Dopamine & norepinephrine are two critical neurotransmitters that regulate your mood and behavior. Both dopamine and norepinephrine are in tricyclic antidepressant medications which are used to treat depression. However, neither dopamine or norepinephrine can cross the blood-brain barrier, which protects your brain, so their precursor is needed in order to increase levels of these neurotransmitters in your brain.
Both dopamine and norepinephrine are synthesized from the same precursor, the amino acid tyrosine. Enzymes are used to convert tyrosine into L-DOPA, which is used as a treatment in Parkinson's disease. Another enzyme can convert L-DOPA into dopamine and later into norepinephrine. Norepinephrine is stored in synaptic vesicles, and can be later broken down by additional enzymes. Each of the neurotransmitters can be broken down into the precursor in order to be reused at a later date.
Dopamine is important in the regulation of your mood. In your brain, there are multiple dopamine pathways, which are used to send dopamine to different areas of the brain. One of the most important dopamine pathways is the mesolimbic dopamine pathway, which projects from the midbrain to the nucleus accumbens. This pathway is thought to be involved in pleasure, delusions, psychosis and drug abuse.
Cocaine has a significant affect on dopamine and dopamine production. Dopamine has four receptors, known as D1, D2, D3 and D4. Cocaine binds to the D2 dopamine receptor, resulting in an increase in dopamine production and a euphoric feeling. Over time, your brain requires more cocaine in order to obtain the same euphoric feeling.
Norepinephrine, also called noradrenaline, acts mainly in an area of your brainstem known as the locus coeruleus. When released, norepinephrine has an impact on the "fight-or-flight" response, which is your body's biological response to stress. In addition, norepinephrine is also involved in pain, cognition, mood, emotions, movement and blood pressure.