Dopamine is a neurotransmitter involved in several functions, such as experiencing pleasure and joy. In addition, dopamine is needed to make the hormones adrenaline and norepinephrine.

In total, eight brain circuits have been found to use dopamine. These circuits all perform a different function in the brain and from this it can be deduced that dopamine is involved in many different tasks. The most important circuits are the following five

• The nigrostriatal circuit;
  This circuit is involved in regulating motor activities. It consists of the substantia nigra, the dorsal part of the striatum, and the frontal brain regions.
• The mesolimbic circuit;
  This circuit is important for behavior determined by reward and punishment. The circuit consists of the tegmentum, the nucleus accumbens, and the limbic system located in the frontal lobe.
• The mesocortical circuit;
  This is the source for the formation of motivation and emotions. From the tegmentum, signals go to the orbitofrontal cortex and the anterior cingulate cortex.
• The orbitofrontal cortex;
  This area is involved in making emotional decisions. This is an area in the frontal cortex, which has connections to the amygdala and cingulate cortex, among others.
• The tubero-infundibular pathway;
  This is where signals from the hypothalamus go to the pituitary gland, and it involves several neurotransmitters in addition to dopamine.

The action of dopamine depends on the receptors it binds to. There are in fact five different receptors, all of which are located in a different place in the brain. As a result, they all have a different function. For example, D1 receptors are mainly found in the striatum and the neocortex, and these receptors are important for motor actions. However, D2 receptors are found in the striatum and limbic system, and are therefore important for emotional behavior.

The above functions already indicate a link between dopamine and the brain's reward system. When pleasant experiences occur, such as eating, drinking, having sex or taking drugs, dopamine is released into the brain. After such an experience, the brain is eager to get dopamine back, in order to get the nice feeling back as well. To satisfy this need, the same action is performed again, and potentially this can lead to the development of addictions.

It is common knowledge that various drugs and medications, such as cocaine for example, affect the action of dopamine. This is because they prevent the used dopamine from being easily reabsorbed to recycle it. This leaves a lot of dopamine active at the same time, causing overstimulation. As you could read above, overstimulation by dopamine creates a nice feeling (it's like candy for the brain). The brain gets used to the high concentrations of dopamine, and next time even more dopamine is needed to give the same feeling.

Author: Myrthe Princen (translated by Joyce Burger)