Acute exposure of ceramide enhances cardiac contractile function in isolated ventricular myocytes

1. The sphingolipid ceramide, a primary building block for all other sphingolipids, is associated with growth arrest, apoptosis, and lipotoxic dysfunction. Interestingly, ceramide may attenuate high glucose-induced myocyte dysfunction, produce Ca2+ influx, and augment smooth muscle contraction. To determine the role of ceramide on cardiac excitation-contraction (E-C) coupling, electrically paced adult rat ventricular myocytes were acutely exposed to a cell-permeable ceramide analog (10 pm-100 microM) and the following indices were determined: peak shortening (PS), time-to-PS, time-to-90% relengthening, and the maximal velocity of shortening and relengthening (+/-dLdt). Intracellular Ca2+ properties were assessed using fura-2AM fluorescent microscopy. 2. Our results revealed a concentration- and time-dependent increase of PS in ventricular myocytes in response to ceramide associated with an increase in +/-dLdt. The maximal increase in PS was approximately 35% from control value and was maintained throughout the first 20 min of ceramide exposure. However, the ceramide-induced increase in PS was not maintained once the exposure time was beyond 20 min. Acute exposure of ceramide significantly enhanced intracellular Ca2+ release, although at a much lower concentration range. The ceramide-induced augmentation of PS was not significantly affected by inhibition of phosphatidylinositol (PI)-3-kinase, protein kinase C (PKC), ceramide-activated protein phosphatase (CAPP), and nitric oxide (NO) synthase. 3. Our data suggest that ceramide acutely augments the contractile function of cardiac myocytes through an alternative mechanism(s) rather than PI-3-kinase, PKC, CAPP, or NO.     

Prenatal lead exposure enhances methamphetamine sensitization in rats

Adult female rats were exposed to lead-free sodium acetate via gavage [0 mg (vehicle control)] or to 16 mg lead as lead acetate for 30 days prior to breeding. Following confirmation of breeding, the female animals continued to be exposed to their respective doses throughout gestation and lactation. When weaned, 16 control and 16 lead-exposed offspring were placed on regular water and food (lead-exposure was discontinued) until postnatal day (PND) 70. At this time, one-half of the control animals and one-half of the lead-treatment animals received intraperitoneal (i.p.) injections of the vehicle (saline) for 10 successive days and the remaining animals in each exposure conditions received daily injections of 1.0 mg/kg (+)-methamphetamine (METH) for 10 days (N = 8/group). Locomotion in automated chambers was monitored daily for 45 min post-injection.Subsequently, during dose-effect testing, all animals received consecutive daily i.p. injections of 0, 1.0, 2.0, and then 4.0 mg/kg METH. The results of the experiment showed that both control and lead-exposed animals exhibited heightened locomotor activity (i.e. behavioral sensitization) to the repeated administration of 1.0 mg/kg METH. More importantly, animals developmentally (perinatally) exposed to lead showed more rapid sensitization than did their control counterparts. These data indicate that early lead exposure increases sensitivity to the locomotor-stimulating effects of METH. In contrast, identically exposed lead animals exhibit diminished METH dose-effect responding when tested in an intravenous (i.v.) self-administration paradigm [Rocha A., Valles R., Bratton G.R., Nation J.R. Developmental lead exposure alters methamphetamine self-administration in the male rat: acquisition and reinstatement. Drug Alcohol Depend 2008a;95:23-29, Rocha A., Valles R., Hart N., Bratton G.R., Nation J.R. Developmental lead exposure attenuates methamphetamine dose-effect self-administration performance and progressive ratio responding in the male rat. Pharmacol Biochem Behav 2008b;89:508-514].     

Prenatal methamphetamine exposure and neonatal neurobehavioral outcome in the USA and New Zealand

Background

Methamphetamine (MA) use among pregnant women is a world-wide problem, but little is known of its impact on exposed infants.

Design

The prospective, controlled longitudinal Infant Development, Environment and Lifestyle (IDEAL) study of prenatal MA exposure from birth to 36 months was conducted in the US and NZ. The US cohort has 183 exposed and 196 comparison infants; the NZ cohort has 85 exposed and 95 comparison infants. Exposure was determined by self-report and meconium assay with alcohol, marijuana, and tobacco exposures present in both groups. The NICU Neurobehavior Scale (NNNS) was administered within 5 days of life. NNNS summary scores were analyzed for exposure including heavy exposure and frequency of use by trimester and dose-response relationship with the amphetamine analyte.

Results

MA exposure was associated with poorer quality of movement, more total stress/abstinence, physiological stress, and CNS stress with more nonoptimal reflexes in NZ but not in the USA. Heavy MA exposure was associated with lower arousal and excitability. First trimester MA use predicted more stress and third trimester use more lethargy and hypotonicity. Dose-response effects were observed between amphetamine concentration in meconium and CNS stress.

Conclusion

Across cultures, prenatal MA exposure was associated with a similar neurobehavioral pattern of under arousal, low tone, poorer quality of movement and increased stress.     

Voluntary exercise ameliorates anxiogenic effects of acute methamphetamine exposure in Swiss-Webster mice

BackgroundThe present experiment examined the ability of voluntary exercise (i.e., home-cage wheel running; HCWR) to ameliorate anxiety-like behavior associated with acute methamphetamine exposure in male, Swiss-Webster mice.MethodsMice were permitted access to home-cage running wheels (Exercise), locked home-cage running wheels or no home-cage running wheels (Sedentary) for 6 weeks and then exposed to different methamphetamine doses (vehicle, 0.25, 0.5, or 1.0 mg/kg) once weekly during an 8 h open-field session for 4 weeks. Group differences in hypothalamic-pituitary-adrenal (HPA) activity also were assessed by weighing adrenal glands.ResultsIt was found that HCWR ameliorated anxiety-like behavior after an injection of either the 0.5 or 1.0 mg/kg methamphetamine dose. Adrenal weights did not differ between Exercise and Sedentary mice.ConclusionTaken together, these results suggest that voluntary exercise ameliorates the anxiogenic effects of methamphetamine depending on the dose, perhaps via a non-HPA mechanism.     

Developmental lead exposure attenuates methamphetamine dose-effect self-administration performance and progressive ratio responding in the male rat

Perinatal (gestation/lactation) lead exposure modifies the reinforcement efficacy of various psychoactive drugs (e.g., cocaine, opiates) across the phases of initial selection, use, and abuse [Nation J.R., Cardon A.L., Heard H.M., Valles R., Bratton G.R. Perinatal lead exposure and relapse to drug-seeking behavior in the rat: a cocaine reinstatement study. Psychopharmacol 2003;168: 236–243.; Nation J.R., Smith K.R., Bratton G.R. Early developmental lead exposure increases sensitivity to cocaine in a self-administration paradigm. Pharmacol Biochem Behave 2004; 77: 127–13; Rocha A., Valles R., Cardon A.L., Bratton G.R., Nation J.R. Enhanced acquisition of cocaine self-administration in rats developmentally exposed to lead. Neuropsychopharmacol 2005; 30: 2058–2064.]. However, changes in sensitivity to methamphetamine across the phases of drug abuse have not been examined in animals perinatally exposed to lead. Because the mainstream popularity of methamphetamine in the United States is increasing and lead exposure continues to be widespread, an examination of this drug and how it may be modified by perinatal exposure to lead is warranted. The studies reported here examined the effects of perinatal lead exposure on adult self-administration of intravenous (i.v.) methamphetamine across the maintenance phase of drug addiction. Experiment 1 examined dose-effect patterns in control and lead-exposed animals. Experiment 2 evaluated control and lead-exposed animals in a progressive ratio task. Female rats were administered a 16-mg lead or a control solution for 30 days prior to breeding with non-exposed males. Exposure continued through pregnancy and lactation and was discontinued at weaning (postnatal day [PND] 21). Animals born to control or lead-exposed dams received indwelling jugular catheters as adults (PND 70) and subsequently were randomly assigned to one of the two studies, using only one male rat per litter for each study. The data showed a general attenuation of the reinforcement efficacy of methamphetamine in animals perinatally exposed to lead, as compared to control animals.     

Lack of behavioral sensitization after repeated exposure to THC in mice and comparison to methamphetamine

Rationale Recent evidence has provided support for the incentive-sensitization model of addiction, where repeated stimulation of neural reward circuits leads to a long-lasting sensitization of mesolimbic dopaminergic activity. This phenomenon has been demonstrated with many drugs of abuse, most often by measuring progressively increased activating effects of drugs on locomotor activity, thought to reflect an underlying neural sensitization. Whether cannabinoids, and in particular Δ⁹-tetrahydrocannabinol (THC), produce similar effects in this model is somewhat controversial, with mixed evidence in the literature. Objectives These experiments were conducted to determine whether behavioral sensitization could be established in mice after repeated exposure to THC. Sensitization to repeated methamphetamine treatment was used as a positive control. Methods The effects of acute and repeated intermittent (every 3–4 days) treatment with THC or methamphetamine on locomotor activity were determined in Institute of Cancer Research (ICR) mice. Additional experiments with THC employed a dosing regimen that increased the number of injections, controlled for behavioral tolerance, examined different aspects of behavior, and used a different species (Sprague–Dawley rats). Results Both methamphetamine and THC acutely increased activity. A robust dose-dependent sensitization was observed after intermittent treatment with methamphetamine but not with THC. Additionally, no evidence for behavioral sensitization to the effects of THC was found with any of the various protocols. Conclusion These data suggest that repeated THC treatment is less likely to produce behavioral sensitization than are other drugs of abuse. It appears that this phenomenon may only occur under very particular conditions, which raises doubts about its relevance to chronic cannabis users.     

Cognitive function and nigrostriatal markers in abstinent methamphetamine abusers

Objective Preclinical investigations have established that methamphetamine (MA) produces long-term changes in dopamine (DA) neurons in the striatum. Human studies have suggested similar effects and correlated motor and cognitive deficits. The present study was designed to further our understanding of changes in brain function in humans that might result from chronic high dose use of MA after at least 3 months of abstinence.Method Brain function in abstinent users was compared to controls using neuroimaging of monoamine transporters and cognitive assessment. Striatal levels of DA transporter (DAT) and vesicular monoamine transporter type-2 (VMAT2) were determined using [¹¹C]methylphenidate and [¹¹C]dihydrotetrabenazine positron emission tomography, respectively. Cognitive function was evaluated using tests of motor function, memory, learning, attention, and executive function.Results Striatal DAT was approximately 15% lower and VMAT2 was 10% lower in MA abusers across striatal subregions. The MA abusers performed within the normal range but performed more poorly compared to controls on three of the 12 tasks.Conclusions Failure to find more substantial changes in transporter levels and neurocognitive function may be attributed to the length of time that MA users were abstinent (ranging from 3 months to more than 10 years, mean 3 years), although there were no correlations with length of abstinence. Persistent VMAT2 reductions support the animal literature indicating a toxic effect of MA on nigrostriatal nerve terminals. However, the magnitude of the MA effects on nigrostriatal projection integrity is sufficiently small that it is questionable whether clinical signs of DA deficiency are likely to develop.An erratum to this article can be found at     

Prolonged exposure of rats to intravenous methamphetamine: behavioral and neurochemical characterization

The translational value of preclinical models of methamphetamine abuse depends in large part on the degree to which the drug regimens used in animals produce methamphetamine exposure patterns similar to those experienced by human methamphetamine abusers. To approximate one common form of methamphetamine abuse, we studied the effects of a schedule of intravenous methamphetamine administration in rats which included 2 weeks of progressively more frequent drug injections (0.125 mg/kg/injection) followed by 40 maintenance days during which animals received 40 daily injections (at 15-min intervals), with the dose gradually increasing (0.125–0.25 mg/kg per injection) every 5–10 days. This treatment produced an emerging behavioral profile characterized by gradually more continuous periods of activation consisting of progressively more intense, focused stereotypy interrupted by episodic bursts of locomotion. We also assessed markers of dopamine neurotransmission (dopamine transporter, vesicular monoamine transporter, and dopamine D1 and D2 receptors) at 15 min and (including dopamine levels) at 6 and 30 days following cessation of methamphetamine treatment. All dopamine components measured in caudate–putamen were significantly reduced at 15 min and 6 days after the final methamphetamine injection. Dopamine D1 and D2 receptors fully recovered after 30 days of drug abstinence, whereas dopamine and the dopamine transporter exhibited significant but incomplete recovery by this time point. In contrast, only the vesicular monoamine transporter exhibited no evidence of recovery over the 30-day withdrawal period. These data are discussed in terms of damage to dopamine terminals and compensatory adjustments in mechanisms maintaining functional dopaminergic transmission.     

The effect of maternal exposure to methamphetamine during pregnancy and lactation period on hippocampal neurons apoptosis in rat offspring

Methamphetamine (METH) is a highly addictive stimulant. The effect of maternal exposure of METH on apoptosis in rat hippocampus was evaluated. Wistar rats were randomly divided into: 1&;2) Rats were given METH during pregnancy or breastfeeding (5?mg/kg i.p.), 3&;4) Rats injected with normal saline and 5&;6) Rats served as control. TUNEL method was used to evaluate apoptotic cells. Mean number of apoptotic cells was significantly increased in CA1, CA3 and DG regions. The CA1 field was significantly improved in the experimental pregnancy and breastfeeding groups. The study showed that METH causes apoptosis in all three hippocampal fields, especially CA1 region.     

Malondialdehyde inhibits cardiac contractile function in ventricular myocytes via a p38 mitogen-activated protein kinase-dependent mechanism

(1) Increased oxidative stress plays a significant role in the etiology of cardiovascular disease. Lipid peroxidation, initiated in the presence of hydroxy radicals resulting in the production of malondialdehyde, directly produces oxidative stress. This study was designed to examine the direct impact of malondialdehyde on ventricular contractile function at the single cardiac myocyte level. Ventricular myocytes from adult rat hearts were stimulated to contract at 0.5 Hz, and mechanical and intracellular Ca(2+) properties were evaluated using an IonOptix Myocam system. Contractile properties analyzed included peak shortening amplitude (PS), time-to-PS (TPS), time-to-90% relengthening (TR(90)), maximal velocity of shortening/relengthening (+/-dLdt), and Ca(2+)-induced intracellular Ca(2+) fluorescence release (CICR) and intracellular Ca(2+) decay (tau). p38 mitogen-activated protein (MAP) kinase phosphorylation was assessed with Western blot. (2) Our results indicated that malondialdehyde directly depressed PS, +/-dLdt and CICR in a concentration-dependent manner and shortened TPS without affecting TR(90) and tau. Interestingly, the malondialdehyde-induced cardiac mechanical effect was abolished by both the p38 MAP kinase inhibitor SB203580 (1 and 10 micro M) and the antioxidant vitamin C (100 micro M). Western blot analysis confirmed direct phosphorylation of p38 MAP kinase by malondialdehyde. (3) These findings revealed a novel role of malondialdehyde and p38 MAP kinase in lipid peroxidation and oxidative stress-associated cardiac dysfunction.     

Sanguinarine: A positive inotropic alkaloid which inhibits cardiac Na,K-ATPase

In isolated, isometrically contracting left guinea pig atria, sanguinarine, a benzophenanthridine alkaloid from the papaveracea Sanguinaria canadensis, produced a concentration-dependent positive inotropic effect. Between 2.3 × 10⁻⁶ M and 6.5 × 10⁻⁵ M, sanguinarine increased contractility by 108% which was comparable to the maximal inotropic effect of ouabain. Within the same concentration range, sanguinarine caused inhibition of Na⁺,K⁺-ATPase isolated from guinea pig myocardium. 100% inhibition of Na⁺,K⁺-ATPase activity occurred at 1 × 10⁻⁴ M sanguinarine. The I₅₀ for enzyme inhibition and the ED₅₀ for the inotropic action of sanguinarine were the same (6–6.5 × 10⁻⁶ M) indicating that both effects may be causally related.     

Acute cardiac dysfunction after short-term diesel exhaust particles exposure

Epidemiological studies show an association between particulate matter exposure and acute heart failure. However, underlying mechanisms remain unclear. In this study, we investigated acute cardiac hemodynamic effects and related mechanisms after 1 day exposure to diesel exhaust particles (DEPs). Male Sprague–Dawley rats were randomized and instilled with 250 μg (low dose) or 500 μg (high dose) of DEP or saline placebo intra-tracheally. The cardiac systolic function by dP/dt₄₀ and diastolic functions by maximal negative dP/dt were both worse in DEP low dose and DEP high dose groups than the control group, respectively. In the heart rate variability analysis, SDNN in DEP low dose and DEP high dose groups were both lower than the control group. The low frequency heart rate variability was higher in the DEP groups compared to the control group. The cardiac IL-1β expression and circulating cardiac troponin I level were higher in the DEP group than the control group. Plasma IL-1β and IL-6 protein were significantly higher in the DEP groups than the control group. In conclusion, DEP exposure causes acute cardiac systolic and diastolic dysfunction. The changes may be related to decreased heart rate variability, increased cardiac inflammatory reaction and myocardial damage.     

国产卡维地洛与美托乐尔治疗心力衰竭对心肺功能的影响

目的　对比观察卡维地洛和美托乐尔治疗慢性收缩性心力衰竭对心、肺功能的影响及其安全性。方法　将 34例在常规心力衰竭治疗 (利尿剂 +地高辛 +ACEI/AⅡ受体拮抗剂 )的基础上 ,心功能为Ⅱ～Ⅲ级及病情稳定的Ⅳ级非瓣膜病变慢性收缩性心力衰竭患者 ,随机分为卡维地洛组 (A组 )、美托乐尔组 (B组 )。采用小剂量逐渐递增给药 ,两组剂量分别为A组 :(2 1 3± 2 8)mg ;B组 :(65± 2 9)mg。治疗前及治疗后 3个月分别评定心功能级别 ,检查血、尿常规 ,血糖 ,血脂 ,肝、肾功能 ,电解质 ,超声心动图 ,气道激发试验以及 6min步行距离 ,并进行治疗前后及组间的对比。结果　两组患者经加用 β 受体阻滞剂 (β B)治疗 3个月后 ,心力衰竭症状、心功能分级、血流动力学指标、运动耐量均较用药前明显改善 ,且组间比较差异无显著性。美托乐尔较卡维地洛有较显著的降心率作用 ,卡维地洛虽增加气道阻力 ,但不足以影响气道的阻塞程度和肺的总通气功能。两药均增高甘油三酯 ,组间比较差异无显著性。未见两药对血细胞 ,电解质 ,肝、肾功能 ,血糖有影响。结论　卡维地洛和美托乐尔对治疗慢性收缩性心力衰竭均有较好疗效。     

Acute kidney damage by PM2.5 exposure in a rat model

PM_2.5 exposure is associated with a glomerular filtration rate (GFR) reduction, and renal tissue damage. The goal of this study was demonstrate the acute effect of PM_2.5 on the kidney. Male rats were acutely exposed to PM_2.5 or filtered air. Blood pressure was mesure and early kidney biomarkers were evaluated in serum and urine samples, and also IL-1β, IL-6 and TNFα were determined. Oxidative biomarkers, angiotensin/bradykinin-related proteins, KIM-1, IL-6 and histology were determined. Blood pressure, GFR, and early kidney damage biomarkers increase together with oxidative biomarkers and angiotensin/bradykinin endocrine-related proteins increased after exposure to PM_2.5. Urinary IL-6 increased after exposure to PM_2.5, whereas in kidney cortex decreased. Histological changes were observed and accompanied by the induction of KIM-1. Acute exposure to PM_2.5 not decline kidney function. However, it can induce early kidney damage biomarkers, oxidative stress, inflammation and angiotensin mediators, which perhabs culminates in a lose of renal function.     

Disturbed atrio-ventricular conduction and normal contractile function in isolated hearts from Ca<Subscript>v</Subscript>1.3-knockout mice

Cardiac L-type calcium channels are formed by two -subunits, Ca_v1.2 (_1C) and Ca_v1.3 (_1D). In contrast to the uniform expression pattern of Ca_v1.2, Ca_v1.3 is highly expressed in sino-atrial node (SAN) and atrial tissue, but not in the ventricle. Accordingly, knockout of Ca_v1.3 (Ca_v1.3^–/–) in mice was shown to lead to a cardiac phenotype characterised by severe bradycardia in vivo and in isolated SAN cells. Ca_v1.3 may therefore constitute a novel pharmacological target for specific bradycardic agents.RNAse protection assays of murine wild type hearts revealed rather high Ca_v1.3 levels comparable to Ca_v1.2, suggesting functional relevance of Ca_v1.3 outside specialised tissues such as SAN. Due to the lack of specific Ca_v1.3 blockers, we directly examined the functional role of Ca_v1.3 using isolated working hearts from adult wild type (WT) and Ca_v1.3^–/– mice. Histological analysis of hearts revealed no pathological changes. Ventricular contractility and inotropic effects of isoproterenol were unaltered in Ca_v1.3^–/– hearts. Severe sinus bradycardia already noted in vivo was accompanied by ventricular extrasystoles. This phenotype was restored to nearly normal values by the cumulative addition of isoproterenol. Electrocardiograms of Ca_v1.3^–/– hearts revealed delayed atrio-ventricular (AV) conduction and a decoupling of heart rate and PR interval duration. Isoproterenol did not improve disturbance of AV conduction.In conclusion, suppression of Ca_v1.3 does not alter ventricular contractile function, and the decrease in sinus node frequency is counterbalanced by adrenergic stimulation. Importantly, bradyarrhythmia is partly due to an intrinsic AV node dysfunction, which is resistant to adrenergic counterbalance. These findings help to predict the clinical pattern of selective Ca_v1.3 blockade.J.M. and L.Y. contributed both equally to this work     

Transcriptomic profiling of Hydra magnipapillata after exposure to naproxen

The extensive use in humans and animals of nonsteroidal anti-inflammatory drugs (NSAIDs) increases their possible impact on aquatic organisms. In the present study, we investigated acute toxicity, morphological responses, and potential physiological and metabolic impacts of naproxen exposure on Hydra magnipapillata. The median lethal concentrations (LC₅₀) of naproxen in H. magnipapillata were 51.999 mg/L, 44.935 mg/L, and 42.500 mg/L after exposure for 24, 48, and 72 h, respectively. Morphological observation of the exposed Hydra showed that 40 mg/L naproxen stimulated the contraction of body column and tentacles after 24 h. A KEGG pathway analysis of the genes differentially expressed in the Hydra after exposure to naproxen for 6, 24, or 48 h demonstrated various cellular and metabolic effects, including protein processing in the endoplasmic reticulum, Wnt signaling, and tryptophan metabolism. These results suggest that exposure to naproxen affects the genetic material, inflammatory processes, and metabolic processes of aquatic organisms.     

A comparison of the effects of sibutramine hydrochloride,bupropion and methamphetamine on dopaminergic function: evidence that dopamine is not a pharmacological target for sibutramine

Sibutramine hydrochloride, a novel monoamine reuptake inhibitor antidepressant, has been studied to determine whether it alters dopaminergic function in the brain. Its effects have been compared with bupropion, a dopamine reuptake inhibitor, and methamphetamine, a dopamine reuptake inhibitor and releasing agent. Sibutramine (0.1–3 mg/kg PO) and methamphetamine (0.3–30 mg/kg PO) both prevented reserpine (0.75 mg/kg IV) ptosis in rats with ED₅₀ values of 0.6 mg/kg and 4.2 mg/kg, respectively. Bupropion (10–100 mg/kg PO) was ineffective against reserpine ptosis. The efflux of [³H]-dopamine from preloaded rat striatal slices was not altered by 10^–7–10^–5 M concentrations of sibutramine, BTS 54 354, BTS 54 505 (secondary and primary amine metabolites, respectively) or bupropion. In contrast, methamphetamine (10^–8–10^–4 M) caused a significant concentration-dependent increase in [³H]-dopamine release. Sibutramine (3 mg/kg IP or 6 mg/kg PO) and bupropion (10 mg/kg IP or 430 mg/kg PO) did not alter 3-methoxy-tyramine (3-MT) levels in rat striatum. Striatal 3-MT concentrations were, however, dose-dependently increased by methamphetamine (0.3–10 mg/kg IP or 0.42–4.2 mg/kg PO). Sibutramine (6 mg/kg PO) did not induce circling in rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal dopaminergic neuronal tract. Bupropion (10–100 mg/kg PO) did not induce circling at the lowest dose, but caused increasing ipsilateral rotation at higher doses. Methamphetamine (0.42 or 4.2 mg/kg PO) induced ipsilateral circling with marked effects at the higher dose. In a two-choice lever pressing model using rats trained to discriminated-amphetamine (0.5 mg/kg IP) from saline, sibutramine (0.3–3 mg/kg IP) generalised to the saline lever. Bupropion (3–30 mg/kg IP) generalised tod-amphetamine at the highest dose, while methamphetamine (0.1–5 mg/kg IP) generalised to this lever at doses as low as 0.3 mg/kg. Overall, the rank order of potency for enhancing central dopaminergic function is methamphetamine > bupropion >> sibutramine. The data therefore indicate that dopamine is unlikely to be an important pharmacological target for reuptake inhibition by sibutramine.     

Acute, nontoxic cadmium exposure inhibits pancreatic protease activities in the mouse.

Toxic effects of cadmium on liver, kidney, lung, and testes have been well established in experimental animals and in cell model systems. However, little is known about the effect of cadmium on pancreas, though the pancreas has been reported to accumulate high concentrations of cadmium. Therefore, in this study we examined the effects of cadmium on the pancreas of mice. A single sc injection of 1 mg Cd/kg to mice had no obvious toxic effects on the liver, kidney, and pancreas at both 1 and 5 days after cadmium treatment. Within the pancreas, however, the activities of trypsin, chymotrypsin, and carboxypeptidase A were significantly decreased at 1 day after cadmium treatment, whereas the activity of carboxypeptidase B was not changed. All pancreatic enzyme activities returned to the control levels by 5 days after cadmium treatment. The concentrations of cadmium in pancreas were very similar at 1 and 5 days after cadmium treatment, indicating a stable deposition of the metal. The concentration of zinc in pancreas was markedly increased at 5 days after cadmium treatment. In order to more fully examine the inhibitory effects of cadmium on these protease activities in pancreas, the direct effects of cadmium on purified proteases were studied in vitro. Contrary to the results in vivo, cadmium increased the activity of purified trypsin in a concentration-dependent manner. Consistent with the in vivo results, the activity of purified carboxypeptidase A was decreased by cadmium treatment in a concentration-dependent fashion in vitro. The activities of chymotrypsin and carboxypeptidase B did not change by the cadmium exposure in vitro. The enhanced activity of trypsin by cadmium was returned to the control levels by subsequent treatment with EDTA, indicating that enhancement was reversible. In addition, the zinc normally contained in purified carboxypeptidase A and carboxypeptidase B was released by the cadmium treatment. These results indicate that cadmium inhibits protease activities within the pancreas in vivo at doses that do not induce overt hepatic, renal, or pancreatic toxicity. Based on in vitro study, the decreases seen in trypsin and chymotrypsin activities might be based on indirect effects of cadmium, whereas the decreases in carboxypeptidase A are probably due to the direct inhibition by the metal.     

Effects of chronic caffeine exposure on adenosinergic modulation of the discriminative-stimulus effects of nicotine, methamphetamine, and cocaine in rats

RATIONALE: Adenosine receptors are involved in cocaine and methamphetamine discrimination and exposure to caffeine can affect behavioral effects of nicotine in rats. OBJECTIVES: Here we investigated the relative involvement of adenosine A(1) and A(2A) receptors in nicotine, cocaine, and methamphetamine discrimination, before and/or during chronic caffeine exposure. MATERIALS AND METHODS: The nonselective adenosine receptor antagonist caffeine, the A(1)-receptor antagonist cyclopentyltheophylline (CPT), and the A(2A)-receptor antagonist MSX-3 were evaluated in rats trained to discriminate 0.4 mg/kg nicotine from saline under a fixed-ratio schedule of food delivery. Effects of adenosine receptor antagonists were then compared in rats discriminating nicotine, methamphetamine, or cocaine from saline during chronic caffeine exposure in their drinking water. RESULTS: Caffeine, CPT, and MSX-3 partially generalized to nicotine and shifted nicotine dose-response curves leftwards. During chronic caffeine exposure, however, all three ligands failed to generalize to nicotine and failed to shift nicotine dose-response curves. In previous experiments, CPT and MSX-3 partially generalized to methamphetamine and cocaine and shifted dose-response curves leftwards. In the present experiments, CPT neither generalized nor shifted dose-response curves for methamphetamine or cocaine during chronic caffeine exposure. However, MSX-3 partially generalized to both psychostimulants and shifted their dose-response curves leftwards. Caffeine partially generalized to cocaine, but not methamphetamine, and shifted both dose-response curves leftwards. CONCLUSIONS: Both adenosine A(1) and A(2A) receptors are capable of modulating the discriminative-stimulus effects of nicotine. Chronic caffeine exposure produces complete tolerance to both A(1)- and A(2A)-mediated effects in nicotine-trained rats. In contrast, chronic caffeine exposure produces tolerance to adenosine A(1)-mediated, but not A(2A)-mediated, effects in methamphetamine- and cocaine-trained rats.