Amygdaloid D-1 dopamine receptor involvement in Pavlovian fear conditioning

The amygdala has long been implicated in conditioned fear. The mesencephali c dopaminergic system provides a rich innervation to the amygdala [J.H. Fal len, P. Ciofi, Distribution of monoamines within the amygdala, in: J.P. Agg leton (Ed.), The Amygdala: Neurobiological Aspects of Emotion, Memory and M ental Dysfunction, Wiley, New York, 1992, pp. 97-114; L.J. Freedman, M.D. C assell, Distribution of dopaminergic fibers in the central division of the extended amygdala of the rat. Brain Research 633 (1994) 243-252; E. Asan, T he catecholaminergic innervation of the rat amygdala. Advances in Anatomy E mbryology and Cell Biology 142 (1996) 1-107]. Specific activation of the me soamygdaloid dopaminergic system has been reported to occur in response to conditioned fear-arousing stimuli [M.L. Coco, C.M. Kuhn, T.D. fly, C.D. Kil ts, Selective activation of mesoamygdaloid dopamine neurons by conditioned stress: attenuation by diazepam. Brain Research 590 (1992) 39-47] suggestin g that dopamine release in the amygdala may contribute to the acquisition a nd/or expression of conditioned fear. Using a 2 x 2 factorial design, Exper iment 1A investigated the effects of bilateral intra-amygdaloid infusions o f the selective D-1 receptor antagonist, SCH 23390 (2.0 mu g 0.5 mu l(-1) s ide(-1)), on the acquisition and expression of Pavlovian conditioned fear m easured by freezing to acoustic and background contextual stimuli. Infusion s of SCH 23390 prior to acquisition training, prior to retention testing or prior to both significantly attenuated conditioned freezing during retenti on testing. Experiment 1B investigated the dose-dependent effects of pre-tr aining infusions of SCH 23390 (0.5, 1.0 and 2.0 mu g) on conditioned fear. Pre-training infusions of SCH 23390 dose-dependently attenuated conditioned freezing during retention testing. Experiment 2A investigated the effects of bilateral infusions of the selective D-1 receptor agonist, SKF 82958 (2. 0 mu g 0.5 mu l(-1) side(-1)) on the acquisition and expression of conditio ned fear. Infusions of SKF 82958 prior to training facilitated conditioned freezing during retention testing. Experiment 2B investigated the dose-depe ndent effects of pre-training infusions of SKF 82958 (1.0, 2.0 and 4.0 mu g ) on conditioned fear. Pre-training infusions of SKF 82958 dose-dependently facilitated conditioned freezing during retention testing. In conclusion, these results suggest that dopamine transmission within the amygdala contri butes to the acquisition and expression of Pavlovian fear conditioning. (C) 1999 Elsevier Science B.V. All rights reserved.