Decreased Signs of Nicotine Withdrawal in Mice Null for the β4 Nicotinic Acetylcholine Receptor Subunit

Abstract

Withdrawal from chronic exposure to nicotine, the main addictive component of tobacco, produces distinctive symptoms in humans. The appearance of these symptoms is a major deterrent when people try to quit smoking. To study which type of nicotine receptor is relevant for the onset of the withdrawal syndrome, we used a mouse model of nicotine withdrawal. Wild-type mice and mice null for the ␤4 (␤4Ϫ/Ϫ) or the ␤2 (␤2Ϫ/Ϫ) nicotinic acetylcholine receptor subunits were implanted with osmotic minipumps delivering 24 mg ⅐ kg Ϫ1 ⅐ d Ϫ1 nicotine for 13 d. Subsequently, a single intraperitoneal injection of the nicotinic receptor antagonist mecamylamine induced behavioral symptoms of withdrawal measured as increased grooming, chewing, scratching, and shaking, plus the appearance of some unique behaviors such as jumping, leg tremors, and cage scratching. Mecamylamine injection triggered comparable withdrawal signs in wild-type and in ␤2Ϫ/Ϫ mice, whereas the ␤4Ϫ/Ϫ mice displayed significantly milder somatic symptoms. In addition, nicotine withdrawal produced hyperalgesia in wild-type but not ␤4 Ϫ/Ϫ mice. Finally, chronic nicotine produced an increase in epibatidine binding in several areas of the brain in both wild-type and in ␤4Ϫ/Ϫ mice, but such receptor upregulation did not correlate with the severity of withdrawal signs.Our results demonstrate a major role for ␤4-containing nicotinic acetylcholine receptors in the appearance of nicotine withdrawal symptoms. In contrast, the ␤2 subunit does not seem to greatly influence this phenomenon. We also show that the upregulation of epibatidine binding sites attributable to chronic nicotine, an effect associated with ␤2-containing receptors, is probably not related to the mechanisms underlying withdrawal.

β2 subunit containing acetylcholine receptors mediate nicotine withdrawal deficits in the acquisition of contextual fear conditioning

“…Genetic knockout studies have resolved this issue. β2 KO mice showed somatic symptoms, such as excessive rearing, body shakes or over-grooming, during withdrawal precipitated by the broad-spectrum nAChR antagonist mecamylamine (Besson et al, 2006;Salas, Pieri, & De Biasi, 2004). In contrast, β4 KO mice exhibited significantly reduced somatic symptoms during mecamylamine-precipitated withdrawal (Salas et al, 2004), suggesting that somatic symptoms of nicotine withdrawal involve β4-containing but not β2-containing nAChRs.…”

“…β2 KO mice showed somatic symptoms, such as excessive rearing, body shakes or over-grooming, during withdrawal precipitated by the broad-spectrum nAChR antagonist mecamylamine (Besson et al, 2006;Salas, Pieri, & De Biasi, 2004). In contrast, β4 KO mice exhibited significantly reduced somatic symptoms during mecamylamine-precipitated withdrawal (Salas et al, 2004), suggesting that somatic symptoms of nicotine withdrawal involve β4-containing but not β2-containing nAChRs. Overall, these investigations together with the current findings demonstrate that β2-containing nAChRs are involved in the effects of nicotine on learning, reward/reinforcement, and cognitive withdrawal symptoms, but not somatic nicotine withdrawal symptoms.…”

Genetic variability in nicotinic acetylcholine receptors and nicotine addiction: Converging evidence from human and animal research

“…In contrast, the somatic symptoms of nicotine withdrawal are present in both β2 KO and WT mice, suggesting that the somatic symptoms of nicotine withdrawal are mediated by other nAChR subunits [7,77,146]. Research with other nAChR subunit KO mice has demonstrated that the β4 [146], α5 [77], and α7 nAChR subunits [148] likely mediate the somatic symptoms of withdrawal. Thus, these studies provide evidence that the various symptoms of nicotine withdrawal are mediated by different nAChR subunits.…”

“…Finally, β4 KO mice have been tested for several phenotypes and show some similarity to α3 and α5 KO mice. For example, β4 KO mice exhibit reduced sensitivity to the hypolocomotor effects of nicotine, have increased resistance to nicotine-induced seizures, and show reduced somatic signs during nAChR antagonist-precipitated withdrawal when compared to WT mice [147,146]. Furthermore, the core body temperature of β4 KO mice is lower than WT mice, and the effects of nicotine on body temperature are reduced in the KO mice [143].…”

Functional Characterization of AT-1001, an α3β4 Nicotinic Acetylcholine Receptor Ligand, at Human α3β4 and α4β2 nAChR

“…[7][8][9][10][11] Further, studies in knockout mice show that the β4 nAChR subunit is necessary for nicotine withdrawal because withdrawal is greatly diminished in β4 null mice, but not in β2 null mice. 12,13 Unlike the wide distribution of α4β2 nAChR in the brain, the α3 and β4 subunits are expressed in a restricted number of brain areas, mainly the medial habenula and interpeduncular nucleus, major cholinergic tracts in the brain that have recently garnered increasing attention for their involvement in various aspects of nicotine dependence. [14][15][16][17] Consistent with the genetic and knockout studies, a transgenic mouse model overexpressing the human CHRNA5/Α3/Β4 genomic cluster showed significantly increased β4* nAChR binding in the medial habenula and increased acquisition of nicotine self-administration.…”