Neurotransmitters are chemical messengers in the brain that are necessary for all brain functions; mood, focus, memory, sleep and energy all depend upon healthy neurotransmitter levels.
Here are a few examples of important neurotransmitter actions:
GABA is used at most of the fast inhibitory synapses in virtually every part of the brain. Many sedative drugs act by enhancing the effects of GABA.
Glutamate is used at most of the fast excitatory synapses in the brain and spinal cord. It is also used at most synapses that are “modifiable”, i.e. capable of increasing or decreasing in strength. Modifiable synapses are thought to be the main memory-storage elements in the brain. Excessive glutamate release can over stimulate the brain and lead to excitotoxicity causing cell death. Excitotoxicity has been implicated in certain chronic diseases including ischemic stroke, epilepsy, Alzheimer’s, and Parkinson’s.
Acetylcholine is distinguished as the transmitter at the neuromuscular junction connecting motor nerves to muscles.
Dopamine has a number of important functions in the brain; this includes regulation of motor behavior, pleasures related to motivation and also emotional arousal. It plays a critical role in the reward system. People with Parkinson’s disease have been linked to low levels of dopamine and people with Schizophrenia have been linked to high levels of dopamine. It has also been associated with addictive behaviors.
Serotonin is a monoamine neurotransmitter; most is produced by and found in the intestine (approximately 90%). Serotonin is responsible for feeling calm and content. It is implicated in both mood disorders and eating disorders.
Fluoxetine (Prozac) is a commonly prescribed selective serotonin reuptake inhibitor (SSRI), which blocks re-uptake of serotonin by the presynaptic cell. This increases the amount of serotonin present at the synapse and allows it to remain there longer, hence potentiating the effect of naturally released serotonin. This medication is most commonly used to treat depression and anxiety.
The standard for evaluating neurotransmitter function has typically been to evaluate symptoms and behavior and to use medications in an attempt to increase or decrease the effect of the suspected neurotransmitters. Unfortunately, these medications can have unwanted side effects. Prozac, along with all of the other medications in its class (SSRIs) can decrease libido and orgasms. Medications that increase GABA can cause unwanted sedation. Some antipsychotic medications, while at times necessary, can cause permanent unwanted facial movements and tremors.