Facilitation of Conditioned Fear Extinction by D-Cycloserine Is Mediated by Mitogen-Activated Protein Kinase and Phosphatidylinositol 3-Kinasecascades and Requires de Novo Protein Synthesis in Basolateral Nucleus of Amygdala

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Neuroscience 134 (2005) 247–260

FACILITATION OF CONDITIONED FEAR EXTINCTION BY D-CYCLOSERINE IS MEDIATED BY MITOGEN-ACTIVATED PROTEIN KINASE AND PHOSPHATIDYLINOSITOL 3-KINASE CASCADES AND REQUIRES DE NOVO PROTEIN SYNTHESIS IN BASOLATERAL NUCLEUS OF AMYGDALA Y. L. YANGa AND K. T. LUb*

Institute of Biotechnology, Department of Molecular Biology and Biochemistry, National Chia-Yi University, 300 University Road, Chia-Yi, Taiwan b Department of Life Science, National Taiwan Normal University, 88 Ming-Chow Road, Sec 4, Taipei, Taiwan a

Key words: extinction, D-cycloserine, MAPK, PI-3 kinase, amygdala.

Abstract—Recent results showed that either systemic or intra-amygdala administration of D-cycloserine, a partial agonist at the glycine modulatory site on the glutamate N-methylD-aspartate receptor facilitates the extinction of conditioned fear. Here we evaluated the role of mitogen-activated protein kinase and phosphatidylinositol 3-kinase in the basolateral nucleus of amygdala on the effect of D-cycloserine. The facilitation effect of D-cycloserine on fear extinction and mitogen-activated protein kinase activation was completely blocked by intra-amygdala administration of mitogen-activated protein kinase inhibitor PD98059 (500 ng/side, bilaterally) or U0-126 (20 M/side, bilaterally). Furthermore, phosphatidylinositol 3-kinase inhibitor (wortmannin, 5.0 g/side, bilaterally) infused into the basolateral nucleus of amygdala significantly reduced both facilitation effect of D-cycloserine and phosphatidylinositol 3-kinase activation. Intra-amygdala administration of a transcription inhibitor (actinomycin D, 10 g dissolved in 1.6 l vehicle; 0.8 l per side) and a translation inhibitor (anisomycin, 125 g dissolved in 1.6 l vehicle; 0.8 l per side) completely blocked the facilitation effect of D-cycloserine. Control experiments indicated the blockage by actinomycin D or anisomycin were not due to lasting damage to the basolateral nucleus of amygdala or state dependency. In addition, none of the active drugs used here altered the expression of conditioned fear. These results suggested that phosphatidylinositol 3-kinase and mitogenactivated protein kinase-dependent signaling cascades and new protein synthesis within the basolateral nucleus of amygdala played important roles in the D-cycloserine facilitation of the extinction of conditioned fear. © 2005 Published by Elsevier Ltd on behalf of IBRO. *Corresponding author. Tel: 886-2-29333149x234; fax: 886-229312904. E-mail address: ktlu@cc.ntnu.edu.tw (K.-T. Lu). Abbreviations: ACT DCS, actinomycin D D-cycloserine; ACT SAL, actinomycin D saline; ANI DCS, anisomycin D-cycloserine; ANI SAL, anisomycin saline; BLA, basolateral nucleus of the amygdala; CS, conditioned stimulus; DCS, D-cycloserine; EDTA, ethylenediaminetetraacetic acid; ISI, interstimulus interval; MAPK, mitogen-activated protein kinase; NMDA, N-methyl-D-aspartate; PD DCS, PD98059 D-cycloserine; PD SAL, PD98059 saline; PI-3K, phosphatidylinositol 3-kinase; US, unconditioned stimulus; U0 DCS, U0-126 D-cycloserine; U0 SAL, U0126 saline; VEH DCS, vehicle D-cycloserine; VEH SAL, vehicle saline; WH DCS, wortmannin D-cycloserine; WH SAL, wortmannin saline. 0306-4522/05$30.00 0.00 © 2005 Published by Elsevier Ltd on behalf of IBRO. doi:10.1016/j.neuroscience.2005.04.003

Fear conditioning occurs when a previously neutral stimulus (conditioned stimulus) is paired with an aversive stimulus (McAllister and McAllister, 1971). Following such pairing the conditioned stimulus is thought to elicit a state of conditioned fear. This is defined in animals by their behavior: freezing, autonomic reactivity, and fear-potentiated startle. A large literature indicates that the basolateral nucleus of the amygdala (BLA) is critically involved in both the acquisition and the expression of conditioned fear (Davis, 2000). Neurotoxic lesions or intra-amygdala infusion of glutamate antagonists into the BLA blocks the expression of conditioned fear. In...
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