Dopamine is not the pleasure chemical; it flags what is worth pursuing
Headlines call dopamine the molecule of pleasure. Pharmacologists now describe it differently: it marks how strongly an outcome should attract or repel us, steering behaviour toward goals. That is why the mere anticipation of a reward raises dopamine levels, and why many addictive drugs hijack it.
Dopamine is a small molecule, the simplest member of the catecholamine family, which also includes norepinephrine and adrenaline. Its core is a benzene ring carrying two hydroxyl groups, with an amine attached by a short chain; that phenethylamine skeleton is shared by many psychoactive drugs. In the brain it works as a neurotransmitter across several distinct pathways, one of which drives the motivational side of reward-seeking.
The body builds it in steps from amino acids found in almost every protein. Phenylalanine becomes tyrosine, tyrosine becomes L-DOPA, and an enzyme then strips off a carboxyl group to yield dopamine. Dopamine in food is useless to the brain because it cannot cross the blood-brain barrier, so neurons must make their own. Dopamine is itself the starting point for norepinephrine and adrenaline. Afterwards, enzymes including monoamine oxidase break it down to homovanillic acid, which the kidneys excrete.
Beyond the brain it acts as a local messenger with wide-ranging jobs: widening blood vessels, increasing sodium and urine output from the kidneys, reducing insulin release from the pancreas, slowing gut movement and damping lymphocyte activity. Except in blood vessels, it is made close to where it acts.
Several disorders involve it. Parkinson's disease arises from the loss of dopamine-producing neurons in a region called the substantia nigra, and levodopa, a pure form of L-DOPA, is its most widely used treatment. Most antipsychotic drugs block dopamine receptors, and reduced dopamine activity is linked to ADHD and restless legs syndrome. Dopamine can also react directly with oxygen to form quinones and free radicals that poison cells, a process that may contribute to the neuron loss seen in Parkinson's.
Source: Dopamine
