A Model of Combined Exposure to Nicotine and Tetrahydrocannabinol via Electronic Cigarettes in Pregnant Rats

Adult Consequences of Repeated Nicotine Vapor Inhalation in Adolescent Rats

INTRODUCTION

There has been a resurgence in nicotine inhalation in adolescents due to the popularity and availability of Electronic Nicotine Delivery Systems (ENDS). Almost five times as many US high-school seniors inhale nicotine vapor daily compared with those who smoke tobacco. This study was conducted to determine the impact of repeated adolescent vapor inhalation of nicotine on behavior in adulthood.

METHODS

Male and female Sprague-Dawley rats were exposed to 30-minute sessions of ENDS vapor inhalation, twice daily, from post-natal day (PND) 31-40. Conditions included vapor from the propylene glycol (PG) vehicle or nicotine (30 mg/mL in the PG). Animals were assessed for effects of nicotine on open field (PND 74-105) and wheel activity (PND 126-180) and for volitional exposure to nicotine vapor (PND 285-395). Plasma nicotine and cotinine were assessed in separate groups of male and female Wistar and Sprague-Dawley rats after a single nicotine inhalation session.

RESULTS

Group mean plasma nicotine ranged from 39 to 59 ng/mL post-session with minimal strain differences detected. Adolescent nicotine exposure enhanced sensitivity to the locomotor stimulating effects of nicotine (0.1-0.8 mg/kg, s.c.) in an open field in female rats, but didn't change the effects of nicotine on wheel activity. Female rats exposed to nicotine (30 mg/mL) vapor as adolescents responded more vigorously than PG-exposed females to nicotine vapor in a fixed ratio 5 challenge.

CONCLUSIONS

Repeated adolescent nicotine vapor inhalation leads to enhanced liability for volitional exposure to nicotine vapor in adulthood in female rats, but minimal change in spontaneous locomotor behavior.

IMPLICATIONS

These results show that adolescent vaping of nicotine can lead to lasting sensitization to the effects of nicotine in adulthood, including volitional responding for nicotine vapor. Demonstration of this in a controlled animal model establishes causality in a manner not possible from longitudinal evidence in human populations. These findings further highlight the importance of decreasing adolescent nicotine exposure to e-cigarettes to reduce consumption in adulthood.

Vaporized nicotine in utero results in reduced birthweight, increased locomotion, and decreased voluntary exercise, dependent on sex and diet in offspring

Rationale Clinical research has shown that prenatal exposure to nicotine may result in increased obesity risk later in life. Preclinical research has corroborated this finding, but few studies have investigated inhaled nicotine or the interaction with diet on obesity risk. Objective The aim of this study was to investigate the effects of prenatal nicotine exposure on both direct and indirect obesity measures, with both sex and diet as factors. Methods Pregnant rats were exposed to either vehicle or nicotine vapor (24 mg/mL or 59 mg/mL) throughout the entire gestational period. Offspring from each treatment group were given either a normal diet or a high fat diet starting at postnatal day 22. Caloric intake, body weight, spontaneous locomotion, sleep/wake activity, and voluntary exercise were measured throughout adolescence. Pregnancy weight gain and pup birthweights were collected to further measure developmental effects of prenatal nicotine exposure. Results Both maternal weight gain during pregnancy and pup weight at birth were decreased with prenatal nicotine exposure. Early adolescent males showed increased spontaneous activity in the open field following prenatal nicotine exposure compared to vehicle counterparts, particularly those given high-fat diet. Additionally, high dose nicotine prenatal treated males ran significantly less distance on the running wheel in late adolescence compared to vehicle counterparts, in the normal diet group only. Conclusion The results presented here show decreased birthweight, hyperactivity, and decreased voluntary exercise in adolescence following prenatal nicotine exposure in dose, sex, and diet dependent manners, which could lead to increased obesity risk in adulthood.

Vaporized Δ9-THC in utero results in reduced birthweight, increased locomotion, and altered wake-cycle activity dependent on dose, sex, and diet in the offspring

AIMS

Preclinical studies have found that chronic ∆9-tetrahydrocannabinol (THC) treatment is directly associated with weight gain when introduced during adolescence and adulthood, but the effect of prenatal THC is unclear. Clinical studies have demonstrated prenatal exposure to THC is a prospective predictor of increased health risks associated with obesity. Our study aims to examine prenatal THC impact on obesity risks in males and females throughout adolescence using a clinically relevant inhalation model.

METHODS

Pregnant rats were exposed to one of the following from gestational day 2 through birth: 10 mg THC, 40 mg THC, or air. Daily 10-min inhalations were conducted in each animal from 0900 to 1200. Offspring from each treatment group were given either a high-fat diet (HFD) or a normal diet (ND). Food and bodyweights were collected daily, while circadian activity, locomotion, and exercise were measured periodically (PND 21-60). Pregnancy weight gain and birth weight were collected to determine early-life developmental effects.

RESULTS

Rats prenatally treated with low-dose THC (LDTHC) generally had lower dark-cycle activity compared with control counterparts, but this altered activity was not observed at the higher dose of THC (HDTHC). In terms of open-field activity, THC doses displayed a general increase in locomotion. In addition, the LDTHC male rats in the ND showed significantly greater exploratory behavior. Prenatal THC had dose-dependent effects on maternal weight gain and birth weight.

CONCLUSIONS

Overall, our findings indicate there are some activity-related and developmental effects of prenatal THC, which may be related to obesity risks later in life.

Adult consequences of repeated nicotine and Δ9-tetrahydrocannabinol (THC) vapor inhalation in adolescent rats

RATIONALE

Use of electronic drug delivery systems (EDDS, "e-cigarettes") to ingest nicotine and Δ9-tetrahydrocannabinol (THC) has surged in adolescents in the USA; five times as many high-school seniors vape nicotine daily using tobacco. At the same time, 19.5% of seniors use cannabis at least monthly, with 12% using EDDS to deliver it.

OBJECTIVES

This study was conducted to examine the impact of repeated adolescent vapor inhalation of nicotine and THC in rats.

METHODS

Female Sprague-Dawley rats were exposed to 30-min sessions of vapor inhalation, twice daily, from post-natal day (PND) 31 to PND 40. Conditions included vapor from the propylene glycol (PG) vehicle, nicotine (60 mg/mL in the PG), THC (100 mg/mL in the PG), or the combination of nicotine (60 mg/mL) and THC (100 mg/mL). Rats were assessed on wheel activity, heroin anti-nociception and nicotine and heroin vapor volitional exposure during adulthood.

RESULTS

Nicotine-exposed rats exhibited few differences as adults, but were less sensitive to anti-nociceptive effects of heroin (1 mg/kg, s.c.). THC- and THC + nicotine-exposed rats were less spontaneously active, and obtained fewer nicotine vapor deliveries as adults. In contrast, THC-exposed rats obtained volitional heroin vapor at rates indistinguishable from the non-THC-exposed groups. Repeated THC exposure also caused tolerance to temperature-disrupting effects of THC (5 mg/kg, i.p.).

CONCLUSIONS

These studies further confirm that the effects of repeated vapor exposure to THC in adolescence last into early to middle adulthood, including decreased volitional consumption of nicotine. Effects of repeated nicotine in adolescence were comparatively minor.

Rats chasing the dragon: A new heroin inhalation method

BACKGROUND

Despite extensive human use of inhalation for ingesting opioids, models in rodents have mostly been limited to parenteral injection and oral dosing. Methods using electronic drug delivery systems (EDDS; "e-cigarettes") have shown efficacy in rodent models but these do not faithfully mimic the most popular human inhalation method of heating heroin to the point of vaporization.

NEW METHOD

Middle aged rats were exposed to vapor created by direct heating of heroin HCl powder in a ceramic e-cigarette type atomizer. Efficacy was determined with a warm water tail withdrawal nociception assay, rectal temperature and self-administration.

RESULTS

Ten minutes of inhalation of vaporized heroin slowed response latency in a warm water tail withdrawal assay and increased rectal temperature in male rats, in a dose-dependent manner. Similar antinociceptive effects in female rats were attenuated by the opioid antagonist naloxone (1.0 mg/kg, s.c.). Female rats made operant responses for heroin vapor in 15-minute sessions, increased their response rate when the reinforcement ratio increased from FR1 to FR5, and further increased their responding when vapor delivery was omitted. Anti-nociceptive effects of self-administered volatilized heroin were of a similar magnitude as those produced by the 10-minute non-contingent exposure.

COMPARISON WITH EXISTING METHODS

Inhalation of directly volatilized heroin successfully produces heroin-typical effects, comparable to EDDS inhalation delivery.

CONCLUSIONS

This study shows that "chasing the dragon" methods of inhalation of heroin can be modeled successfully in the rat. Inhalation techniques may be particularly useful for longer term studies deep into the middle age of rats.

Sex Differences in Response-Contingent Cannabis Vapor Administration During Adolescence Mediate Enduring Effects on Behavioral Flexibility and Prefrontal Microglia Activation in Rats

Introduction: Cannabis is the most used illicit drug in the United States. With many states passing legislation to permit its recreational use, there is concern that cannabis use among adolescents could increase dramatically in the coming years. Historically, it has been difficult to model real-world cannabis use to investigate the causal relationship between cannabis use in adolescence and behavioral and neurobiological effects in adulthood. Materials and Methods: We used a response-contingent vapor administration model to investigate long-term effects of cannabis use during adolescence on the medial prefrontal cortex (mPFC) and mPFC-dependent behaviors in male and female rats. Results: Adolescent (35- to 55-day-old) female rats had significantly higher rates of responding for vaporized Δ9-tetrahydrocannabinol (THC)-dominant cannabis extract (CANTHC) compared with adolescent males. In adulthood (70-110 days old), female, but not male, CANTHC rats also took more trials to reach criterion and made more regressive errors in an automated attentional set-shifting task compared with vehicle rats, thereby indicating sex differences in behavioral flexibility impairments. Notably, sex-treatment interactions were not observed when rats of each sex were exposed to a noncontingent CANTHC vapor dosing regimen that approximated CANTHC vapor deliveries earned by females. No differences were observed in effort-based decision making in either sex. In the mPFC, female (but not male) CANTHC rats displayed more reactive microglia with no changes in myelin basic protein expression or dendritic spine density. Conclusion: Altogether, these data reveal important sex differences in rates of responding for CANTHC vapor in adolescence that may confer enduring alterations to mPFC structure and function and suggest that there may be subtle differences in the effects of response-contingent versus noncontingent cannabis exposure that should be systematically examined in future studies.

Characterization of cannabinoid plasma concentration, maternal health, and cytokine levels in a rat model of prenatal Cannabis smoke exposure

Cannabis sativa has gained popularity as a "natural substance", leading many to falsely assume that it is not harmful. This assumption has been documented amongst pregnant mothers, many of whom consider Cannabis use during pregnancy as benign. The purpose of this study was to validate a Cannabis smoke exposure model in pregnant rats by determining the plasma levels of cannabinoids and associated metabolites in the dams after exposure to either Cannabis smoke or injected cannabinoids. Maternal and fetal cytokine and chemokine profiles were also assessed after exposure. Pregnant Sprague-Dawley rats were treated daily from gestational day 6-20 with either room air, i.p. vehicle, inhaled high-Δ9-tetrahydrocannabinol (THC) (18% THC, 0.1% cannabidiol [CBD]) smoke, inhaled high-CBD (0.7% THC, 13% CBD) smoke, 3 mg/kg i.p. THC, or 10 mg/kg i.p. CBD. Our data reveal that THC and CBD, but not their metabolites, accumulate in maternal plasma after repeated exposures. Injection of THC or CBD was associated with fewer offspring and increased uterine reabsorption events. For cytokines and chemokines, injection of THC or CBD up-regulated several pro-inflammatory cytokines compared to control or high-THC smoke or high-CBD smoke in placental and fetal brain tissue, whereas smoke exposure was generally associated with reduced cytokine and chemokine concentrations in placental and fetal brain tissue compared to controls. These results support existing, but limited, knowledge on how different routes of administration contribute to inconsistent manifestations of cannabinoid-mediated effects on pregnancy. Smoked Cannabis is still the most common means of human consumption, and more preclinical investigation is needed to determine the effects of smoke inhalation on developmental and behavioural trajectories.

Adult consequences of repeated nicotine and Δ 9 -tetrahydrocannabinol (THC) vapor inhalation in adolescent rats

The use of Electronic Drug Delivery Systems (EDDS, "e-cigarettes") to ingest nicotine and Δ 9 -tetrahydrocannabinol (THC) has surged in adolescent populations in the United States, as five times as many high-school seniors vape nicotine daily as use tobacco. At the same time 19.5% of seniors use cannabis at least monthly, with 12% using EDDS to deliver it. This study was conducted to examine the impact of repeated adolescent vapor inhalation of nicotine and THC in rats. Female Sprague-Dawley rats were exposed to 30-minute sessions of vapor inhalation, twice daily, from Post-Natal Day (PND) 31 to PND 40. Conditions included vapor from the propylene glycol (PG) vehicle, Nicotine (60 mg/mL in the PG), THC (100 mg/mL in the PG) or the combination of Nicotine (60 mg/mL) and THC (100 mg/mL). Rats were assessed on wheel activity, heroin anti-nociception and nicotine and heroin vapor volitional exposure during adulthood. Nicotine exposed rats exhibited few differences as adults, but were less sensitive to anti-nociceptive effects of heroin (1 mg/kg, s.c.). THC- and THC+Nicotine-exposed rats were less spontaneously active, and obtained fewer nicotine vapor deliveries as adults. In contrast, THC exposed rats obtained volitional heroin vapor at rates indistinguishable from the non-THC-exposed groups. Repeated THC exposure also caused tolerance to temperature-disrupting effects of THC (5 mg/kg, i.p.). These studies further confirm that the effects of repeated vapor exposure to THC in adolescence last into early to middle adulthood, including decreased volitional consumption of nicotine. Effects of repeated nicotine in adolescence were comparatively minor.

Rats Chasing the Dragon: A new heroin inhalation method

Rationale

Despite extensive human use of the inhalation route for ingesting opioids, models in rodents have mostly been limited to parenteral injection and oral dosing. Methods using electronic drug delivery systems (EDDS; "e-cigarettes") have shown efficacy in rodent models but these do not faithfully mimic the most popular human inhalation method of heating heroin to the point of vaporization.

Objective

This study was designed to determine if direct volatilization of heroin hydrochloride delivers effective heroin doses to rodents.

Methods

Middle aged rats were exposed to vapor created by direct heating of heroin HCl powder in a ceramic e-cigarette type atomizer. Efficacy was determined with a warm water tail withdrawal nociception assay, rectal temperature and self-administration.

Results

Ten minutes of inhalation of vaporized heroin slowed response latency in a warm water tail withdrawal assay and increased rectal temperature in male rats, in a dose-dependent manner. Similar antinociceptive effects in female rats were attenuated by the opioid antagonist naloxone (1.0 mg/kg, s.c.). Female rats made operant responses for heroin vapor in 15-minute sessions, increased their response rate when the reinforcement ratio increased from FR1 to FR5, and further increased their responding when vapor delivery was omitted. Anti-nociceptive effects of self-administered volatilized heroin were of a similar magnitude as those produced by the 10-minute non-contingent exposure.

Conclusions

This study shows that "chasing the dragon" methods of inhalation of heroin can be modeled successfully in the rat. Inhalation techniques may be particularly useful for longer term studies deep into middle age of rat species.

Tobacco Smoke Exposure in Pregnant Dogs: Maternal and Newborn Cotinine Levels: A Pilot Study

Active and passive smoking in pregnant women is associated with perinatal morbidity and mortality risk, including abortion, preterm birth, low birthweight, and malformations. No data are available on intrauterine exposure to smoking during pregnancy in dogs. This study aimed to fill this gap by exploring the detectability and quantity of cotinine, the major metabolite of nicotine, in maternal (serum and hair) and newborn (amniotic fluid and hair) biospecimens collected at birth in dogs. For this purpose, twelve pregnant bitches, six exposed to the owner's smoke and six unexposed, were enrolled. A further six non-pregnant bitches exposed to passive smoke were included to investigate the role of pregnancy status on cotinine uptake. Exposed dogs, dams, and puppies had greater cotinine concentrations than unexposed ones. Although without statistical significance, serum and hair cotinine concentrations were higher in pregnant compared to non-pregnant bitches, suggesting a different sensitivity to tobacco smoke exposure during gestation. The present results provide evidence for cotinine transplacental passage in the dog. It is conceivable that fragile patients such as pregnant, lactating, and neonate dogs may be more susceptible to the harmful effects of second-hand smoke exposure. Owners should be sensitized to the risk of smoke exposure for their pets.

Influence of prenatal cannabinoid exposure on early development and beyond

Public perception surrounding whether cannabis use is harmful during pregnancy often diverges greatly from the recommendations of doctors and healthcare providers. In contrast to the medical guidance of abstinence before, during, and after pregnancy, many women of reproductive age believe cannabis use during pregnancy is associated with little potential harm. Legalization and social cues support public perceptions that cannabis use during pregnancy is safe. Moreover, pregnant women may consider cannabis to be a safe alternative for treating pregnancy related ailments, including morning sickness. Compounding the problem is a lack of medical and federal guidance on safe, low, or high-risk levels of cannabis use. These issues mirror the continuing debate surrounding alcohol use and health, in particular, whether there are safe or lower risk levels of alcohol consumption during pregnancy. Clinical studies to date suffer from several limitations. First, most human studies are correlative in nature, meaning that causal associations cannot be made between in utero cannabis exposure and health and behavioral outcomes later in life. Due to obvious ethical constraints, it is not possible to randomly assign pregnant mothers to cannabis or other drug exposure conditions-a requirement needed to establish causality. In addition, clinical studies often lack quantitative information on maternal exposure (i.e., dose, frequency, and duration), include a small number of individuals, lack replication of outcome measures across cohorts, rely on self-report to establish maternal drug use, and suffer from unmeasured or residual confounding factors. Causal associations between maternal cannabis exposure and offspring outcomes are possible in preclinical cohorts but there is a large amount of heterogeneity across study designs and developmental differences between rodents and humans may limit translatability. In this review, we summarize research from human and preclinical models to provide insight into potential risks associated with prenatal cannabinoid exposure (PCE). Finally, we highlight gaps in knowledge likely to contribute to the growing divide between medical guidance and public attitudes regarding cannabis use during pregnancy.

Sex Differences in the Behavioural Outcomes of Prenatal Nicotine and Tobacco Exposure

Smoking remains the leading cause of preventable death worldwide. A combination of biological and environmental risk factors make women especially vulnerable to nicotine addiction, making it harder for them to quit smoking. Smoking during pregnancy, therefore, is still a major health concern, with epidemiological data suggesting a role for gestational nicotine exposure in the development of several behavioural disorders. Given there are significant sex-specific behavioural outcomes related to smoking in adolescence and adulthood, it is probable that the behavioural outcomes following gestational nicotine or tobacco exposure are similarly sex-dependent. This is an especially relevant topic as the current landscape of nicotine use shifts toward vaping, a mode of high doses of nicotine delivery that is largely believed to be a safer alternative to cigarettes among the public as well as among pregnant women. Here we review existing clinical and preclinical findings regarding the sex-dependent behavioural outcomes of prenatal nicotine exposure. We also highlight the challenges within this literature, particularly those areas in which further research is necessary to improve consistency within, and between, clinical and preclinical findings.

The effects of prenatal nicotine and THC E-cigarette exposure on motor development in rats

RATIONALE

In the USA, nicotine and cannabis are the most common licit and illicit drugs used among pregnant women. Importantly, nicotine and cannabis are now being combined for consumption via e-cigarettes, an increasingly popular delivery device. Both nicotine and tetrahydrocannabinol (THC), the primary psychoactive component of cannabis, cross the placenta barrier. However, the consequences of prenatal cannabis use are not well understood, and less is known about potential combination effects when consumed with nicotine, especially via e-cigarettes.

OBJECTIVE

The present study used a rodent model to examine how prenatal e-cigarette exposure to nicotine, THC, and the combination impacts motor development among offspring.

METHODS

Pregnant Sprague-Dawley rats were exposed to nicotine (36 mg/mL), THC (100 mg/mL), the combination, or vehicle via e-cigarette inhalation from gestational days (GD) 5-20. One sex pair per litter was tested on an early sensorimotor development task (postnatal days [PD] 12-20) and a parallel bar motor coordination task (PD 30-32).

RESULTS

Combined prenatal exposure to nicotine and THC delayed sensorimotor development, even though neither drug produced impairments on their own. In contrast, prenatal exposure to either nicotine or THC impaired motor coordination, whereas combined exposure exacerbated these effects, particularly among females.

CONCLUSIONS

These data illustrate that prenatal exposure to either nicotine or THC may alter motor development, and that the combination may produce more severe effects. These findings have important implications for pregnant women as we better understand the teratogenic effects of these drugs consumed via e-cigarettes.