Enhanced dopamine efflux in the amygdala by a predictive, but not a non-predictive, stimulus: facilitation by prior repeated d-amphetamine
Section snippets
Subjects
A total of 14 male Lister hooded rats was used (Charles River, Margate, Kent, U.K.), weighing 300–350 g immediately prior to surgery. Animals were housed in pairs under a 12-h : 12-h light–dark cycle (lights on 08.00). Housing conditions were maintained at 22±2°C and 55±10% humidity. Following recovery from surgery, animals were reduced to 85% of their free-feeding weight by restriction of access to food. Access to water remained ad libitum. All experimental procedures used were subject to U.K.
Histology
Histological examination verified that all dialysis sites were located in the vicinity of the central nucleus of the amygdala, and were within ±0.6 mm of the intended coordinates in the rostral–caudal dimension (see Fig. 2a). Glial reaction was of very limited extent, and restricted to the location of the probe (Fig. 2b).
Initial tray approach
During these initial training sessions, sensitized and control animals showed similar approach responses to the sucrose pellet US (Fig. 3; main effect of Group: F1,12=0.9, NS;
Discussion
The present findings suggest that dopamine overflow in the amygdala increases in response to the presentation of a stimulus of acquired motivational or affective significance. Extracellular levels of dopamine within the amygdala were found to increase during a session containing presentations of a stimulus immediately preceding those of a sucrose US (CS+US test session), but not during a session in which the stimulus was explicitly unpaired with the same US (CS−/US control session). In both
Conclusions
The present results suggest that mesoamygdaloid dopamine is stimulated during exposure to an initially neutral stimulus of acquired motivational significance. Prior repeated d-amphetamine was additionally found to enhance this mesoamygdaloid dopamine response and the acquisition of affective significance by a stimulus associated with an event of intrinsic biological significance. These data may therefore highlight a role for the mesoamygdaloid dopamine projection in appetitive Pavlovian
Acknowledgements
We thank the Wellcome Trust for their financial support of this work. We gratefully acknowledge the extensive support and assistance of Presearch Ltd (Letchworth Garden City, U.K.).
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