As we discussed in our previous posts, most neurotransmitters are classified as either inhibitory or excitatory. Inhibitory neurotransmitters slow down the flow of information by calming and reducing the activity of neurons; they help to bring balance to the body. Excitatory neurotransmitters generally increase the flow of information. It is the balance between the inhibitory and excitatory neurotransmitters that has the greatest effect on your body functions. We discussed inhibitory neurotransmitters in a previous post; this post will deal with excitatory neurotransmitters.

The main excitatory neurotransmitters in the body are dopamine, norepinephrine, epinephrine and glutamate.

Dopamine plays a number of important functions in the brain. It is very important in the reward system whereby we feel pleasure, achieve heightened arousal and do much of our learning. Every type of reward that has been studied increases the level of dopamine transmission in the brain. A wide variety of highly addictive drugs, including cocaine and amphetamines (i.e., methamphetamine, “speed”, Adderall, Vyvanse, Dexedrine) act directly on the dopamine system.  Dopamine also helps with focus, concentration and memory as well as motivation. Several important diseases are associated with dysfunctions in the dopamine system, including Parkinson’s disease, schizophrenia and ADD/ADHD.

Norepinephrine is made from dopamine and plays many roles it the body. It along with epinephrine are responsible for the “fight-or-flight” response to stress, which increases your heart-rate, increases blood sugar and increases blood flow to the muscles to allow you to act or react to stressors. Norepinephrine also affects blood pressure and heart rate, although it’s most widely known impact is on alertness, arousal, decision making, attention and focus. Several ADHD medications, such as methylphenidate (Ritalin/Concerta), amphetamines (Adderall, Dexedrine) and atomoxetine (Strattera) are used to increase norepinephrine levels in the brain in an attempt to help improve focus and concentration. Other classes of drugs seek to modulate norepinephrine in the brain to improve depression, including venlafaxine (Effexor), duloxetine (Cymbalta) and bupropion (Wellbutrin).

Epinephrine (also known as adrenaline) is released in reaction to stress and is partially responsible for the “fight-or-flight” response. It affects a number of important functions, including heart rate, breathing and blood pressure. Imbalances in epinephrine can lead to “adrenaline junkies”, a term that is often used to describe people that seem to enjoy stress and stressful activities. Unfortunately, they also usually suffer from constant need for urgency, have trouble relaxing or sleeping and keep ‘the pedal to the medal’ as they race through life.

Glutamate is the most abundant excitatory neurotransmitter in the human brain. It plays key roles in cognitive functions like learning and memory. Imbalances in glutamate levels are associated with Alzheimer’s disease, seizures and forms of autism. Interestingly, glutamate is also used as a flavor enhancer in the form of monosodium glutamate (MSG).

If the balance between the inhibitory and the excitatory neurotransmitters is disrupted for some reason, many symptoms can develop. We will cover the many symptoms of neurotransmitter imbalance next.