Mesencephalic dopamine (DA) cells of the ventral tegmental area (VTA) and substantia nigra zona compacta play critical roles in movement, motivation and mentation. Responses of DA neurons to a salient stimulus determine the likelihood and the strength of a behavioral reaction to the stimulus. The two forms of firing that are most readily distinguished are regular single-spike firing and firing in bursts of action potentials. The firing pattern of a neuron is determined by two factors. The first is the underlying membrane conductances expressed by the cell — the ion channels in the membrane, and how they open and close with time, membrane potential, and intracellular regulators. The second factor is the afferent inputs to the neuron. The chapter deals with the synaptic inputs to the neurons, with particular emphasis on the ventral tegmental neurons. Synaptic potentials mediated by excitatory amino acids can be detected in both principal and secondary cells of the VTA.