Dopamine and noradrenaline efflux in the prefrontal cortex in the light and dark period: Effects of novelty and handling and comparison to the nucleus accumbens

We used on-line microdialysis measurements of dopamine and noradrenaline ex tracellular concentrations in the medial prefrontal cortex of awake, freely moving rats during the dark and the light period of the day to study wheth er (i) basal efflux would be higher in the active, dark period than in the inactive, light period; (ii) the activation induced by environmental stimul i would be dependent on these conditions. When determined one day after can nula placement, noradrenaline and dopamine levels were higher during the da rk. Maximal relative increases induced by novelty and handling were 150% an d 175-200%, respectively, and were very similar in the light and the dark, but the net increases were higher in the dark. Separate groups were tested one week after cannula placement to ensure recovery of possibly disturbed c ircadian rhythms. While basal levels in the dark were now approximately twi ce those in the light, the maximal relative and net increases after both no velty and handling were very similar. Basal levels of dopamine in the nucle us accumbens (one day after cannula placement) were not different in the li ght or dark, but were increased by novelty and handling to about 130% only in the light period, not in the dark. Thus, in the prefrontal cortex, dopamine strongly resembles noradrenaline, in that basal efflux was state dependent, whereas activation by stimuli was not. In the nucleus accumbens, basal dopamine efflux was not state depende nt, but activation by stimuli was. These results suggest that there are dif ferential effects of circadian phase on basal activity and responsiveness o f the mesolimbic vs the mesocortical dopamine system. (C) 2000 IBRO. Publis hed by Elsevier Science Ltd. All rights reserved.