Molecule of the Day: Dopamine
Dopamine (C8H11NO2) is an important neurotransmitter involved in many signalling pathways in the body. At room temperature, it is a white powder that is freely soluble in water.
Dopamine plays a key role in the brain’s reward system and is associated with feelings of euphoria and pleasure. As a result, stimuli that cause greater amounts of dopamine to bind to the corresponding receptors on the post-synaptic membrane induce appetitive behaviour.
For example, drugs such as amphetamine bind to and inhibit dopamine reuptake transporters present on the pre-synaptic membrane, and can also inhibit monoamine oxidase, which normally metabolises dopamine. This causes the concentration of dopamine in the synaptic cleft to increase, and the resultant rise in binding of dopamine receptors leads to feelings of pleasure. However, in combination with the resultant tolerance, this can lead to addiction and dependence on such drugs.
Dopamine is biosynthesised from tyrosine in the human body, via the intermediacy of L-DOPA:
Low dopamine levels have been linked to Parkinson’s disease; this is because the main symptoms arise from the death of dopamine-producing cells in the brain. Consequently, one of the main methods of treating it is the injection of L-DOPA; while this does not recover the cells’ ability to produce dopamine, it can stimulate the remaining cells, and is also metabolised to form dopamine (see above).