Patterns of dopamine overflow in mouse nucleus accumbens during intracranial self-stimulation

Dopamine (DA) overflow in the mouse nucleus accumbens during intracranial s elf-stimulation (ICSS) of the median forebrain bundle was estimated by chro noamperometry with removable carbon fibre electrodes. The specificity of th e voltammetric signal was confirmed pharmacologically. The parameters of st imulation (50 Hz, 0.5 s train length) allowed us to obtain measurable DA re lease and to maintain ICSS. Continuous (CR) and fixed-ratio (FR8) schedule of reinforcement showed differing correspondence of the patterns of DA rele ase with the patterns of stimulation/nose-poking. The CR schedule induced a high rate nose-poking and tonic increase in dopamine overflow, which becam e decreased following the first periods of self-stimulations. The FR schedu le induced stable peaks of DA overflow during the entire period of ICSS. We conclude that the availability of a readily-releasable pool of DA in presy naptic terminals determined the pattern of dopamine overflow in the nucleus accumbens during ICSS in mice. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.