The brain is awash in chemicals. Among these chemicals, there’s one that always stands out: dopamine. It is the driving force behind every human being’s sinful predilections and forbidden cravings. It is associated with addiction, attention, motivation, and all the hedonistic pursuits ever known to man. But mainstream culture aside, what roles does dopamine specifically play in the brain that make it highly controversial even in neuroscience?
Dopamine: An Overview
Known to many as the “feel-good” chemical, the catecholamine neurotransmitter dopamine is not as plentiful as it has been conceived to be. In fact, it is so scarce, that only 0.3% of the brain’s millions of neurons produce this. Although this is the case, it is responsible for several vital bodily functions, such as the following:
- Circadian rhythm– Dopamine latches onto its receptor to signal the body to wake up by suppressing levels of melatonin early in the morning.
- Memory– The neurotransmitter appears to control what is retained in the memory based on an imagined response to a certain information.
- Motor functions- Dopamine also regulates the control of motor functions via the basal ganglia. The basal ganglia depend on a certain amount of the neurotransmitter to perform at peak efficiency. The lack of dopamine in the brain gives way to delayed and uncoordinated motor functions. On the flip side, the excess of it causes the body to make unnecessary movements, as repetitive tics.
- Prolactin secretion- Dopamine manufactured by neurons in the arcuate nucleus of the hypothalamus is ejected into the hypothalamo-hypophysial blood vessels of the median eminence, which supply the pituitary gland. This acts on the lactotrope cells that produce prolactin.
Role of Dopamine in Learning
Dopamine has been seen as crucial to learning. When the brain is presented with an unexpected reward, dopamine increases, prompting the limbic reward system to take note and remember how to repeat such positive experience. On the other hand, negative encounters hamper dopamine as a signal to avoid repeating them. This is a vital learning mechanism, which also involves memory-formation and motivation.
Scientists believe the brain establishes a new temporary neural network to process new stimuli. Each replication of the same experience triggers the identical neural firing sequence along an identical neural journey, with every duplication strengthening the synapses among the neurons involved. Neuroscientists say, “Neurons that fire together, wire together.”
If this occurs often, a secure neural network is set up, as if imprinted, allowing the brain to reliably access the information eventually. Hence, a discrete act of learning has been initiated, reinforced, and embedded, a process referred to as Long-Term Potentiation (LTP). A person experiences this model of learning when memorizing facts and figures or a foreign language’s vocabulary.
Drug use affects LTP. In an experiment conducted on rats, Julie Kauer of theBrown University, found that morphine hindered LTP in the ventral tegmentum area (VTA), a key part of the brain’s limbic system, and that such process continued for about 24 hours thereafter. Morphine blocks an enzyme (guanylate cyclase) that inhibits the release of dopamine, as if removing a brake on it. Kauer explains that morphine makes lasting changes in the brain by blocking a mechanism that’s believed to be the key to memory making, thus reinforcing the previous assumption that addiction is a form of pathological learning.
Alcoholics are commonly observed to have memory problems, which may be due to the negative effects alcohol produces on the hippocampus, the center of new-memory formation.
When adolescent rats were given alcohol, they exhibited significant damage on their hippocampi. In a separate study, rats that were fed alcohol over a four-day period to simulate alcoholism were found to have a substantial decline on their hippocampi. Notwithstanding, in a possible sign of the brain’s innate ability to recover, the rats experienced a growth spurt in their hippocampal cells after they stopped drinking. In contrast, extremely small amounts of alcohol administered to rats actually boosted their memory-formation by increasing expression of a memory-related receptor dubbed NR1.
Role of Dopamine In Depression
Researchers say they’ve found a new way in which prolonged exposure to the chemical messenger dopamine may play a role in depression. If confirmed by further studies, they say the discovery could lead to a new understanding of this complex disorder as well as better treatment. Current anti-depression treatments are primarily based on the lack of serotonin and norepinephrine in the brain, according to researcher Li-Huei Tsai, professor of pathology at Harvard Medical School, in a news release. He emphasizes that the new research magnifies the importance of the dopaminergic system, which has been a less considered target in the current antidepression treatment methods.
The studies show that certain receptors in the brain respond to dopamine in a previously unknown way that occurs over a period of hours rather than minutes or seconds. In this manner, researchers say the chemical may affect the brain indefinitely.
In lab tests conducted on mice, researchers found prolonged exposure to dopamine through this pathway inactivated a regulatory protein in the brain known as Akt and caused the mice to behave as if they were depressed in reaction to stress. Further, inactivation of this protein caused a molecular chain of events that caused the mice to become desensitized to certain drugs. Researchers assert this type of prolonged exposure to dopamine may also help explain the impact of drug abuse on the brain.
This mechanism is said to be more essential compared to those earlier described for prolonged stimulation by dopamine, in the same way with those with psychiatric disorders, according to Marc Caron, PhD, professor of cell biology at Duke University, in a news release.
Role of Dopamine In ADHD
Attention deficit hyperactive disorder (ADHD) is a developmental disorder with consequences known to compromise academic and occupational achievement and raise a person’s susceptibility to depression, substance abuse, accidental injury, and/or even death.
It can, in most cases, be successfully treated with medications that increase the production of dopamine. Scientists have long speculated that too little supply of dopamine can give way to ADHD. The following image shows a PET (positron emission tomography) scan of a control subject versus a subject with ADHD. The subject with ADHD showed lower levels of dopamine transporters in the nucleus accumbens.
Recent evidence has strengthened such supposition and points to the defects of dopamine transporters in the brain as the main cause: the transporters take up too much of the chemical messenger before it can be moved from one brain cell to another.
A research spearheaded by Donald Gilbert, a pediatric neurologist at Cincinnati Children’s Hospital, discovered how the brain’s motor cortex suppresses movement in 16 children and adolescent subjects, both pre- and post-administration of medications that elevate the brain’s dopamine supply.
Role of Dopamine In Schizophrenia
Pharmacological treatments support the idea that an overactive dopamine system may result in schizophrenia: medications that block dopamine receptors, specifically D2 receptors, suppress schizophrenia symptoms.
The brain regions thalamus and the striatum are influenced by dopaminergic activity. Manzano et al. explain that schizophrenia is a result of altered levels of D2 binding potential in those two regions of the brain. The authors state that schizophrenia patients who are not on antipsychotic medications have a lower thalamic D2 binding potential. Additionally, schizophrenia patients who are not given any medications display a higher number of D2 receptors in the striatum.
Role of Dopamine In Parkinson’s Disease
One of the most important discoveries in systems neuroscience over the last 15 years has been about the key role of dopamine in control of motor function.
In the following illustration, we can see that dopamine-producing nerve cells die off, leaving too little dopamine in the system:
Dopamine cell firing was found to encode differences between the expected and obtained outcomes of actions. Although activity of dopamine cells does not specify movements themselves, a recent study in humans has suggested that tonic levels of dopamine in the dorsal striatum may in part enable normal movement by encoding sensitivity to the energy cost of a movement, providing an implicit “motor motivational” signal for movement.
Scientists have investigated the motivational hypothesis of dopamine by studying motor performance of patients with Parkinson’s disease who have marked dopamine depletion in the dorsal striatum and compared their performance with that of elderly healthy adults. All participants performed rapid sequential movements to visual targets associated with different risk and different energy costs, countered or assisted by gravity. In conditions of low energy cost, patients performed surprisingly well, similar to prescriptions of an ideal planner and healthy participants. As more energy is spent, however, performance of patients with Parkinson disease declined significantly below the prescriptions for action by an ideal planner and below performance of healthy elderly participants. The results showed that the ability for efficient planning depends on the energy cost of action and that dopamine mediates on the effect of energy cost on action.
Dopamine Regulation and Administration
As implied previously, regulation of dopamine plays a crucial role in a person’s 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. To help relieve their symptoms, patients are administered with L-DOPA, a drug that can be converted in the brain to dopamine.
Dysfunction in various dopaminergic systems is known to be associated with various disorders. Reduced dopamine in the pre-frontal cortex and disinhibited striatal dopamine release is seen in schizophrenic patients. Loss of dopamine in the striatum is a cause of the loss of motor control seen in Parkinson’s patients. Studies have indicated that there is abnormal regulation of dopamine release and reuptake in Tourette’s syndrome. Dopamine appears to be essential in mediating sexual responses. Moreover, microdialysis research have discovered that addictive drugs boost extracellular dopamine. Neuro-imaging has shown a relationship between euphoria and psycho-stimulant-induced increases in extracellular dopamine. These effects of dopamine dysfunction indicate the essence of maintaining dopamine functionality through homeostatic mechanisms that have been attributed to the delicate balance between synthesis, storage, release, metabolism, and reuptake, as these mechanisms are present both at the level of cell populations and at the level of individual nerve cells.
The Natural/Safe Means to Increase Dopamine
If you are experiencing stiff, achy muscles and noticing some cognitive impairment, and loss of balance and coordination, you may have low levels of the neurotransmitter dopamine. In your brain, dopamine plays a big role in two important areas – motor skills and focus. This is the thing to blame for the mental fog that leads to burners left on, keys locked in your house, and not being able to remember the chapter you just read. It is also attributable for rigid muscles, tremors, and falling down.
To increase supply of dopamine in the brain, doctors administer amphetamine medications such as Ritalin (methylphenadate) or Adderall (dextroamphetamine). However, they still give priority to natural means, which include the following:
- Theanine (found only in black and green tea leaves)
- Essential fatty acids
Dopamine levels change very slowly, so whatever method is preferred, it is advised that the person gives it ample time before he or she decides on the merits. Doctors don’t usually test the person for low dopamine levels and, instead, diagnose it according to the reported symptoms.
As you can probably tell, dopamine plays a big role in our daily lives. This neurotransmitter plays a big role in formulating memory, regulating sleep, focusing attention, and controlling motor function. Understanding dopamine and how it works is key to understanding how your brain works. In the future, we will discuss other neurotransmitters such as serotonin and glutamate.