α7 Nicotinic acetylcholine receptors in the central amygdaloid nucleus alter naloxone-induced withdrawal following a single exposure to morphine.
BACKGROUND
Negative motivational withdrawal from acute opiate dependence was induced by an opioid antagonist, and the withdrawal signs prevented by pretreatment with nicotine.


OBJECTIVE
The present study was undertaken to examine the mechanism of nicotine-induced attenuation of withdrawal precipitated by naloxone in rats administered a single dose of morphine.


METHODS
Conditioned place aversion (CPA) was precipitated by naloxone in rats exposed once to morphine. Nicotinic acetylcholine receptor (nAChR) agonists were microinjected into the central amygdaloid nucleus (CeA) before naloxone was administered. Additionally, c-Fos expression in the amygdala was measured in rats exposed to α7 nAChR ligands.


RESULTS
The microinjection of nicotine (0.3 and 1.0 μg/μl) into the CeA dose-dependently inhibited naloxone-induced CPA. This inhibition of CPA was reversed by methyllycaconitine (MLA), an α7 nAChR antagonist. CPA was also significantly attenuated by the microinjection of tropisetron (3.0 μg/μl), an α7 nAChR agonist and 5-hydroxytriptamine 3 (5-HT(3)) receptor antagonist, but not by ondansetron (1.0 and 3.0 μg/μl), a 5-HT(3) receptor antagonist. The microinjection of PNU-282987 (3.0 μg/μl), a selective α7 nAChR agonist, into the CeA also inhibited CPA. Furthermore, nicotine increased c-Fos expression in the CeA, but not the medial or basolateral amygdaloid nucleus. The increase of c-Fos in the CeA was significantly inhibited by MLA.


CONCLUSIONS
Nicotine-induced attenuation of CPA precipitated by naloxone is mediated by the α7 nAChR subtype, and the CeA is one of the regions of the brain involved in the effect of nicotine on acutely opiate-dependent subjects.
Department of Clinical Pharmacy, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1, Shikata-cho, Kita-ku, Okayama, 700-8558, Japan.
Shigeru
S
Ishida
Yoichi
Y
Kawasaki
Hiroaki
H
Araki
Masato
M
Asanuma
Hisashi
H
Matsunaga
Toshiaki
T
Sendo
Hiromu
H
Kawasaki
Yutaka
Y
Gomita
Yoshihisa
Y
Kitamura
D000679:Amygdala / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003213:Conditioning, Psychological / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D008297:Male; D008845:Microinjections; D009020:Morphine / Q000009:adverse effects*; D009270:Naloxone / Q000494:pharmacology*; D018722:Nicotinic Agonists / Q000494:pharmacology / Q000627:therapeutic use; D018733:Nicotinic Antagonists / Q000494:pharmacology / Q000627:therapeutic use; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000378:metabolism / Q000502:physiology*; D013375:Substance Withdrawal Syndrome / Q000378:metabolism / Q000517:prevention & control* / Q000523:psychology; D064569:alpha7 Nicotinic Acetylcholine Receptor
C579165:Chrna7 protein, rat; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D016760:Proto-Oncogene Proteins c-fos; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D009270:Naloxone; D009020:Morphine