Differences in Cognitive Task Performance, Reinforcement Enhancement, and Nicotine Dependence Between Menthol and Nonmenthol Cigarette Smokers.

INTRODUCTION: Menthol has been shown to target similar brain regions and neural receptors as nicotine, yet the association between menthol cigarette use and cognitive performance remains unknown. AIMS AND METHODS: This study examined differences in cognitive task performance between menthol (MS) and nonmenthol (NMS) cigarette smokers after acute cigarette consumption. Sixty white and black and/or African American, nonabstinent, MS (n = 30) and NMS (n = 30) were assessed presmoking and postsmoking their preferred cigarette on four computerized tasks: Continuous Performance Task (CPT; alerting attention), N-Back Task (working memory), Finger Tapping Task (motor control), and Apple Picker Task (reinforcement enhancement). Self-reported nicotine dependence and objective smoking topography measures were also compared between groups. RESULTS: Initial unadjusted analyses showed a significant effect of cigarette type × time on CPT speed (p = .042), where MS improved while NMS group worsened in CPT speed after smoking. After controlling for baseline cigarette craving and cigarette nicotine levels, the effect of cigarette type × time for all cognitive outcomes was statistically nonsignificant (ps > .05). However, there remained a significant effect of cigarette type, where MS versus NMS had poorer CPT (p = .046) and N-Back Task accuracy (p = .006) but faster N-Back speed (p = .039). There were no statistically significant differences between groups on reinforcement enhancement, nicotine dependence, or smoking behavior outcomes (ps > .05). CONCLUSIONS: Contrary to our hypotheses, results did not find a significant effect of cigarette type on the change in cognitive performance after acute smoking in nonabstinent smokers. Further studies are needed to clarify the specific pharmacological effects of nicotine and menthol on cognitive functioning. IMPLICATIONS: The current study is the first to compare the potential enhancement of cognitive task performance after acute cigarette smoking between satiated menthol and nonmenthol cigarette smokers. Study results suggest that acute menthol cigarette use may not enhance cognitive function above and beyond nonmenthol cigarettes to increase dependence among menthol smokers. However, the contribution of other psychological factors (eg, craving, mood) and cigarette characteristics (eg, nicotine content) may be involved in cognitive function enhancement to perpetuate dependence and smoking persistence for menthol smokers.

Prolonging the Reduction of Nicotine Self-Administration in Rats by Coadministering Chronic Nicotine With Amitifadine, a Triple Monoamine Reuptake Inhibitor With CYP2B6 Inhibitory Actions.

INTRODUCTION: Existing treatments can aid tobacco smoking cessation, but they have low efficacy. Because there is a network of neural systems involved in tobacco addiction, combination treatments may provide greater efficacy. Chronic nicotine and amitifadine have each been shown to significantly reduce nicotine self-administration in rats. This study was conducted to determine if the combination of chronic nicotine with amitifadine, a triple monoamine reuptake inhibitor with CYP2B inhibitory effects, would reduce nicotine self-administration to a greater extent than either alone or placebo. METHODS: This study tested the combination of nicotine plus amitifadine in young adult female Sprague-Dawley rats self-administering nicotine (0.03 mg/kg/infusion). This combination was compared with each treatment alone and the vehicle during continuing nicotine self-administration as well as during resumption of self-administration after a week of enforced abstinence, modeling a quit attempt. Finally, we studied the residual effects of these therapies after discontinuation of treatment. RESULTS: Treatment with either chronic nicotine or amitifadine alone significantly reduced nicotine self-administration relative to controls. The combination of the treatments significantly enhanced this effect. After treatment withdrawal, all of the groups showed increases in nicotine self-administration, but only the combined treatment group remained significantly below control rates of nicotine self-administration. CONCLUSIONS: This study showed the promise of amitifadine as a possible new treatment for smoking cessation and suggested that amitifadine is more effective when given with chronic nicotine. The improved efficacy of the amitifadine and nicotine combination may be potentiated by amitifadine's inhibitory effects on CYP2B, which slows nicotine metabolism. IMPLICATIONS: This study replicated the effects that chronic nicotine or chronic amitifadine, a triple reuptake inhibitor, significantly reduces nicotine self-administration in rats. It extends those findings by showing that the combination of chronic nicotine plus amitifadine causes significantly greater reduction in nicotine self-administration than either drug treatment alone. The combination of chronic amitifadine and chronic nicotine also causes a persistent significant reduction in nicotine self-administration after the end of treatment. The amitifadine and nicotine treatment should be assessed in humans to determine whether this combination provides greater efficacy in smoking cessation than transdermal nicotine treatment alone.

Preclinical toxicity evaluation of a novel immunotoxin, D2C7-(scdsFv)-PE38KDEL, administered via intracerebral convection-enhanced delivery in rats.

D2C7-(scdsFv)-PE38KDEL (D2C7-IT) is a novel immunotoxin that reacts with wild-type epidermal growth factor receptor (EGFRwt) and mutant EGFRvIII proteins overexpressed in glioblastomas. This study assessed the toxicity of intracerebral administration of D2C7-IT to support an initial Food and Drug Administration Investigational New Drug application. After the optimization of the formulation and administration, two cohorts (an acute and chronic cohort necropsied on study days 5 and 34) of Sprague-Dawley (SD) rats (four groups of 5 males and 5 females) were infused with the D2C7-IT formulation at total doses of 0, 0.05, 0.1, 0.4 µg (the acute cohort) and 0, 0.05, 0.1, 0.35 µg (the chronic cohort) for approximately 72 h by intracerebral convection-enhanced delivery using osmotic pumps. Mortality was observed in the 0.40 µg (5/10 rats) and 0.35 µg (4/10 rats) high-dose groups of each cohort. Body weight loss and abnormal behavior were only revealed in the rats treated with high doses of D2C7-IT. No dose-related effects were observed in clinical laboratory tests in either cohort. A gross pathologic examination of systemic tissues from the high-dose and control groups in both cohorts exhibited no dose-related or drug-related pathologic findings. Brain histopathology revealed the frequent occurrence of dose-related encephalomalacia, edema, and demyelination in the high-dose groups of both cohorts. In this study, the maximum tolerated dose of D2C7-IT was determined to be between 0.10 and 0.35 µg, and the no-observed-adverse-effect-level was 0.05 µg in SD rats. Both parameters were utilized to design the Phase I/II D2C7-IT clinical trial.

Acute and chronic glutamate NMDA antagonist treatment attenuates dopamine D1 antagonist-induced reduction of nicotine self-administration in female rats.

Multiple interacting neural systems are involved in sustaining nicotine reinforcement. We and others have shown that dopamine D1 receptors and glutamate NMDA receptors both play important roles in nicotine reinforcement. Blockade of D1 receptors with the antagonist SCH-23390 (0.02 mg/kg) both acutely and chronically significantly decreased nicotine self-administration in rats. Blockade of NMDA receptors (10 mg/kg) acutely with memantine significantly increased nicotine self-administration, but chronic blockade of NMDA receptors with memantine significantly decreased nicotine self-administration. The current study examined the interactions of acute and chronic administration of SCH-23390 and memantine on nicotine self-administration in female rats. Replicating earlier studies, acute and chronic SCH-23390 significantly decreased nicotine self-administration and memantine had a biphasic effect with acute administration increasing nicotine self-administration and chronic memantine showed a non-significant trend toward decreasing it. However, chronic interaction study showed that memantine significantly attenuated the decrease in nicotine self-administration caused by chronic SCH-23390. These studies provide important information that memantine attenuates the efficacy of D1 antagonist SCH 23390 in reducing nicotine-self-administration. These two drugs do not appear to have mutually potentiating effects to aid tobacco cessation.

Embryonic exposures to cadmium and PAHs cause long-term and interacting neurobehavioral effects in zebrafish.

Developmental exposure to either polycyclic aromatic hydrocarbons (PAHs) or heavy metals has been shown to cause persisting and overlapping neurobehavioral effects in animal models. However, interactions between these compounds have not been well characterized, despite their co-occurrence in a variety of environmental media. In two companion studies, we examined the effects of developmental exposure to cadmium (Cd) with or without co-exposure to prototypic PAHs benzo[a]pyrene (BaP, Exp. 1) or fluoranthene (FA, Exp. 2) using a developing zebrafish model. Zebrafish embryos were exposed to Cd (0-0.3 µM), BaP (0-3 µM), FA (0-1.0 µM), or binary Cd-PAH mixtures from 5 to 122 h post fertilization (hpf). In Exp. 1, Cd and BaP produced independent effects on an array of outcomes and interacting effects on specific outcomes. Notably, Cd-induced deficits in dark-induced locomotor stimulation were attenuated by BaP co-exposure in the larval motility test and BaP-induced hyperactivity was attenuated by Cd co-exposure in the adolescent novel tank test. Likewise, in Exp. 2, Cd and FA produced both independent and interacting effects. FA-induced increases on adult post-tap activity in the tap startle test were attenuated by co-exposure with Cd. On the predator avoidance test, FA- and 0.3 µM Cd-induced hyperactivity effects were attenuated by their co-exposure. Taken together, these data indicate that while the effects of Cd and these representative PAHs on zebrafish behavior were largely independent of one another, binary mixtures can produce sub-additive effects for some neurobehavioral outcomes and at certain ages. This research emphasizes the need for detailed risk assessments of mixtures containing contaminants of differing classes, and for clarity on the mechanisms which allow cross-class toxicant interactions to occur.

Prenatal and perinatal exposure to Per- and polyfluoroalkyl substances (PFAS)-contaminated drinking water impacts offspring neurobehavior and development.

Per- and polyfluoroalkyl substances (PFAS) are persistent organic pollutants ubiquitous in the environment and humans. In-utero PFAS exposure is associated with numerous adverse health impacts. However, little is known about how prenatal PFAS mixture exposure affects offspring's neurobehavioral function. This study aims to determine the causal relationship between in-utero PFAS mixture exposure and neurobehavioral changes in Sprague-Dawley rat offspring. Dams were exposed via drinking water to the vehicle (control), an environmentally relevant PFAS mixture, or a high-dose PFAS mixture. The environmentally relevant mixture was formulated to resemble measured tap water levels in Pittsboro, NC, USA (10 PFAS compounds; sum PFAS =758.6 ng/L). The high-dose PFAS load was 3.8 mg/L (5000×), within the range of exposures in the experimental literature. Exposure occurred seven days before mating until birth. Following exposure to PFAS-laden water or the vehicle during fetal development, neurobehavioral toxicity was assessed in male and female offspring with a battery of motor, cognitive, and affective function tests as juveniles, adolescents, and adults. Just before weaning, the environmentally relevant exposure group had smaller anogenital distances compared to the vehicle and high-dose groups on day 17, and males in the environmentally relevant exposure group demonstrated lower weights than the high-dose group on day 21 (p < 0.05). Reflex development delays were seen in negative geotaxis acquisition for both exposure groups compared to vehicle-exposed controls (p = 0.009). Our post-weaning behavioral measures of anxiety, depression, and memory were not found to be affected by maternal PFAS exposure. In adolescence (week five) and adulthood (week eight), the high PFAS dose significantly attenuated typical sex differences in locomotor activity. Maternal exposure to an environmentally relevant PFAS mixture produced developmental delays in the domains of pup weight, anogenital distance, and reflex acquisition for rat offspring. The high-dose PFAS exposure significantly decreased typical sex differences in locomotor activity.

Persisting neurobehavioral consequences of daily or intermittent paternal cannabis administration in F1 and F2 Rats.

Repeated paternal preconception exposure to Δ9-tetrahydrocannabinol (Δ9-THC) alone or together with the other constituents in a cannabis extract has been shown in our earlier studies in rats to cause significant neurobehavioral impairment in their offspring. In the current study, we compared the effects of daily cannabis extract (CE) exposure to cannabis on two consecutive days per week, modeling weekend cannabis use in human. The CE contained Δ9-THC as well as cannabidiol and cannabinol. We also extended the investigation of the study to cross-generational effects of grand-paternal cannabis exposure on the F2 generation and included testing the effects of paternal cannabis exposure on responding for opiate self-administration in F1 and F2 generation offspring. We replicated the findings of neurobehavioral impairment in F1 offspring of male rats exposed to cannabis extract containing 4 mg/kg/day of Δ9-THC daily for four weeks prior to mating with drug naïve females. The 4-week cannabis extract exposure caused a significant decrease in weight gain in the male rats exposed daily. In contrast, their offspring showed significantly greater body weights and anogenital distances (AGD) in the third to fourth weeks after birth. The behavioral effects seen in the F1 generation were increased habituation of locomotor activity in the figure-8 maze in female offspring and increased lever pressing for the opiate drug remifentanil in male offspring. The F2 generation showed significantly impaired negative geotaxis and an elimination of the typical sex-difference in locomotor activity, with effects not seen in the F1 generation. This study shows that daily paternal cannabis exposure for four weeks prior to mating causes significant neurobehavioral impairment in the F1 and F2 offspring. Intermittent exposure on two consecutive days per week for four weeks caused comparable neurobehavioral impairment. In sum, there should be concern about paternal as well as maternal exposure to cannabis concerning neurobehavioral development of their offspring.

Developmental exposure to pesticides that disrupt retinoic acid signaling causes persistent retinoid and behavioral dysfunction in zebrafish.

Early developmental exposure to environmental toxicants may play a role in the risk for developing autism. A variety of pesticides have direct effects on retinoic acid (RA) signaling and as RA signaling has important roles in neurodevelopment, such compounds may cause developmental neurotoxicity through an overlapping adverse outcome pathway. It is hypothesized that a pesticide's embryonic effects on retinoid function may correspond with neurobehavioral disruption later in development. In the current studies, we determined the effects of RA-acting pesticides on neurobehavioral development in zebrafish. Buprofezin and imazalil caused generalized hypoactivity in the larval motility test, whereas chlorothalonil and endosulfan I led to selective hypoactivity and hyperactivity, respectively. With buprofezin, chlorothalonil, and imazalil, hypoactivity and/or novel anxiety-like behaviors persisted in adulthood and buprofezin additionally decreased social attraction responses in adulthood. Endosulfan I did not produce significant adult behavioral effects. Using qPCR analyses of adult brain tissue, we observed treatment-induced alterations in RA synthesis or catabolic genes, indicating persistent changes in RA homeostasis. These changes were compound-specific, with respect to expression directionality, and potential patterns of homeostatic disruption. Results suggest the likely persistence of disruptions in RA signaling well into adulthood and may represent compensatory mechanisms following early life stage exposures. This study demonstrates that early developmental exposure to environmental toxicants that interfere with RA signaling causes short as well as long-term behavioral disruption in a well-established zebrafish behavioral model and expand upon the meaning of the RA adverse outcome pathway, indicating that observed effects likely correspond with the nature of underlying homeostatic effects.

Zebrafish model systems for developmental neurobehavioral toxicology.

Zebrafish offer many advantages that complement classic mammalian models for the study of normal development as well as for the teratogenic effects of exposure to hazardous compounds. The clear chorion and embryo of the zebrafish allow for continuous visualization of the anatomical changes associated with development, which, along with short maturation times and the capability of complex behavior, makes this model particularly useful for measuring changes to the developing nervous system. Moreover, the rich array of developmental, behavioral, and molecular benefits offered by the zebrafish have contributed to an increasing demand for the use of zebrafish in behavioral teratology. Essential for this endeavor has been the development of a battery of tests to evaluate a spectrum of behavior in zebrafish. Measures of sensorimotor plasticity, emotional function, cognition and social interaction have been used to characterize the persisting adverse effects of developmental exposure to a variety of chemicals including therapeutic drugs, drugs of abuse and environmental toxicants. In this review, we present and discuss such tests and data from a range of developmental neurobehavioral toxicology studies using zebrafish as a model. Zebrafish provide a key intermediate model between high throughput in vitro screens and the classic mammalian models as they have the accessibility of in vitro models and the complex functional capabilities of mammalian models.

Branched-chain amino acids alter neurobehavioral function in rats.

Recently, we have described a strong association of branched-chain amino acids (BCAA) and aromatic amino acids (AAA) with obesity and insulin resistance. In the current study, we have investigated the potential impact of BCAA on behavioral functions. We demonstrate that supplementation of either a high-sucrose or a high-fat diet with BCAA induces anxiety-like behavior in rats compared with control groups fed on unsupplemented diets. These behavioral changes are associated with a significant decrease in the concentration of tryptophan (Trp) in brain tissues and a consequent decrease in serotonin but no difference in indices of serotonin synaptic function. The anxiety-like behaviors and decreased levels of Trp in the brain of BCAA-fed rats were reversed by supplementation of Trp in the drinking water but not by administration of fluoxetine, a selective serotonin reuptake inhibitor, suggesting that the behavioral changes are independent of the serotonergic pathway of Trp metabolism. Instead, BCAA supplementation lowers the brain levels of another Trp-derived metabolite, kynurenic acid, and these levels are normalized by Trp supplementation. We conclude that supplementation of high-energy diets with BCAA causes neurobehavioral impairment. Since BCAA are elevated spontaneously in human obesity, our studies suggest a potential mechanism for explaining the strong association of obesity and mood disorders.

Effects of caffeine on alcohol consumption and nicotine self-administration in rats.

BACKGROUND: Caffeine, alcohol, and nicotine are 3 of the most widespread self-administered psychoactive substances, which are known to be extensively co-administered. However, little is known about the degree to which they may mutually potentiate each other's consumption. METHODS: In the current set of studies, we examined in rats the effect of caffeine administration on alcohol drinking and intravenous (i.v.) self-administration of nicotine. In male alcohol-preferring (P) rats, caffeine (5, 10, and 20 mg/kg) or the saline vehicle was administered acutely either by subcutaneous (S.C.) injection or orally (PO) by gavage. In a chronic study, the effect of PO caffeine (5 and 20 mg/kg) on alcohol intake over a 10-day period was tested. In another experiment, the effect of acute PO administration of caffeine (20 mg/kg) or saline on saccharin intake (0.2% solution) was determined in P rats. Effects of 20 mg/kg caffeine on motor activity were also determined in P rats. Finally, the effects of acute PO caffeine administration on nicotine self-administration in Sprague-Dawley rats were also determined. RESULTS: Both routes of administration of caffeine, S.C. and PO, caused a significant dose-related decrease in alcohol intake and preference during free access to alcohol and after 4-day deprivation of alcohol. However, the low dose of 5 mg/kg caffeine increased alcohol intake. Acute PO caffeine also reduced saccharin intake. Acute systemic administration of 20 mg/kg caffeine did not exert a significant effect on motor activity. In Sprague-Dawley rats trained to self-administer i.v. nicotine, acute PO administration of caffeine significantly increased self-administration of nicotine in a dose-related manner. CONCLUSIONS: These results suggest that adenosine receptor systems may play a role in both alcohol and nicotine intake and deserve further study regarding these addictions.

Developmental exposure of zebrafish to neonicotinoid pesticides: Long-term effects on neurobehavioral function.

Neonicotinoid compounds are commonly used insecticides which have become increasingly used as replacements of older generations of insecticides, such as organophosphates. Given the established neurotoxicity of cholinergic toxicants, developmental neurotoxicity studies are needed to identify in vertebrate species the potential toxicity of these insecticides which act on nicotinic cholinergic receptors. Previously, developmental exposure to a neonicotinoid insecticide imidacloprid was shown to cause persisting neurobehavioral toxicity in zebrafish. The current study evaluated neurobehavioral effects of embryonic exposure to two other neonicotinoid insecticides, clothianidin (1-100 µM) and dinotefuran (1-100 µM) in zebrafish (5-120 h post-fertilization), concentrations below the threshold for increased lethality and overt dysmorphogenesis. Neurobehavioral tests were conducted at larval (6 days), adolescent (10 weeks) and adult (8 months) ages. Both compounds caused short-term behavioral effects on larval motility, although these effects were distinct from one another. At a lower concentration (1 µM) clothianidin increased dark-induced locomotor stimulation the second time the lights turned off, while a higher concentration (100 µM) reduced activity in the dark at its second presentation. By contrast, dinotefuran (10-100 µM) caused a general decrease in locomotion. Specific longer-term neurobehavioral toxicity after early developmental exposure was also seen. clothianidin (100 µM) reduced locomotor activity in the novel tank in adolescence and adulthood, as well as reduced baseline activity in the tap startle test (1-100 µM) and reduced activity early (1-10 µM) or throughout the predator avoidance test session (100 µM). In addition to locomotor effects, clothianidin altered the diving response in a dose-, age- and time-block-dependent manner (1 µM, 100 µM), causing fish to remain further away from a fast predator cue (100 µM) relative to controls. Dinotefuran produced comparatively fewer effects, increasing the diving response in adulthood (10 µM), but not adolescence, and suppressing initial locomotor activity in the predator avoidance test (1-10 µM). These data indicate that neonicotinoid insecticides may carry some of the same risks for vertebrates posed by other classes of insecticides, and that these adverse behavioral consequences of early developmental exposure are evident well into adulthood.

Embryonic exposure to PFAS causes long-term, compound-specific behavioral alterations in zebrafish.

Per- and polyfluoroalkyl substances (PFAS) are commonly used as surfactants and coatings for industrial processes and consumer products. These compounds have been increasingly detected in drinking water and human tissue, and concern over their potential effects on health and development is growing. However, relatively little data are available for their potential impacts on neurodevelopment and the degree to which different compounds within this class may differ from one another in their neurotoxicity. The present study examined the neurobehavioral toxicology of two representative compounds in a zebrafish model. Zebrafish embryos were exposed to 0.1-100uM perfluorooctanoic acid (PFOA) or 0.01-1.0uM perfluorooctanesulfonic acid (PFOS) from 5 to 122 h post-fertilization. These concentrations were below threshold for producing increased lethality or overt dysmorphologies, and PFOA was tolerated at a concentration 100× higher than PFOS. Fish were maintained to adulthood, with behavioral assessments at 6 days, 3 months (adolescence) and 8 months of age (adulthood). Both PFOA and PFOS caused behavioral changes in zebrafish, but PFOS and PFOS produced strikingly different phenotypes. PFOA was associated with increased larval motility in the dark (100uM), and enhanced diving responses in adolescence (100uM) but not adulthood. PFOS was associated with a reversed light-dark response in the larval motility test (0.1-1uM), whereby the fish were more active in the light than the dark. PFOS also caused time-dependent changes in locomotor activity in the novel tank test during adolescence (0.1-1.0uM) and an overall pattern of hypoactivity in adulthood at the lowest concentration (0.01uM). Additionally, the lowest concentration of PFOS (0.01uM) reduced acoustic startle magnitude in adolescence, but not adulthood. These data suggest that PFOS and PFOA both produce neurobehavioral toxicity, but these effects are quite distinct from one another.

Developmental exposure to the flame retardant, triphenyl phosphate, causes long-lasting neurobehavioral and neurochemical dysfunction.

BACKGROUND: Human exposures to organophosphate flame retardants result from their use as additives in numerous consumer products. These agents are replacements for brominated flame retardants but have not yet faced similar scrutiny for developmental neurotoxicity. We examined a representative organophosphate flame retardant, triphenyl phosphate (TPP) and its potential effects on behavioral development and dopaminergic function. METHODS: Female Sprague-Dawley rats were given low doses of TPP (16 or 32 mg kg-1  day-1 ) via subcutaneous osmotic minipumps, begun preconception and continued into the early postnatal period. Offspring were administered a battery of behavioral tests from adolescence into adulthood, and littermates were used to evaluate dopaminergic synaptic function. RESULTS: Offspring with TPP exposures showed increased latency to begin eating in the novelty-suppressed feeding test, impaired object recognition memory, impaired choice accuracy in the visual signal detection test, and sex-selective effects on locomotor activity in adolescence (males) but not adulthood. Male, but not female, offspring showed marked increases in dopamine utilization in the striatum, evidenced by an increase in the ratio of the primary dopamine metabolite (3,4-dihydroxyphenylacetic acid) relative to dopamine levels. CONCLUSIONS: These results indicate that TPP has adverse effects that are similar in some respects to those of organophosphate pesticides, which were restricted because of their developmental neurotoxicity.

Mitochondrial dysfunction and oxidative stress contribute to cross-generational toxicity of benzo(a)pyrene in Danio rerio.

The potential for polycyclic aromatic hydrocarbons (PAHs) to have adverse effects that persist across generations is an emerging concern for human and wildlife health. This study evaluated the role of mitochondria, which are maternally inherited, in the cross-generational toxicity of benzo(a)pyrene (BaP), a model PAH and known mitochondrial toxicant. Mature female zebrafish (F0) were fed diets containing 0, 12.5, 125, or 1250 µg BaP/g at a feed rate of 1% body weight twice/day for 21 days. These females were bred with unexposed males, and the embryos (F1) were collected for subsequent analyses. Maternally-exposed embryos exhibited altered mitochondrial function and metabolic partitioning (i.e. the portion of respiration attributable to different cellular processes), as evidenced by in vivo oxygen consumption rates (OCRs). F1 embryos had lower basal and mitochondrial respiration and ATP turnover-mediated OCR, and increased proton leak and reserve capacity. Reductions in mitochondrial DNA (mtDNA) copy number, increases in mtDNA damage, and alterations in biomarkers of oxidative stress were also found in maternally-exposed embryos. Notably, the mitochondrial effects in offspring occurred largely in the absence of effects in maternal ovaries, suggesting that PAH-induced mitochondrial dysfunction may manifest in subsequent generations. Maternally-exposed larvae also displayed swimming hypoactivity. The lowest observed effect level (LOEL) for maternal BaP exposure causing mitochondrial effects in offspring was 12.5 µg BaP/g diet (nominally equivalent to 250 ng BaP/g fish). It was concluded that maternal BaP exposure can cause significant mitochondrial impairments in offspring.

Chronic sazetidine-A at behaviorally active doses does not increase nicotinic cholinergic receptors in rodent brain.

Chronic nicotine administration increases α4ß2 neuronal nicotinic acetylcholine receptor (nAChR) density in brain. This up-regulation probably contributes to the development and/or maintenance of nicotine dependence. nAChR up-regulation is believed to be triggered at the ligand binding site, so it is not surprising that other nicotinic ligands also up-regulate nAChRs in the brain. These other ligands include varenicline, which is currently used for smoking cessation therapy. Sazetidine-A (saz-A) is a newer nicotinic ligand that binds with high affinity and selectivity at α4ß2* nAChRs. In behavioral studies, saz-A decreases nicotine self-administration and increases performance on tasks of attention. We report here that, unlike nicotine and varenicline, chronic administration of saz-A at behaviorally active and even higher doses does not up-regulate nAChRs in rodent brains. We used a newly developed method involving radioligand binding to measure the concentrations and nAChR occupancy of saz-A, nicotine, and varenicline in brains from chronically treated rats. Our results indicate that saz-A reached concentrations in the brain that were ∼150 times its affinity for α4ß2* nAChRs and occupied at least 75% of nAChRs. Thus, chronic administration of saz-A did not up-regulate nAChRs despite it reaching brain concentrations that are known to bind and desensitize virtually all α4ß2* nAChRs in brain. These findings reinforce a model of nicotine addiction based on desensitization of up-regulated nAChRs and introduce a potential new strategy for smoking cessation therapy in which drugs such as saz-A can promote smoking cessation without maintaining nAChR up-regulation, thereby potentially increasing the rate of long-term abstinence from nicotine.

Time-dependent effects of nicotine on reversal of dizocilpine-induced attentional impairment in female rats.

Nicotine and nicotinic compounds have been found to attenuate the attentional impairments caused by the glutamate NMDA antagonist dizocilpine (MK-801). The timing of the nicotine effect on attention in rodents has not yet been determined. In the current study, we tested the interaction of dizocilpine with nicotine. Nicotine was given at a range of times (30 to 240 min) prior to dizocilpine administration and before testing on an operant signal detection task. Each rat was assessed with each dose timing. This protocol was repeated twice with one week between phases of testing. In the first phase, correct rejection performance was significantly impaired by 0.05 mg/kg of dizocilpine and this impairment was significantly attenuated by nicotine given sc 30-150 min prior to dizocilpine administration. The greater dizocilpine-induced percent correct rejection impairment seen during the first phase of drug challenge, was significantly attenuated by nicotine given 30 or 90 min before the start of the 1-h test session. During the second phase, the dizocilpine-induced repeated acquisition impairment was more modest. During this phase of testing nicotine administered 60, 90 or 150 min before testing significantly attenuated the dizocilpine-induced impairment. In both phases of testing, nicotine administration 240 min prior to testing was not seen to attenuate the dizocilpine-induced impairment. During the first phase but not the second phase, dizocilpine administration caused a significant impairment in percent hit. Nicotine was not found to have a significant effect in the second phase. Response omissions were significantly increased by dizocilpine during the first, but not the second phase. Nicotine was not found to have any significant effects on response omission. Overall, our data show that nicotine administration prior to dizocilpine administration was able to significantly improve dizocilpine-induced attentional impairment in a time-dependent manner.

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.

Persistent neurobehavioral and neurochemical anomalies in middle-aged rats after maternal diazinon exposure.

Diazinon is an organophosphate pesticide that has a history of wide use. Developmental exposures to organophosphates lead to neurobehavioral changes that emerge early in life and can persist into adulthood. However, preclinical studies have generally evaluated changes through young adulthood, whereas the persistence or progression of deficits into middle age remain poorly understood. The current study evaluated the effects of maternal diazinon exposure on behavior and neurochemistry in middle age, at 1 year postpartum, comparing the results to our previous studies of outcomes at adolescence and in young adulthood (4 months of age) (Hawkey 2020). Female rats received 0, 0.5 or 1.0 mg/kg/day of diazinon via osmotic minipump throughout gestation and into the postpartum period. The offspring were tested on a battery of locomotor, affective, and cognitive tests at young adulthood and during middle age. Some of the neurobehavioral consequences of developmental DZN seen during adolescence and young adulthood faded with continued aging, whereas other neurobehavioral effects emerged with aging. At middle age, the rats showed few locomotor effects, in contrast to the locomotor hyperactivity that had been observed in adolescence. Notably, though, DZN exposure during development impaired reference memory performance in middle-aged males, an effect that had not been seen in the younger animals. Likewise, middle-aged females exposed to DZN showed deficient attentional accuracy, an effect not seen in young adults. Across adulthood, the continued potential for behavioral defects was associated with altered dopaminergic function, characterized by enhanced dopamine utilization that was regionally-selective (striatum but not frontal/parietal cortex). This study shows that the neurobehavioral impairments from maternal low dose exposure to diazinon not only persist, but may continue to evolve as animals enter middle age.

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.