A microdialysis study of nucleus accumbens core and shell dopamine during operant responding in the rat
Section snippets
Subjects
The subjects for this experiment were 55 male Sprague–Dawley rats (Harlan Sprague Dawley, Indianapolis, IN). The rats were housed in a colony that was maintained at 23°C on a 12 h light/dark cycle (lights on 07.00). Rats were initially food deprived to 85% of their free-feeding body weight, but then allowed a modest growth (up to 95% of original weight) over the course of the experiment. Water was available ad libitum in the home cages. Prior to guide cannula implantation, rats were group
Baseline neurochemistry
The baseline neurochemical data for DA are shown in Table 1. ANOVA indicated that there was no significant difference (F1,11=0.25; n.s.) in baseline levels of DA between core (14.9, ±1.5 pg/45 μl) and shell (13.8, ±1.6 pg/45 μl) control groups. In addition, as depicted in Table 1, no significant differences were found in baseline DA levels between control and experimental groups in either the core or the shell in any of the three operant procedures.
Behavioural results
Lever pressing data were gathered during the 30 min
Discussion
Lever pressing on three different operant schedules (VI30, FR5, VI/FR) was accompanied by increases in extracellular DA in both the core and the shell of the nucleus accumbens. It appears that DA release in the nucleus accumbens shell may be more responsive than in the core during operant responding. This effect was somewhat mild; within any one of the schedule conditions there was not a significant difference between core and shell, yet a difference did emerge when data were collapsed across
Conclusions
This experiment demonstrated that extracellular DA levels in both core and shell increased significantly during the performance of lever pressing. DA release in the shell of the nucleus accumbens appeared to be somewhat more responsive to lever pressing than DA release in the core. In addition, across the three lever pressing conditions there was a significant correlation between response rate and increases in DA release, but not a correlation between number of pellets obtained and increases in
Unlinked References
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Acknowledgements
This work was supported by a grant from the National Science Foundation. Many thanks to Jennifer Trevitt for her help this manuscript, and to Dr Laura Nisenbaum for the image analysis of histology sections.
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2016, Behavioural ProcessesCitation Excerpt :This led to the suggestion that mesolimbic DA helps to translate estimates of reinforcer availability into decisions to work for reward, and that mesolimbic DA release could being used as a motivational signal regulating behavioral activation and the decision of whether or not to engage in effortful activity (Hamid et al., 2016). Some studies involving food reinforcement in trained animals have shown that increases in DA release were more strongly associated with the instrumental response, or conditioned stimuli signaling reinforcer availability, rather than reinforcement delivery per se (Sokolowski et al., 1998; Roitman et al., 2004; Segovia et al., 2011). Furthermore, the role of DA systems in instrumental learning (e.g. Beninger and Gerdjikov, 2004) is not limited to situations involving positive reinforcement.
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Present address: Department of Pharmacological and Physiological Sciences, University of Chicago, Chicago IL 60637, U.S.A.