Extracellular ATP Neurotransmission and Nicotine Sex-Specifically Modulate Habenular Neuronal Activity in Adolescence

The recent increase in the use of nicotine products by teenagers has revealed an urgent need to better understand the impact of nicotine on the adolescent brain. Here, we sought to examine the actions of extracellular ATP as a neurotransmitter and to investigate whether ATP and nicotinic signaling interact during adolescence. With the GRABATP (G-protein-coupled receptor activation-based ATP sensor), we first demonstrated that nicotine induces extracellular ATP release in the medial habenula, a brain region involved in nicotine aversion and withdrawal. Using patch-clamp electrophysiology, we then demonstrated that activation of the ATP receptors P2X or P2Y1 increases the neuronal firing of cholinergic neurons. Surprisingly, contrasting interactive effects were observed with nicotine exposure. For the P2X receptor, activation had no observable effect on acute nicotine-mediated activity, but during abstinence after 10 d of nicotine exposure, coexposure to nicotine and the P2X agonist potentiated neuronal activity in female, but not male, neurons. For P2Y1 signaling, a potentiated effect of the agonist and nicotine was observed with acute exposure, but not following extended nicotine exposure. These data reveal a complex interactive effect between nicotinic and ATP signaling in the adolescent brain and provide mechanistic insights into extracellular ATP signaling with sex-specific alterations of neuronal responses based on prior drug exposure.SIGNIFICANCE STATEMENT In these studies, it was discovered that nicotine induces extracellular ATP release in the medial habenula and subsequent activation of the ATP purinergic receptors increases habenular cholinergic neuronal firing in the adolescent brain. Interestingly, following extended nicotine exposure, nicotine was found to alter the interplay between purinergic and nicotinic signaling in a sex-specific manner. Together, these studies provide a novel understanding for the role of extracellular ATP in mediating habenular activity and reveal how nicotine exposure during adolescence alters these signaling mechanisms, which has important implications given the high incidence of e-cigarette/vape use by youth.

Differential Expression Patterns of Lynx Proteins and Involvement of Lynx1 in Prepulse Inhibition

Negative allosteric modulators, such as lynx1 and lynx2, directly interact with nicotinic acetylcholine receptors (nAChRs). The nAChRs are integral to cholinergic signaling in the brain and have been shown to mediate different aspects of cognitive function. Given the interaction between lynx proteins and these receptors, we examined whether these endogenous negative allosteric modulators are involved in cognitive behaviors associated with cholinergic function. We found both cell-specific and overlapping expression patterns of lynx1 and lynx2 mRNA in brain regions associated with cognition, learning, memory, and sensorimotor processing, including the prefrontal cortex (PFC), cingulate cortex, septum, hippocampus, amygdala, striatum, and pontine nuclei. Since lynx proteins are thought to play a role in conditioned associations and given the expression patterns across brain regions, we first assessed whether lynx knockout mice would differ in a cognitive flexibility task. We found no deficits in reversal learning in either the lynx1^–/– or lynx2^–/– knockout mice. Thereafter, sensorimotor gating was examined with the prepulse inhibition (PPI) assessment. Interestingly, we found that both male and female lynx1^–/– mice exhibited a deficit in the PPI behavioral response. Given the comparable expression of lynx2 in regions involved in sensorimotor gating, we then examined whether removal of the lynx2 protein would lead to similar behavioral effects. Unexpectedly, we found that while male lynx2^–/– mice exhibited a decrease in the baseline startle response, no differences were found in sensorimotor gating for either male or female lynx2^–/– mice. Taken together, these studies provide insight into the expression patterns of lynx1 and lynx2 across multiple brain regions and illustrate the modulatory effects of the lynx1 protein in sensorimotor gating.

Nicotine e-cigarette vapor inhalation and self-administration in a rodent model: Sex- and nicotine delivery-specific effects on metabolism and behavior

E-cigarettes, which deliver vaporized nicotine, have dramatically risen in popularity in recent years, despite many unanswered questions about safety, efficacy in reducing dependence, and overall impact on public health. Other factors, such as sex, also play an important role in determining behavioral and neurochemical responses to drugs of abuse. In these studies, we sought to develop a protocol for vaporized e-cigarette nicotine self-administration in rats, as a foundation to better understand the differing effects of nicotine exposure routes on behavior and physiological function. We report a novel method that elicits robust nicotine vapor self-administration in male and female rats. Our findings indicate that 5-mg/ml nicotine vape solution provides a high level of consistency in lever-pressing behavior for both males and females. Moreover, in male rats, we find that such e-cigarette nicotine vapor induces similar blood levels of nicotine's main metabolite, cotinine, as that found with intravenous nicotine self-administration. Therefore, the breathing pattern during vapor exposure in males leads to similar levels of titrated nicotine intake as with intravenous nicotine self-administration. Interestingly, a differential effect was found in the females, in which the same conditions of vapor exposure led to decreased cotinine levels with vapor compared to intravenous self-administration. Finally, differences in nicotine-mediated locomotion provide further support of the physiological effects of e-cigarette vapor inhalation. Taken together, our findings reveal important sex differences in nicotine intake based on the route of exposure, and we further establish a protocol for nicotine vapor self-administration in rats.

Adolescent Cannabinoid and Nicotine Exposure Differentially Alters Adult Nicotine Self-Administration in Males and Females

INTRODUCTION

During adolescence, exposure to nicotine or cannabis independently induces effects on neuromaturation and later cognitive function. However, the potential effect of both drugs under co-use conditions has become of increasing concern given the prevalence of e-cigarettes, legalization of cannabis, and availability of synthetic "spice" cannabinoid agonists.

AIMS AND METHODS

The current studies investigated the effects of exposure to a cannabinoid receptor agonist (WIN55,212-2) and/or nicotine over a discrete time period in mid-adolescence on later intravenous nicotine self-administration in adult male and female mice. We further examined whether cannabinoid agonist administration in adulthood would alter nicotine reinforcement, with either acute or chronic pairing across 7 days.

RESULTS

We found that adult males exhibited increased nicotine self-administration at a lower, rewarding nicotine dose following adolescent cannabinoid exposure, either alone or with nicotine coadministration. In contrast, adult females demonstrated an opposing effect in which adolescent cannabinoid and nicotine coexposure resulted in decreased nicotine intake compared with the nicotine only and control groups. Furthermore, after maintaining nicotine self-administration across sessions, pretreatment with a low dose of the cannabinoid agonist decreased nicotine intake in both male and female control mice, and this lowering effect was evidenced after both acute and chronic treatment. However, the cannabinoid agonist was ineffective in altering nicotine intake in mice previously exposed to nicotine, cannabinoid agonist, or both during adolescence.

CONCLUSIONS

These data provide evidence that adolescent drug exposure can alter later nicotine reinforcement in a sex-specific manner and can further modulate the effectiveness of interventions in reducing nicotine intake during adulthood.

IMPLICATIONS

These studies demonstrate a significant impact of nicotine, cannabinoids, or coexposure on developmental processes during adolescence. Differential effects were observed within each sex, with opposing results found for cannabinoid exposure on nicotine intake in males and females. Intriguingly, we also evidenced resistance to the lowering effects of a cannabinoid agonist on nicotine intake in adulthood based on adolescent drug exposure. Thus, these findings have important implications for our understanding of the impact of nicotine and cannabinoids (eg, Δ9-tetrahydrocannabinol (THC) and synthetic "spice" cannabinoids) during development, with further implications for the effectiveness of therapeutic interventions based on prior drug exposure in youth.

The Novel CYP2A6 Inhibitor, DLCI-1, Decreases Nicotine Self-Administration in Mice

During tobacco and e-cigarette use, nicotine is mainly metabolized in the human liver by cytochrome P450 2A6 (CYP2A6). Given that a slower CYP2A6 metabolism has been associated with less vulnerability to develop nicotine dependence, the current studies sought to validate a novel CYP2A6 inhibitor, (5-(4-ethylpyridin-3-yl)thiophen-2-yl)methanamine (DLCI-1), for its effects on intravenous nicotine self-administration. Male and female mice were trained to self-administer nicotine across daily sessions. Once stable responding was achieved, DLCI-1 or vehicle control was administered prior to nicotine sessions. We found that the lower 25 mg/kg and moderate 50 mg/kg doses of DLCI-1 induced a significant decrease in nicotine intake for both males and females. DLCI-1 was further shown to be more effective than a moderate 1 mg/kg dose of bupropion on reducing nicotine intake and did not exert the adverse behavioral effects found with a high 75 mg/kg dose of bupropion. Although mice treated with DLCI-1 self-administered significantly less nicotine, similar nicotine-mediated behavioral effects on locomotion were observed. Together, along with the analysis of nicotine metabolites during self-administration, these findings support the contention that blocking hepatic nicotine metabolism would allow for similar activation of nicotinic acetylcholine receptors at lower nicotine doses. Moreover, these effects of DLCI-1 were specific to nicotine self-administration, as DLCI-1 did not result in any behavioral changes during food self-administration. Taken together, these studies validate DLCI-1 as a novel compound to decrease nicotine consumption, which may thereby promote tobacco and nicotine product cessation. SIGNIFICANCE STATEMENT: Current pharmacological approaches for nicotine and tobacco cessation have only been able to achieve limited efficaciousness in promoting long-term abstinence. In this work, we characterize the effects of a novel compound, (5-(4-ethylpyridin-3-yl)thiophen-2-yl)methanamine (DLCI-1), which inhibits the main enzyme that metabolizes nicotine, and we report a significant decrease in intravenous nicotine self-administration in male and female mice, supporting the potential of DLCI-1 as a novel tobacco cessation pharmacotherapeutic.

Nontypical Bacillus cereus outbreak in a child care center

On October 29, 1998, The Garland Health Department in Texas investigated seven illnesses at a church day school. The six children and one adult had handled hydrated, orange-colored rice before consuming a meal. B. cereus organisms were found in the rice at an estimated concentration of 5.6 x 10(5) per gram. As far as the authors can determine, this outbreak is the first one documented to have occurred from indirect ingestion of B. cereus by way of contaminated hands, as opposed to ingestion of the toxin in the food product in which the organisms grew.

Morphometric and stereological analysis of the effects of 17 beta-estradiol on the glandular epithelium of the castrated guinea pig lateral prostate

Upon administration of pharmacological doses of estradiol to castrated guinea pigs, the secretory cells of the lateral prostate underwent hypertrophy which resulted from significant increases in nuclear and cytoplasmic volume. There were quantitative increases in the small highly electron-dense granules and multivesicular bodies when compared with the castrated control. The dramatic increase in the number of highly electron-dense granules probably occurred at the expense of the low electron-dense granules. The average size of the condensing granules and mitochondria decreased significantly after estradiol administration. However, significant increase in the number of mitochondria was detected when compared with the castrated control. Ultrastructural data revealed no significant changes in the absolute dimensions of granular endoplasmic reticulum or of the Golgi complex, suggesting that estradiol exerted no significant stimulatory effects on these organelles. Pharmacological doses of estrogen appear to regulate the expression of secretory granules and multivesicular bodies in the lateral prostate of castrated guinea pigs.

Morphometric and stereological study of the glandular epithelium of the lateral prostate of the intact and castrated guinea pig

The glandular epithelium of the lateral prostate of the guinea pig was described within the framework of a morphometric model in terms of relative densities and absolute dimensions. A combination of direct measurement and point and intersection counting techniques was used. The quantitative data generated in the intact animals were compared with those of castrated controls. Castration was accompanied by a significant decrease in height of the glandular epithelium and in sizes of secretory and basal cells and their corresponding nuclei. On a per cell basis, significant decreases in total volume and surface area of granular endoplasmic reticulum were detected after castration. This was accompanied by a significant reduction in the total volume of Golgi cisternae. The total volume, surface area, and number of highly electron-dense and clear granules decreased significantly compared with the intact control animals. However, no significant changes in these parameters of low electron-dense granules were found. Significant reductions in the total volume and surface area of condensing granules, lysosomes, and mitochondria, but not their number, were detected. The average sizes of condensing granules, secretory granules, lysosomes, and mitochondria were decreased significantly after castration. The present study showed that the alterations in the secretory function of the secretory cells of the lateral prostate was reflected by the quantitative changes in granular endoplasmic reticulum, Golgi complexes, and secretory granules on a per cell basis. The data generated in the present study will serve as a baseline for further studies of the lateral prostate of the guinea pig.

Differential effect of clofibrate on inflammation-induced alterations in plasma proteins in the rat

Daily intramuscular injections of clofibrate begun 6h before the initiation of inflammation induced by the subcutaneous injection of turpentine exerted a differential, dose-dependent inhibition of the anticipated acute-phase globulin response. Specifically, clofibrate at 140mg/kg muted the increase in alpha(2)-macrofoetoprotein, but did not affect that of seromucoid or haptoglobin and only transiently inhibited the rise in copper and the rebound in transferrin. A higher dose, 280mg/kg, markedly suppressed alpha(2)-macrofoetoprotein appearance and the rebound in transferrin, somewhat inhibited the increase in seromucoid and haptoglobin and only transiently affected the rise in plasma copper; 420mg of clofibrate/kg very nearly abolished the appearance of alpha(2)-macrofoetoprotein, markedly suppressed the transferrin rebound and the increases in seromucoid and haptoglobin and again only transiently affected the increase in copper. Clofibrate did not diminish the localized inflammatory response, did not cause microscopically detectable liver damage and did not prevent the hypozincaemia, hypoalbuminaemia and enhanced amino acid uptake by liver usually associated with inflammation. Thus it is unlikely that clofibrate exerted its dose-dependent selective inhibition by muting the initial stimulus or by impairing hepatic metabolism. This seemingly selective action of clofibrate on plasma-protein alterations during inflammation may provide a means of elucidating the function of individual acute-phase globulin during disease. Clofibrate of itself, apart from inflammation, produced decreases in plasma zinc, copper, transferrin and seromucoid and an increase in hepatic amino acid uptake that were to some extent dependent on the dose of the drug.