Nicotine and ethanol interaction on conditioned taste aversions induced by both drugs

Nicotine limits avoidance conditioning with opioids without interfering with the ability to discriminate an opioid-interoceptive state

Approximately 90 % of individuals undergoing treatment for opioid use disorder (OUD) report comorbid use of nicotine. As such, further investigation into underlying mechanisms contributing to the extreme comorbidity between nicotine and opioid use are warranted. Nicotine administration significantly escalates self-administration of opioids and this increase in motivational efficacy persists despite contingent punishment of opioid consumption. Additionally, both systemic and intra-insular administration of nicotine produces a rightward shift in the dose-response function in both morphine-induced conditioned place preference and taste avoidance paradigms, particularly at higher doses (5-20 mg/kg). Two possible interpretations arise from these outcomes. One is that nicotine may specifically affect learning about the malaise-inducing effects of morphine thus facilitating acceptance of higher doses of morphine. Another interpretation is that it more generally reduces sensitivity to the interoceptive effects of morphine such that higher doses are needed to produce comparable effects in nicotine-treated, relative to control, rats. To further address these possibilities, we asked whether nicotine administration interfered with the ability to discriminate the morphine interoceptive state, irrespective of its hedonic evaluation, at a dose that is impacted by nicotine in avoidance conditioning paradigms. First, we demonstrated that systemic nicotine pretreatment significantly attenuates taste avoidance induced by a low dose of morphine (3 mg/kg). Next, we used an occasion setting paradigm with this same dose of morphine to test whether systemic nicotine pretreatment interferes with the ability to discriminate between saline- and morphine-induced interoceptive states. Within this task, nicotine had no effect on the ability to effectively discriminate between the interoceptive effects of morphine and saline. Collectively, these data suggest that nicotine may be specifically altering the overall hedonic assessment of morphine perhaps by interfering with learning about its deleterious consequences.

The incentive amplifying effects of nicotine: Roles in alcohol seeking and consumption

Nicotine has a unique profile among drugs of abuse. To the noninitiated user, nicotine has powerful aversive effects and its relatively weak euphorigenic effects undergo rapid tolerance. Despite this, nicotine is commonly abused despite negative heath consequences, and nicotine users have enormous difficulty quitting. Further, nicotine is one of the most commonly co-abused substances, in that it is often taken in combination with other drugs. One explanation of this polydrug use is that nicotine has multiple appetitive and consummatory conditioning effects. For example, nicotine is a reinforcement enhancer in that it can potently increase the incentive value of other stimuli, including those surrounding drugs of abuse such as alcohol. In addition, nicotine also has a unique profile of neurobiological effects that alter regulation of alcohol intake and interoception. This review discusses the psychological and biological mechanisms surrounding nicotine's appetitive conditioning and consummatory effects, particularly its interactions with alcohol.

Acute nicotine treatment enhances compulsive-like remifentanil self-administration that persists despite contextual punishment

Opioid use disorder (OUD) and opioid-related deaths remain a significant public health crisis having reached epidemic status globally. OUDs are defined as chronic, relapsing conditions often characterized by compulsive drug seeking despite the deleterious consequences of drug taking. The use of nicotine-containing products has been linked to increased likelihood of prescription opioid misuse, and there exists a significant comorbidity between habitual nicotine use and opioid dependence. In rodent models, nicotine administration nearly doubles the amount of opioids taken in intravenous self-administration paradigms. Here, we examined the effect of acute systemic nicotine administration in male rats on responding for the synthetic opioid remifentanil (RMF) in a contextual punishment paradigm using either an exteroceptive punisher (foot-shock) or an interoceptive punisher (histamine). Nicotine administration, relative to saline, increased RMF intake in both unpunished and punished contexts, regardless of form of punishment, and resulted in significantly higher motivation to obtain RMF in the previously punished context, as measured by progressive ratio breakpoint. Additionally, regardless of context, nicotine-treated rats were slower to extinguish RMF responding following drug removal and displayed higher levels of cue-induced reinstatement than saline-treated controls. Furthermore, these data support that, compared with histamine adulteration, contingent foot-shock is a more potent form of punishment, as histamine punishment failed to support contextual discrimination between the unpunished and punished contexts. In contrast to RMF administration, augmentation of responding for an audiovisual cue by nicotine pretreatment was lost following contextual punishment. In conclusion, acute nicotine administration in adult male rats significantly enhances compulsive-like responding for RMF that persists despite contingent punishment of drug-directed responding.

Systemic nicotine enhances opioid self-administration and modulates the formation of opioid-associated memories partly through actions within the insular cortex

Habitual use of nicotine containing products increases propensity to misuse prescription opioids and its prevalence is substantially increased in individuals currently involved in opioid-treatment programs. Nicotine enhances self-administration of many classes of drugs in rodents, though evidence for direct effects on opioids is lacking. We sought to measure the effects of nicotine pretreatment on the reinforcing efficacy of opioids in both self-administration and contextual conditioning paradigms. First, we measured the effect of systemic nicotine pretreatment on self-administration of two opioids. Additionally, we measured the degree to which systemic nicotine pretreatment impacts the formation of morphine-associated contextual memories in conditioned taste avoidance and place preference paradigms. Given the involvement of the insula in the maintenance of substance abuse, its importance in nicotine addiction, and findings that insular inactivation impairs contextual drug conditioning, we examined whether nicotine administered directly to the insula could recapitulate the effects of systemic nicotine. We demonstrate that systemic nicotine pretreatment significantly enhances opioid self-administration and alters contextual conditioning. Furthermore, intra-insula nicotine similarly altered morphine contextual conditioning by blocking the formation of taste avoidance at all three morphine doses tested (5.0, 10, and 20 mg/kg), while shifting the dose–response curve of morphine in the place preference paradigm rightward. In conclusion, these data demonstrate that nicotine facilitates opioid intake and is partly acting within the insular cortex to obfuscate aversive opiate memories while potentiating approach to morphine-associated stimuli at higher doses.

Non-nicotine constituents in e-cigarette aerosol extract attenuate nicotine's aversive effects in adolescent rats

BACKGROUND

Development of preclinical methodology for evaluating the abuse liability of electronic cigarettes (ECs) in adolescents is urgently needed to inform FDA regulation of these products. We previously reported reduced aversive effects of EC liquids containing nicotine and a range of non-nicotine constituents (e.g., propylene glycol, minor tobacco alkaloids) compared to nicotine alone in adult rats as measured using intracranial self-stimulation. The goal of this study was to compare the aversive effects of nicotine alone and EC aerosol extracts in adolescent rats as measured using conditioned taste aversion (CTA), which can be conducted during the brief adolescent period.

METHODS AND RESULTS

In Experiment 1, nicotine alone (1.0 or 1.5 mg/kg, s.c.) produced significant CTA in adolescent rats in a two-bottle procedure, thereby establishing a model to study the effects of EC extracts. At a nicotine dose of 1.0 mg/kg, CTA to Vuse Menthol EC extract, but not Aroma E-Juice EC extract, was attenuated compared to nicotine alone during repeated two-bottle CTA tests (Experiment 2a). At a nicotine dose of 0.5 mg/kg, CTA to Vuse Menthol EC extract did not differ from nicotine alone during the first two-bottle CTA test but extinguished more rapidly across repeated two-bottle tests (Experiment 2b).

CONCLUSIONS

Non-nicotine constituents in Vuse Menthol EC extracts attenuated CTA in a two-bottle procedure in adolescents. This model may be useful for anticipating the abuse liability of ECs in adolescents and for modeling FDA-mandated changes in product standards for nicotine or other constituents in ECs.

Nicotine Produces a High-Approach, Low-Avoidance Phenotype in Response to Alcohol-Associated Cues in Male Rats

BACKGROUND

Nicotine and alcohol use are highly comorbid. Modulation of drug-paired extrinsic and intrinsic cues likely plays a role in this interaction, as cues can acquire motivational properties and augment drug seeking. The motivational properties of cues can be measured through Pavlovian conditioning paradigms, in which cues either elicit approach following pairing with the reinforcing properties of alcohol or elicit avoidance following pairing with the aversive consequences of alcohol. The present experiments tested whether nicotine would enhance the incentive properties of an appetitive ethanol (EtOH) cue and diminish the avoidance of an aversive EtOH cue in Pavlovian paradigms.

METHODS

In experiment 1, male Long-Evans rats with or without prior chronic intermittent access to EtOH were administered nicotine or saline injections prior to Pavlovian conditioned approach (PavCA) sessions, during which conditioned approach to the cue ("sign-tracking") or the EtOH delivery location ("goal-tracking") was measured. In experiment 2, male Long-Evans rats were administered nicotine or saline injections prior to pairing a flavor cue with increasing doses of EtOH (i.p.) in an adaptation of the conditioned taste avoidance (CTA) paradigm.

RESULTS

Results from PavCA indicate that, regardless of EtOH exposure, nicotine enhanced responding elicited by EtOH-paired cues with no effect on a similar cue not explicitly paired with EtOH. Furthermore, nicotine reduced sensitivity to EtOH-induced CTA, as indicated by a rightward shift in the dose-response curve of passively administered EtOH. The ED₅₀ , or the dose of EtOH that produced a 50% reduction in intake relative to baseline, was significantly higher in nicotine-treated rats compared to saline-treated rats.

CONCLUSIONS

We conclude that nicotine increases the approach and diminishes the avoidance elicited by Pavlovian cues paired, respectively, with the reinforcing and aversive properties of EtOH consumption in male rats. As such, nicotine may enhance alcoholism liability by engendering an attentional bias toward cues that predict the reinforcing outcomes of drinking.

Nicotine pre-treatment reduces sensitivity to the interoceptive stimulus effects of commonly abused drugs as assessed with taste conditioning paradigms

BACKGROUND

Drug pre-exposure attenuates sensitivity to the interoceptive stimulus properties of additional subsequently administered drugs in drug-induced conditioned taste avoidance (CTA) and conditioned place preference (CPP) paradigms. Specifically, nicotine, commonly used in conjunction with other addictive substances, attenuates acquisition of ethanol and caffeine CTAs and morphine-induced CPP.

METHODS

Because nicotine use is comorbid with a number of substance use disorders, we systematically examined the effects of nicotine pre-exposure on two different conditioning paradigms involving integration of the interoceptive stimulus properties of multiple commonly abused drugs, in male and female rats, designed to examine both the aversive and reinforcing properties of these drugs.

RESULTS

Nicotine dose-dependently interfered with acquisition of CTA to passively administered morphine, ethanol, and cocaine, but not lithium chloride, demonstrating that the effects of nicotine are not simply a matter of reduced orosensory processing or an inability to learn such associations. Moreover, nicotine-treated rats required higher doses of drug in order to develop CTA and did not show increased acceptance of the taste of self-administered ethanol compared with saline-treated rats.

CONCLUSIONS

These data demonstrate that nicotine pre-exposure attenuates sensitivity to the stimulus effects of multiple drugs in two conditioning paradigms, in a manner which is consistent with a reduced ability to integrate the interoceptive properties of abused drugs. Through reducing these stimulus properties of drugs of abuse, concomitant nicotine use may result in a need to increase either the frequency or strength of doses during drug-taking, thus likely contributing to enhanced addiction liability in smokers.

Propylene glycol, a major electronic cigarette constituent, attenuates the adverse effects of high-dose nicotine as measured by intracranial self-stimulation in rats

BACKGROUND

Non-nicotine tobacco constituents may contribute to the abuse liability of tobacco products. We previously reported that electronic cigarette (EC) refill liquids containing nicotine and a range of non-nicotine constituents attenuated the anhedonic/aversive effects of nicotine in an intracranial self-stimulation (ICSS) model. The alcohol propylene glycol (PG) is a primary ingredient in these and other EC liquids, yet its abuse potential has not been established. The goal of this study was to evaluate the effects of parenteral administration of PG alone and PG combined with nicotine on ICSS in rats.

METHODS AND RESULTS

PG alone did not affect ICSS at concentrations up to 100%. PG (25% or 60%) did not affect nicotine's reinforcement-enhancing (ICSS threshold-decreasing) effects at low to moderate nicotine doses, but attenuated nicotine's reinforcement-attenuating/aversive (ICSS threshold-increasing) effects at a high nicotine dose. PG concentrations similar to those in EC liquid doses used in our previous studies (1% or 3%) modestly attenuated the ICSS threshold-elevating effects of a high nicotine dose.

CONCLUSIONS

PG attenuated elevations in ICSS thresholds induced by high-dose nicotine, which may reflect an attenuation of nicotine's acute aversive/anhedonic and/or toxic effects. PG may have contributed to the attenuated ICSS threshold-elevating effects of EC liquids reported previously. Further examination of PG in models of addiction and toxicity is needed to understand the consequences of EC use and to inform the development of EC product standards by the FDA.

Nicotine affects ethanol-conditioned taste, but not place, aversion in a simultaneous conditioning procedure

The conditioned taste aversion (CTA) induced by ethanol is a key factor limiting ethanol intake. Nicotine, a drug co-consumed with ethanol, may decrease this aversion by modulating the unconditioned effects of ethanol or by disrupting the association between ethanol and its associated cues. This study analyzed ethanol-induced CTA and conditioned place aversion (CPA) in Long-Evans rats with subchronic exposure to nicotine. The rats were treated with nicotine (0.0 or 0.4 mg/kg) three times before conditioning (on lickometer training sessions 3, 4, and 5) and across conditioning days. During the conditioning the rats were given ethanol (1.3 g/kg) preceded and followed by presentation of a taste (NaCl) and tactile (rod or hole floors) conditioned stimulus (CS+), respectively. On CS- conditioning days, the rats were given vehicle and exposed to alternative stimuli. Three CTA and CPA testing sessions were then conducted. It was found that nicotine reduced ethanol-induced CTA and enhanced locomotor activity, but did not significantly modify the magnitude of ethanol-induced CPA. The effects of nicotine on CTA were observed during both conditioning and testing sessions, and were specific to the NaCl CS+, having no effect on reactivity to water. The dissociation between the effect of nicotine on ethanol-induced CTA and CPA suggests that nicotine does not alter ethanol's motivational properties by generally increasing its positive rewarding effects, nor does it blunt all aversive-like responses to this drug. Instead, nicotine may impede ethanol-induced CTA induced by ethanol by disrupting the neural underpinnings of this specific form of associative learning.

Effects of nicotine-containing and "nicotine-free" e-cigarette refill liquids on intracranial self-stimulation in rats

BACKGROUND

Animal models are needed to inform FDA regulation of electronic cigarettes (ECs) because they avoid limitations associated with human studies. We previously reported that an EC refill liquid produced less aversive/anhedonic effects at a high nicotine dose than nicotine alone as measured by elevations in intracranial self-stimulation (ICSS) thresholds, which may reflect the presence of behaviorally active non-nicotine constituents (e.g., propylene glycol) in the EC liquids. The primary objective of this study was to assess the generality of our prior ICSS findings to two additional EC liquids. We also compared effects of "nicotine-free" varieties of these EC liquids on ICSS, as well as binding affinity and/or functional activity of nicotine alone, nicotine-containing EC liquids, and "nicotine-free" EC liquids at nicotinic acetylcholine receptors (nAChRs).

METHODS AND RESULTS

Nicotine alone and nicotine dose-equivalent concentrations of both nicotine-containing EC liquids produced similar lowering of ICSS thresholds at low to moderate nicotine doses, indicating similar reinforcement-enhancing effects. At high nicotine doses, nicotine alone elevated ICSS thresholds (a measure of anhedonia-like behavior) while the EC liquids did not. Nicotine-containing EC liquids did not differ from nicotine alone in terms of binding affinity or functional activity at nAChRs. "Nicotine-free" EC liquids did not affect ICSS, but bound with low affinity at some (e.g., α4ß2) nAChRs.

CONCLUSIONS

These findings suggest that non-nicotine constituents in these EC liquids do not contribute to their reinforcement-enhancing effects. However, they may attenuate nicotine's acute aversive/anhedonic and/or toxic effects, which may moderate the abuse liability and/or toxicity of ECs.

Abuse liability assessment of an e-cigarette refill liquid using intracranial self-stimulation and self-administration models in rats

BACKGROUND

The popularity of electronic cigarettes (ECs) has increased dramatically despite their unknown health consequences. Because the abuse liability of ECs is one of the leading concerns of the Food and Drug Administration (FDA), models to assess it are urgently needed to inform FDA regulatory decisions regarding these products. The purpose of this study was to assess the relative abuse liability of an EC liquid compared to nicotine alone in rats. Because this EC liquid contains non-nicotine constituents that may enhance its abuse liability, we hypothesized that it would have greater abuse liability than nicotine alone.

METHODS

Nicotine alone and nicotine dose-equivalent concentrations of EC liquid were compared in terms of their acute effects on intracranial self-stimulation (ICSS) thresholds, acquisition of self-administration, reinforcing efficacy (i.e., elasticity of demand), blockade of these behavioral effects by mecamylamine, nicotine pharmacokinetics and nicotinic acetylcholine receptor binding and activation.

RESULTS

There were no significant differences between formulations on any measure, except that EC liquid produced less of an elevation in ICSS thresholds at high nicotine doses.

CONCLUSIONS

Collectively, these findings suggest that the relative abuse liability of this EC liquid is similar to that of nicotine alone in terms of its reinforcing and reinforcement-enhancing effects, but that it may have less aversive/anhedonic effects at high doses. The present methods may be useful for assessing the abuse liability of other ECs to inform potential FDA regulation of those products.

Nicotine Enhances the Hypnotic and Hypothermic Effects of Alcohol in the Mouse

BACKGROUND

Ethanol (EtOH) and nicotine abuse are 2 leading causes of preventable mortality in the world, but little is known about the pharmacological mechanisms mediating co-abuse. Few studies have examined the interaction of the acute effects of EtOH and nicotine. Here, we examine the effects of nicotine administration on the duration of EtOH-induced loss of righting reflex (LORR) and characterize the nature of their pharmacological interactions in C57BL/6J mice.

METHODS

We assessed the effects of EtOH and nicotine and the nature of their interaction in the LORR test using isobolographic analysis after acute injection in C57BL/6J male mice. Next, we examined the importance of receptor efficacy using nicotinic partial agonists varenicline and sazetidine. We evaluated the involvement of major nicotinic acetylcholine receptor (nAChR) subtypes using nicotinic antagonist mecamylamine and nicotinic α4- and α7-knockout mice. The selectivity of nicotine's actions on EtOH-induced LORR was examined by testing nicotine's effects on the hypnotic properties of ketamine and pentobarbital. We also assessed the development of tolerance after repeated nicotine exposure. Last, we assessed whether the effects of nicotine on EtOH-induced LORR extend to hypothermia and EtOH intake in the drinking in the dark (DID) paradigm.

RESULTS

We found that acute nicotine injection enhances EtOH's hypnotic effects in a synergistic manner and that receptor efficacy plays an important role in this interaction. Furthermore, tolerance developed to the enhancement of EtOH's hypnotic effects by nicotine after repeated exposure of the drug. α4* and α7 nAChRs seem to play an important role in nicotine-EtOH interaction in the LORR test. In addition, the magnitude of EtOH-induced LORR enhancement by nicotine was more pronounced in C57BL/6J than DBA/2J mice. Furthermore, acute nicotine enhanced ketamine and pentobarbital hypnotic effects in the mouse. Finally, nicotine enhanced EtOH-induced hypothermia but decreased EtOH intake in the DID test.

CONCLUSIONS

Our results demonstrate that nicotine synergistically enhances EtOH-induced LORR in the mouse.

Dorsal hippocampal cannabinoid CB1 receptors mediate the interactive effects of nicotine and ethanol on passive avoidance learning in mice

The present study evaluated the involvement of the dorsal hippocampal cannabinoid CB1 receptors in the combined effect of ethanol and nicotine on passive avoidance learning in adult male mice. The results indicated that pre-training administration of ethanol (1 g/kg, i.p.) impaired memory retrieval. Pre-test administration of ethanol (0.5 and 1 g/kg, i.p.) or nicotine (0.5 and 0.7 mg/kg, s.c.) significantly reversed ethanol-induced amnesia, suggesting a functional interaction between ethanol and nicotine. Pre-test microinjection of a selective CB1 receptor agonist, ACPA (3 and 5 ng/mouse), plus an ineffective dose of ethanol (0.25 g/kg) or nicotine (0.3 mg/kg) improved memory retrieval, while ACPA by itself could not reverse ethanol-induced amnesia. Pre-test intra-CA1 microinjection of a selective CB1 receptor antagonist, AM251 (0.5-2 ng/mouse), did not lead to a significant change in ethanol-induced amnesia. However, pre-test intra-CA1 microinjection of AM251 prevented the ethanol (1 g/kg) or nicotine (0.7 mg/kg) response on ethanol-induced amnesia. In order to support the involvement of the dorsal hippocampal CB1 receptors in nicotine response, the scheduled mixed treatments of AM251 (0.1-1 ng/mouse), ACPA (5 ng/mouse) and nicotine (0.3 mg/kg) were used. The results indicated that AM251 reversed the response of ACPA to the interactive effects of nicotine and ethanol in passive avoidance learning. Furthermore, pre-test intra-CA1 microinjection of the same doses of ACPA or AM251 had no effect on memory retrieval. These findings show that the cannabinoid CB1 receptors of dorsal hippocampus are important in the combined effect of ethanol and nicotine on passive avoidance learning.

Exposure to nicotine during periadolescence or early adulthood alters aversive and physiological effects induced by ethanol

The majority of smokers begin their habit during adolescence, which often precedes experimentation with alcohol. Interestingly, very little preclinical work has been done examining how exposure to nicotine during periadolescence impacts the affective properties of alcohol in adulthood. Understanding how periadolescent nicotine exposure influences the aversive effects of alcohol might help to explain why it becomes more acceptable to this preexposed population. Thus, Experiment 1 exposed male Sprague Dawley rats to either saline or nicotine (0.4mg/kg, IP) from postnatal days 34 to 43 (periadolescence) and then examined changes in the aversive effects of alcohol (0, 0.56, 1.0 and 1.8g/kg, IP) in adulthood using the conditioned taste aversion (CTA) design. Changes in blood alcohol concentration (BAC) as well as alcohol-induced hypothermia and locomotor suppression were also assessed. To determine if changes seen were specific to nicotine exposure during periadolescence, the procedures were replicated in adults (Experiment 2). Preexposure to nicotine during periadolescence attenuated the acquisition of the alcohol-induced CTAs (at 1.0g/kg) and the hypothermic effects of alcohol (1.0g/kg). Adult nicotine preexposure produced similar attenuation in alcohol's aversive (at 1.8g/kg) and hypothermic (1.8g/kg) effects. Neither adolescent nor adult nicotine preexposure altered BACs or alcohol-induced locomotor suppression. These results suggest that nicotine may alter the aversive and physiological effects of alcohol, regardless of the age at which exposure occurs, possibly increasing its overall reinforcing value and making it more likely to be consumed.

The effects of nicotine on ethanol-induced conditioned taste aversions in Long-Evans rats

RATIONALE

Overall drug acceptability is thought to be a function of the balance between its rewarding and aversive effects, the latter of which is reportedly affected by polydrug use.

OBJECTIVES

Given that nicotine and alcohol are commonly co-used, the present experiments sought to assess nicotine's impact on ethanol's aversive effects within a conditioned taste aversion design.

MATERIALS AND METHODS

Experiment 1 examined various doses of nicotine (0, 0.4, 0.8, 1.2 mg/kg) to determine a behaviorally active dose, and experiment 2 examined various doses of ethanol (0, 0.5, 1.0, 1.5 g/kg) to determine a dose that produced intermediate aversions. Experiment 3 then examined the aversive effects of nicotine (0.8 mg/kg) and ethanol (1.0 g/kg) alone and in combination. Additionally, nicotine's effects on blood alcohol concentrations (BAC) and ethanol-induced hypothermia were examined.

RESULTS

Nicotine and ethanol combined produced aversions significantly greater than those produced by either drug alone or the summed aversive effects of the individual compounds. These effects were unrelated to changes in BAC, but nicotine and ethanol combined produced a prolonged hypothermic effect which may contribute to the increased aversions induced by the combination.

CONCLUSIONS

These data demonstrate that nicotine may interact with ethanol, increasing ethanol's aversive effects. Although the rewarding effects of concurrently administered nicotine and ethanol were not assessed, these data do indicate that the reported high incidence of nicotine and ethanol co-use is unlikely due to reductions in the aversiveness of ethanol with concurrently administered nicotine. It is more likely attributable to nicotine-related changes in ethanol's rewarding effects.

Interactive effects of ethanol and nicotine on learning in C57BL/6J mice depend on both dose and duration of treatment

OBJECTIVE AND RATIONALE

Alcohol and nicotine are commonly co-abused; one possible explanation for co-abuse is that each drug ameliorates the aversive effects of the other. Both drugs have dose-dependent effects on learning and memory. Thus, this study examined the interactive effects of acute ethanol and acute, chronic, or withdrawal from chronic nicotine on fear conditioning in C57BL/6J mice.

MATERIALS AND METHODS

Conditioning consisted of auditory conditioned stimulus-foot-shock unconditioned stimulus pairings. For acute studies, saline or ethanol, then saline or nicotine was administered before training, and saline or nicotine was also administered before testing. For chronic and withdrawal studies, saline or nicotine was administered chronically, and ethanol or saline was administered before training.

RESULTS

Acute nicotine (0.09 mg/kg) reversed ethanol-induced deficits (1.0 and 1.5 g/kg) in contextual and cued fear conditioning, whereas a low dose of ethanol (0.25 g/kg) reversed nicotine (6.3 mg kg(-1) day(-1)) withdrawal-induced deficits in contextual conditioning. Tolerance developed for the effects of nicotine on ethanol-induced deficits in conditioning and cross-tolerance between chronic nicotine and acute ethanol was seen for the enhancing effects of ethanol on conditioning.

CONCLUSIONS

The complex and sometimes polar actions of ethanol and nicotine on behavior may contribute to co-abuse of these drugs. Specifically, smoking may initially reduce the aversive effects of ethanol, but tolerance develops for this effect. In addition, low doses of alcohol may lessen nicotine withdrawal symptoms.

Multiple substance use among young males

Neurobiological studies hypothesize a common final pathway of addictive behavior in the mesolimbic dopaminergic system. Nicotine has been shown to sensitize the reward pathway, thereby causing increased drug-seeking behavior. Since there is evidence to suggest that nicotine, alcohol and other psychoactive substances act on the same final pathway and seem to augment their effects in animal subjects, drug intake behavior of humans would likely be reflected in increased substance use of nicotine-dependent persons. We used biological markers of substance use as well as questionnaires to assess the levels of psychoactive substance use among 18-year-old males in a naturalistic cross-sectional setting. We found that increasing levels of nicotine dependence were related to higher levels of alcohol abuse and dependence. Furthermore, higher levels of nicotine dependence were associated with elevated levels of recent cannabinoid use.

Effects of ethanol on nicotine-induced conditioned place preference in C57BL/6J mice

It has been shown that small doses of ethanol (<or= 1.0 g/kg) may antagonize the discriminative stimulus properties of nicotine. The aim of the present study was to evaluate whether ethanol could antagonize nicotine's rewarding effects in the conditioned place preference procedure. For comparison, effects of ethanol on nicotine-induced seizures were assessed. Male C57BL/6J mice were used in all experiments. Lower doses of nicotine (0.3 and 0.6 mg/kg, s.c.) induced significant conditioned place preference, while higher doses (0.9 and 1.2 mg/kg) induced neither conditioned place preference nor conditioned place aversion. In the following experiments, ethanol (0.5 or 1.0 g/kg, i.p.) was administered 5 min before 0.3 mg/kg nicotine. Ethanol did not antagonize nicotine-induced conditioned place preference. Contrary to our hypothesis, a non-significant (p = 0.07) enhancement of nicotine-induced place preference conditioning was observed in mice pre-treated with 1.0 g/kg ethanol. Both doses of ethanol (0.5 and 1.0 g/kg) suppressed seizures elicited by a high dose of nicotine (6.0 mg/kg). Ethanol totally eliminated clonic-tonic component of nicotine-induced seizures. Maximal blood ethanol levels after i.p. administration of 0.5 or 1.0 g/kg ethanol exceeded 60 and 115 mg%, respectively. The present results may indicate that the rewarding and seizure-inducing effects of nicotine are differentially modulated by clinically relevant concentrations of ethanol in mice.

Nicotine-induced conditioned taste aversion in the rat: Effects of ethanol

It has been shown that small doses of ethanol antagonise the discriminative stimulus properties of nicotine in the rat. The aim of the present study was to evaluate whether ethanol could antagonise the aversive stimulus effects of nicotine. Wistar rats were trained to associate nicotine injections with a novel tasting fluid (0.1% saccharin) in the conditioned taste aversion procedure. Nicotine (0.3 mg/kg, s.c.) was injected 5 min after the end of a 20-min exposure to the saccharin solution. Ethanol (0.25-0.5 g/kg, i.p.) was administered 5 or 50 min before nicotine. In general, ethanol did not inhibit nicotine-induced conditioned taste aversion. Contrary to the findings in drug discrimination studies, a slight but significant enhancement of nicotine-induced taste aversion conditioning was observed after ethanol pre-treatment. Blood ethanol levels were measured in a separate group of rats. Maximal blood ethanol levels after i.p. administration of 0.25 or 0.5 g/kg ethanol exceeded 20 and 80 mg%, respectively. Concluding, the present results may indicate that ethanol does not attenuate nicotine-induced conditioned taste aversion in the rat.

Effects of chronic caffeine pre-exposure on conditioned and unconditioned psychomotor activity induced by nicotine and amphetamine in rats

Three experiments examined the effects of chronic pre-exposure to caffeine on the subsequent conditioned and unconditioned locomotor activating effects of nicotine or amphetamine in rats. Rats were given daily intraperitoneal injections of caffeine anhydrous (0, 10 or 30 mg/kg base) for 30 days. Conditioning (environment-drug pairings) began after the last day of caffeine pre-exposure. Pre-exposure to 30 mg/kg of caffeine enhanced the acute and chronic locomotor effects of amphetamine (0.5 mg/kg). A similar enhancement of activity was not seen with the high (0.421 mg/kg base) or low dose (0.175 mg/kg) of nicotine. In a drug-free test, the distinct environment paired with amphetamine and the high dose of nicotine evoked increases in activity relative to controls. Caffeine pre-exposure did not affect expression of this conditioned hyperactivity. These effects of caffeine pre-exposure on amphetamine-induced activity could not be attributed to non-specific effects of caffeine.

Asymmetric serial interactions between ethanol and cocaine in taste aversion learning

Although the interaction between ethanol and cocaine is well documented, it has generally been limited to situations in which the two drugs are given concurrently. Little exists on the interaction between ethanol and cocaine when one drug is given prior to the other. In Experiment 1, female Long-Evans rats were given five exposures to ethanol (2 g/kg ip) or vehicle prior to taste aversion conditioning with cocaine (32 mg/kg sc) for a total of five conditioning trials. In Experiment 2, rats were given five exposures to cocaine (32 mg/kg sc) or vehicle prior to taste aversion conditioning with ethanol (2 g/kg ip) for a total of five conditioning trials. Ethanol-preexposed, cocaine-conditioned animals (Experiment 1) displayed attenuated aversions to the cocaine-associated solution, drinking significantly greater amounts of saccharin than vehicle-preexposed, conditioned subjects. Conversely, cocaine-preexposed, ethanol-conditioned animals (Experiment 2) displayed robust aversions to the ethanol-associated solution, drinking levels comparable to those consumed by vehicle-preexposed, conditioned subjects and drinking significantly less than controls. Although the basis for these asymmetric effects is not known, they may have implications for abuse vulnerability in that drug history may impact subsequent drug toxicity that, in turn, may alter drug acceptability.

Alcohol tolerance and nicotine cross-tolerance in adolescent mice

The present experiment was designed to evaluate the development of tolerance to alcohol and cross-tolerance to nicotine in adolescent mice. C57BL/6J mice (30-40 days old) were injected IP with alcohol (2.5 g/kg) for 4 consecutive days. A control group received four saline injections. On the test day, all subjects received an alcohol injection. Tolerance to alcohol's hypothermic effect was observed. Mice (male and female) exposed to alcohol for the 4 previous days showed less hypothermic response to an alcohol challenge than animals injected for 4 days with saline and then challenged with alcohol. Tolerance to alcohol's motor incoordinating effects and differences in blood alcohol concentrations were not observed. Thirty days following alcohol treatment, the same mice received a single nicotine injection (1 mg/kg) to assess cross-tolerance. Nicotine's effect on locomotor activity (open field test) and rectal temperature varied as a function of prior adolescent alcohol exposure and gender. Specifically, female mice who had been exposed to alcohol administrations were more resistant to nicotine's effect on locomotion and temperature than saline-treated animals. In summary, these data demonstrate that adolescent mice develop tolerance to some, but not all, alcohol-induced responses, and that female mice are cross-tolerant to nicotine's effects on temperature and activity.

Preexposure effects of nicotine and acetaldehyde on conditioned taste aversion induced by both drugs

Previous assessments have demonstrated an interaction between ethanol and nicotine in the conditioned taste-aversion (CTA) paradigm. The present study assessed whether acetaldehyde, the primary reinforcing metabolite of ethanol, would interact with nicotine as well. In six experiments, water-deprived male Wistar rats were preexposed to either acetaldehyde (0.2 or 0.3 g/kg, IP) or nicotine (0.8, 1.2, or 2 mg/kg, SC) for 3 consecutive days and then subsequently conditioned, 24 h later, with either nicotine (0.8, 1.2, or 2 mg/kg, SC) or acetaldehyde (0.2 or 0.3 g/kg, IP), respectively. There were 4 conditioning days and 4 drug-free test days, each spaced 72 h apart. On test days, animals were offered a free choice between water and saccharin. The results of the following set of experiments demonstrated a dose-related interaction between nicotine and acetaldehyde, where lower doses of each drug failed to attenuate CTA induced by one another, but a higher nicotine dose (2 mg/kg) attenuated the formation of a CTA induced by acetaldehyde (0.3 g/kg). It was argued that the primary metabolite of ethanol may play a role in the interaction between nicotine and ethanol previously observed.

The effects of aminotriazole and acetaldehyde on an ethanol drug discrimination with a conditioned taste aversion procedure

The present study was designed to investigate whether acetaldehyde shares stimulus properties with ethanol using the conditioned taste aversion (CTA) baseline of drug discrimination learning. Animals were trained to discriminate ethanol (0.8 g/kg, i.p.) from saline using 11 consecutive cycles consisting of a pairing day and three nonpairing days. On pairing days, all animals were injected with ethanol 30 min prior to a 20-min limited access to a saccharin solution (0.1% w/v) and then immediately injected with either LiCl (0.15 M, 1.8 meq) or distilled water. On the three following nonpairing days, animals were injected with saline and 30 min later presented with the same saccharin solution for 20 min. No injections followed on these nonpairing days. Results showed that animals acquired discriminative stimulus control for ethanol after seven pairings. Pretreatment with the catalase inhibitor did not alter the discriminative control for ethanol. Generalization tests revealed that acetaldehyde substituted for ethanol at a dose of 0.3 g/kg. The results of the present study suggest that catalase inhibition did not reverse or alter the discriminative stimulus effects of ethanol. However, generalization tests showed that acetaldehyde (0.3 g/kg) will substitute for ethanol suggesting that these two drugs share some similar properties.

Cocaine and ethanol interaction in the conditioned taste aversion paradigm

The aim of this study was to examine the relationship between cocaine and ethanol in a variant of the conditioned taste aversion (CTA) paradigm. The preexposure CTA procedure formed the basis of the following set of experiments. Experiments 1a and 1b assessed whether cocaine and ethanol were functionally related with overlapping stimulus properties as reflected in the preexposure CTA procedure. Male Wistar rats with restricted water access were preexposed to cocaine or ethanol for 3 consecutive days. Twenty-four hours after the last preexposure session, rats were conditioned to either ethanol or cocaine, respectively. The results of this set of experiments revealed a symmetrical interaction between cocaine and ethanol, where cocaine and ethanol effectively blocked CTA to one another. These findings suggested that there may be overlapping stimulus properties between cocaine and ethanol, which may be detected in this procedure.