Extracellular dopamine dynamics in rat caudate-putamen during experimenter-delivered and intracranial self-stimulation

Intracranial self-stimulation is an operant behavior whereby animals are co nditioned to press a lever in order to receive an electrical stimulation of their dopamine neurons. This paradigm is thought to stimulate brain reward pathways and, as such, has been used to clarify the role of dopamine in re ward. Striatal extracellular dopamine concentrations were monitored during the acquisition and maintenance of self-stimulation and compared to dopamin e release generated by experimenter-delivered and yoked stimulation. Fast-s can cyclic voltammetry in conjunction with carbon-fiber microelectrodes was used to monitor evoked dopamine release in the caudate-putamen during elec trical stimulation of the substantia nigra/ventral tegmental area. The sub- second temporal resolution of fast-scan cyclic voltammetry coupled with the micron spatial resolution of the microelectrodes allowed for the measureme nt of dopamine neurotransmission in real-time. Single experimenter-delivere d stimulations, identical to those used during self-stimulation, evoked dop amine release in the caudate-putamen both before and after the self-stimula tion sessions. Likewise, yoked stimulations of the substantia nigra/ventral tegmental area delivered to animals untrained to perform self-stimulation resulted in an increase in extracellular dopamine levels. During training s essions, experimenter-delivered stimulations evoked dopamine release. Howev er, as the animals began lever-pressing, extracellular dopamine levels subs equently declined. Taken together, these results suggest that dopamine functions as an alertin g device, wherein increases in extracellular dopamine are obtained by unpre dicted or novel rewarding stimuli, but not by those which can be anticipate d. (C) 2000 IBRO. Published by Elsevier Science Ltd.