Cerebral Cortex, Vol. 13, No. 4, 371-380,
April 2003
© 2003 Oxford University Press
Significance of Dopamine Transmission in the Rat Medial Prefrontal Cortex for Conditioned Fear
1 Present address: Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge CB2 2EB, UK , 2 Present address: Department of Neuroscience, University of Edinburgh, 1 George Square, Edinburgh EH8 9JZ, UK , Laboratory of Behavioral Neurobiology, Swiss Federal Institute of Technology Zurich (ETH), Switzerland
Address correspondence to Joram Feldon, Laboratory of Behavioral Neurobiology, Swiss Federal Institute of Technology Zurich (ETH), Schorenstrasse 16, 8603 Schwerzenbach, Switzerland. Email: feldon{at}behav.biol.ethz.ch.
Previous studies have demonstrated activation of dopamine transmission in the medial prefrontal cortex (mPFC) by conditioned fear stimuli. Therefore, the present study investigated the functional significance of mPFC dopamine for a conditioned fear response to a tone. We examined the effects of inhibition or stimulation of mPFC dopamine transmission by local microinfusion of the D1/D2-receptor antagonist cis-flupenthixol or the indirect dopamine receptor agonist D-amphetamine, respectively, in a classical fear-conditioning paradigm in Wistar rats. Rats received tone–shock pairings and were later exposed to the tone alone. Freezing was used as measure of conditioned fear. Presence of the drugs in the mPFC during the tone–shock pairings did not affect freezing during subsequent presentation of the tone alone. However, when cis-flupenthixol and D-amphetamine were present in the mPFC during presentation of the tone alone, freezing to the tone was reduced. We demonstrated that the decreased freezing could be explained neither by state dependency nor infusion-induced alterations in activity. Our data indicate that mPFC dopamine transmission is important for the retrieval/expression, but not the formation, of conditioned fear. The reduction of conditioned fear by prefrontal infusion of both cis-flupenthixol and D-amphetamine may reflect normal expression of conditioned fear requires an optimal level of mPFC dopamine activity.
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