A neurotransmitter is a chemical messenger used by neurons (nerve cells) to communicate in one direction with other neurons. These neurotransmitters are either excitatory or inhibitory. Each cell receives its instructions through nerve processes called dendrites and it passes on instructions to the next cell through its axon. The gap between the axon of one cell and the dendrite of the next is called a synapse.
Special molecules in the dendrite are called receptors. They are shaped to receive only one type of neurotransmitter, which fits it like a key in a lock. The result is that if an excitatory neurotransmitter reaches the specific receptor, the cell tends to fire. If an inhibitory neurotransmitter reaches the receptor, the cell does not fire.
If neurotransmitters of either type are in short supply, or if they are blocked from reaching their proper receptors, (as a result of either genetics and/or chemical use) cell function tends to be abnormal. The lack of neurotransmitter function then results in maladaptive behavior.
The human brain is very capable of automatically manufacturing the quantity of chemicals it needs IF it is given the raw materials (nutrients from foods) to do so. However, normal diet does not supply enough of the raw materials the brain needs to manufacture the needed level of neurotransmitters. Additionally, stress, worry, chemical use, poor nutrition, pollution and other factors of modern life are known to deplete neurotransmitter levels.
In order to ingest the required amount of food to provide the necessary amount of amino acids needed to maintain normal neurotransmitter levels we would have to eat each day:
- Several pounds of fish
- Gallons of whole milk,
- Platters of cheese and turkey
Not only is this impractical it is impossible, so therefore another source of nutritional support is necessary so we do not gain hundreds of pounds.
Next we will look at a few of the more familiar neurotransmitters and their function.
Neurotransmitter Functions
We discussed earlier there is a balance of these neurotransmitters. What happens if we become deficient or have too much of one or more of these? What causes these interruptions to the natural balance? How can we compensate and help our body rebuild and rebalance? Below is a table of the specific neurotransmitters that are involved with the our daily lives and affect our moods, feelings, ability to focus and concentrate, energy, self-confidence, and our pleasure.
Click on the links in this chart for more information about different transmitters and amino acid building blocks.
Neuro Transmitter |
Amino Acid (Building block) | Deficiency | Toxicity | Genetics or Natural Depletion | External/Chemical Source of Depletion | Present in Foods |
---|---|---|---|---|---|---|
Dopamine | l-phenylalanine |
Reduced pleasure, reduced ability to feel attachment and love, lack of remorse about actions |
Schizophrenia like symptoms, voices “in your head” |
Depleted by trauma. If mother and/or father had diminished dopamine this level can be passed on via genetics. |
Depleted by all stimulant drugs, Rx or otherwise. If stimulants, including nicotine and caffeine, used during pregnancy this can lower available dopamine in fetus. |
Lean beef, Shellfish, Fowl, Soy products |
GABA | l-glutamine |
Anxious, Racing thoughts, panic |
Excessive sedation |
Depleted by trauma. Reduced levels in parents can result in DNA/RNA reduction of GABA in child. |
Depleted by sedative drugs, including tranquilizers and alcohol |
Lean beef & pork, Sesame seeds, Fowl, Sunflower seeds |
Norepinephrine | l-phenylalanine |
Lack of energy, lack of drive, reduced focus on goals |
Manic (extremely hyperactive), increased heart rate and BP |
Diminished dopamine results in reduce Norepinephrine. |
Depleted by stimulants of all kinds. Can be made inactive by marijuana. |
Lean beef, Shellfish, Fowl, Soy products |
Enkephalin (Opioids) | l-phenylalanine, glycine, methionine |
Deep sense of inadequacy, incompleteness. Reduced ability to combat physical pain |
Excessive sedation, can be fatal if combined with other sedating agents. |
Opioid levels passed from parents to offspring. Trauma reduces availability |
All drugs effecting opioid system will eventually reduce natural supply if used for prolonged periods. |
Seafood, Fowl, Lima beans, Ham |
Endorphins (Opioids) | l-phenylalanine, glycine, methionine |
Deep sense of inadequacy, incompleteness. Reduced ability to combat physical pain |
Excessive sedation, can be fatal if combined with other sedating agents. |
Opioid levels passed from parents to offspring. Trauma reduces availability |
All drugs effecting opioid system will eventually reduce natural supply if used for prolonged periods. |
|
Serotonin | 5HTP |
Edgy, irritable, tearful, irrational emotions |
Can result in “serotonin syndrome” if multiple SSRI’s used together |
Females more susceptible to reduced availability during menstrual periods. Prolonged lack of direct sunlight reduces serotonin |
Drugs which prolong action of serotonin may result in excessive breakdown of the transmitter. All psychedelic drugs, LSD, PCP etc reduce serotonin. |
Turkey, Ham, Milk, Cheese |
This is all good information, but exactly what are neurotransmitters?
Nerve impulses always flow in one direction - from the branched extensions called dendrites, down the neuron to the presynaptic terminals. The join between the presynaptic terminals of one neuron and the dendrites of another is called the synapse. The two neurons do not actually touch each other but are separated by a space called the synaptic cleft. When a nerve impulse arrives at a presynaptic terminal it causes neurotransmitters to be released into the synaptic cleft. The neurotransmitters then bind with special "postsynaptic receptors" in the dendrites of the receiving neuron. When a postsynaptic receptor receives a neurotransmitter it can either cause a nerve impulse to travel down the neuron or it can inhibit a nerve impulse depending on the neurotransmitter released.
Neurotransmitters which propagate nerve impulses in the receiving neuron are called excitatory neurotransmitters. Those which inhibit nerve impulses are called inhibitory neurotransmitters.
Neurotransmitters are sythesized in the cell body (the soma) and migrate down the axon to the presynaptic terminals. Here they are stored in little packets called vesicles which fuse with the synaptic membrane. When a depolarizing current (the action potential) is received, these vesicles release their contents into the synaptic cleft.
Many different substances effect the transmission of nerve impulses across the synapse and many of these are falsely called neurotransmitters. To be a neurotransmitter a substance must:
- be synthezised within neurons
- be released from the presynaptic terminal in response to an action potential (essentially a nerve impulse).
- cause a biological effect in the postsynaptic receptors.
- a mechanism must exist to inactivate or remove the transmitter from the receptor
Neurotransmitters activate receptors by "sticking" to them and thus preventing other neurotransmitters from activating them. Inactivation of the transmitter happens in one of three ways:
- reabsorption of the neurotransmitter into the neuron. This is known as reuptake and is the normal process.
- destruction of the neurotransmitter with special chemicals called enzymes. This is known as enzymatic degradation.
- by the neurotransmitter becoming deteched from the receptor and drifting out of the synaptic cleft. This is known as diffusion.
Substances that effect neurotransmission but are not neurotransmitters can be broadly divided into two categories - agonists and antagonists. Agonists make transmission of nerve impulses more likely. They do this in a number of ways including preventing reuptake (cocaine works this way), actually triggering the receptor themselves (nicotine works this way) and by making the receptor more responsive (a lot of anti-anxiety drugs work like this). Antagonists do the opposite - they interfere with nerve transmission across the synapse sometimes by blocking receptor sites (many spider and snake venoms work this way) and sometimes by preventing release of the neurotransmitter from the presynaptic terminal (many anti-psychotic drugs operate like this).