trans-metanicotine and Cerebellar-Ataxia

We have demonstrated that nicotine attenuated ethanol-induced ataxia via nicotinic-acetylcholine-receptor (nAChR) subtypes α(4)β(2) and α(7). In the present study, ethanol (2g/kg; i.p.)-induced ataxia was assessed by Rotorod performance following repeated intracerebellar infusion of α(4)β(2)- and α(7)-selective agonists. Localization of α(4)β(2) and α(7) nAChRs was confirmed immunohistochemically. Cerebellar NO(x) (nitrite+nitrate) was determined flurometrically. Repeated intracerebellar microinfusion of the α(4)β(2)-selective agonist, RJR-2403 (for 1, 2, 3, 5 or 7 days) or the α(7)-selective agonist, PNU-282987 (1, 2, 3 or 5 days), dose-dependently attenuated ethanol-induced ataxia. These results suggest the development of cross-tolerance between ethanol-induced ataxia and α(4)β(2) and α(7) nAChR agonists. With RJR-2403, the cross-tolerance was maximal after a 5-day treatment and lasted 48h. Cross-tolerance was maximal after a 1-day treatment with PNU-282987 and lasted 72h. Pretreatment with α(4)β(2)- and α(7)-selective antagonists, dihydro-β-erythroidine and methyllycaconitine, respectively, prevented the development of cross-tolerance confirming α(4)β(2) and α(7) involvement. Repeated agonist infusions elevated cerebellar NO(x) 16h after the last treatment while acute ethanol exposure decreased it. Pretreatment with repeated RJR-2403 or PNU-282987 reversed ethanol-induced decrease in NOx. The NO(x) data suggests the involvement of the nitric oxide (NO)-cGMP signaling pathway in the cross-tolerance that develops between α(4)β(2)- and α(7)-selective agonists and ethanol ataxia. Both α(4)β(2) and α(7) subtypes exhibited high immunoreactivity in Purkinje but sparse expression in molecular and granular cell layers. Our results support a role for α(4)β(2) and α(7) nAChR subtypes in the development of cross-tolerance between nicotine and ethanol with the NO signaling pathway as a potential mechanism.

Topics: alpha7 Nicotinic Acetylcholine Receptor; Animals; Behavior, Animal; Benzamides; Bridged Bicyclo Compounds; Cerebellar Ataxia; Cerebellum; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Drug Tolerance; Ethanol; Injections, Intraventricular; Male; Mice; Motor Activity; Nicotine; Nicotinic Agonists; Nitrates; Nitrites; Psychomotor Performance; Receptors, Nicotinic; Time Factors

We have recently reported that mediation of intracerebellar nicotine-induced attenuation of cerebellar delta9-THC ataxia was via the alpha4beta2 nAChR. The present study was meant to investigate the role of cerebellar nitric oxide (NO)-guanylyl cyclase (GC) signaling in the alpha4beta2-mediated attenuation in CD-1 male mice. Drugs were given via intracerebellar microinfusion using stereotaxically implanted guide cannulas, with ataxia evaluated by Rotorod. Intracerebellar microinfusion of SNP (sodium nitroprusside, NO donor; 15, 30, 60 pg) and SMT (S-methylisothiourea, inhibitor of inducible NO synthase; 70, 140, 280 fg) significantly enhanced and reduced, respectively, intracerebellar RJR-2403 (selective alpha4beta2 agonist)-induced attenuation of delta9-THC ataxia dose-dependently. Intracerebellar isoliquiritigenin (GC-activator; 1, 2, 4 pg) and ODQ (1H[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, GC inhibitor; 200, 400, 800 fg), significantly enhanced and reduced, respectively, intracerebellar RJR-2403-induced attenuation of delta9-THC ataxia dose-dependently. Further support for the role of NO was evidenced via increases in cerebellar NO(x) (nitrate+nitrite) levels following microinfusion of nicotine or RJR-2403 as compared to control, whereas delta9-THC significantly decreased NO(x) levels. "Nicotine/RJR-2403+delta9-THC" treated mice had cerebellar NO(x) levels significantly increased as compared to mice infused with delta9-THC alone. Results of the present investigation support the role of cerebellar NO-GC signaling in alpha4beta2 nAChR subtype-mediated attenuation of delta9-THC ataxia.

Topics: Animals; Area Under Curve; Cerebellar Ataxia; Cerebellum; Chalcones; Cyclic GMP; Dronabinol; Enzyme Inhibitors; Guanylate Cyclase; Male; Mice; Microinjections; Nicotine; Nicotinic Agonists; Nitric Oxide; Nitroprusside; Oxadiazoles; Postural Balance; Quinoxalines; Receptor, Cannabinoid, CB1; Receptors, Nicotinic; Stereotaxic Techniques

We have previously demonstrated that acute intracerebellar nicotine or N-methyl-4-(3-pyridinyl)-3-buten-1-amine (RJR-2403), a selective alpha(4)beta(2) nicotinic acetylcholine receptor (nAChR) agonist, dose dependently attenuates Delta(9)-tetrahydrocannabinol (Delta(9)THC)-induced ataxia. Presently, we have shown that intracerebellar nicotine (1.25, 2.5, and 5 ng; once daily for 5 days) and RJR-2403 (250, 500, and 750 ng; once daily for 5 days) significantly attenuate cerebellar Delta(9)-THC-induced ataxia dose dependently, suggesting the development of cross-tolerance between nicotine or RJR-2403 with Delta(9)-THC in male CD-1 mice. Intracerebellar RJR-2403 (750 ng) microinfused for 1, 2, 3, 5, and 7 days (once daily) significantly attenuated Delta(9)-THC-induced ataxia in the 3-, 5-, and 7-day treatment groups; optimal cross-tolerance was evident at day 5 and persisted till 36 h after the last RJR-2403 microinfusion. Intracerebellar microinfusion of hexamethonium (nAChR antagonist; 1 microg) or dihydro-beta-erythroidine hydrobromide (alpha(4)beta(2) nAChR antagonist; 500 ng) for 5 days 10 min before daily intracerebellar nicotine or RJR-2403 microinfusion virtually abolished cross-tolerance between nicotine or RJR-2403 and Delta(9)-THC, indicating nAChR participation. In addition, microinfusion of antagonists 10 min after daily intracerebellar nicotine or RJR-2403 failed to alter the cross-tolerance, suggesting possible involvement of downstream cerebellar second-messenger mechanisms. Finally, the cerebellar concentration of nitric oxide products [total sum of nitrite + nitrate (NO(x))] was increased after 5 days of intracerebellar nicotine or RJR-2403 treatment, which was decreased by acute intracerebellar Delta(9)-THC treatment. The "nicotine or RJR-2403 + Delta(9)-THC" treatments significantly increased cerebellar NO(x) levels compared with treatment with Delta(9)-THC alone, supporting a functional correlation between cerebellar nitric oxide production and cerebellar Delta(9)-THC-induced ataxia and suggesting participation of nitric oxide in the observed cross-tolerance between nicotine/RJR-2403 and Delta(9)-THC.

Topics: Animals; Cerebellar Ataxia; Cerebellum; Dihydro-beta-Erythroidine; Dronabinol; Drug Tolerance; Hexamethonium; Male; Mice; Nicotine; Nitric Oxide

In spite of widespread association of nicotine and cannabinoids in humans, very few studies in which nicotine and cannabinoids are co-administered have been reported. Previously, we have reported that intracerebellar (ICB) Delta(9)-tetrahydrocannabinol (Delta(9)-THC) produces dose-dependent cerebellar ataxia. The present study investigated the functional consequences of ICB microinfusion of nicotine on ICB Delta(9)-THC ataxia in CD-1 male mice. Nicotine (0.625, 1.25, 2.5, 5 ng; ICB) markedly attenuated Delta(9)-THC ataxia dose dependently, which was abolished by ICB hexamethonium (5 microg), thus suggesting that the attenuation by nicotine occurred via the nicotinic acetylcholine receptor (nAChR). To further investigate which specific nAChR subtype was involved, ICB microinfusion of RJR-2403 (250, 375, 500, 750 ng), a alpha(4)beta(2) selective nAChR agonist, markedly attenuated Delta(9)-THC ataxia. DHbetaE (500 ng), a alpha(4)beta(2) selective nAChR antagonist, virtually abolished RJR-2403-induced attenuation of Delta(9)-THC ataxia. ICB microinfusion of MLA, a alpha(7) selective nAChR antagonist (1, 5 microg) failed to antagonize nicotine or RJR-2403-induced attenuation of Delta(9)-THC ataxia. This suggested a lack of a role of the alpha(7) subtype and further reinforced the significance of alpha(4)beta(2). Additionally, ICB treatment with DHbetaE virtually abolished nicotine-induced attenuation of Delta(9)-THC ataxia that suggested alpha(4)beta(2) as the primary cerebellar nAChR subtype. Lack of effect of ICB DHbetaE or MLA alone on Delta(9)-THC ataxia ruled out a tonic effect of the alpha(4)beta(2) subtype. The results of the present investigation, therefore, strongly support involvement of the cerebellar alpha(4)beta(2), but not alpha(7), nicotinic receptor subtype in the mediation via nicotine and RJR-2403 on attenuation of Delta(9)-THC ataxia.

Topics: alpha7 Nicotinic Acetylcholine Receptor; Animals; Cannabinoid Receptor Agonists; Cerebellar Ataxia; Cerebellum; Disease Models, Animal; Dose-Response Relationship, Drug; Dronabinol; Drug Synergism; Hexamethonium; Male; Marijuana Abuse; Mice; Microinjections; Nicotine; Nicotinic Agonists; Nicotinic Antagonists; Receptors, Cannabinoid; Receptors, Nicotinic; Smoking; Time Factors