Smoking And Heroine Have Surprisingly Similar Affect On Brain’s Reward System
“That was good!” “Do it again.” This is what the rat brain says when researchers use nicotine, as well as ‘hard drugs’ such as heroin with it in the laboratory. New research indicates that the effects of nicotine and opiates on the brain’s reward system are equally strong in a key pleasure-sensing areas of the brain — the nucleus accumbens.“Testing rat brain tissue, we found remarkable overlap between the effects of nicotine and opiates on dopamine signaling within the brain’s reward centers,” says Daniel McGehee, Associate Professor in Anesthesia & Critical Care at the University of Chicago Medical Center.
McGehee and colleagues are exploring the control of dopamine, a key neurotransmitter in reward and addiction. Dopamine is released in areas such as the nucleus accumbens by naturally rewarding experiences such as food, sex, some drugs, and the neutral stimuli or ‘cues’ that become associated with them.
Nicotine and opiates are very different drugs, but the endpoint, with respect to the control of dopamine signaling, is almost identical. “There is a specific part of the nucleus accumbens where opiates have been shown to affect behavior, and when we tested nicotine in that area, the effects on dopamine are almost identical,” says McGehee.
This research is important to scientists because it demonstrates overlap in the way the two drugs work, complementing previous studies that showed overlapping effects on physiology of the ventral tegmenal area, another key part of the brain’s reward circuitry. The hope is that this study will help identify new methods for treating addiction — and not just for one drug type.
“It also demonstrates the seriousness of tobacco addiction, equating its grip on the individual to that of heroin. It reinforces the fact that these addictions are very physiological in nature and that breaking away from the habit is certainly more than just mind over matter,” says McGehee. This is certainly a preposterous conclusion from rat brain experiments. Clinical evidence with humans proves at least, that quitting cigarettes is ways more often successful than quitting heroin.J Neurosci. 2008 Feb 13;28(7):1672-81.
Committee on Neurobiology, University of Chicago, Chicago, Illinois 60637, USA.
Behaviorally relevant stimuli prompt midbrain dopamine (DA) neurons to switch from tonic to burst firing patterns. Similar shifts to burst activity are thought to contribute to the addictive effects of opiates and nicotine. The nucleus accumbens DA overflow produced by these drugs is a key element in their pathological effects. Using electrochemical techniques in brain slices, we explored the effects of opioids on single-spike and burst stimuli-evoked DA overflow in the dorsal and ventral striatum. In specific subregions of the nucleus accumbens, mu-opioids inhibit DA overflow elicited with single-spike stimuli while leaving that produced by burst stimuli unaffected. This is similar to published effects of nicotinic receptor blockade or desensitization, and is mediated by opioid receptor-induced inhibition of cholinergic interneurons. Whereas delta-opioids have similar effects, kappa-opioids inhibit evoked DA overflow throughout the striatum in a manner that is not overcome with high-frequency stimuli. These observations reveal remarkable mechanistic overlap between the effects of nicotine and opiates within the dopamine reward pathway.