Answered By: Addiction Specialist

Answer: Please refer to the earlier question about cocaine for definitions of a synapse and neurotransmitters. At lower doses, amphetamine increases the concentration of dopamine in the synapse in 3 ways: (1) It binds to a receptor on the nerve before the synapse and causes it to release dopamine; (2) In the nerve before the synapse, dopamine is kept in little balloon-like structures called vesicles. Amphetamines cause these balloons to break, releasing their dopamine inside the neuron; (3) There is an enzyme (a little machine in the cell) in the neuron before the synapse called "monoamine oxidase" whose job it is to destroy any free dopamine floating around outside of a vesicle. Amphetamines bind to this enzyme and prevent it from working, which allows the dopamine that got released from the vesicle to stay around inside the neuron. This action of amphetamines only happens at higher doses. (4) There is a transporter on the neuron before the synapse whose job it is to transport the dopamine that gets released into the synapse when a signal comes along out of the synapse back into the cell that released it. The removal of this dopamine is how the neuron after the synapse knows the signal is over. Cocaine binds to this same transporter and prevents it from bringing the dopamine back in. Amphetamines bind the transporter and actually cause it to reverse, pumping dopamine out of the cell and into the synapse. Amphetamines also have some of the above effects on nerves that use a neurotransmitter called norepinephrine. Go to http://www.cnsforum.com/imagebank/item/Drug_amphet_high/default.aspx for a great visual representation of this.

Answered on: October 22, 2008