Nicotine and the Brain
Your brain is the key player in nicotine's action. Like a computer, your brain processes, stores and uses information. In a computer, information travels in the form of electricity moving through wires; information transfer is a binary process, with switches being either "on" or "off." In your brain, neurons are the cells that transfer and integrate information. Each neuron has thousands of inputs from other neurons throughout the brain. Each of these signals is included in the calculation of whether or not the neuron will pass the signal it receives on to other neurons in the pathway.
A synapse is the site where two neurons come into contact. The presynaptic neuron releases a neurotransmitter, which binds to receptors on the postsynaptic cell. This allows signals to be transmitted from neuron to neuron in the brain.
While signals are conducted through individual neurons as electric current, communication between neurons is mediated by chemical messengers, called neurotransmitters. Neurotransmitters traverse the physical space between two neurons and bind to special protein receptors on the postsynaptic cell. Once bound, these receptors set in motion physiological changes within the neuron that allow it to send the signal on down the line.
Each neurotransmitter has its own specific family of receptors. Nicotine works by docking to a subset of receptors that bind the neurotransmitter acetylcholine. Acetylcholine is the neurotransmitter that (depending on what region of the brain a neuron is in):
- Delivers signals from your brain to your muscles
- Controls basic functions like your energy level, the beating of your heart and how you breathe
- Acts as a "traffic cop" overseeing the flow of information in your brain
- Plays a role in learning and memory
Acetylcholine is released from one neuron and binds to receptors on adjacent neurons.
Like acetylcholine, nicotine leads to a burst of receptor activity. However, unlike acetylcholine, nicotine is not regulated by your body. While neurons typically release small amounts of acetylcholine in a regulated manner, nicotine activates cholinergic neurons (which mainly use acetylcholine to communicate to other neurons) in many different regions throughout your brain simultaneously. This stimulation leads to:
- Increased release of acetylcholine from the neurons, leading to heightened activity in cholinergic pathways throughout your brain. This cholinergic activity calls your body and brain to action, and this is the wake-up call that many smokers use to re-energize themselves throughout the day. Through these pathways, nicotine improves your reaction time and your ability to pay attention, making you feel like you can work better.
- Stimulation of cholinergic neurons promotes the release of the neurotransmitter dopamine in the reward pathways of your brain. This neural circuitry is supposed to reinforce behaviors that are essential to your survival, like eating when you're hungry. Stimulating neurons in these areas of the brain brings on pleasant, happy feelings that encourage you to do these things again and again. When drugs like cocaine or nicotine activate the reward pathways, it reinforces your desire to use them again because you feel so at peace and happy afterwards.
- Release of glutamate, a neurotransmitter involved in learning and memory - Glutamate enhances the connections between sets of neurons. These stronger connections may be the physical basis of what we know as memory. When you use nicotine, glutamate may create a memory loop of the good feelings you get and further drive the desire to use nicotine.
Nicotine also increases the level of other neurotransmitters and chemicals that modulate how your brain works. For example, your brain makes more endorphins in response to nicotine. Endorphins are small proteins that are often called the body's natural pain killer. It turns out that the chemical structure of endorphins is very similar to that of heavy-duty synthetic painkillers like morphine. Endorphins can lead to feelings of euphoria also. If you're familiar with the runner's high that kicks in during a rigorous race, you've experienced the "endorphin rush." This outpouring of chemicals gives you a mental edge to finish the race while temporarily masking the nagging pains you might otherwise feel.