One of the neurotransmitters playing a major role in addiction is dopamine. Many of the concepts that apply to dopamine apply to other neurotransmitters as well.
As a chemical messenger, dopamine is similar to adrenaline. Dopamine affects brain processes that control movement, emotional response, and ability to experience pleasure and pain.
Dopamine is also a neurohormone released by the hypothalamus. Its main function as a hormone is to inhibit the release of prolactin from the anterior lobe of the pituitary. Prolactin (PRL) or Luteotropic hormone (LTH) is a peptide hormone discovered by Dr. Henry Friesen, primarily associated with lactation.
Prolactin has many effects including regulating lactation, orgasms, and stimulating proliferation of oligodendrocyte precursor cells.
- stimulates the mammary glands to produce milk (lactation)
- provides the body with sexual gratification after sexual acts: The hormone counteracts the effect of dopamine, which is responsible for sexual arousal. The amount of prolactin can be an indicator for the amount of sexual satisfaction and relaxation. Unusually high amounts are suspected to be responsible for impotence and loss of libido.
- decreases normal levels of sex hormone; estrogens in women and testosterone in men.
Regulation of dopamine plays a crucial role in our mental and physical health. Neurons containing the neurotransmitter dopamine are clustered in the midbrain in an area called the substantia nigra . In Parkinson’s disease, the dopamine- transmitting neurons in this area die. As a result, the brains of people with Parkinson’s disease contain almost no dopamine.
Dopamine has many functions in the brain, including important roles in behavior and cognition, voluntary movement, motivation and reward, inhibition of prolactin production (involved in lactation), sleep, mood, attention, and learning.
In nature, we learn to repeat behaviors that lead to maximize rewards. Dopamine is therefore hypothesized to provide a teaching signal to parts of the brain responsible for acquiring new behavior. Dopamine’s role in experiencing pleasure has been questioned by several researchers. It has been argued that dopamine is more associated with anticipatory desire and motivation (commonly referred to as “wanting”) as opposed to actual consummatory pleasure (commonly referred to as “liking”).
Cerebral dopamine depletion is the hallmark of Parkinson’s disease. Other pathological states have also been associated with dopamine dysfunction, such as schizophrenia, autism, and attention deficit hyperactivity disorder, as well as drug abuse.
Motivation and pleasure
Dopamine is commonly associated with the pleasure system of the brain, providing feelings of enjoyment and reinforcement to motivate a person proactively to perform certain activities. Dopamine is released (particularly in areas such as the nucleus accumbens and prefrontal cortex) by naturally rewarding experiences such as food, sex, drugs, and neutral stimuli that become associated with them. Recent studies indicate that aggression may also stimulate the release of dopamine in this way. This theory is often discussed in terms of drugs such as cocaine, nicotine, and amphetamines, which directly or indirectly lead to an increase of dopamine in the mesolimbic reward pathway of the brain, and in relation to neurobiological theories of chemical addiction (not to be confused with psychological dependence), arguing that this dopamine pathway is pathologically altered in addicted persons.
Disease and drugs can produce faulty sensitization
Sensitization or desensitization normally occurs with drug exposure. However, addiction or mental illness can tamper with the reuptake system. This disrupts the normal levels of neurotransmitters in the brain and can lead to faulty desensitization or sensitization. If this happens in a region of the brain that serves emotion or motivation, the individual can suffer severe consequences.
Consider an example. Cocaine prevents dopamine reuptake by binding to proteins that normally transport dopamine. Not only does cocaine “bully” dopamine out of the way-it hangs on to the transport proteins much longer than dopamine does. As a result, more dopamine remains to stimulate neurons, which causes prolonged feelings of pleasure and excitement. Amphetamine also increases dopamine levels. Again, the result is over-stimulation of these pleasure-pathway nerves in the brain.
Dopamine can be made from Tyrosine but Tyrosine is not an essential amino acid. But is essential to the brain as the brain cannot make it and needs the liver to produce it from the essential amino acid DLPA
Liver Disease and gut infections also effect the production of dopamine in the brain.
There is a need to balance low or high blood sugar in order to allow the brain to receive the Tyrosine. Insulin surges, low blood sugar and anemia effect the production of the brain’s ability to produce both these NT’s.
Inactivation and degradation
Dopamine is inactivated by reuptake via the dopamine transporter, then enzymatic breakdown by catechol-O-methyl transferase (COMT) and monoamine oxidase (MAO). Dopamine that is not broken down by enzymes is repackaged into vesicles for reuse
The most important way to inactivate used dopamine is reuptake but this is hindered by a lack of Magnesium or Methyl donors.
The following conditions use up the Methyl donors needed to recycle dopamine: Hypothyroidism, low HCl in the stomach caused by H Pylori or other causes, use of Birth control pills, antacids, estrogen replacement therapy to name a few.
Dopamine is biosynthesized in the body (mainly by nervous tissue and the medulla of the adrenal glands) first by the hydroxylation of the amino acid L-tyrosine to L-DOPA via the enzyme tyrosine 3-monooxygenase, also known as tyrosine hydroxylase, and then by the decarboxylation of L-DOPA by aromatic L-amino acid decarboxylase (which is often referred to as dopa decarboxylase). In some neurons, dopamine is further processed into norepinephrine by dopamine beta-hydroxylase.
In neurons, dopamine is packaged after synthesis into vesicles, which are then released into the synapse in response to a presynaptic action potential.
Tyrosine, which can be synthesized in the body from the essential amino acid phenylalanine, is found in many high protein food products such as soy products, chicken, turkey, fish, peanuts, almonds, avocados, bananas, milk, cheese, yogurt, cottage cheese, lima beans, pumpkin seeds, and sesame seeds. Tyrosine can also be obtained through supplementation.