Basic Brain Anatomy

Neurons

Neurotransmitters

Dopamine

                           

Dopamine

Dopamine is a neurotransmitter that is made from an amino acid called tyrosine.  Amino acids are the molecular units that make up proteins which among other things build cells in the body.  Tyrosine is an essential amino acid that humans obtain from their diets.  The synthesis of dopamine from amino acid is controlled by enzymes.  The enzymes are responsible for adding or taking off atoms of the molecule, thus making molecules such as dopamine.  Dopamine is synthesized in the terminal buttons of neurons.

tyrosine                   dopamine

Certain neurons contain dopamine and have receptors that respond to its release.  In the brain there are three primary systems that involve dopamine; the nigrostriatal, mesolimbic and mesorcortical systems.  These circuits have their nuclei (clusters of cell bodies) in the substantia nigra (SN) and the ventral tegmental area (VTA), respectively.  This means that the circuits have dopamine synthesized in these two areas.

• The substantia nigra projections are part of the nigrostrital system.  The axons of the nigrostriatal system project to the caudate nucleus and putamen of the basal ganglia.  Because the basal ganglia is highly implemented, a decrease in the number of dopamine neurons in the SN and its pathway is believed to lead to Parkinson's Disease  and Parkinsonian-like symptoms.
  

• The mesolimbic system involves the VTA and its projections lead to areas of the limbic system, including the nucleus accumbens (NAc), amygdala, and hippocampus. The NAc is important in the reinforcement aspects of many normal activities as well as drugs of abuse. When a person eats, drinks, has sex or takes a drug, this pathway is excited. The excitation is pleasurable and people want to further stimulate it to feel good. This is partly why people will become gluttonous, sex addicts, and why certain drugs of abuse are so dangerous.
  

• The third system, the mesocortical system, also originates in the VTA, but it projects to the pre-frontal cortex, instead of the limbic system. These neurons have an excitatory effect and are involved in memory formation, planning, decision-making and problem solving. The interworkings of the mesolimbic and mesocortical systems are the main focus of addiction theory.