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.)