Dopamine release at behaviorally relevant parameters of nigrostriatal stimulation: effects of current and frequency.

Released dopamine was monitored voltammetrically in the rat striatum in response to electrical stimulation of the nigrostriatal bundle. Stimulation parameters encompassed those typically used in behavioral studies. Dopamine released during intracranial self-stimulation (ICSS)-like stimulation reached a maximum within the first minute of stimulation, then rapidly decreased. The pattern of release obtained with continuous stimulation as a function of current and frequency supports the view that as the stimulation current is increased, a greater number of neurons are stimulated, while increasing the frequency of stimulation results in a fixed population of neurons being stimulated more intensely. Computer modeling of stimulated release from a population of dopaminergic nerve terminals was used to interpret effects of current and frequency and to predict ICSS release patterns as a function of schedule of reinforcement.