Cerebral Hemispheres 2
NEUROSCIENTIFICALLY CHALLENGED

NEUROSCIENCE MADE SIMPLER

Cocaine's Addictive Influence Begins Even Before Euphoria


It has long been known in the addiction field that exposure to drug-associated stimuli, commonly referred to as relapse triggers, is one of the primary causes of relapse in abstinent addicts. Neuroscience studies have added evidential support for this perspective by providing a molecular explanation for it. It is thought to principally involve two neurotransmitters: dopamine and glutamate, and a region of the reward system called the ventral tegmental area (VTA).

The VTA is part of the midbrain, and two major dopamine pathways—the mesolimbic and mesocortical—run through it. It is chock full of dopamine, glutamate, and GABA neurons. When a subject who has acquired the self-administration of a drug like cocaine is exposed to environmental stimuli they have associated with the drug, glutamate and dopamine are released from the VTA. This rush of neurotransmitters activates another area of the reward system, the nucleus accumbens, and usually leads to an attempt to reinstate drug-using behavior.

As might be expected, cocaine use itself also results in increased dopamine and glutamate transmission in the VTA. Interestingly, however, this increased neurotransmitter activity begins before the pharmacological effects of cocaine can occur. While it takes about 10 seconds for cocaine to cross the blood-brain barrier and exert its psychotropic influence, dopamine levels rise almost immediately. Thus, it would seem that the reinforcing qualities of the drug may not be solely attributable to the euphoria it produces.

Roy Wise, Bin Wang, and Zhi-Bing You published an article last week in PloS One that investigates this phenomenon. They injected cocaine methiodide (MI)—an analogue to cocaine that does not cross the blood-brain barrier to have a psychotropic effect—into rats and measured the resultant changes in neurotransmitter levels.

In rats that had never been exposed to cocaine, the MI had no effect. But in those that had previously acquired cocaine self-administration, the MI caused VTA glutamate release. It was also enough to cause these rats to reacquire cocaine-seeking behavior that had been rendered extinct.

This study speaks to the complexity and potency of the inclination toward relapse. While it has been known that external cues can cause changes in brain chemistry that predispose one toward relapse, this is the first evidence that internal cues (besides the actual rewarding mental influences of the drug) may also play a role in reinstating drug use. Fortunately, these added influences can be avoided by continued abstinence from the drug. But once a drug is used, how pleasurable the resultant experience is may have little to do with the re-emergence of drug cravings.

 

Roy A. Wise, Bin Wang, Zhi-Bing You, Antonio Verdejo García (2008). Cocaine Serves as a Peripheral Interoceptive Conditioned Stimulus for Central Glutamate and Dopamine Release. PLoS ONE, 3 (8) DOI:10.1371/journal.pone.0002846

YOUR BRAIN, EXPLAINED

Sleep. Memory. Pleasure. Fear. Language. We experience these things every day, but how do our brains create them? Your Brain, Explained is a personal tour around your gray matter. Building on neuroscientist Marc Dingman’s popular YouTube series, 2-Minute Neuroscience, this is a friendly, engaging introduction to the human brain and its quirks using real-life examples and Dingman’s own, hand-drawn illustrations.

  • An informative, accessible and engaging book for anyone who has even the slightest interest in how the brain works, but doesn’t know where to begin. - Dean Burnett, PhD, author, Happy Brain and Idiot Brain

  • ...a highly readable and accessible introduction to the operation of the brain and current issues in neuroscience... a wonderful introduction to the field. - Frank Amthor, PhD, Professor of Psychology, The University of Alabama at Birmingham, author, Neuroscience for Dummies

  • Dingman weaves classic studies with modern research into easily digestible sections, to provide an excellent primer on the rapidly advancing field of neuroscience. - Moheb Costandi, author, Neuroplasticity and 50 Human Brain Ideas You Really Need to Know

  • Reading like a collection of detective stories, Your Brain, Explained combines classic cases in the history of neurology with findings stemming from the latest techniques used to probe the brain’s secrets. - Stanley Finger, PhD, Professor Emeritus of Psychological & Brain Sciences, Washington University (St. Louis), author, Origins of Neuroscience

BIZARRE

This book shows a whole other side of how brains work by examining the most unusual behavior to emerge from the human brain. In it, you'll meet a woman who is afraid to take a shower because she fears her body will slip down the drain, a man who is convinced he is a cat, a woman who compulsively snacks on cigarette ashes, and many other unusual cases. As uncommon as they are, each of these cases has something important to teach us about everyday brain function.

  • Dingman brings the history of neuroscience back to life and weaves in contemporary ideas seamlessly. Readers will come along for the ride of a really interesting read and accidentally learn some neuroscience along the way. - Erin Kirschmann, PhD, Associate Professor of Psychology & Counseling, Immaculata University

  • A unique combination of storytelling and scientific explanation that appeals to the brain novice, the trained neuroscientist, and everyone in between. Dingman explores some of the most fascinating and mysterious expressions of human behavior in a style that is case study, dramatic novel, and introductory textbook all rolled into one. - Alison Kreisler, PhD, Neuroscience Instructor, California State University, San Marcos

  • Through case studies of both exceptional people as well as those with disorders, Bizarre takes us on a fascinating journey in which we learn more about what is going on in our skull. - William J. Ray, PhD, Emeritus Professor of Psychology, The Pennsylvania State University, author, Abnormal Psychology

  • Bizarre is a collection of stories of how the brain can create zombies, cult members, extra limbs, instant musicians, and overnight accents, to name a few of the mind-scratching cases. After reading this book, you will walk away with a greater appreciation for this bizarre organ. If you are a fan of Oliver Sacks' books, you're certain to be a fan of Dingman's Bizarre. - Allison M. Wilck, PhD, Researcher and Assistant Professor of Psychology, Eastern Mennonite University