Memory-Boosting Drug Reduces Drug Cues for Cocaine Addicts
D-cycloserine has long been approved by the Food and Drug Administration (FDA) as an antibiotic for treating tuberculosis, but has also been found to be effective in combined treatments for obsessive-compulsive disorder, anxiety, fear/phobias, social anxiety disorder, autism, and chronic neuropathic pain. Although it is only used as an antibiotic in cases of tuberculosis, D-cycloserine is also a central nervous system stimulant that causes action on certain neurotransmitter receptors for glutamate—a chemical involved in the brain’s learning and memory function.
Lead researcher Dr. Mary Torregrossa and colleagues used the old drug that is known to have little occurrences of serious side effects in combination with behavioral therapy on rats that self-administered cocaine for several weeks. The rats’ behavioral habits regarding self-administered cocaine consumption are considered to mimic the habits of human drug consumption. The researchers’ findings were published in the August 4 online issue of The Journal of Neuroscience.
The researchers’ study involved 168 male Sprague Dawley rats who were trained to self-administer cocaine in response to drug-taking cues for weeks. Then, the drug-taking cues were removed under a treatment method known as extinction therapy. This type of behavioral therapy trains the addict’s mind to disassociate drug-taking cues from the motivation to seek or consume drugs. For example, even after completing rehabilitation therapy, a recovered cocaine addict may be incited to take cocaine once again in response to visual cues like seeing a former drug dealer or a location where the individual once consumed drugs, and scent cues like the smell of fumes. For this reason, drug addicts have a high tendency to relapse into their previous drug habits.
Extinction therapy, which has been effective in suppressing drug cravings and preventing relapse in numerous studies, tends to work best in controlled environments, like a treatment facility. So far, it has been difficult to maintain the suppression of drug cravings long after the addict has completed recovery. With the addition of D-cycloserine to this therapy, the efficacy of extinction therapy is expanded beyond where the therapy takes place, giving the recovered addict a better chance to avoid relapse.
In the researchers’ study, the drug-taking cue was removed from the rats’ accustomed drug-taking environment or a controlled environment that discourages drug-consuming behavior, much like human extinction therapy. Then the rats were administered D-cycloserine immediately following the drug cue extinction therapy to help them retain extinction learning. After receiving an extinction therapy session while in the therapeutic environment, the rats were administered the drug to a specific brain region called the nucleus accumbens core, where the formation of drug addiction and drug-related memories are believed to take place. Following this post-extinction D-cycloserine administration, the rats were less likely to reinstate drug-seeking behavior when exposed to the drug-taking environment. In order to be effective, the researchers found, D-cycloserine had to be administered following the extinction therapy; otherwise the rats were not as well capable of resisting cue-induced relapse.
The researchers’ study models the efficacy of extinction therapy combined with pharmacological therapy for the treatment of addiction. D-cycloserine removed the context-specificity of extinction therapy, making recovery from cocaine possible beyond rehabilitation therapy.
Sources: Science Daily, Memory-Boosting Drug May Help Cocaine Addicts Avoid Relapse, August 4, 2010
The Journal of Neuroscience, Mary T. Torregrossa, Hayde Sanchez, and Jane R. Taylor, D-Cycloserine Reduces the Context Specificity of Pavlovian Extinction of Cocaine Cues through Actions in the Nucleus Accumbens, August 4, 2010