The effects of chronic nicotine on spatial learning and bromodeoxyuridine incorporation into the dentate gyrus of the rat

Rationale Nicotine is reported to improve learning and memory in experimental animals. Improved learning and memory has also been related to increased neurogenesis in the dentate gyrus (DG) of the hippocampal formation. Surprisingly, recent studies suggest that self-administered nicotine depresses cell proliferation in the DG. Objective To test the hypothesis that the effects of nicotine on cell proliferation in the DG and learning and memory depend upon the nicotine dose administered. Methods Rats were chronically infused from subcutaneous osmotic mini pumps with nicotine (0.25 or 4 mg kg⁻¹ day⁻¹) or the saline vehicle for 10 days. Half the rats in each treatment group were trained to locate a hidden platform in a water maze task on days 4–7; a probe trial was performed on day 8. The remaining rats remained in their home cages. The effects of nicotine and of training in the water maze task on cell genesis in the DG were determined by measuring 5-bromo-2′-deoxyuridine (BrDU) uptake using fluorescence immunohistochemistry. Results Training in the water maze task increased cell proliferation in the DG. Infusions of nicotine at 4 mg kg⁻¹ day⁻¹, but not 0.25 mg kg⁻¹ day⁻¹, decreased cell proliferation in both untrained animals and animals trained in the maze and impaired spatial learning. Conclusions The data suggest that learning in the water maze task is impaired by higher doses of nicotine tested, and that this response may be related to reduced cell genesis in the DG.     

Preexposure during or following adolescence differently affects nicotine-rewarding properties in adult rats

Rationale Many people come in contact with psychoactive drugs, yet not all of them become addicts. Epidemiology shows that a late approach with cigarette smoking is associated with a lower probability to develop nicotine dependence. Exposure to nicotine during periadolescence, but not similar exposure in the postadolescent period, increases nicotine self-administration in rats, but underlying mechanisms remain poorly understood. Objective We investigated whether exposure to nicotine during or after adolescence would alter rewarding properties of the same drug at adulthood, as assessed by place conditioning. Materials and methods Periadolescent (PND 34–43) or postadolescent (PND 60–69) rats were injected with saline or nicotine (0.4 mg kg⁻¹) for 10 days. The rats received three pairings with saline and three pairings with nicotine (0, 0.3, or 0.6 mg kg⁻¹) 5 weeks after pretreatment. The rats were then tested for place conditioning in a drug-free state. Results Upon first exposure to the apparatus, animals pretreated with nicotine during adolescence showed elevated novelty-induced activation. The 0.3 (but not the 0.6) mg kg⁻¹ dose failed to produce both ongoing locomotor sensitization and place conditioning in animals pretreated with nicotine following adolescence. This suggests a rightward shift in the dose–response curve, namely, a reduced efficacy of nicotine. Conversely, the same dose was effective in saline-pretreated controls and noteworthy in rats pretreated during adolescence. Conclusion Exposure following the adolescent period might diminish the risk to develop nicotine dependence. As for human implications, findings are consistent with a reduced vulnerability to nicotine addiction in people who start smoking late in their life.     

Effect of a novel nicotinic receptor antagonist, N,N′-dodecane-1,12-diyl-bis-3-picolinium dibromide, on nicotine self-administration and hyperactivity in rats

Rationale and objective Recent work has shown that the novel compound N,N′-dodecane-1,12-diyl-bis-3-picolinium dibromide (bPiDDB) may selectively block nicotinic acetylcholine receptors involved in regulating dopamine release. The current experiments examined the acute effect of bPiDDB on nicotine self-administration, sucrose-maintained responding, and nicotine-induced changes in acute and sensitized locomotor activity. Methods Rats were first trained to respond for either nicotine (i.v.) or sucrose pellets using a standard two-lever operant conditioning procedure using a fixed ratio 5 schedule of reinforcement and were then pretreated with bPiDDB (0, 0.3, 1, or 3 mg kg⁻¹) 15 min prior to the session. In separate experiments, rats were assessed for nicotine-induced changes in locomotor activity following pretreatment with bPiDDB (1 or 3 mg kg⁻¹) or mecamylamine (1 mg kg⁻¹); pretreatments were assessed with both acute and repeated nicotine (0.4 mg kg⁻¹) treatment. Results Results showed that bPiDDB dose-dependently decreased nicotine self-administration, but not sucrose-maintained responding. In the locomotor experiments, bPiDDB attenuated the hyperactivity produced by acute and repeated nicotine; however, this effect was not robust compared to mecamylamine. In contrast to mecamylamine, bPiDDB did not block the initial hypoactivity produced by acute nicotine. Conclusion Since bPiDDB decreased nicotine self-administration specifically, this novel nicotinic receptor antagonist may constitute a lead for the development of a clinically useful treatment for tobacco dependence.     

Examining the clinical efficacy of bupropion and nortriptyline as smoking cessation agents in a rodent model of nicotine withdrawal

Rationale At present, there is a lack of an established animal model to demonstrate the clinical efficacy of smoking cessation agents in the laboratory. The aim of this study was to compare the effects of the antidepressants bupropion and nortriptyline, clinically proven smoking cessation aids, within a rodent model of a nicotine withdrawal based on somatic measures. Materials and methods Male hooded Lister rats were chronically exposed to nicotine (3.16 mg kg¹ day¹) for 7 days via SC implanted ALZET osmotic minipumps. Animals were acutely pre-treated with bupropion (10, 30 or 60 mg/kg, IP) or nortriptyline (1.5, 4.7 and 15 mg/kg, IP), and nicotine withdrawal was precipitated by mecamylamine (1 mg/kg). Results Precipitation of nicotine withdrawal led to an increase in somatic signs including body shakes, chews, eye blinks, foot licks, head shakes and ptosis. Bupropion dose-dependently decreased the total abstinence scores and reduced the occurrence of some individual somatic signs. Pre-treatment with 60 mg/kg bupropion did not result in a significant increase in total abstinence scores or individual somatic signs scores after mecamylamine challenge, compared to the mecamylamine control group, suggesting nicotine withdrawal is fully attenuated at this dose. Similarly, the highest dose of nortriptyline reduced total abstinence scores and some individual somatic signs to the level of the mecamylamine control group. However, nortriptyline was only effective at alleviating somatic measures of withdrawal at doses which also suppressed locomotor activity. Conclusion In concurrence with clinical findings proposing alleviation of withdrawal states as a possible mechanism of bupropion and nortriptyline’s smoking cessation action, both drugs were found to ameliorate somatic signs of nicotine withdrawal in rodents.     

Combined exposure to nicotine and ethanol throughout full gestation results in enhanced acquisition of nicotine self-administration in young adult rat offspring

Rationale Epidemiological evidence shows positive correlation between either maternal cigarette smoking or alcohol consumption on subsequent drug-taking behavior in offspring. However, the consequences of full gestational exposure to both drugs have not been studied experimentally despite concurrent use frequently reported among women of childbearing age. Such comorbid gestational drug exposure may increase susceptibility to acquiring cigarette smoking (i.e., nicotine self-administration), a major gateway drug. Objectives We developed a noninvasive rat model for exposure to both nicotine (2–6 mg kg⁻¹ day⁻¹) and EtOH (4 g/kg gavage) that continued throughout pregnancy and postnatal (P) days 2–12, the rodent equivalent of the human third trimester, a critical brain developmental period. Offspring with this full gestational exposure to both drugs (Nic+EtOH) were compared to controls: nicotine alone, EtOH alone, pair-fed (comparable nutrition and handling), and ad libitum chow-fed. At P60–90, offspring had unlimited chronic access to acquire i.v. nicotine self-administration. Results There were no differences in gender ratio, stillbirths, birth weights, righting reflex, eye opening age, or weight gain. However, Nic+EtOH offspring of both genders acquired nicotine self-administration (15 or 30 μg kg⁻¹ injection⁻¹) more rapidly, at a higher percentage, and at a higher level than offspring in the other cohorts. Conclusion Full gestational Nic+EtOH exposure produced no overt alterations in standard postnatal measures but resulted in an enhanced acquisition of nicotine self-administration in young adult offspring.     

Reinforcement enhancing effect of nicotine and its attenuation by nicotinic antagonists in rats

Rationale Recent studies have demonstrated that nicotine can enhance operant responding for other nonpharmacological reinforcing stimuli. However, the nature of the reinforcement-enhancing effect of nicotine remains largely unknown. Objective The present study determined the dose dependency of the ability of nicotine to increase lever-pressing responses maintained by a compound visual stimulus (VS) in rats and examined its sensitivity to pharmacological antagonism of nicotinic acetylcholine receptors (nAChRs). Materials and methods Male Sprague–Dawley rats were trained in daily 1-h sessions to lever press for delivery of a VS (1 s lever light on and 60 s house light off) on a fixed ratio 5 schedule. During these sessions, eight scheduled response-independent intravenous infusions of nicotine (total amount: 0, 0.06, 0.12, 0.24, 0.48 mg kg⁻¹ h⁻¹) were delivered. In pharmacological tests, a nonselective nAChR antagonist mecamylamine, α4β2-selective antagonist dihydro-β-erythroidine (DHβE), and α7-selective antagonist methyllycaconitine (MLA) were administered in different groups of rats 30 min before the session. Results The VS maintained a moderate level of lever-pressing responses and nicotine dose-dependently increased responses for the VS presentations. Preteatment of mecamylamine and DHβE but not MLA significantly attenuated the nicotine-enhanced responding. However, mecamylamine had no effect on responding for the VS in rats that received scheduled saline infusions. Conclusions These results demonstrate dose dependency of the reinforcement-enhancing effect of nicotine and suggest that activation of the α4β2- but not α7-containing nAChRs may mediate this effect.     

Effects of a nicotine conjugate vaccine on the acquisition and maintenance of nicotine self-administration in rats

Rationale Immunization of rats against nicotine using a nicotine conjugate vaccine reduces the distribution of nicotine to brain in rats and attenuates some of nicotine's physiological and behavioral effects. It is not known whether such a vaccine can attenuate nicotine's reinforcing effects. Objective The present experiment was conducted to determine whether a nicotine conjugate vaccine could interfere with the acquisition and maintenance of nicotine self-administration (NSA) in rats given 23 h day⁻¹ access to nicotine. Methods To examine acquisition of NSA, rats were vaccinated with nicotine or control immunogen prior to being given access to a 0.01 mg kg⁻¹ infusion⁻¹ nicotine under a fixed-ratio(FR) 1 schedule for week 1, FR 2 for week 2, and FR 3 for week 3. Acquisition of cocaine self-administration (CSA) was similarly examined to determine the specificity of vaccination effects. To examine maintenance of NSA, rats were initially trained to self-administer nicotine under an FR 3 schedule, and then vaccinated with nicotine or control immunogen while NSA continued to be monitored. Results NSA was significantly lower in vaccinated rats compared to controls during the acquisition protocol, with a 38% decrease in the number of infusions during the last week of training. The percentage of rats meeting acquisition criteria in the vaccinated group was lower (36%) than that in the control group (70%), but this difference was not statistically significant. Vaccination did not affect acquisition of CSA, demonstrating its specificity for nicotine. Maintenance of NSA was significantly reduced in vaccinated rats as compared to controls after the final vaccine injection, with a mean reduction of 57%. There was no evidence in either protocol that vaccinated rats attempted to compensate for altered nicotine distribution by increasing nicotine intake. Conclusion These data suggest that vaccination against nicotine can reduce the reinforcing effects of nicotine in rats and may have therapeutic potential for the treatment of tobacco dependence.     

Preadolescent tobacco smoke exposure leads to acute nicotine dependence but does not affect the rewarding effects of nicotine or nicotine withdrawal in adulthood in rats

Epidemiological studies indicate that parental smoking increases the risk for smoking in children. However, the underlying mechanisms by which parental smoking increases the risk for smoking are not known. The aim of these studies was to investigate if preadolescent tobacco smoke exposure, postnatal days 21-35, affects the rewarding effects of nicotine and nicotine withdrawal in adult rats. The rewarding effects of nicotine were investigated with the conditioned place preference procedure. Nicotine withdrawal was investigated with the conditioned place aversion procedure and intracranial self-stimulation (ICSS). Elevations in brain reward thresholds in the ICSS paradigm reflect a dysphoric state. Plasma nicotine and cotinine levels in the preadolescent rats immediately after smoke exposure were 188 ng/ml and 716 ng/ml, respectively. Preadolescent tobacco smoke exposure led to the development of nicotine dependence as indicated by an increased number of mecamylamine-precipitated somatic withdrawal signs in the preadolescent tobacco smoke exposed rats compared to the control rats. Nicotine induced a similar place preference in adult rats that had been exposed to tobacco smoke or air during preadolescence. Furthermore, mecamylamine induced place aversion in nicotine dependent rats but there was no effect of preadolescent tobacco smoke exposure. Finally, preadolescent tobacco smoke exposure did not affect the elevations in brain reward thresholds associated with precipitated or spontaneous nicotine withdrawal. These studies indicate that passive exposure to tobacco smoke during preadolescence leads to the development of nicotine dependence but preadolescent tobacco smoke exposure does not seem to affect the rewarding effects of nicotine or nicotine withdrawal in adulthood.     

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.     

Mecamylamine elicits withdrawal-like signs in rats following a single dose of nicotine

Rationale

The ability of nicotine to induce dependence (result in a withdrawal syndrome) is typically thought to require long-term, daily smoking. Emerging evidence suggests that symptoms of nicotine withdrawal may occur following only a few cigarettes. Whether acute exposure to nicotine can induce dependence in animals has not been well established.

Objective

The objective of this paper is to examine whether the nicotinic acetylcholine receptor antagonist mecamylamine elicits withdrawal-like signs in rats following acute nicotine exposure.

Methods and Results

Mecamylamine (3.0 mg/kg, s.c.) administered ≈2 h after a single dose of nicotine (0.5 mg/kg, s.c.) elicited increases in intracranial self-stimulation (ICSS) thresholds and somatic signs, two well-established effects of withdrawal from long-term (chronic) nicotine exposure. The magnitude of these effects remained constant across five daily test sessions. A lower dose of mecamylamine (1.5 mg/kg, s.c.) had little or no effect on ICSS thresholds or somatic signs following acute nicotine exposure, but precipitated robust increases in these measures during a chronic nicotine infusion. Finally, rats exhibited a small increase in ICSS thresholds over time following a single nicotine injection (0.5 mg/kg, s.c.), possibly reflecting a modest spontaneous withdrawal-like effect.

Conclusions

Mecamylamine elicited withdrawal-like signs in rats following a single dose of nicotine. The different effects of mecamylamine 1.5 mg/kg following acute versus chronic nicotine exposure supports the notion that these models simulate the early and more advanced stages of nicotine dependence, respectively. While further optimization and validation of these models is necessary, they may provide a novel approach for studying the earliest stages of nicotine dependence.     

Interactive effects of ethanol and nicotine on learning in C57BL/6J mice depend on both dose and duration of treatment

Objective and rationale Alcohol and nicotine are commonly co-abused; one possible explanation for co-abuse is that each drug ameliorates the aversive effects of the other. Both drugs have dose-dependent effects on learning and memory. Thus, this study examined the interactive effects of acute ethanol and acute, chronic, or withdrawal from chronic nicotine on fear conditioning in C57BL/6J mice. Materials and methods Conditioning consisted of auditory conditioned stimulus-foot-shock unconditioned stimulus pairings. For acute studies, saline or ethanol, then saline or nicotine was administered before training, and saline or nicotine was also administered before testing. For chronic and withdrawal studies, saline or nicotine was administered chronically, and ethanol or saline was administered before training. Results Acute nicotine (0.09 mg/kg) reversed ethanol-induced deficits (1.0 and 1.5 g/kg) in contextual and cued fear conditioning, whereas a low dose of ethanol (0.25 g/kg) reversed nicotine (6.3 mg kg⁻¹ day⁻¹) withdrawal-induced deficits in contextual conditioning. Tolerance developed for the effects of nicotine on ethanol-induced deficits in conditioning and cross-tolerance between chronic nicotine and acute ethanol was seen for the enhancing effects of ethanol on conditioning. Conclusions The complex and sometimes polar actions of ethanol and nicotine on behavior may contribute to co-abuse of these drugs. Specifically, smoking may initially reduce the aversive effects of ethanol, but tolerance develops for this effect. In addition, low doses of alcohol may lessen nicotine withdrawal symptoms.     

Animal model of menopausal depressive-like state in female mice: prolongation of immobility time in the forced swimming test following ovariectomy

Rationale The onset of menopause produces a depressive state in women, but the mechanism involved in menopause-induced depression is poorly understood.Objectives Building upon previous studies that used the duration of immobility in male rodents during the forced swimming test as a behavioral measure of the depression-like state, we investigated whether the duration of immobility in female mice was altered following bilateral ovariectomy. We also evaluated the chronic effects of estradiol, antidepressants, scopolamine, and diazepam on both the duration of immobility and uterine weight.Methods We bilaterally resected the ovaries of ICR albino female mice at 9 weeks of age. The day after the surgery, drug treatment was started once per day for 2 weeks, after which, the behavioral test was administered. The duration of immobility was measured during the last 4 min of the 6-min trial.Results Bilateral ovariectomy significantly increased the duration of immobility. Chronic treatment with estradiol (15–30 μg kg⁻¹ day⁻¹) prevented the prolongation of immobility following ovariectomy and produced a significant increase in uterine weight. Chronic treatment with imipramine, fluvoxamine, and milnacipran at 5, 10, and 15 mg kg⁻¹ day⁻¹, respectively, significantly reduced the duration of immobility, whereas treatment with scopolamine or diazepam (0.5, 1.0, and 2.0 mg kg⁻¹ day⁻¹ for both) was ineffective.Conclusion Based on these results, we suggest that the prolongation of immobility in female mice following ovariectomy may be a useful tool for investigating menopausal depression.     

Tobacco smoke exposure induces nicotine dependence in rats

Rationale

Tobacco smoke contains nicotine and many other compounds that act in concert on the brain reward system. Therefore, animal models are needed that allow the investigation of chronic exposure to the full spectrum of tobacco smoke constituents.

Objectives

The aim of these studies was to investigate if exposure to tobacco smoke leads to nicotine dependence in rats.

Methods

The intracranial self-stimulation procedure was used to assess the negative affective aspects of nicotine withdrawal. Somatic signs were recorded from a checklist of nicotine abstinence signs. Nicotine self-administration sessions were conducted to investigate if tobacco smoke exposure affects the motivation to self-administer nicotine. Nicotinic receptor autoradiography was used to investigate if exposure to tobacco smoke affects central α7 nicotinic acetylcholine receptor (nAChR) and non-α7 nAChR levels (primarily α4β2 nAChRs).

Results

The nAChR antagonist mecamylamine dose-dependently elevated the brain reward thresholds of the rats exposed to tobacco smoke and did not affect the brain reward thresholds of the untreated control rats. Furthermore, mecamylamine induced more somatic withdrawal signs in the smoke-exposed rats than in the control rats. Nicotine self-administration was decreased 1 day after the last tobacco smoke exposure sessions and was returned to control levels 5 days later. Tobacco smoke exposure increased the α7 nAChR density in the CA2/3 area and the stratum oriens and increased the non-α7 nAChR density in the dentate gyrus.

Conclusion

Tobacco smoke exposure leads to nicotine dependence as indicated by precipitated affective and somatic withdrawal signs and induces an upregulation of nAChRs in the hippocampus.     

Behavioral manifestations of the nicotine abstinence syndrome in the rat: peripheral versus central mechanisms

The nicotine abstinence syndrome was studied in the rat utilizing a modified rating scale of the opiate abstinence syndrome. Rats were infused with 10.27 mg/kg per day nicotine hydrogen tartrate for 7 days via subcutaneous minipumps. The behavior of each animal was observed before, during and after termination of the nicotine infusion. The abstinence signs in the withdrawal sessions included gasps, genital licks, ptosis, shakes, teeth chatter, yawns and changes in locomotor activity. Abstinence was induced through surgical removal of the pump or through administration of a nicotinic receptor antagonist, acting either centrally and peripherally (mecamylamine 1 mg/kg SC) or peripherally only (chlorisondamine 1 mg/kg SC). Statistical evaluation revealed a significant increase in overall abstinence signs both at 16 (P < 0.05) and 40 h (P < 0.01) after termination of the nicotine infusion, as compared to the number of signs in the nicotine treated animals’ baseline sessions and to the number of signs in control animals (P < 0.05). There was also a significant reduction in locomotor activity during both withdrawal sessions. Animals injected with mecamylamine or chlorisondamine displayed a larger increase in the abstinence score (P < 0.001) than the spontaneously abstinent animals. Acute administration of different doses of nicotine or of the peripherally acting nicotinic receptor agonist tetramethylammonium (0.8 mg/kg SC) reversed the behavioral nicotine abstinence syndrome. Our results show that a nicotine abstinence syndrome can be elicited in rats on a chronic nicotine regimen either by acute withdrawal of nicotine or by the administration of nicotinic receptor antagonists and that peripheral nicotinic receptors may contribute significantly to the overall withdrawal reaction. Received: 21 March 1996/Final version: 30 September 1996     

Adolescent nicotine exposure produces less affective measures of withdrawal relative to adult nicotine exposure in male rats

Vulnerability to nicotine addiction is significantly increased in individuals who begin smoking during adolescence; however, the underlying mechanisms of this phenomenon remain unclear. This study examined the motivational effects of nicotine withdrawal in adolescent (PND 27-42) and adult (PND 60-75) rats using the conditioned place aversion paradigm. Male Wistar rats were tested for their initial preference for either of two distinct compartments of our conditioning apparatus. Rats were then implanted with subcutaneous (sc) pumps that produce equivalent blood plasma levels of nicotine for 14 days. Conditioning was conducted over the last 8 days of nicotine exposure. Rats received the nicotinic antagonist mecamylamine (1.5 or 3.0 mg/kg, sc) to precipitate withdrawal in their initially preferred compartment, and on alternate days they received saline in their non-preferred compartment. Following conditioning, rats were re-tested for their preference for each compartment. A subsequent study was conducted to examine potential developmental differences in learning place aversion produced by another aversive stimulus, lithium chloride (LiCl). Rats received LiCl (0, 10, 30, or 100 mg/kg, sc) in their initially preferred side using similar conditioning procedures. Adults displayed robust place aversion produced by nicotine withdrawal. This effect was lower in adolescent rats even in a group of young rats that received 7 additional days of nicotine exposure prior to conditioning. This developmental difference was specific to nicotine withdrawal since there were no differences between adolescents and adults in learning place aversion with LiCl. Our findings demonstrating reduced effects of nicotine withdrawal constitute a powerful basis for the increased vulnerability to nicotine dependence during adolescence.     

Effect of acute and repeated exposure to low doses of hydrazine on hepatic microsomal enzymes and biochemical parameters in vivo

A single dose of hydrazine (3 mg·kg⁻¹ i.p.) caused hepatic accumulation of triglycerides and depletion of ATP in rats after 9 h. Repeated exposure of rats to hydrazine (≊2.5 mg·kg⁻¹ per day) for 10 days resulted in depletion of hepatic reduced glutathione (GSH) and triglycerides. Repeated exposure to hydrazine also caused a significant (time dependent) induction ofp-nitrophenol hydroxylase (NPH) activity together with changes in other hepatic microsomal enzymes. These included 7-pentoxyresorufinO-deethylase (PROD) and 7-ethoxyresorufin O-de ethylase (EROD) activity, total cytochrome P450, cytochrome b₅ and cytochrome P450 reductase activity. Repeated exposure to lower levels of hydrazine (≊0.250 mg·kg⁻¹ per day) caused no significant hepatic biochemical or microsomal changes after 5 or 10 days except for an increase in NPH activity (17%) and liver ATP (15%) after 5 days.     

Discriminating effects of a nucleotide-rich yeast extract,ProbioticumR, as an immunomodulator contrasted with actions in chronic immuno-inflammatory disease (adjuvant-induced arthritis) in rodents

Following previous observations that yeast ribonucleic acid (RNA) and nucleotide components exhibit immuno-stimulation in mice it was decided to determine the effects of a commercially-available yeast extract used for growth enhancement in domestic animals which is rich in RNA and nucleotides, Probioticum^R (Chemoforma AG, Augst, Switzerland) in standard immune models in mice and for effects on the progression of adjuvant-induced polyarthritis in rats. Probioticum (PB) (1 g kg⁻¹ day⁻¹) given p.o. for 6 weeks to mice, which were also immunized during the last 6 weeks with sheep red blood cells, produced activation of macrophages (detected by specific monoclonal antibodies) in cells of the bone marrow, increased antigen specific cells in the spleen, and a small reduction of thymus T-lymphocytes compared with control animals. High oral doses (up to 300–500 mg kg⁻¹ day⁻¹) of PB given alone or with indomethacin p.o. during the inductive or established phases of adjuvant-induced arthritis failed to affect the course of this disease. Thus, the immunological properties of PB appear principally to involve macrophage- and B-cell activation, with some possible minor alterations in T-cell activity. The immunological effects of PB do not appear to be important for the prevention of adjuvant arthritis nor do they influence the prostaglandin-dependent components of the disease influenced by indomethacin.     

Pharmacokinetics of dihydroartemisinin following oral artesunate treatment of pregnant women with acute uncomplicated falciparum malaria

Objective To determine the pharmacokinetic properties of dihydroartemisinin (DHA) following oral artesunate treatment in women with recrudescent multi-drug resistant falciparum malaria, in the second and third trimesters of pregnancy.Methods Serial plasma concentrations of artesunate and DHA were measured in 24 women after the final dose of a 3 day treatment with artesunate (4 mg kg⁻¹ day⁻¹) and atovaquone (20 mg kg⁻¹ day⁻¹) plus proguanil (8 mg kg⁻¹ day⁻¹), daily. Conventional non-compartmental modelling and a population one-compartment pharmacokinetic model were applied to the data.Results Artesunate was very rapidly eliminated. For DHA the median [90% range] estimate of oral clearance (CI/F) was 4.0 [0.8–20.7] l hour⁻¹ kg⁻¹, total apparent volume of distribution (Vd/f) was 3.4 [0.9–60.7] l/kg, and terminal elimination half-life was 1.0 [0.6–2.4] h.Conclusion The kinetics of DHA are modified by pregnancy. The plasma levels of the active antimalarial metabolite DHA are lower than reported previously in non-pregnant adults. Dose-optimisation studies in pregnant women are needed.     

In rats chronically treated with clozapine, tyrosine depletion attenuates the clozapine-induced in vivo increase in prefrontal cortex dopamine and norepinephrine levels

We previously reported that depletion of brain tyrosine attenuated the acute clozapine (CLZ)-induced increase in medial prefrontal cortex (MPFC) dopamine (DA) levels. This effect was now examined after chronic CLZ treatment. Male rats received CLZ (10 mg kg⁻¹ day⁻¹) in drinking water for 21 days. On day 18, a cannula was stereotaxically implanted over the MPFC. A microdialysis probe was inserted on day 20. On day 21 after a stable baseline was reached, rats received an acute injection of vehicle (VEH) or a tyrosine- and phenylalanine-free mixture of neutral amino acid [NAA(−)] (total 1 g kg⁻¹, i.p., two injections, 1 h apart) followed by CLZ (10 mg kg⁻¹, i.p.) or VEH. Basal tyrosine or norepinephrine (NE) levels were not different between the groups, but basal DA was higher in the group treated chronically with CLZ (p<0.05). Acute CLZ (10 mg kg⁻¹, i.p.) increased MPFC DA and NE levels to 370% and 510% of baseline, respectively, and similarly in rats chronically pretreated with CLZ or VEH. NAA(−) did not affect basal MPFC DA or NE levels but significantly attenuated acute CLZ-induced DA (220% of baseline) and NE (330% of baseline) levels (p<0.01) in rats pretreated chronically with CLZ or with VEH. These data demonstrate that even after chronic CLZ administration, the acute CLZ-induced increases in MPFC DA and NE levels depend on the availability of brain tyrosine. Judicious manipulation of brain tyrosine levels may provide a useful probe as well as a mechanism for enhancing psychotropic drug actions.     

Diminished nicotine withdrawal in adolescent rats: implications for vulnerability to addiction

Rationale Enhanced reinforcing effects of nicotine during adolescence appear to contribute to the rapid development of dependence in this age group. However, the contribution of nicotine withdrawal to dependence in adolescents is unclear.Objective We compared motivational and somatic signs of nicotine withdrawal in adolescent and adult rats.Materials and methods In experiment 1, motivational signs of nicotine withdrawal were compared using intracranial self-stimulation procedures after administration of mecamylamine (1.5 mg/kg, i.p.) in adolescent and adult rats made dependent on nicotine (9 mg/kg/day). Somatic signs of withdrawal were compared in two experiments using various doses of nicotine (adolescent doses: 0, 1.6, 3.2, 4.7 mg/kg/day; adult doses: 0, 1, 2.1, 3.2 mg/kg/day, expressed as nicotine base) to produce dependence and one dose of mecamylamine (1.5 mg/kg, i.p.) to precipitate withdrawal (experiment 2) and in a subsequent experiment, using various doses of mecamylamine (0, 0.75, 1.5, 3.0 mg/kg, i.p.) to precipitate withdrawal and a dose of nicotine (adolescent dose: 4.7 mg/kg/day; adult dose: 3.2 mg/kg/day) that produced equivalent nicotine blood levels in these age groups (experiment 3).Results Adolescents did not display the decreases in brain reward function observed in adults experiencing withdrawal, and displayed fewer somatic signs of nicotine withdrawal relative to adults regardless of the dosing procedure used.Conclusion The negative effects of nicotine withdrawal are lower during adolescence relative to later periods of development. Both the enhanced rewarding effects and the diminished nicotine withdrawal likely contribute to the rapid development of nicotine use during adolescence.