D-cycloserine and the facilitation of extinction of conditioned fear: consequences for reinstatement

Psychosocial approaches of acute stress reactions

What are the conceptual and empirical bases for current interventions for acute stress reactions following trauma exposure? This review compares the two major alternatives to managing acute stress reactions, outlines their conceptual bases and critiques the evidence for their efficacy in preventing subsequent stress disorders. The review integrates current evidence for cognitive behavior therapy with recent neuroscience findings that fear reduction learning can be enhanced by modulating glutamatergic systems. D-cycloserine provides exciting opportunities to enhance the effects of cognitive-behavioral therapy, and points to closer understanding of the biological mechanisms that underpin clinical gains achieved by psychological therapies.

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

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-methyl-d-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 microM/side, bilaterally). Furthermore, phosphatidylinositol 3-kinase inhibitor (wortmannin, 5.0 microg/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 microg dissolved in 1.6 microl vehicle; 0.8 microl per side) and a translation inhibitor (anisomycin, 125 microg dissolved in 1.6 microl vehicle; 0.8 microl 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 mitogen-activated 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.

Learning and memory

Learning and memory processes are thought to underlie a variety of human psychiatric disorders, including generalised anxiety disorder and post-traumatic stress disorder. Basic research performed in laboratory animals may help to elucidate the aetiology of the respective diseases. This chapter gives a short introduction into theoretical and practical aspects of animal experiments aimed at investigating acquisition, consolidation and extinction of aversive memories. It describes the behavioural paradigms most commonly used as well as neuroanatomical, cellular and molecular correlates of aversive memories. Finally, it discusses clinical implications of the results obtained in animal experiments in respect to the development of novel pharmacotherapeutic strategies for the treatment of human patients.

Facilitation of fear extinction by D-cycloserine: theoretical and clinical implications

Anxiety disorders are among the most common psychological disturbances in the industrialized world. Current behavioral therapy procedures for these disorders are somewhat effective, but their efficacy could be substantially improved. Because these procedures are largely based on the process of extinction, manipulations that enhance extinction may lead to improvements in treatment effectiveness. We review the evidence that D-cycloserine (DCS), a partial NMDA agonist, facilitates extinction of learned fear in rats. Although only a few studies have examined the effects of DCS on extinction of learned fear, this work suggests that this drug may have a number of potential clinical benefits. In addition, attempts at interpreting this research illustrate our limited understanding of the processes involved in extinction.