequences. And some genes are active at different times or in different tissues throughout the development and life of the organism. Where and when a gene’s protein product is made can sometimes produce in dramatic differences between organisms, contributing to their overall appearance and unique abilities.

The Science Of Addiction: Genetics And The Brain

  • Funding

    The content here is based upon work funded by the Utah State Board of Education and a Science Education Drug Abuse Partnership Award , from The National Institute on Drug Abuse, National Institutes of Health Grant Number R25DA15461.

    The contents provided here are solely the responsibility of the authors and do not necessarily represent the official views of the funders.

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The Reward Pathway Is Fundamental

Food, nurturing, and social interaction are essential for the survival of not only humans, but also of animals. These needs shaped the first reward pathway in an ancestral animal that lived millions of years ago.

Once it appeared, the genes that shape the reward pathway passed from generation to generation through a process called natural selection. Because the reward pathway increased animals’ chances of reproducing, it was “selected” for, meaning it was genetically transmitted from one generation to the next. Over time, the reward pathway remained a central part of the brain, even as the rest of the brain became more complex.

Because animals and humans share the reward pathwayand most of the genes that govern itanimals are also susceptible to drug addiction. This similarity makes animals a convenient tool for researchers who study addiction.

The structures near the base and center of the human brain are evolutionarily very old. We share many of these structures with fish, amphibians, birds, and reptiles.

Animal Models For Addiction Research

LSD cell signaling project (stop motion)

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