MADE FROM

A short chemical assembly line

Start The amino acid tyrosine, from the diet

Step 1 The enzyme tyrosine hydroxylase makes L-DOPA, the slow step

Step 2 L-DOPA is converted to dopamine

Later Dopamine can be turned into norepinephrine

L-DOPA sits one step before dopamine.

THE PATHWAYS

Two main routes

Both start in the midbrain, but they end in different places and do different jobs.

One molecule, several jobs.

REWARD

A signal of better than expected

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Reward learning

Dopamine neurons fire more when an outcome is better than expected, and less when it is worse

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Motivation

Dopamine helps drive effort toward a goal

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Movement

Dopamine in the striatum helps start and smooth movements

Dopamine is more about wanting and learning than about pleasure.

PARKINSON'S

When the source cells die

What happens Dopamine neurons in the substantia nigra die off

Effect Dopamine in the striatum falls, causing tremor, stiffness, and slowed movement

Treatment L-DOPA crosses the blood-brain barrier on the LAT1 carrier and is then converted to dopamine

Dopamine itself cannot cross the barrier, but its precursor can.

Addiction and psychosis

Cocaine blocks the dopamine transporter, and amphetamine promotes dopamine release, so both raise dopamine in the nucleus accumbens. Many antipsychotic drugs block dopamine D2 receptors, which shows how a single transmitter can link to very different conditions.

Too little dopamine and too much dopamine cause different problems.

UNIT 7 STUDY COMPLETE

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Ready for the Fab Challenge?

You've followed dopamine from its precursor to its pathways and seen what its loss does.