Normal Dopamine Function

The gap where an electrical signal jumps from one neuron to another is called the synaptic cleft. This is a closeup of the cleft between one neuron and another. Since the impulse cannot cross a gap as electricity, it crosses as a chemical message by means of "messengers" called neurotransmitters. One important neurotransmitter involved in the experience of pleasure is called dopamine.

Here, dopamine, shown in yellow, is produced in the neuron shown at the top and packaged in containers called vesicles. As an electrical impulse arrives at the neuron's terminal, the vesicle moves to the neural membrane and releases its load of dopamine into the synaptic cleft.

The dopamine crosses the gap and binds to receiver sites, or receptors, on the membrane of the next neuron. When dopamine occupies a receptor, various actions take place in that neuron: certain ions, shown in green, exit or enter, and certain enzymes are released or inhibited. The result is that a new electrical impulse is generated in this neuron, and the "message" continues on.

After the dopamine has bound to the receptor, eventually it comes off again and is removed fom the synaptic cleft and back into the first neuron by reuptake pumps. (For normal nerve transmission, it is important that the dopamine not stay in the cleft.)

This is what happens to nerve cell transmission when cocaine, shown in red, enters the brain's reward pathway. Cocaine blocks the reuptake pumps which act to remove dopamine from the synapse. More dopamine accumulates in the synapse, resulting in feelings of intense pleasure.

Unfortunately, prolonged cocaine use may cause the brain to adapt, such that it comes to depend on the presence of cocaine to function normally, "downregulating" the amount of dopamine present naturally.

Then, if the person stops using cocaine, there is not enough dopamine in the synapses, and the person experiences the opposite of pleasure--depression, fatigue, and low mood. The immediate, worst symptoms are called withdrawal.

Even long after the person has stopped using cocaine, brain abnormalities can persist, causing feelings of discomfort and craving for more of the drug to relieve these feelings.

Dopamine Function When Cocaine is Added