Dopamine

Dopamine is an important neurotransmitter that regulates our emotional responses, movement, pain, and the brain’s pleasure and reward center. Without dopamine, we wouldn’t be able to feel pleasure or motivation; however, it can also play a role in addiction.

Introduction

Dopamine is a neurotransmitter, which is a chemical released by neurons (nerve cells) to send signals to other nerve cells (R).

Dopamine is produced in the dopaminergic neurons in the ventral tegmental area (VTA) of the midbrain, the substantia nigra pars compacta, and the arcuate nucleus of the hypothalamus (R).

There are several distinct dopamine pathways in the brain, one of which plays a major role in reward-motivated behavior (R).

Dopamine levels in the brain is increased by most types of rewards, and dopamine neuronal activity is increased by most addictive drugs (R).

Dopamine has many roles in humans, which include: movement, memory, pleasure and reward, behavior and cognition, attention, inhibition of prolactin production, sleep, mood, and learning (R).

Dysfunctions of the dopamine system causes several important diseases such as Parkinson’s disease, schizophrenia, restless legs syndrome and attention deficit hyperactivity disorder (ADHD) (R).

Benefits of Dopamine

1) Dopamine Helps Movement

The basal ganglia, which is the largest and most important sources of dopamine in the brain, regulates movement (R).

The basal ganglia plays a central role in action selection, or choosing what to do next (R).

Dopamine contributes to the action selection process. In order for the basal ganglia to function well, it requires dopamine to be released at the input nuclei (R).

A certain amount of dopamine is required to function at peak efficiency (R). Hence, the threshold is set by dopamine for initiating action (R).

When an increase in dopamine activity causes an action, the basal ganglia circuit is altered and makes the same response easier to evoke when similar situations arise in the future (R).

2) Dopamine Mediates Pleasure

Dopamine mediates pleasure in the brain (R).

When exposed to a rewarding stimulus, the brain responds by increasing release of dopamine (R).

A wide variety of rewarding events strongly activate dopamine neurons in some brain areas (R).

During these pleasurable situations, dopamine is released and stimulates one to seek out the pleasurable activity (R). This means that many types of pleasurable experiences such as sex, food, games or even drug abuse can increase dopamine release (R).

The brain reward system serves to promote survival of the species by rewarding behaviors necessary for continued survival such as seeking food, reproduction, shelter, drink, etc (R).  These activities that are essential to species survival and activate this pathway are associated with ‘feeling good’ (R).

The reinforcement role of dopamine can also be aided by the addition of histamine (R).

3) Dopamine Helps Memory

Memory is strongly modulated by dopamine activity in the brain (R).

Dopamine is essential for hippocampal long-term memory (R).

Dopamine has an effect on episodic memory that is the part of long-term memory, which leads people to recall actual events (R).

It influences which episodic memories are formed and how they are represented, enabling memory for past experience to support future adaptive behavior (R).

4) Dopamine Increases Your Attention

Dopamine has a role in focus and attention (R).

Dopamine dysfunction in frontal lobes can cause a decline in attention or even attention deficit disorders (R).

Studies showed that moderate levels of dopamine improve the capacity of individuals to switch attention efficiently between tasks. Furthermore, moderate levels of dopamine direct attention more efficiently to stimuli that are relevant to ongoing tasks (R).

5) Dopamine Inhibits Prolactin

Dopamine that is released by the hypothalamus also acts as a hormone in the brain (R).

Dopamine is the main neuroendocrine inhibitor of the secretion of prolactin from the anterior pituitary gland (R).

Some cells produce prolactin in absence of dopamine. Thus dopamine inhibits the release of prolactin (R).

6) Dopamine Helps Parkinson’s Disease

Dopamine is responsible for the communication between two regions in the brain which are the substantia nigra and the corpus striatum. This is critical to produce smooth, purposeful movement. Loss of dopamine in this circuit results in impaired movement (R).

The nerve cells in this circuit produce dopamine. Parkinson’s disease occurs when these nerve cells become impaired and/or die (R).

When approximately 60 to 80% of the dopamine-producing cells are damaged and do not produce enough dopamine, the motor symptoms of Parkinson’s disease appear (R).

Low dopamine levels contribute to the painful symptoms that frequently occur in Parkinson’s disease (R).

7) Dopamine Can Decrease Inflammation

Dopamine is shown to interact with the immune system.

Although the immune effects are quite complex and nuanced, overall, it decreases inflammation and Th1 and Th17 dominance.  However, it also suppress the tolerance-inducing Treg cells (by inhibiting IL-10 and TGF-b) (R).

The D3 and D5 receptors are more inflammatory, while the D1, D2 and D4 receptors are more anti-inflammatory (R).

Low levels of dopamine would stimulate mainly the Dopamine 3 receptor in T cells, favoring Th1-like responses and T cell activity, whereas moderate dopamine levels would stimulate the Dopamine 5 receptor as well, inhibiting T cell function (R).

Higher dopamine levels promote complex effects in T cells, but overall decrease T cell response and inflammation (R).

Stimulation of D5 receptors on Dendritic Cells causes Th17 dominance (by increasing production of IL-23), which opposes its immune inhibitory effects in other situations (R).

Higher dopamine might possibly contribute to multiple sclerosis, whereas higher levels can help alleviate Rheumatoid Arthritis, IBD and Lupus (R).

Dopamine treatment can decrease inflammation and have other therapeutic effects (R).

8) Dopamine Helps Increase Bone Strength

Dopamine has an effect on calcium metabolism, and can help increase bone strength.

In a study done on mice missing the dopamine transporter gene, they were shown to have weaker bone strength and less bone mass (R).

Cons of Dopamine

1) Excess Dopamine May Cause Schizophrenia

The dopamine hypothesis proposes that schizophrenia is caused by excessive production of dopamine (R).

Studies support the idea that an overactive dopamine system may result in schizophrenia: Medications that block dopamine receptors, specifically D2 receptors, reduce schizophrenia symptoms (R).

Some evidence suggest that the negative symptoms and some of the cognitive deficits of schizophrenia may be related to decreased prefrontal cortex  function which, in turn, based on indirect evidence, may be associated with decreased mesocortical dopamine activity (R).

Thus, some features of negative schizophrenia (social withdrawal, apathy, anhedonia) are thought to be related to a low dopaminergic state in certain areas of the brain (R).

Schizophrenia is characterized by abnormally low prefrontal dopamine activity (causing deficit symptoms) leading to excessive dopamine activity in mesolimbic dopamine neurons (causing positive symptoms) (R).

2) Dopamine Can Cause Nausea

There are dopamine receptors located in the stomach and intestines.

They can help relieve nausea and vomiting, or even acid reflux (R).

However, dopamine can also cause constipation (R).

3) Dopamine Can Fuel Addiction

Narcotics such as cocaine, nicotine, and amphetamines act increase dopamine in the striatum and can lead to addiction (R).

The reinforcing effects of these drugs don’t only come about because of increased dopamine, but also because of the fast rate that dopamine increases. The faster the increases, the more intense the reinforcing effects (R).

Long-term drug use seems to be associated with decreased dopamine function, as evidenced by reductions in D2 dopamine receptors and dopamine release in the striatum in addicted subjects (R).

4) High Levels of Dopamine Can Cause Aggression

High levels of dopamine can cause aggression and blocking dopamine receptors decreases aggression in people (R).

Dopamine and Sleep

Dopamine receptors play a part in modulating sleep (R).

Activation of the D1 receptor induces arousal and wakefulness and a reduction of slow wave sleep and REM sleep (R).

Activation of the D2 dopamine receptor causes biphasic effects. Low doses reduce wakefulness and increase Slow Wave and REM sleep (predominant activation of the D(2) autoreceptor), whereas large doses induce the opposite effect (predominant facilitation of the D(2) postsynaptic receptor) (R).

Compounds that block both D1 and D2 receptors reduce wakefulness and increase deep sleep (R).

Activation of the D3 receptor induces sleepiness and sleep in laboratory animals and man (R).

During wakefulness there occurs an increase of burst firing activity of dopamine neurons, and an enhanced release of dopamine in the VTA, the nucleus accumbens (NAc), and a number of forebrain structures (R).

Patients suffering from Parkinson’s Disease may also have sleep disturbances. These disturbances result from a low amount of dopamine (dopamine, via the D2 receptor, can help REM sleep) (R).

Dopamine, Food Desire and Weight

Dopamine (along with serotonin, opioids, cannabinoids, orexin, leptin and ghrelin) mediates the rewarding effects of food (R).

Dopamine is associated with the desire to eat the food and with conditioning of food cues.  So dopamine will cause you to desire food when you simply smell it (R).

Dopamine is also involved with the motivation to perform the behaviors necessary to buy/prepare and consume the food (R).

Dopamine causes you to ‘want’ food as opposed ‘like’ the food (R).

Mutant mice that do not synthesize Dopamine die of starvation owing to a lack of motivation to eat. Restoring DA neurotransmission in the striatum rescues these animals, whereas restoring it in the nucleus accumbens does not (R).

Because dopamine is released when someone eats food, this could contribute to overeating if someone has low dopamine because – they will seek to increase that dopamine with food (R).

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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3124340/figure/F1/

Changing Your Dopamine Levels

Increasing Dopamine

Decreasing Dopamine

In cases of schizophrenia, dopamine levels can be decreased by using anti-psychotic drugs (R).

Choline can antagonize dopamine directly or interfere with receptor function.

Melatonin suppresses dopamine activity (R).

Magnesium and Lithium also decreases the effect of dopamine (R, R).

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