The StarNet Case Control Study Nicotine, Neurotransmission, and the Reward Pathway University of Washington Department of Genome Sciences

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 brain Different parts of the brain are involved in different functions, like vision, movement, thinking, memory.

The reward pathway The reward pathway is a neural network 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

Model of a neuron Developed by Eric Chudler, Neuroscience for Kids Neurotransmitter 1 Cell body Dendrite Axon terminal Neurotransmitter 2 Electrical impulse

When neurotransmitter binds to the dendrites…

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

The Synapse: How neurons talk to each other Neurotransmitters are chemical signals that transfer a message from one neuron to the next across the synapse. Transmitting neuron Receiving neuron

Dopamine is the neurotransmitter in the reward pathway Stimulation of neurons in the ventral tegmental area results in release of dopamine in the nucleus accumbens (emotional center) and the prefrontal cortex (thinking).

Dopamine levels are tightly controlled through its synthesis, breakdown, and recycling back into vesicles. DDC TH=Tyrosine hydroxylaseDT=Dopamine transporter DOPA=dihydrophenylalanine COMT=Catechol-O-methyltransferase DDC=DOPA decarboxylaseMAO=Monoamine oxidase DR=Dopamine receptor

Nicotine replaces the neurotransmitter, acetylcholine, in the reward pathway 1. Normally, acetylcholine binds to its receptor on neurons in the VTA, leading to release of dopamine in the nucleus accumbens (NA) and prefrontal cortex (PC). 2. Nicotine also binds to acetylcholine receptors in the VTA, resulting in dopamine release in the NA and PC.

How does nicotine interact with neurotransmission and the reward pathway? 1. Nicotine binds to acetylcholine receptors in the ventral tegmental area. 2. An electrical impulse travels down the neuron axon Dopamine is released at axon terminals in the nucleus accumbens and prefrontal cortex. 5. Dopamine binds to dopamine receptors on other neurons. 6. This leads to increase or decrease in electric impulse on receiving neuron, resulting in the rewarding effects often reported by smokers. This feels good! 7. Dopamine is reabsorbed through dopamine transporter.

What is the impact of nicotine interacting with the reward pathway? Addiction!

What genes might be involved in differences in smoking behavior? DDC On Student Sheet A3.3, circle the proteins that might account for differences in smoking behavior.

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 of the addiction process Helping people understand their own risk for becoming addicted to nicotine, which may motivate them to quit smoking or never begin Helping people choose the best cessation program based on their genes

What are some drawbacks 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 may get unwanted information about other behaviors. 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.