Lesson 3

The Science of Nicotine Addiction

Where does nicotine go in your body?

It goes to your lungs, and then via the bloodstream to your heart and all parts of the body, including your brain.

How does the body get rid of nicotine?

• Nicotine circulates throughout the body in the bloodstream.

• Eventually it is carried to the liver, where enzymes break it down into other compounds.

• These compounds are carried by the bloodstream to the kidneys and then excreted from the body in urine.

A look at the brainDifferent parts of the brain are involved in different functions, like vision, movement, thinking, memory.

The Reward PathwayThe reward pathway is a neural pathway used for

reinforcing behaviors that are important for survival.

Eating makes me happy!

Nicotine also stimulates the reward pathway.

This feels good!

To understand how this works, we need to learn about neurons and neurotransmission...

Neurons

• Have a cell body, dendrites, and axon• Use electrical impulses and chemical signals

Neurotransmission is…The process of transferring messages between neurons.

Its purpose is to carry signals from one part of the brain to another or to other parts of the body, like muscles.

Synapse

Dopamine is the neurotransmitter in the reward pathway

Stimulation of neurons in the VTA area results in release of dopamine in the NA (emotional center) and the prefrontal cortex (thinking).

(VTA)(NA)

How Does Nicotine Interact with Neurotransmission and the Reward Pathway?

Nicotine binds to receptors on neurons in the ventral tegmental area.

An electrical impulse travels down the neuron axon.

Dopamine is released at axon terminals in the nucleus accumbens and prefrontal cortex.

Dopamine binds to dopamine receptors on other neurons.

This leads to the rewarding effects of smoking, such as relaxation, a “buzz”, or an increased ability to focus.

This feels good!

What is the impact of nicotine interacting with the reward

pathway?

Addiction!

What genes might be involved in differences in smoking behavior?

Nicotine receptors

Dopamine receptors; enzymes that make or break down dopamine

Enzymes involved in nicotine breakdown

The reward pathway is involved in other addictive behaviors

• Cocaine slows the re-uptake of dopamine in the nucleus accumbens.

• Methamphetamine results in increased dopamine release as well as blocking the re-uptake of dopamine in the nucleus accumbens.

• Other addictive behaviors, like gambling and risk taking involve

the reward pathway.

What are some benefits of identifying variants in genes associated with

smoking behavior?

• Increasing our understanding for the addiction process

• Helping people understand their own risk for becoming addicted to nicotine or other addictive drugs or behaviors

• Helping to choose the best cessation program for an individual based on their genes

What are some risks of identifying variants in genes associated with

smoking behavior?• The same gene variants may also be associated with the

use of other addictive drugs or addictive behaviors. By learning about genes that affect smoking behavior, people also get information about other behaviors (which they may not want). A gene that affects different traits is called pleiotropic.

• People who carry a risk variant may face discrimination getting jobs, health insurance, or life insurance.

• The frequency of a risk variant may be higher in a certain group, leading to stigmatization of that group.