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Nicotine is a potent parasympathomimetic alkaloid found in the nightshade family of plants (Solanaceae) and is a stimulant drug. Nicotine is a nicotinic acetylcholine receptor (nAChR) agonist,〔 except at nAChRα9 and nAChRα10 where it acts as an antagonist. It is made in the roots of and accumulates in the leaves of the nightshade family of plants. Nicotine is found in the leaves of ''Nicotiana rustica'' in amounts of 2–14%, the tobacco plant ''Nicotiana tabacum'', ''Duboisia hopwoodii'' and ''Asclepias syriaca''. It constitutes approximately 0.6–3.0% of the dry weight of tobacco〔(【引用サイトリンク】title=Smoking and Tobacco Control Monograph No. 9 )〕 and is present in the range of 2–7 µg/kg of various edible plants.〔(【引用サイトリンク】title=Determination of the Nicotine Content of Various Edible Nightshades (Solanaceae) and Their Products and Estimation of the Associated Dietary Nicotine Intake )〕 It functions as an antiherbivore chemical; consequently, nicotine was widely used as an insecticide in the past〔 〕 and neonicotinoids such as imidacloprid are currently widely used. Nicotine is addictive.〔 In lesser doses (an average cigarette yields about 2 mg of absorbed nicotine), the substance acts as a stimulant in mammals, while high amounts (50–100 mg) can be harmful.〔(【引用サイトリンク】title=Nicotine (PIM) )〕〔(【引用サイトリンク】 How Drugs Can Kill )〕〔 This stimulant effect is a contributing factor to the addictive properties of tobacco smoking. Nicotine's addictive nature includes psychoactive effects, drug-reinforced behavior, compulsive use, relapse after abstinence, physical dependence and tolerance. Nicotine is associated with cardiovascular disease, potential birth defects, and poisoning.〔 ''In vitro'' studies have associated it with cancer, but carcinogenicity has not been demonstrated ''in vivo''.〔 There is inadequate research to demonstrate that nicotine is associated with cancer in humans.〔 ''Medicinal'' nicotine as a tool to quitting smoking has a good safety history.〔 During pregnancy, there are risks to child later in life for type 2 diabetes, obesity, hypertension, neurobehavioral defects, respiratory dysfunction, and infertility.〔 Nicotine is regarded as a potentially lethal poison.〔 It is unlikely that a person would overdose on nicotine through smoking alone.〔 The use of electronic cigarettes, which are designed to be refilled with nicotine-containing e-liquid, has renewed interest in nicotine overdoses, especially with regard to the possibility of young children ingesting the liquids.〔 ==Psychoactive effects== Nicotine's mood-altering effects are different by report: in particular it is both a stimulant and a relaxant. First causing a release of glucose from the liver and epinephrine (adrenaline) from the adrenal medulla, it causes stimulation. Users report feelings of relaxation, sharpness, calmness, and alertness. Like any stimulant, it may very rarely cause the often uncomfortable akathisia. By reducing the appetite and raising the metabolism, some smokers may lose weight as a consequence. When a cigarette is smoked, nicotine-rich blood passes from the lungs to the brain within seven seconds and immediately stimulates nicotinic acetylcholine receptors; this indirectly promotes the release of many chemical messengers such as acetylcholine, norepinephrine, epinephrine, arginine vasopressin, serotonin, dopamine, and beta-endorphin in parts of the brain. Nicotine also extends the duration of positive effects of dopamine and increases sensitivity in brain reward systems. Most cigarettes contain 1–3 milligrams of inhalable nicotine. Studies suggest that when smokers wish to achieve a stimulating effect, they take short quick puffs, which produce a low level of blood nicotine. Nicotine is unique in comparison to most drugs, as its profile changes from stimulant to sedative with increasing dosages and use, a phenomenon described by Paul Nesbitt in his doctoral dissertation〔Nesbitt P (1969). Smoking, physiological arousal, and emotional response. Unpublished doctoral dissertation, Columbia University.〕 and subsequently referred to as "Nesbitt's paradox." 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「nicotine」の詳細全文を読む スポンサード リンク
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