The dopamine network, in general, provides positive feedback that reinforces our desire to seek out pleasurable activities.īut three years ago, Lammel and his colleagues discovered a parallel dopamine network that responds to unpleasurable stimuli by releasing dopamine into different areas of the brain than does the dopamine reward network. Nicotine, like cocaine and heroin, is known to cause addiction by activating the body's reward network: Nicotine binds to receptors on cells that release the neurotransmitter dopamine into the brain, where it affects everything from pain perception and mood to memory. Lammel, Liu, graduate student Amanda Tose and their colleagues described the brain circuits involved in nicotine aversion in a paper accepted by the journal Neuron and now posted online. "The inhibitory inputs and the desensitization of nicotine receptors on the dopamine neurons themselves both contribute to decreased dopamine signaling in the reward pathway, then decreased feelings of pleasure and, therefore, behavioral aversion," Liu said. from UC Berkeley, also found that nicotine receptors in the reward pathway become desensitized by high doses of nicotine, which probably contributes to the negative experience of high doses. Lammel and Christine Liu, who recently obtained her Ph.D. This could actually be a very effective treatment for nicotine addiction in the future, which we currently do not have." Now that we have an understanding of the different brain circuits, we think we can maybe develop a drug so that, when nicotine is taken at a low dose, these brain circuits can be coactivated to induce an acute aversive effect. "What we found is that the brain circuits that are activated after a high aversive dose are actually different from those that are activated when nicotine is delivered at a low dose. In contrast, the brain circuits that mediate the aversive effects of nicotine are largely understudied," said Stephan Lammel, UC Berkeley associate professor of molecular and cell biology. "Decades of research have focused on understanding how nicotine reward leads to drug addiction and what are the underlying brain circuits. The new research, conducted in mice, suggests that this aversive network could be manipulated to treat nicotine dependence. As a result, nicotine overdoses are rare, though the advent of e-cigarettes has made "nic-sick" symptoms like nausea and vomiting, dizziness, rapid heartbeat and headaches more common. Though most addictive drugs at high doses can cause physiological symptoms that lead to unconsciousness or even death, nicotine is unique in making people physically ill when inhaled or ingested in large quantities. University of California, Berkeley, researchers have now mapped out part of the brain network responsible for the negative consequences of nicotine, opening the door to interventions that could boost the aversive effects to help people quit smoking.
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