Inhibition of nicotine-induced seizures in rats by combining vaccination against nicotine with chronic nicotine infusion

The ability of a nicotine vaccine to protect against nicotine-induced seizures was studied in rats. Groups of 10 rats were vaccinated with 3 doses of either a nicotine conjugate vaccine over 6 weeks to elicit high titers of nicotine-specific antibodies or with a control vaccine. Rats were then pretreated with a 1-week subcutaneous infusion of either nicotine 1 mg/kg/day or saline and then received a single 2 mg/kg ip dose of nicotine to provoke seizures. Vaccination reduced the incidence of seizures. The combination of vaccination and pretreatment with nicotine infusion was more effective than either treatment alone. These data suggest that vaccination is protective against this toxic effect of nicotine and that combining vaccination and chronic nicotine administration may provide a novel strategy for blocking some effects of nicotine.     

Regional myocardial blood flow during nicotine infusion after chronic coronary artery occlusion: effect of beta-adrenergic blockade

In eight dogs a portion of the left ventricular free wall (LVFW) was rendered collateral-dependent (CD) by gradual occlusion of the left anterior descending coronary artery with a surgically implanted Ameroid constrictor. Six to 8 weeks later, the dogs were anesthetized and regional myocardial blood flow was measured with 7-10-micron radioactive microspheres during (a) control conditions, (b) nicotine alone (24 micrograms/kg/min i.v.), and (c) nicotine (24 micrograms/kg/min i.v.) after beta-adrenergic blockade with propranolol. During control conditions, mean transmural flow was similar in CD, border, and normal regions of the LVFW. Nicotine alone increased flow in all regions of the LVFW, with normal (+ 104%) greater than CD (+ 56%). These changes in flow were accompanied by increases in mean arterial pressure (+ 34%) and mean aortic flow (+ 54%). Nicotine after beta-adrenergic blockade appreciably raised mean arterial pressure (+ 83%) and mean left atrial pressure (+ 307%), but caused no increase in flow to any region of the LVFW. The results indicate (a) that the nicotine-induced increase in flow is blunted in a CD region, and that (b) beta-adrenergic blockade unmasks coronary vasoconstrictor mechanisms during nicotine infusion which prevent increases in flow to either normal or CD regions despite increased perfusion pressure and augmented myocardial oxygen demands.     

Stress triggered rise in plasma aldosterone is lessened by chronic nicotine infusion

The ability of nicotine infusion to modulate plasma aldosterone levels in response to different stressors was investigated. Sprague-Dawley rats given nicotine (5 mg/kg/day) or saline for 14 days were subjected to stress. Baseline plasma aldosterone (86+/-17 pmol/l) was unaffected by nicotine. Aldosterone was significantly elevated by restraint (450+/-72 pmol/l) and especially with cold (1249+/-172 pmol/l) or immobilization (1779+/-247 pmol/l) stress. Nicotine infusion attenuated the rise in aldosterone with restraint and cold stress, but not immobilization. These results reveal that nicotine infusion can attenuate the aldosterone response, depending on the type of stress.     

Altered synaptosomal ATPase activity in rat brain following prolonged in vivo treatment with nicotine

Effects of prolonged in vivo treatment with nicotine on synaptosomal ATPase activity in rat brain were examined by employing doses of nicotine (0.02 and 0.04 mg/ml in the drinking water) which simulated intake by moderate and heavy smokers. Under these conditions the "low" dose of nicotine resulted in increased body weight whereas "high" dose of nicotine inhibited weight gain. Examination of synaptosomal ATPase activities revealed a dose and time dependent stimulatory/inhibitory effect. With "low" dose of nicotine, maximum stimulatory effect on ATPase activity was seen at the end of the 3rd week, while "high" dose stimulated the enzyme activities maximally by the 2nd week itself; further treatment up to the 4th week caused inhibition of the ATPase activities (10% to 43% decrease).     

异丙酚麻醉前后鼠脑ATPase活性的动态变化

目的　观察异丙酚 (propofol)麻醉不同时期大鼠大脑皮层、海马和脑干Na+ ,K+ ATPase、Ca2 + ATPase活性的动态变化 ,探讨异丙酚的全麻作用机制。方法　♀SD大鼠 40只 ,按麻醉不同时期随机分为 5组。分别在腹腔注射 (ip) 10ml·kg-1生理盐水 2min后 (对照组 ) ,ip异丙酚 10 0mg·kg-12min后、翻正反射消失前 (诱导期组 ) ,翻正反射消失后 3 0min(麻醉期组 ) ,翻正反射刚恢复、尚未完全清醒时 (恢复期组 ) ,动物完全清醒后 (清醒期组 ) ,断头取脑。用分光光度法测定各脑区Na+ ,K+ ATP酶和Ca2 + ATP酶的活性。结果　与对照组比较 ,异丙酚 10 0mg·kg-1使大脑皮层、海马和脑干的Na+ ,K+ ATP酶和Ca2 + ATP酶的活性在诱导期即降低 ,麻醉期进一步降低 (P <0 0 5 ,P <0 0 1) ,恢复期开始升高 ,但仍低于对照组 ,清醒期基本恢复到对照组水平。结论　异丙酚 10 0mg·kg-1能明显抑制脑ATP酶活性且与行为变化平行 ,提示ATP酶可能在异丙酚的全麻机制中发挥重要作用     

In vitro effects of pyrethroids on rat brain and liver ATPase activities

In vitro sensitivity of rat brain and liver ATPases to pyrethroid insecticides, belonging to three categories based on the structural configuration, was studied. Rat brain and liver P2 fractions were prepared by the conventional centrifugation method, and rat brain synaptosomes were prepared by Ficoll-sucrose gradient centrifugation method. Na+, K+-ATPase and oligomycin-sensitive and -insensitive Mg2+- ATPases were determined in brain P2 fraction, whereas in liver P2 fraction only oligomycin-sensitive and -insensitive Mg2+-ATPase activities were determined. [3H]Ouabain binding studies were carried with rat brain synaptosomes. Most of the pyrethroid compounds tested inhibited brain and liver oligomycin-sensitive Mg2+-ATPases at micromolar concentrations. Type II compounds were more effective as compared to Type I compounds. Oligomycin-insensitive Mg2+-ATPase was not affected by any of the compounds tested except deltamethrin, which showed significant effect on liver enzyme. Na+, K+-ATPase of brain was less sensitive to these pyrethroids as compared to oligomycin-sensitive Mg2+-ATPase. [3H]Ouabain binding to rat brain synaptosomes was not affected significantly by these pyrethroid insecticides. These results suggest that inhibition of oligomycin-sensitive Mg2+-ATPase may be involved in the toxicity of pyrethroid compounds.     

Effect of acute nicotine on Fos protein expression in rat brain during chronic nicotine and its withdrawal

To study the cholinergic regulation of hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei and interpeduncular nucleus (IPN) we investigated the effects of acute nicotine (0.5 mg/kg, SC, 60 min) on Fos-like immunostaining (IS) during chronic nicotine and its withdrawal in rats. Nicotine or saline was infused to rats via osmotic minipumps (4 mg/kg/day) for 7 days; on the seventh day, the minipumps were removed surgically. In control rats, acute nicotine increased Fos IS significantly in all three brain areas studied. On the seventh day of nicotine infusion this effect partially persisted in IPN but was abolished in PVN and SON. After 72-h withdrawal nicotine-induced elevation of Fos IS was similar to that of control rats in all three areas. The observed attenuation of the response to acute nicotine during constant nicotine infusion in PVN and SON may be attributable to the desensitization of nicotinic acetylcholine receptors (nAChRs) mediating the effects of nicotine in these areas or in their input areas. IPN is connected to midbrain limbic system, so in agreement with our earlier observations, it seems that limbic nicotinic receptors do not very readily desensitize during chronic nicotine infusion. These findings support the suggestions that there are differences in the level of desensitization of nAChRs.     

硫喷妥钠对大鼠不同脑区ATP酶活性的影响

目的　探讨硫喷妥钠对大鼠不同脑区ATP酶活性的动态影响 ,是否与麻醉作用有关。方法　采用♂SD大鼠 4 0只 ,随机分为 5组 ,生理盐水 (10mL·kg- 1,ip)对照期组及给硫喷妥钠 (30mg·kg- 1,ip)后的诱导期组、麻醉期组、恢复期组、清醒期组。断头取脑 ,用分光光度法测定大脑皮层、脑干、海马和纹状体Na+,K+ ATP酶、Ca2 + ATP酶活性。结果给硫喷妥钠后大脑皮层的Na+,K+ ATP酶活性在诱导期和恢复期显著降低 ,而Ca2 + ATP酶活性在诱导期和麻醉期显著升高 ,到清醒期时 ,两种酶活性均恢复到对照期组水平 ;脑干的Na+,K+ ATP酶、Ca2 + ATP酶活性在给硫喷妥钠后诱导期、麻醉期和恢复期均显著低于对照期组 ,直至清醒期仍与对照组有显著性差异 ,而以诱导期最低。海马、纹状体的Na+、K+ ATP酶和Ca2 + ATP酶活性则在整个麻醉期间无明显变化。结论　硫喷妥钠的全麻作用可能与其影响大脑皮层和脑干的ATP酶活性有关     

Analgesia induced by chronic nicotine infusion in rats: differences by gender and pain test

RATIONALE: Acute administration of nicotine induces analgesia with subsequent development of tolerance. In human studies, females are less sensitive to the analgesic effects of nicotine than males. Few previous animal studies have investigated analgesic effects of chronic nicotine administration or addressed gender differences. OBJECTIVES: To investigate whether chronic administration of nicotine induces analgesia in male and female rats as assessed by a battery of standard pain assays, if tolerance develops, and if hyperalgesia occurs following cessation of nicotine. METHODS: Nicotine (free base; 6 mg/kg/day i.v.) or saline was administered for 2 weeks via implanted osmotic pumps. Pain behavior was assessed before, during, and for 3 weeks after nicotine infusion by measuring tail flick latency, hot-plate latency, and thermal paw withdrawal latency. The paw-withdrawal threshold to non-noxious mechanical stimuli was also measured. Effects of nicotine infusion, gender, and time were assessed by three-way analyses of variance. RESULTS: Both male and female rats exhibited a comparable degree of analgesia in the hot-plate test with development of tolerance during the 2-week infusion period. Males, but not females, showed analgesia in the tail flick test. Analgesia was not observed for thermally evoked paw withdrawal in either males or females, nor did nicotine affect non-noxious mechanically evoked paw withdrawals. Males and females showed cessation of weight gain during the first week of nicotine infusion. CONCLUSIONS: Chronic nicotine-induced analgesia was confirmed in both male and female rats as assessed using the hot-plate test which reflects integrated pain behavior. Males, but not females, exhibited analgesia in a nociceptive withdrawal reflex test (tail flick), indicating that nicotine-induced analgesia may depend on both the type of pain test and gender. The lack of nicotine-induced analgesia assessed by the tail flick reflex test in female rats is consistent with recent human studies showing that nicotine reduces pain elicited by brief noxious cutaneous stimulation in male but not female subjects.     

Continuous nicotine infusion reduces nicotine self-administration in rats with 23-h/day access to nicotine

The effects of continuous nicotine infusion on nicotine self-administration (NSA) were studied in rats as a model of nicotine replacement therapy (NRT) in humans. A NSA model in which rats had 23-h/day access to nicotine was used to approximate nicotine access conditions in cigarette smokers. In order to estimate serum nicotine concentrations associated with NSA, arterial and venous serum nicotine concentrations were measured during a simulation of NSA. Nicotine was noncontingently administered as 30 doses/12 h of 0.03 mg/kg/i.n.f. or 60 doses/12 h of 0.01 mg/kg/i.n.f. daily. Venous serum nicotine concentrations were measured after the first nicotine dose of the day, and arterial and venous concentrations were measured after doses in the middle of the day. The range of mean concentrations measured was similar to those reported in cigarette smokers (venous concentrations 6-59 ng/ml, arterial concentrations 42-96 ng/ml). The effects of continuous nicotine infusion on NSA were studied by noncontingently administering nicotine at various rates via osmotic pump to animals self-administering nicotine (0.01 or 0.03 mg/kg/i.n.f.) during 23-h/day sessions. Continuous nicotine infusion at all infusion rates substantially suppressed NSA, but suppression was rate-related only for the 0.01-mg/kg/inf NSA unit dose. Nicotine infusion rates producing venous serum nicotine concentrations equaling or exceeding the peak venous levels associated with simulated NSA were more effective than lower infusion rates only at the lower NSA unit dose. The highest nicotine infusion rate had no sustained effect on food-maintained responding, demonstrating its specificity for suppression of NSA. These data provide a model for studying NRT in the rat.     

Tolerance, cross-tolerance, and receptors after chronic nicotine or oxotremorine

Saline, 8.0 mg/kg/hr nicotine, or 1.0 mg/kg/hr oxotremorine was continuously infused into the jugular veins of DBA female mice. After 10 days of treatment, respiratory rate, Rotarod performance, Y-maze crossings, Y-maze rears, heart rate, and body temperature were measured after challenge with 2.0 mg/kg nicotine or saline or 0.2 mg/kg oxotremorine. Nicotine-infused mice were tolerant to the effects of nicotine for all six tests and oxtremorine-infused mice were tolerant to the effects of oxotremorine for all six tests and to the effects of nicotine on heart rate and body temperature. Oxotremorine infusion reduced the Bmax for [3H]-L-QNB binding, but had no effect on Bmax for either [3H]-DL-nicotine or [125I]-alpha-BTX binding. Conversely nicotine infusion did not alter the Bmax for [3H]-L-QNB binding, but increased the Bmax for both [3H]-DL-nicotine and [125I]-alpha-BTX binding. These results indicate that tolerance developed to the effects of two cholinergic agents, nicotine and oxotremorine, and that some cross-tolerance to the effects of nicotine occurred in oxotremorine-treated mice. Treatment with oxotremorine caused down-regulation of muscarinic receptors, while treatment with nicotine caused up-regulation of nicotinic receptors. Although some cross-tolerance to the effects of nicotine occurred in oxotremorine-treated mice, this did not appear to result from changes in nicotinic receptors.     

Heterogeneous distribution of mianserin in rat brain during chronic continuous infusion

The mianserin (MIS) distribution in 12 brain regions was investigated after 2- and 14-day continuous MIS infusion, starting with 19 mg/kg/day on the first day. There was no significant difference between the 2nd and 14th day with respect to MIS concentration, brain/serum concentration ratio in whole brain or MIS serum level. The MIS distribution was heterogeneous on the 2nd and 14th day and did not change with time. The concentrations were highest in cortex and hippocampus and lowest in cerebellum, hypothalamus, and bulbus olfactorious and septum. This distribution pattern differs from those found with tricyclic antidepressant drugs.     

Effects of chronic smoke exposure on the cardiovascular responses to acute nicotine infusion in the rat

Rats were exposed daily to cigarette smoke for 17-22 weeks in order to characterize mean arterial pressure and regional hemodynamic effects of chronic smoke exposure and to determine if cardiovascular reactivity to acute nicotine infusions is altered by chronic smoke exposure. Urethane-anesthetized animals were instrumented with miniaturized pulsed-Doppler flow probes on the iliac and mesenteric vascular beds. Under resting conditions sham-smoked and smoke-exposed animals had similar levels of mean arterial pressure and mesenteric blood flow; however, resting heart rate was lower in the smoke-exposed group, while iliac blood flow was elevated in the smoke-exposed group. Acute nicotine infusion (6.25, 12.5 and 25 micrograms/kg per min) produced equivalent, dose-dependent pressor effects as well as increases in iliac and mesenteric resistance in sham and smoke-exposed groups. Thus, chronic cigarette smoke-exposure in rats may exert significant cardiovascular effects other than on arterial pressure such as lowered heart rate and elevated blood flow to skeletal muscle beds, while cardiovascular responses to nicotine are not altered by chronic smoke-exposure.     

Exposure to chronic intermittent nicotine vapor induces nicotine dependence

Animal models of drug exposure are important tools for the study of the neurobiological mechanisms of nicotine dependence and as preclinical models for medication development. There are few non-invasive animal models of nicotine exposure and currently there is no known animal model of second-hand exposure to nicotine. We hypothesized that chronic administration of nicotine vapors would produce blood levels of nicotine in rodents that are clinically relevant to those observed in human smoking and that rodents exposed to nicotine vapors would develop dependence to nicotine. We developed a system that vaporizes nicotine in the air in a stable, reliable and consistent manner. Intermittent exposure to nicotine vapor (0.2 mg/m³) for 8 or 14 h per day for 7 days produced a concentration of nicotine in the blood of 22 ng/mL. Sixteen hours after removal from nicotine vapors, rats showed significant somatic withdrawal signs precipitated by mecamylamine (1.5 mg/kg). These results provide a new rodent model of nicotine dependence using vapor administration that produces consistent levels of nicotine in the blood that are relevant for both heavy smoking and second-hand smoking, using a non-invasive technique that mimics the intermittent aspect and route of administration in humans.     

Morphine-nicotine interaction in conditioned place preference in mice after chronic nicotine exposure

Previously we found that morphine's effects on locomotor activity and brain dopamine metabolism were enhanced in mice after cessation of 7-week oral nicotine treatment. In the present experiments we show that such chronic nicotine exposure cross-sensitizes NMRI mice to the reinforcing effect of morphine in the conditioned place preference paradigm. The nicotine-treated mice developed conditioned place preference after being conditioned twice with morphine 5 mg/kg s.c. whereas in control mice a higher dose (10 mg/kg) of morphine was required. Since the reinforcing effect of morphine is mediated via micro-opioid receptors we used [3H]DAMGO autoradiography to study whether the number (B(max)) or affinity (K(D)) of mu-opioid receptors in the mouse brain are affected following chronic nicotine exposure. However, no changes were found in the number or affinity of micro-opioid receptors in any of the brain areas studied. Neither did we find alterations in the functional activity of mu-opioid receptors studied by [35S]GTPgammaS-binding. In conclusion, chronic oral nicotine treatment augments the reinforcing effects of morphine in mice, and this cross-sensitization does not seem to be mediated by micro-opioid receptors.