Impact of acute nicotine exposure on monoaminergic systems in adolescent and adult male and female rats.

Adolescence is a period of risk for beginning tobacco addiction. Differential neural response to nicotine in adolescents vs. adults may help explain the increased vulnerability to nicotine self-administration seen with adolescent onset. We indexed the effects of acute nicotine ditartrate (0.4 mg/kg, salt weight) administration on dopamine (DA) and serotonin (5HT) as well as the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in several brain regions (nucleus accumbens, striatum and frontal cortex) of 6-week old (adolescent) and 10-week old (young adult) Sprague-Dawley rats. When nicotine was administered DA concentrations in the accumbens were significantly higher in adults than in adolescents, whereas there was no age-related difference without nicotine. However neither age group showed a significant effect of nicotine vs. age-matched controls. DA turnover in the accumbens was significantly greater in adolescent females in response to nicotine, but adult females did not show this effect and neither did males of either age group. DA turnover in the striatum was significantly higher in adolescents than adults regardless of nicotine administration. In the frontal cortex, there was a more complex effect. Without nicotine, adult male rats had higher DA concentrations than adolescent males, whereas female rats did not differ from adolescent to adult ages. When given nicotine, the age effect was no longer seen in males. However, there was not a significant effect of nicotine vs. age-matched controls in either age group. No age or nicotine effects were seen in females. 5HT in the accumbens was significantly increased by nicotine administration in adults but not in adolescents. Altered neural responsivity of adolescents to nicotine-induced neural effects particularly in accumbens DA and 5HT may be related to the increased nicotine dose concentrations they self-administer.

Chronic infusions of mecamylamine into the medial habenula: Effects on nicotine self-administration in rats.

The habenula is an epithalamic structure through which descending connections go from the telencephalon to the brainstem, putting it in a key location to provide feedback control over the ascending projections from the brainstem to the telencephalon. The medial habenula has a high concentration of nicotinic receptors. We assessed the role of medial habenular nicotinic receptors for nicotine self-administration (SA) in female young adult Sprague-Dawley rats. The rats had bilateral chronic infusion cannulae placed into the medial habenula nucleus. Each cannula was connected to a slow delivery osmotic minipump to chronically infuse mecamylamine (100 µg/side/day) or vehicle for four consecutive weeks. The rats were tested for nicotine SA for the first two weeks of mecamylamine infusion. Then, they had one week of enforced abstinence, during which they had no access to the nicotine SA. Finally, they had one week of resumed nicotine SA access. There was a significantly differential mecamylamine effects in animals with lower and higher pretreatment baseline nicotine SA. Rats with lower baseline nicotine SA levels showed a nearly significant mecamylamine-induced reduction in SA while those with higher baseline levels of SA showed a significant mecamylamine-induced increase in nicotine SA. This study determined that medial habenular nicotinic receptors are important for nicotine reinforcement. Baseline level of performance makes a crucial difference for the involvement of habenular mechanisms in nicotine reinforcement with nicotinic activation being important for maintaining nicotine self-administration for those with lower levels of baseline self-administration and the opposite effect with subjects with higher levels of baseline self-administration.

Lorcaserin, a 5-HT2C agonist, decreases nicotine self-administration in female rats.

Lorcaserin, a selective 5-hydroxytryptamine(2C) (5-HT(2C)) agonist, has been shown to facilitate weight loss in obese populations. It was assessed for its efficacy in reducing nicotine self-administration in young adult female Sprague-Dawley rats. The effect of short-term doses (subcutaneous) on nicotine self-administration (0.03 mg/kg per infusion) with a fixed ratio 1 schedule was assessed in 3-h sessions. Short-term lorcaserin doses (0.3125-20 mg/kg) were administered in a counterbalanced order. Significant reduction of nicotine self-administration was achieved with all of the short-term doses in this range. Tests of lorcaserin on locomotor activity detected prominent sedative effects at doses greater than 1.25 mg/kg with more modest transient effects seen at 0.625 to 1.25 mg/kg. Long-term effects of lorcaserin on locomotor activity were tested with repeated injections with 0.625 mg/kg lorcaserin 10 times over 2 weeks. This low lorcaserin dose did not cause an overall change in locomotor activity relative to that of saline-injected controls. Long-term lorcaserin (0.625 mg/kg) significantly reduced nicotine self-administration over a 2-week period of repeated injections. Long-term lorcaserin at this same dose had no significant effects on food self-administration over the same 2-week period of repeated injections. These studies support development of the 5-HT(2C) agonist lorcaserin to aid tobacco smoking cessation.

Sazetidine-A, a selective alpha4beta2 nicotinic receptor desensitizing agent and partial agonist, reduces nicotine self-administration in rats.

Adequate treatment of tobacco addiction remains problematic. Part of the problem with treatment is a poor understanding of the pharmacologic aspects of nicotine contributing to addiction. In addition to activating nicotinic acetylcholine receptors, nicotine also desensitizes them. It is currently not known how much of each of nicotine's actions contribute to its particular behavioral effects. Sazetidine-A (saz-A) is a novel nicotinic receptor-desensitizing agent and partial agonist with high selectivity for alpha4beta2 receptors. The current experiments were conducted to determine whether saz-A would reduce nicotine self-administration in rats and to characterize its ancillary effects. Adult male Sprague-Dawley rats were allowed to self-administer nicotine. After initial food pellet training followed by 10 sessions of nicotine self-administration training, the rats were administered saz-A (0.1-3 mg/kg s.c.) or the saline vehicle in a repeated-measures counterbalanced design. Saz-A at the 3 mg/kg dose significantly decreased nicotine self-administration relative to performance of the same rats after saline injections. In a second study, long-term administration of this dose of sazetidine-A over the course of 10 sessions significantly reduced nicotine self-administration with no apparent diminution of effect. Saz-A in this dose range had only modest effects on locomotor activity, without any overall decrease in activity over a 1-h-long session. Saz-A significantly reduced food self-administration, but this effect was smaller than its effect on nicotine self-administration. Saz-A, which is a selective alpha4beta2-desensitizing agent and partial agonist, effectively reduces nicotine self-administration. This type of treatment holds promise for a new therapy to aid smoking cessation.

Mercury-induced cognitive impairment in metallothionein-1/2 null mice.

Metallothioneins are central for the metabolism and detoxification of transition metals. Exposure to mercury during early neurodevelopment is associated with neurocognitive impairment. Given the importance of metallothioneins in mercury detoxification, metallothioneins may be a protective factor against mercury-induced neurocognitive impairment. Deletion of the murine metallothionein-1 and metallothionein-2 genes causes choice accuracy impairments in the 8-arm radial maze. We hypothesize that deletions of metallothioneins genes will make metallothionein-null mice more vulnerable to mercury-induced cognitive impairment. We tested this hypothesis by exposing MT1/MT2-null and wild-type mice to developmental mercury (HgCl(2)) and evaluated the resultant effects on cognitive performance on the 8-arm radial maze. During the early phase of learning metallothionein-null mice were more susceptible to mercury-induced impairment compared to wildtype mice. Neurochemical analysis of the frontal cortex revealed that serotonin levels were higher in metallothionein-null mice compared to wild-type mice. This effect was independent of mercury exposure. However, dopamine levels in mercury-exposed metallothionein-null mice were lower compared to mercury-exposed wild-type mice. This work shows that deleting metallothioneins increase the vulnerability to developmental mercury-induced neurocognitive impairment. Metallothionein effects on monoamine transmitters may be related to this cognitive effect.

Adolescent vs. adult-onset nicotine self-administration in male rats: duration of effect and differential nicotinic receptor correlates.

Adolescence is the life stage when tobacco addiction typically begins. Adolescent neurobehavioral development may be altered by nicotine self-administration in a way that persistently potentiates addiction. Previously, we showed that female adolescent rats self-administer more nicotine than do adults and that the increased nicotine intake then persists through the transition to adulthood [E.D. Levin, A. Rezvani, D. Montoya, J. Rose, H. Swartzwelder, Adolescent-onset nicotine self-administration modeled in female rats, Psychopharmacology 169 (2003) 141-149.]. In the current study, male Sprague-Dawley rats were given access to nicotine via the standard operant IV self-administration procedure (nicotine bitartrate dose of 0.03 mg/kg/infusion). One group of male rats started during adolescence the other group started in young adulthood. After the end of the four-week period of self-administration brain regions of the rats were assessed for alpha4beta2 nicotinic receptor binding. We found that male rats, like females, show higher nicotine self-administration when starting during adolescence as compared to starting in adulthood (p<0.001). Indeed, the effect in adolescent males was even greater than that in females, with more than triple the rate of nicotine self-administration vs. the adult-onset group during the first 2 weeks. The adolescent onset nicotine-self-administering rats also had significantly greater high affinity nicotinic receptor binding in the midbrain and the striatum, whereas hippocampal binding did not differ between the age groups. Striatal values significantly correlated with nicotine self-administration during the first 2 weeks in the adult-onset group but not the adolescent-onset rats, suggesting that the differences in self-administration may depend in part on underlying disparities in synaptic responses to nicotine. After the initial 2 weeks, nicotine self-administration in male rats declined toward adult-like levels, as the adolescent rats approached adulthood. This study showed that adolescent male rats self-administer significantly more nicotine than do male adult rats, but that adolescent-onset nicotine self-administration in male rats declines over weeks of continued use to approach adult-onset levels. In a previous study, we found that female rats also show greater nicotine self-administration with adolescent onset vs. adult onset, but that the females continued higher rates of self-administration into adulthood. Our results thus reinforce the concept that the adolescent brain is unusually receptive to the effects of nicotine in a manner that reinforces the potential for addiction.

Increased nicotine self-administration following prenatal exposure in female rats.

There is a significant association between maternal cigarette smoking during pregnancy and greater subsequent risk of smoking in female offspring. In animal models, prenatal nicotine exposure causes persistent alterations in cholinergic and monoaminergic systems, both of which are important for nicotine actions underlying tobacco addiction. Accordingly, the current study was conducted to determine if there is a cause-and-effect relationship between prenatal nicotine exposure and nicotine self-administration starting in adolescence. Pregnant rats were administered nicotine (6 mg/kg/day) by osmotic minipump infusion throughout gestation and then, beginning in adolescence and continuing into adulthood, female offspring were given access to nicotine via a standard operant IV self-administration procedure (0.03 mg/kg/infusion). Gestational nicotine exposure did not alter the initial rate of nicotine self-administration. However, when animals underwent one week of forced abstinence and then had a second opportunity to self-administer nicotine, the prenatally-exposed animals showed a significantly greater rate of self-administration than did the controls. Prenatal nicotine exposure causes increased nicotine self-administration, which is revealed only when the animals are allowed to experience a period of nicotine abstinence. This supports a cause-and-effect relationship between the higher rates of smoking in the daughters of women who smoke cigarettes during pregnancy and implicates a role for nicotine in this effect. Our results further characterize the long-term liabilities of maternal smoking but also point to the potential liabilities of nicotine-based treatments for smoking cessation during pregnancy.

Persistent neurobehavioral effects of early postnatal domoic acid exposure in rats.

Domoic acid (DA) is a marine biotoxin, produced by the diatom Pseudo-nitzchia spp., which has been shown to cause cognitive impairment in adults who are exposed via contaminated seafood. The neurobehavioral consequences of developmental exposure are much less well understood. In a previous study, we showed that a single prenatal exposure to DA in rats at mid-gestation caused neurobehavioral changes that persist into adulthood including increased susceptibility to the benchmark amnestic drug scopolamine. In the current study, we examined the lasting neurobehavioral consequences of DA exposure on the first day of postnatal life, a time in rats marking the completion of the major phase of neuroproliferation and corresponding to week 24 of human gestation. The effects of DA exposure at doses from 0.025-0.1 mg/kg (s.c.) twice per day on each of postnatal days 1 and 2 were compared with vehicle-treated controls and rats treated by the same protocol with 1 mg/kg of kainic acid. Following kainic acid exposure, a sex-selective effect was seen with females but not males showing a significant slowing of response latency in the radial-arm maze. The high DA dose of 0.1 mg/kg was quite toxic causing lethality in all of the offspring exposed and this group was excluded from further analysis. When the offspring in the 0.05 mg/kg DA dose group were tested, significant hypoactivity in the Figure-8 maze was observed during adolescence. No significant DA effects were seen in response latency or choice accuracy on the radial-arm maze during either acquisition or with challenge of the amnestic drug scopolamine. Early postnatal DA exposure in the rat can be lethal and sublethal exposure can cause neurobehavioral effects manifest in modest hypoactivity during the adolescent period. However, the sublethal persistent neurobehavioral toxicity appears to be less pervasive than reported effects following DA administered mid-gestation.

Persisting neurobehavioral effects of developmental copper exposure in wildtype and metallothionein 1 and 2 knockout mice.

BACKGROUND: Metallothioneins (MT) are small proteins, which are crucial for the distribution of heavy and transition metals. Previously, we found in mice that knockout of MT 1 and 2 genes (MTKO) impaired spatial learning and potentiated the learning impairment caused by developmental mercury exposure. The current study examined the neurocognitive and neurochemical effects of MTKO with the developmental copper (Cu) supplementation. METHODS: Wildtype (WT) and MTKO mice were given supplemental Cu (0, 10 or 50 mg/l) in their drinking water during gestation and until weaning. When the mice were young adults they were trained on the win-shift 8-arm radial maze test of spatial learning and memory. After cognitive testing, their brains were analyzed for norepinepherine, dopamine and serotonin levels. RESULTS: In the spatial learning test, wildtype mice showed the normal sex difference with males performing more accurately than the females. This effect was eliminated by MTKO and restored by moderate Cu supplementation during development. In neurochemical studies, MTKO caused a significant overall increase in serotonin in all of the regions studied: the frontal cortex, posterior cortex, hippocampus, striatum, midbrain, and brainstem. MTKO also caused a significant increase in norepinepherine in the brainstem and hippocampus. In wildtype mice, Cu supplementation during development caused a significant decline in dopamine and norepinepherine in the midbrain and dopamine in the frontal cortex. These effects were blocked by MTKO. CONCLUSIONS: The normal sex difference in spatial working memory accuracy, which was eliminated by MTKO, was restored by moderate copper supplementation. MTKO increased serotonin across all brain areas studied and increased norepinepherine only in the hippocampus and brainstem. MTKO blocked copper-induced decreases in dopamine and norepinepherine in the midbrain and dopamine in the frontal cortex.

Chronic nicotine and dizocilpine effects on regionally specific nicotinic and NMDA glutamate receptor binding.

Chronic nicotine administration has long been known to increase the number of high-affinity alpha4beta2 nicotinic receptors with lesser effects on low-affinity alpha7 nicotinic receptors. Nicotine has been shown to promote the release of a variety of neurotransmitters including glutamate. Nicotine may also interact directly with the glutamatergic receptors. Nicotinic-glutamate interactions may be critical to the long-term effects of nicotine. Conversely, glutamatergic drugs may interact with the nicotinic system. Such interactions have important implications in interpretation of the mechanism of drug actions, especially when the drugs are given together. The current study examined the effects of chronic administration of nicotine (5 mg of the nicotine base/kg/day for 28 days), dizocilpine (MK-801) (0.3 mg/kg/day for 28 days), an NMDA receptor antagonist, as well as the combination of the two drugs on nicotinic and NMDA receptor densities in discrete brain regions. The chronic dose of dizocilpine used was behaviorally active causing a dramatic reduction in prepulse inhibition (PPI) of acoustic startle response. The nicotine dose used did not significantly affect PPI but previously we have found it to be behaviorally active in improving working memory function. High-affinity nicotinic receptor binding, as has been seen previously, was significantly increased by chronic nicotine in most areas. Chronic dizocilpine alone did not affect high-affinity nicotinic receptor binding, but it did modify the effects of chronic nicotine, attenuating nicotine-induced increases in the frontal cortex and striatum. Low-affinity nicotinic binding was significantly increased by chronic nicotine in only one area, the cerebellum. Chronic dizocilpine significantly increased low-affinity nicotinic binding in several brain areas, the colliculi, hippocampus, and the hypothalamus. The combination of nicotine and dizocilpine attenuated the effects of each with diminished nicotine-induced increased nicotinic low-affinity binding in the cerebellum and diminished dizocilpine-induced increased nicotinic low-affinity binding in the hippocampus and hypothalamus. In contrast, chronic nicotine and dizocilpine had a mutually potentiating effect of increasing nicotinic low-affinity binding in the frontal cortex. NMDA receptor binding was affected only in the hippocampus, where both dizocilpine and nicotine significantly increased binding. Chronic nicotine effects on receptor regulation are significantly affected by concurrent blockade of NMDA glutamate receptors.

Nicotine and clozapine actions on pre-pulse inhibition deficits caused by N-methyl-D-aspartate (NMDA) glutamatergic receptor blockade.

Pre-pulse inhibition (PPI) is a phenomenon of neurobehavioral plasticity in which the motor response to a startling stimulus is inhibited by a preceding stimulus of a lower intensity. Most often this is tested in the auditory mode. PPI is impaired in a variety of clinical states, most notably schizophrenia. PPI is easily modeled in experimental animals and serves as a useful basis for determining the neural bases for behavioral plasticity. In the current study we examined the interactions of N-methyl-D-aspartate (NMDA) glutamate and nicotinic cholinergic receptor systems in the expression of PPI. Female Sprague-Dawley rats were tested for auditory PPI after s.c. injections of the NMDA antagonist dizocilpine (also known as MK-801), the prototypic nicotinic agonist nicotine or both. Vehicle (saline) injections served as the control. Nicotine (0.2-0.8 mg/kg) by itself caused a modest but significant dose-related improvement in PPI. Dizocilpine (25-100 microg/kg) caused a dramatic dose-related impairment in PPI. Interestingly, the low to moderate doses of nicotine potentiated the PPI impairment by dizocilpine. In a second experiment nicotine and dizocilpine interactions with the atypical antipsychotic drug clozapine were assessed. As in the first experiment, nicotine potentiated the adverse effects of dizocilpine on PPI. The combination of nicotine with clozapine effectively attenuated the PPI impairment caused by dizocilpine when neither alone was effective. Inasmuch as PPI is impaired in schizophrenia, its reversal by the antipsychotic drug clozapine may depend on co-administration of nicotine by smoking in the patients. Development of nicotinic-based co-treatments for schizophrenia may achieve this benefit of nicotine without the hazards of smoking. Sensory modulation deficit, which is a syndrome of sensory over-responsiveness may also benefit from such combination therapy.

Distinct properties and advantages of a novel peroxisome proliferator-activated protein [gamma] selective modulator.

Antidiabetic thiazolidinediones (TZDs) and non-TZD compounds have been shown to serve as agonists of the peroxisome proliferator-activated receptor gamma (PPARgamma). Here, we report the identification and characterization of a novel non-TZD selective PPARgamma modulator (nTZDpa). nTZDpa bound potently to PPARgamma with high selectivity vs. PPARalpha or PPARdelta. In cell-based assays for transcriptional activation, nTZDpa served as a selective, potent PPARgamma partial agonist and was able to antagonize the activity of PPARgamma full agonists. nTZDpa also displayed partial agonist effects when its ability to promote adipogenesis in 3T3-L1 cells was evaluated. Assessment of protein conformation using protease protection or solution nuclear magnetic resonance spectroscopy methods showed that nTZDpa produced altered PPARgamma conformational stability vs. full agonists, thereby establishing a physical basis for its observed partial agonism. DNA microarray analysis of RNA from 3T3-L1 adipocytes treated with nTZDpa or several structurally diverse PPARgamma full agonists demonstrated qualitative differences in the affected gene expression profile for nTZDpa. Chronic treatment of fat-fed, C57BL/6J mice with nTZDpa or a TZD full agonist ameliorated hyperglycemia and hyperinsulinemia. However, unlike the TZD, nTZDpa caused reductions in weight gain and adipose depot size. Feed efficiency was also substantially diminished. Unlike TZDs, nTZDpa did not cause cardiac hypertrophy in mice. When a panel of PPARgamma target genes was examined in white adipose tissue, nTZDpa produced a different in vivo expression pattern vs. the full agonist. These findings establish that novel selective PPARgamma modulators can produce altered receptor conformational stability leading to distinctive gene expression profiles, reduced adipogenic cellular effects, and potentially improved in vivo biological responses. Such compounds may lead to preferred therapies for diabetes, obesity, or metabolic syndrome.

Olanzapine interactions with nicotine and mecamylamine in rats: effects on memory function.

Olanzapine is a widely used atypical antipsychotic drug. It is quite effective in reducing psychotic symptoms. However, the syndrome of schizophrenia encompasses more than psychosis. There is a pronounced cognitive impairment among other negative neurobehavioral symptoms. Classic antipsychotic drugs such as haloperidol do not alleviate cognitive impairment associated with schizophrenia and have been shown to exacerbate the dysfunction. The atypical antipsychotic drugs have a different profile of receptor actions and may have a different array of actions on cognitive function. The purpose of the current studies was to determine the effects of olanzapine on working memory function as measured by choice accuracy in the radial-arm maze. In determining the cognitive effects of any antipsychotic drug it is critical to determine its interactions with nicotinic manipulations since the great majority of people with schizophrenia smoke cigarettes and alterations in nicotinic receptors have been found in people with schizophrenia. Olanzapine caused a significant working memory impairment. Nicotine attenuated olanzapine-induced memory deficits. It may be the case that nicotinic co-treatment will be useful in addressing the cognitive impairment of schizophrenia.

Targeted deletion of the PRL receptor: effects on islet development, insulin production, and glucose tolerance.

PRL and placental lactogen (PL) stimulate beta-cell proliferation and insulin gene transcription in isolated islets and rat insulinoma cells, but the roles of the lactogenic hormones in islet development and insulin production in vivo remain unclear. To clarify the roles of the lactogens in pancreatic development and function, we measured islet density (number of islets/cm(2)) and mean islet size, beta-cell mass, pancreatic insulin mRNA levels, islet insulin content, and the insulin secretory response to glucose in an experimental model of lactogen resistance: the PRL receptor (PRLR)-deficient mouse. We then measured plasma glucose concentrations after ip injections of glucose or insulin. Compared with wild-type littermates, PRLR-deficient mice had 26-42% reductions (P < 0.01) in islet density and beta-cell mass. The reductions in islet density and beta-cell mass were noted as early as 3 wk of age and persisted through 8 months of age and were observed in both male and female mice. Pancreatic islets of PRLR-deficient mice were smaller than those of wild-type mice at weaning but not in adulthood. Pancreatic insulin mRNA levels were 20-30% lower (P < 0.05) in adult PRLR-deficient mice than in wild-type mice, and the insulin content of isolated islets was reduced by 16-25%. The insulin secretory response to ip glucose was blunted in PRLR-deficient males in vivo (P < 0.05) and in isolated islets of PRLR-deficient females and males in vitro (P < 0.01). Fasting blood glucose concentrations in PRLR-deficient mice were normal, but glucose levels after an ip glucose load were 10-20% higher (P < 0.02) than those in wild-type mice. On the other hand, the glucose response to ip insulin was normal. Our observations establish a physiologic role for lactogens in islet development and function.

Fat, carbohydrate, and calories in the development of diabetes and obesity in the C57BL/6J mouse.

We have previously shown that the C57BL/6J (B6) mouse will develop obesity and diabetes if raised on a high-fat diet. Because high fat feeding is associated with hyperphagia, the present study was designed to separate the effects of fat from those of excess caloric consumption in this animal model. B6 mice were fed a low-fat diet (LF group) diet, high-fat diet (HF group) diet, or high-fat-restricted diet (HFR group), in which intake animals were pair-fed a high-fat diet to caloric level consumed by LF for 11 weeks. Within 3 weeks, HFR were significantly heavier than LF and, after 11 weeks, weight and glucose levels, but not insulin, were significantly increased in HFR when compared to LF. Body composition analysis showed the weight increase in HFR arose from an increase in percent fat consumed. We conclude that reducing the number of kilocalories consumed from a high-fat diet attenuates but does not prevent the development of type 2 diabetes and obesity in the B6 mouse.

Effect of the H, K-ATPase inhibitor, esomeprazole magnesium, on gut total antioxidant capacity in mice.

Antioxidant depletion is believed to be a mechanism involved in the pathophysiology of several upper gastrointestinal disorders, and H, K-ATPase inhibitors can alter free radical production by neutrophils. We hypothesized that the H, K-ATPase inhibitor esomeprazole magnesium would decrease gut free radical production with a concomitant increase in gut total antioxidant capacity. A/J mice (n = 10/group) received either vehicle (control) or one of three concentrations of esomeprazole magnesium in vehicle by once-daily gavage for 10 days. Using tissue extracts from stomach and colon, total antioxidant capacity, lipid peroxide levels, and constitutive Cu/Zn-superoxide dismutase were measured using validated assays. There was a dose-related increase in total antioxidant capacity (analysis of variance, P < 0.001) in stomach, but there was no change in the colon. In the assessment of free radical production, there was a trend toward decreased lipid peroxide levels in stomach from mice receiving esomeprazole. In stomach, Cu/Zn-superoxide dismutase activity was increased (ANOVA: p=.03) in mice receiving esomeprazole. In conclusion, gastric total antioxidant capacity and Cu/Zn-superoxide dismutase activity are increased by esomeprazole, and these changes may result in part from decreased free radical production. The present results support the notion that the pharmacological effects of this agent on upper intestinal tissue are more complex than previously thought, and appear to involve both enzymatic and nonenzymatic tissue antioxidants.

Assessing the effects of chronic sazetidine-A delivery on nicotine self-administration in both male and female rats.

RATIONALE: Sazetidine-A is a selective α4ß2 nicotinic receptor desensitizing agent and partial agonist. It has been shown in previous studies to significantly reduce nicotine self-administration in rats after acute or repeated injections. However, the effects of continuous chronic infusions of sazetidine-A on maintenance of nicotine self-administration and relapse after abstinence have yet to be examined. OBJECTIVES: This study evaluated the efficacy of continuous sazetidine-A infusions (sc) over a period of 4 weeks to reduce nicotine self-administration in male and female Sprague-Dawley rats. METHODS: Sazetidine-A was administered via Alzet osmotic minipumps to young adult female and male rats at doses of 0, 2 or 6 mg/kg/day for 4 weeks. The effects of sazetidine-A on IV nicotine self-administration were examined in repeated 3-h sessions over the first 2 weeks of infusion followed by 1 week of forced abstinence from nicotine and 1 week of resumed nicotine access. RESULTS: The 6 mg/kg/day sazetidine-A dose significantly reduced overall nicotine self-administration compared with vehicle control across the sessions for both male (p < 0.001) and female (p < 0.05) rats. The lower 2 mg/kg/day sazetidine-A infusion dose was effective in reducing nicotine self-administration for male (p < 0.001), but not female rats. No attenuation in sazetidine-A effectiveness was seen over the course of the 4-week treatment. In the vehicle control group, male rats self-administered significantly (p < 0.001) more nicotine than females. CONCLUSIONS: The continuing effectiveness of sazetidine-A in reducing nicotine self-administration in both male and female rats supports its promise as a new treatment to help people successfully quit smoking.

Persistent behavioral impairment caused by embryonic methylphenidate exposure in zebrafish.

As more adults take the stimulant medication methylphenidate to treat attention deficit hyperactivity disorder (ADHD) residual type, the risk arises with regard to exposure during early development if people taking the medication become pregnant. We studied the neurobehavioral effects of methylphenidate in zebrafish. Zebrafish offer cellular reporter systems, continuous visual access and molecular interventions such as morpholinos to help determine critical mechanisms underlying neurobehavioral teratogenicity. Previously, we had seen that persisting neurobehavioral impairment in zebrafish with developmental chlorpyrifos exposure was associated with disturbed dopamine systems. Because methylphenidate is an indirect dopamine agonist, it was thought that it might also cause persistent behavioral impairment after developmental exposure. Zebrafish embryos were exposed to the ADHD stimulant medication methylphenidate 0-5 days post fertilization (12.5-50mg/l). They were tested for long-term behavioral effects as adults. Methylphenidate exposure (50mg/l) caused significant increases in dopamine, norepinepherine and serotonin on day 6 but not day 30 after fertilization. In the novel tank diving test of predatory avoidance developmental methylphenidate (50mg/l) caused a significant reduction in the normal diving response. In the three-chamber spatial learning task early developmental methylphenidate (50mg/l) caused a significant impairment in choice accuracy. These data show that early developmental exposure of zebrafish to methylphenidate causes a long-term impairment in neurobehavioral plasticity. The identification of these functional deficits in zebrafish enables further studies with this model to determine how molecular and cellular mechanisms are disturbed to arrive at this compromised state.

D-cycloserine selectively decreases nicotine self-administration in rats with low baseline levels of response.

Expanding the variety of treatments available to aid smoking cessation will allow the treatments to be customized to particular types of smokers. The key is to understand which subpopulations of smokers respond best to which treatment. This study used adult female Sprague-Dawley rats to evaluate the efficacy of D-cycloserine, a partial NMDA glutamate receptor agonist, in reducing nicotine self-administration. Rats were trained to self-administer nicotine (0.03 mg/kg/infusion, i.v.) via operant lever response (FR1) with a secondary visual reinforcer. Two studies of D-cycloserine effects on nicotine self-administration were conducted: an acute dose-effect study (0, 10, 20 and 40 mg/kg, s.c.) and a chronic study with 40 mg/kg given before each test session for two weeks. Effects on rats with low or high pretreatment baseline levels of nicotine self-administration were assessed. In the acute study there was a significant interaction of D-cycloserine×baseline level of nicotine self-administration. In the low baseline group, 10 mg/kg D-cycloserine significantly decreased nicotine self-administration. In the high baseline group, 40 mg/kg significantly increased nicotine self-administration. In the repeated injection study, there was also a significant interaction of d-cycloserine×baseline level of nicotine self-administration. Chronic D-cycloserine significantly reduced nicotine self-administration selectively in rats with low baseline nicotine use, but was ineffective with the rats with higher levels of baseline nicotine self-administration. NMDA glutamate treatments may be particularly useful in helping lighter smokers successfully quit smoking, highlighting the need for diverse treatments for different types of smokers.

Histamine H(1) antagonist treatment with pyrilamine reduces nicotine self-administration in rats.

Nicotine has been definitively shown to be critically involved in the neural bases of tobacco addiction. However, nicotine releases a wide variety of neurotransmitters. Nicotine-induced dopamine release has been shown to play a key role in facilitating nicotine self-administration. Other transmitter systems may also play important roles in the pharmacological effects of nicotine and may provide important leads for combating nicotine self-administration. Clozapine, an antipsychotic drug, which blocks a variety of different transmitter receptors including serotonin 5HT(2) and histamine H(1) receptors, has been found to decrease smoking. Previously we found that the serotonin 5HT(2) antagonist, ketanserin, significantly reduced nicotine self-administration. In the current study, we assessed histamine H(1) receptor interaction with nicotine self-administration. Young adult female Sprague-Dawley rats were fitted with IV catheters and trained to self-administer nicotine (0.03mg/kg/infusion). Acute doses of 40mg/kg of pyrilamine, a histamine H(1) antagonist, significantly reduced nicotine self-administration. We also found that repeated injections (20mg/kg) or chronic infusion via osmotic minipumps (50mg/kg/day) of pyrilamine also significantly decreased nicotine self-administration. The peripherally restricted H(1) antagonist ebastine was ineffective in reducing nicotine self-administration, pointing to central H(1) receptor blockade as key for the effectiveness of pyrilamine. H(1) antagonists may be a promising avenue to explore for new treatments to aid smoking cessation.