Role of α7- and β4-containing nicotinic acetylcholine receptors in the affective and somatic aspects of nicotine withdrawal: studies in knockout mice.
To assess which nicotinic acetylcholine receptors (nAChRs) are involved in the aversive aspects of nicotine withdrawal, brain reward function and the somatic signs of nicotine withdrawal were assessed in mice that lack α7 and β4 nAChR subunits. Brain reward function was assessed with the intracranial self-stimulation (ICSS) procedure, in which elevations in ICSS thresholds reflect an anhedonic mood state. At 3-6 h of spontaneous nicotine/saline withdrawal, thresholds were elevated in nicotine-withdrawing α7(+/+) and β4(+/+), but not α7(-/-) or β4(-/-), mice compared with saline-withdrawing mice, indicating a delay in the onset of withdrawal in the knockout mice. From 8 to 100 h of withdrawal, thresholds in α7(+/+) and α7(-/-) mice were equally elevated, whereas thresholds in β4(+/+) and β4(-/-) mice returned to baseline levels. Somatic signs were attenuated in nicotine-withdrawing β4(-/-), but not α7(-/-), mice. Administration of a low dose of the nAChR antagonist mecamylamine induced threshold elevations in α7(-/-), but not α7(+/+), mice, whereas the highest dose tested only elevated thresholds in α7(+/+) mice. Mecamylamine-induced threshold elevations were similar in β4(-/-) and β4(+/+) mice. In conclusion, null mutation of the α7 and β4 nAChR subunits resulted in a delayed onset of the anhedonic aspects of the spontaneous nicotine withdrawal syndrome. Previous findings of attenuated somatic signs of nicotine withdrawal in β4(-/-), but not α7(-/-), mice were confirmed in the present study, indicating an important role for β4-containing nAChRs in the somatic signs of nicotine withdrawal. The mecamylamine-precipitated withdrawal data suggest that compensatory adaptations may occur in constitutive α7(-/-) mice or that mecamylamine may interact with other receptors besides nAChRs in these mice. In summary, the present results indicate an important role for α7 and β4-containing nAChRs in the anhedonic or somatic signs of nicotine withdrawal.
Department of Psychiatry, School of Medicine, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0603, USA.
Astrid K
AK
Stoker
Berend
B
Olivier
Athina
A
Markou
D000339:Affect / Q000502:physiology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D004343:Drug Implants; D004567:Electrodes, Implanted; D008464:Mecamylamine / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000502:physiology*; D009538:Nicotine / Q000008:administration & dosage / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000008:administration & dosage / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000235:genetics* / Q000502:physiology*; D012653:Self Stimulation; D013375:Substance Withdrawal Syndrome / Q000235:genetics* / Q000523:psychology*; D064569:alpha7 Nicotinic Acetylcholine Receptor
C579166:Chrna7 protein, mouse; C486720:Chrnb4 protein, mouse; D004343:Drug Implants; D009419:Nerve Tissue Proteins; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D008464:Mecamylamine; D009538:Nicotine