Answer: A smoker's neurotransmitters are replaced with new chemicals.
Step-by-step explanation:
Neurotransmitters are including glycine, glutamate, monoamines, norepinephrine and more.
When a smoker is using nicotine, the nicotine is binding to nicotinic receptors that can be found in the brain and then they can enhance the release of the neurotransmitters such as serotonin or dopamine and that is why it is causing addiction. Nicotine is also able to release neurotransmitters.