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Genome-wide association studies in humans have suggested that variants of the cadherin-13 (CDH13) gene are associated with substance use disorder, subjective response to amphetamine, and attention deficit hyperactivity disorder. To examine the role of the Cdh13 and its peptide ligand adiponectin (AdipoQ) in addiction-related behaviors, we assessed Cdh13 knockout (KO) rats and AdipoQ KO mice using intravenous cocaine self-administration and conditioned place preference (CPP) paradigms. During intravenous cocaine self-administration, male Cdh13 heterozygous (+/-) and KO (-/-) rats showed increased cue-induced reinstatement compared with wild-type (WT) rats when presented with a cocaine-paired stimulus, whereas female Cdh13 rats showed no differences across genotype. Cdh13 -/- rats showed higher responding for a saccharin reinforcer and learned the choice reaction time (RT) task more slowly than WTs. However, we found no differences between Cdh13 -/- and +/+ rats in responding for sensory reinforcement, number of premature responses in the RT task, tendency to approach a Pavlovian food cue, CPP and locomotor activation to cocaine (10 or 20 mg/kg). In AdipoQ -/- mice, there was a significant increase in CPP to methamphetamine (1 mg/kg) but not to a range of d-amphetamine doses (0.5, 1, 2 and 4 mg/kg). Taken together, these data suggest that Cdh13 and AdipoQ regulate sensitivity to psychomotor stimulants and palatable rewards without producing major changes in other behaviors. In humans, these two genes may regulate sensitivity to natural and drug rewards, thus influencing susceptibility to the conditioned drug effects and relapse.

Genome-wide association studies typically evaluate the autosomes and sometimes the X Chromosome, but seldom consider the Y or mitochondrial (MT) Chromosomes. We genotyped the Y and MT Chromosomes in heterogeneous stock (HS) rats (Rattus norvegicus), an outbred population created from 8 inbred strains. We identified 8 distinct Y and 4 distinct MT Chromosomes among the 8 founders. However, only 2 types of each nonrecombinant chromosome were observed in our modern HS rat population (generations 81-97). Despite the relatively large sample size, there were virtually no significant associations for behavioral, physiological, metabolome, or microbiome traits after correcting for multiple comparisons. However, both Y and MT Chromosomes were strongly associated with the expression of a few genes located on those chromosomes, which provided a positive control. Our results suggest that within modern HS rats there are no Y and MT Chromosomes differences that strongly influence behavioral or physiological traits. These results do not address other ancestral Y and MT Chromosomes that do not appear in modern HS rats, nor do they address effects that may exist in other rat populations, or in other species., Competing Interests: Conflicts of interest RK is a scientific advisory board member, and consultant for BiomeSense, Inc., has equity and receives income. He is a scientific advisory board member and has equity in GenCirq. He is a consultant for DayTwo, and receives income. He has equity in and acts as a consultant for Cybele. He is a co-founder of Biota, Inc., and has equity. He is a cofounder of Micronoma, and has equity and is a scientific advisory board member. The terms of these arrangements have been reviewed and approved by the University of California, San Diego in accordance with its conflict of interest policies., (© The Author(s) 2024. Published by Oxford University Press on behalf of The Genetics Society of America.)

Organisms must regulate their behavior flexibly in the face of environmental challenges. Failure can lead to a host of maladaptive behavioral traits associated with a range of neuropsychiatric disorders, including attention deficit hyperactivity disorder, autism, and substance use disorders. This maladaptive dysregulation of behavior is influenced by genetic and environmental factors. For example, environmental enrichment produces beneficial neurobehavioral effects in animal models of such disorders. The present study determined the effects of environmental enrichment on a range of measures related to behavioral regulation using a large cohort of male, outbred heterogeneous stock (HS) rats as subjects. Subjects were reared from late adolescence onwards either in pairs in standard housing with minimal enrichment (n = 200) or in groups of 16 in a highly enriched environment consisting of a large multi-level cage filled with toys, running wheels, and shelters (n = 64). Rats were subjected to a battery of tests, including: (i) locomotor response to novelty, (ii) light reinforcement, (iii) social reinforcement, (iv) reaction time, (v) a patch-depletion foraging test, (vi) Pavlovian conditioned approach, (vii) conditioned reinforcement, and (viii) cocaine conditioned cue preference. Results indicated that rats housed in the enriched environment were able to filter out irrelevant stimuli more effectively and thereby regulate their behavior more efficiently than standard-housing rats. The dramatic impact of environmental enrichment suggests that behavioral studies using standard housing conditions may not generalize to more complex environments that may be more ethologically relevant., (© 2024. The Author(s).)

The authors present a steady-state-, particle-size-, and dose-dependent dissolution-permeation model that describes particle dissolution within the concentration boundary layer (CBL) adjacent to a semipermeable surface. It is critical to understand how particle size and dose affect the behavior of dissolving particles in the presence of a CBL adjacent to a semipermeable surface both in vivo and in vitro . Control of particle size is ubiquitous in the pharmaceutical industry; however, traditional pharmaceutical assumptions of particle dissolution typically ignore particle dissolution within the length scale of the CBL. The CBL does not physically prevent particles from traveling to the semipermeable surface (mucus, epithelial barrier, synthetic membrane, etc.), and particle dissolution can occur within the CBL thickness (δ C ) if the particle is sufficiently small (∼ d particle ≤ δ C ). The total flux (the time rate transport of molecules across the membrane surface per unit area) was chosen as a surrogate parameter for measuring the additional mass generated by particles dissolving within the donor CBL. Mass transfer experiments aimed to measure the total flux of drug using an ultrathin large-area membrane diffusion cell described by Sinko et al. with a silicone-based membrane ( Mol. Pharmaceutics 2020, 17, (7) 2319-2328, DOI: 10.1021/acs.molpharmaceut.0c00040). Suspensions of ibuprofen, a model weak-acid drug, with three different particle-size distributions with average particle diameters of 6.6, 37.4, and 240 μm at multiple doses corresponding to a range of suspension concentrations with dimensionless dose numbers of 2.94, 14.7, 147, and 588 were used to test the model. Experimentally measured total flux across the semipermeable membrane/CBL region agreed with the predictions from the proposed model, and at a range of relatively low suspension concentrations, dependent on the average particle size, there was a measurable effect on the flux due to the difference in δ C that formed at the membrane surface. Additionally, the dose-dependent total flux across the membrane was up to 10% higher than the flux predicted by the standard Higuchi-Hiestand dissolution model where the effects of confinement were ignored as described by Wang et al. ( Mol. Pharmaceutics 2012, 9 (5), 1052-1066, DOI: 10.1021/mp2002818).

Neural networks (NNs) have witnessed widespread deployment across various domains, including some safety-critical applications. In this regard, the demand for verifying means of such artificial intelligence techniques is more and more pressing. Nowadays, the development of evaluation approaches for NNs is a hot topic that is attracting considerable interest, and a number of verification methods have been proposed. Yet, a challenging issue for NN verification is pertaining to the scalability when some NNs of practical interest have to be evaluated. This work aims to present INNAbstract, an abstraction method to reduce the size of NNs, which leads to improving the scalability of NN verification and reachability analysis methods. This is achieved by merging neurons while ensuring that the obtained model (i.e., abstract model) overapproximates the original one. INNAbstract supports networks with numerous activation functions. In addition, we propose a heuristic for nodes' selection to build more precise abstract models, in the sense that the outputs are closer to those of the original network. The experimental results illustrate the efficiency of the proposed approach compared to the existing relevant abstraction techniques. Furthermore, they demonstrate that INNAbstract can help the existing verification tools to be applied on larger networks while considering various activation functions.

Choice behavior requires animals to evaluate both short- and long-term advantages and disadvantages of all potential alternatives. Impulsive choice is traditionally measured in laboratory tasks by utilizing delay discounting (DD), a paradigm that offers a choice between a smaller immediate reward, or a larger more delayed reward. This study tested a large sample of Heterogeneous Stock (HS) male (n = 896) and female (n = 898) rats, part of a larger genetic study, to investigate whether measures of reward maximization overlapped with traditional models of delay discounting via the patch depletion model using a Sequential Patch Depletion procedure. In this task, rats were offered a concurrent choice between two water "patches" and could elect to "stay" in the current patch or "leave" for an alternative patch. Staying in the current patch resulted in decreasing subsequent reward magnitudes, whereas the choice to leave a patch was followed by a delay and a resetting to the maximum reward magnitude. Based on the delay in a given session, different visit durations were necessary to obtain the maximum number of rewards. Visit duration may be analogous to an indifference point in traditional DD tasks. Males and females did not significantly differ on traditional measures of DD (e.g. delay gradient; AUC). When examining measures of patch utilization, females made fewer patch changes at all delays and spent more time in the patch before leaving for the alternative patch compared to males. Consistent with this, there was some evidence that females deviated from reward maximization more than males. However, when controlling for body weight, females had a higher normalized rate of reinforcement than males. Measures of reward maximization were only weakly associated with traditional DD measures and may represent distinctive underlying processes. Taken together, females performance differed from males with regard to reward maximization that were not observed utilizing traditional measures of DD, suggesting that the patch depletion model was more sensitive to modest sex differences when compared to traditional DD measures in a large sample of HS rats., (© 2023. The Author(s).)

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., Competing Interests: Conflict of interest The authors C.P.K. and P.J.M. have no conflicts of interest to declare., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Rationale: Nicotine promotes alcohol intake through pharmacological and behavioral interactions. As an example of the latter, nicotine can facilitate approach toward food- and alcohol-associated stimuli ("sign-tracking") in lever-Pavlovian conditioned approach (PavCA) paradigms. However, we recently reported that nicotine can also enhance approach toward locations of reward delivery ("goal-tracking") triggered by ethanol-predictive stimuli when the location of ethanol delivery is non-static (i.e., a retractable sipper bottle)., Objective: To determine whether the non-static nature of the reward location could have biased the development of goal-tracking in our previous study (Loney et al., 2019); we assessed the effect of nicotine in a lever-PavCA paradigm wherein the location of ethanol delivery was static (i.e., a stationary liquid receptacle). Then, to determine whether nicotine's enhancement of goal-tracking is unique to ethanol-predictive stimuli, we assessed the effect of systemic nicotine on approach triggered by food-predictive stimuli in a lever-PavCA paradigm., Methods: Long-Evans rats were used in two PavCA experiments wherein a lever predicted the receipt of ethanol (15% vol/vol; experiment 1) or food (experiment 2) into a stationary receptacle. Prior to testing, rats were administered nicotine (0.4 mg/kg subcutaneously) or saline systemically., Results: In both experiments, nicotine increased measures of goal-tracking, but not sign-tracking., Conclusion: Nicotine can facilitate approach to reward locations without facilitating approach to reward-predictive stimuli. As such, conceptualization of the mechanisms by which nicotine affects behavior must be expanded to explain an enhancement of goal-tracking by nicotine., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Angelyn, Loney and Meyer.)

Background: Mesolimbic circuits regulate the attribution of motivational significance to incentive cues that predict reward, yet this network also plays a key role in adapting reward-seeking behavior when the contingencies linked to a cue unexpectedly change. Here, we asked whether mesoaccumbal GABA (gamma-aminobutyric acid) projections enhance adaptive responding to incentive cues of abruptly altered reward value, and whether these effects were distinct from global activation of all ventral tegmental area GABA circuits., Methods: We used a viral targeting system to chemogenetically activate mesoaccumbal GABA projections in male rats during a novel cue-dependent operant value-shifting task, in which the volume of a sucrose reward associated with a predictive cue is suddenly altered, from the beginning and throughout the session. We compared the results with global activation of ventral tegmental area GABA neurons, which will activate local inhibitory circuits and long loop projections., Results: We found that activation of mesoaccumbal GABA projections decreases responding to incentive cues associated with smaller-than-expected rewards. This tuning of behavioral responses was specific to cues associated with smaller-than-expected rewards but did not impact measures related to consuming the reward. In marked contrast, activating all ventral tegmental area GABA neurons resulted in a uniform decrease in responding to incentive cues irrespective of changes in the size of the reward., Conclusions: Targeted activation of mesoaccumbal GABA neurons facilitates adaptation in reward-seeking behaviors. This suggests that these projections may play a very specific role in associative learning processes., (Copyright © 2020. Published by Elsevier Inc.)

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.

Sensitivity to cocaine and its associated stimuli ("cues") are important factors in the development and maintenance of addiction. Rodent studies suggest that this sensitivity is related, in part, to the propensity to attribute incentive salience to food cues, which, in turn, contributes to the maintenance of cocaine self-administration, and cue-induced relapse of drug-seeking. Whereas each of these traits has established links to drug use, the relatedness between the individual traits themselves has not been well characterized in preclinical models. To this end, the propensity to attribute incentive salience to a food cue was first assessed in two distinct cohorts of 2716 outbred heterogeneous stock rats (HS; formerly N:NIH). We then determined whether each cohort was associated with performance in one of two paradigms (cocaine conditioned cue preference and cocaine contextual conditioning). These measure the unconditioned locomotor effects of cocaine, as well as conditioned approach and the locomotor response to a cocaine-paired floor or context. There was large individual variability and sex differences among all traits, but they were largely independent of one another in both males and females. These findings suggest that these traits may contribute to drug-use via independent underlying neuropsychological processes.

Population protocols are a well established model of computation by anonymous, identical finite-state agents. A protocol is well-specified if from every initial configuration, all fair executions of the protocol reach a common consensus. The central verification question for population protocols is the well-specification problem : deciding if a given protocol is well-specified. Esparza et al. have recently shown that this problem is decidable, but with very high complexity: it is at least as hard as the Petri net reachability problem, which is TOWER-hard, and for which only algorithms of non-primitive recursive complexity are currently known. In this paper we introduce the class WS 3 of well-specified strongly-silent protocols and we prove that it is suitable for automatic verification. More precisely, we show that WS 3 has the same computational power as general well-specified protocols, and captures standard protocols from the literature. Moreover, we show that the membership and correctness problems for WS 3 reduce to solving boolean combinations of linear constraints over N . This allowed us to develop the first software able to automatically prove correctness for all of the infinitely many possible inputs., (© The Author(s) 2021.)

Preclinical evaluation of modern oral dosage forms requires more advanced in vitro devices as the trend of selecting low solubility, high permeability compounds for commercial development continues. Current dissolution methodologies may not always be suitable for such compounds due to excessive fluid volume, high fluid shear rates, heterogeneity of shear rates, suboptimal fluid flow, and, ultimately, the lack of absorption ability (Gray The Science of USP 1 and 2 Dissolution: Present Challenges and Future Relevance; Pharmaceutical Research , 2009; Vol. 26; pp 1289-1302). Herein, a new dissolution apparatus is introduced in combination with an ultrathin, semipermeable polymer membrane that mimics human passive absorption for lipophilic compounds. The ultrathin large-area polydimethylsiloxane (PDMS) membrane (UTLAM) absorption system is designed to mimic the dissolution and passive transcellular diffusion process representing the oral absorption pathway. A simple spin-casting method was developed to fabricate the ultrathin highly uniform membranes. To minimize membrane resistance to diffusion and maximize transport across the polymer membrane, 10-40 μm PDMS membranes were successfully prepared. A new diffusion cell was designed and tested to support the UTLAM and incorporates a hydrofoil impeller for more desirable hydrodynamics and mixing, using ibuprofen as a model weak acidic drug. UTLAM permeability was sufficiently high that the aqueous boundary layer contributed to the overall permeability of the system. This diffusion cell system demonstrated that, when the aqueous diffusion layer contributes to the overall resistance to transport, the pH at which absorption is 50% of maximum (pH 50% ) shifts from the p K a to higher values, demonstrating why weak acid drugs can exhibit high absorption at pH's significantly greater than their p K a . High rates of transport across the UTLAM are possible for drugs with high partition coefficients (i.e., BCS II compounds even under mostly ionized conditions), and PDMS UTLAMs may be tailored to simulate human intestinal passive absorption rates.

Background: Multiple factors contribute to the etiology of addiction, including genetics, sex, and a number of addiction-related behavioral traits. One behavioral trait where individuals assign incentive salience to food stimuli ("sign-trackers", ST) are more impulsive compared to those that do not ("goal-trackers", GT), as well as more sensitive to drugs and drug stimuli. Furthermore, this GT/ST phenotype predicts differences in other behavioral measures. Recent studies have implicated the gut microbiota as a key regulator of brain and behavior, and have shown that many microbiota-associated changes occur in a sex-dependent manner. However, few studies have examined how the microbiome might influence addiction-related behaviors. To this end, we sought to determine if gut microbiome composition was correlated with addiction-related behaviors determined by the GT/ST phenotype., Methods: Outbred male (N=101) and female (N=101) heterogeneous stock rats underwent a series of behavioral tests measuring impulsivity, attention, reward-learning, incentive salience, and locomotor response. Cecal microbiome composition was estimated using 16S rRNA gene amplicon sequencing. Behavior and microbiome were characterized and correlated with behavioral phenotypes. Robust sex differences were observed in both behavior and microbiome; further analyses were conducted within sex using the pre-established goal/sign-tracking (GT/ST) phenotype and partial least squares differential analysis (PLS-DA) clustered behavioral phenotype., Results: Overall microbiome composition was not associated to the GT/ST phenotype. However, microbial alpha diversity was significantly decreased in female STs. On the other hand, a measure of impulsivity had many significant correlations to microbiome in both males and females. Several measures of impulsivity were correlated with the genus Barnesiella in females. Female STs had notable correlations between microbiome and attentional deficient. In both males and females, many measures were correlated with the bacterial families Ruminocococcaceae and Lachnospiraceae., Conclusions: These data demonstrate correlations between several addiction-related behaviors and the microbiome specific to sex., Competing Interests: Declaration of Competing Interest JFC & TGD are in receipt of research funding from 4D‐Pharma, Mead Johnson, Nutricia, and Cremo. Timothy Dinan has been an invited speaker at meetings organized by Servier, Lundbeck, Janssen, and AstraZeneca. John Cryan has been an invited speaker at meetings organized by Mead Johnsen, Alkermes, and Janssen., (Copyright © 2020 The Author(s). Published by Elsevier B.V. All rights reserved.)

Purpose: The purpose of this investigation was to evaluate diagnostic agreement in anterior-posterior (AP) categorization of the maxilla and mandible between a skeletal-landmark analysis and a facial-landmark analysis for treatment planning of orthognathic surgery and orthodontics., Materials and Methods: This retrospective, consecutive case series of adult patients who presented to the Mayo Clinic orthodontic department compared maxillary and mandibular AP diagnoses. Steiner's analysis of the sella-nasion-A point angle and sella-nasion-B point angle was used for a skeletal-landmark diagnosis. Element II of Andrews' 6 elements of orofacial harmony was used for a facial-landmark diagnosis. Both diagnoses were categorized as either deficient, optimal, or excessive for each jaw. Categorization of the skeletal landmark was determined by normative data, whereas the facial landmark provides a customized categorization unique to each individual., Results: Weighted κ statistics were completed to test agreement between the categories determined by the skeletal and facial landmarks. The maxilla showed poor agreement, and the mandible showed slight agreement., Conclusions: No agreement was found for AP categorization of the maxilla and mandible between skeletal-landmark and facial-landmark analyses. Most mandibles were diagnosed as retrognathic by the facial landmark, whereas most were diagnosed as optimal by the skeletal landmark. When the 2 landmarks disagreed, the facial landmark defined the optimal position farther anterior. The landmark chosen for diagnosis will impact the optimal jaw position and can affect orthognathic and orthodontic outcomes., (Copyright © 2019 American Association of Oral and Maxillofacial Surgeons. Published by Elsevier Inc. All rights reserved.)

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 ED 50 , 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., (© 2019 by the Research Society on Alcoholism.)

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., (Copyright © 2018 Elsevier B.V. All rights reserved.)

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., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Background: Aversion to the orosensory properties of concentrated ethanol (EtOH) solutions is often cited as a primary barrier to initiation of drinking and may contribute to abstention. These aversive properties include gustatory processes which encompass both bitter-like taste qualities and trigeminal-mediated irritation. Chronic intermittent EtOH access (CIA) results in substantial and persistent increases in EtOH consumption, but the degree to which this facilitation involves sensory responding to EtOH and other bitter stimuli is currently undetermined., Methods: Long-Evans rats were given brief-access licking tests designed to examine the immediate, taste-guided assessment of the palatability of EtOH and quinine solutions. Rats were assessed once in a naïve state and again following previous brief-access exposure, or following 4 weeks of CIA. The relationship between the sensitivity to the aversive orosensory properties of EtOH and quinine following EtOH access and the impact of antecedent quinine exposure on the acceptance of EtOH were determined in 2 parallel studies., Results: Both brief access to EtOH and 4-week CIA resulted in substantial rightward shifts in the concentration-response function of brief-access EtOH licking, indicating that EtOH exposure increased acceptance of the taste of EtOH. The initial sensitivity to the aversive orosensory properties of EtOH and quinine was positively correlated in naïve rats, such that rats that were initially more accepting of quinine were also more accepting of EtOH. Rats that sampled quinine immediately prior to tasting EtOH exhibited successive positive contrast in that they were more accepting of highly concentrated EtOH, relative to a water-control group., Conclusions: Increased EtOH acceptance following exposure is, at least in part, facilitated by a decrease in its aversive sensory properties. Both long- and short-term access increase the palatability of the taste of EtOH in brief-access licking tests. Moreover, the sensitivity to the bitterness of quinine was predictive of acceptance of EtOH indicating some commonality in the sensory mechanisms that mediate the initial acceptance of the 2 stimuli. Accordingly, immediate prior exposure to quinine results in increased acceptance of EtOH, suggesting that successive positive contrast between oral stimuli may contribute to increased alcohol consumption., (Copyright © 2017 by the Research Society on Alcoholism.)

Environmental rewards and Pavlovian reward cues can acquire incentive salience, thereby eliciting incentive motivational states and instigate reward-seeking. In rats, the incentive salience of food cues can be measured during a Pavlovian conditioned approach paradigm, in which rats engage in cue-directed approach ("sign-tracking") or approach the food delivery location ("goal-tracking"). While it has been shown that dopamine signaling is necessary for sign-tracking, some studies have suggested that norepinephrine is involved in learning to sign-track as well. Thus, in order to investigate the influence of norepinephrine in Pavlovian conditioned approach, we administered three adrenergic drugs while rats learned that a food cue (an illuminated, retractable lever) preceded the delivery of banana-flavored food pellets into a food-cup. We found that pre-session injections of disulfiram (a dopamine-β-hydroxylase inhibitor) inhibited the development of sign-tracking, but goal-tracking was only affected at the high dose. In one experiment, post-session injections of disulfiram blocked the development of sign-tracking, although this effect was not replicated in a separate set of rats. Post-session injections of prazosin (an α1-adrenergic receptor antagonist) and propranolol (a β-adrenergic receptor antagonist) also blocked the development of sign-tracking but not goal-tracking. Taken together, these results suggest that adrenergic transmission mediates the acquisition of sign-tracking but not goal-tracking, and thus plays a selective role in the attribution of incentive salience food cues., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Rationale: Individuals prone to attribute incentive salience to food-associated stimuli ("cues") are also more sensitive to cues during drug seeking and drug taking. This may be due in part to a difference in sensitivity to the affective or other stimulus properties of the drug. In rats, these properties are associated with 50-kHz ultrasonic vocalizations (USVs), in that they are elicited during putative positive affective and motivational states, including in response to drugs of abuse., Objectives: We sought to determine whether individual differences in the tendency to attribute incentive salience to a food cue (as measured by approach) were associated with differences in cocaine-induced USVs. We also tested whether the food cue would elicit USVs and if this response was related to approach to the food cue., Methods: In experiment 1, rats underwent Pavlovian conditioned approach (PavCA) training where they learned to associate a cue (an illuminated lever) with the delivery of a food pellet into a food cup. Subjects were categorized based on their approach to the cue ("sign-trackers") or to the food cup ("goal-trackers"). Rats subsequently underwent nine testing days in which they were given saline or cocaine (10 mg/kg i.p) and placed into a locomotor chamber. In experiment 2, rats were first tested in the locomotor chambers for one saline-treated day followed by one cocaine-treated day and then trained in PavCA. USVs were recorded from a subset of individuals during the last day of PavCA to determine if the food cue would elicit USVs., Results: Sign-trackers produced 5-24 times more cocaine-induced 50 kHz USVs compared to goal-trackers for all days of experiment 1, and this response sensitized with repeated cocaine, only in sign-trackers. Similarly in experiment 2, individuals that produced the most cocaine-induced USVs on a single exposure also showed the greatest tendency to sign-track during PavCA. Lastly, while sign-trackers produced more USVs during PavCA generally, the cue itself did not elicit additional USVs in sign- or goal-trackers., Conclusions: These results indicate a robust and consistent relationship between approach to a food cue and cocaine-induced USV production. Thus, these USVs may index the neurobiological differences underlying the behavioral distinctions of sign- and goal-trackers.

Rationale: Some individuals are particularly responsive to reward-associated stimuli ("cues"), including the effects of these cues on craving and relapse to drug-seeking behavior. In the cases of nicotine and alcohol, cues may acquire these abilities via the incentive-enhancing properties of the drug., Objectives: To determine the interaction between cue-responsivity and nicotine reinforcement, we studied the patterns of nicotine self-administration in rats categorized based on their tendency to approach a food-predictive cue ("sign-trackers") or a reward-delivery location ("goal-trackers"). In a second experiment, we determined whether nicotine and ethanol altered the incentive value of a food cue., Methods: Rats were classified as sign- or goal-trackers during a Pavlovian conditioned approach paradigm. Rats then self-administered intravenous nicotine (0.03 mg/kg infusions) followed by extinction and cue-induced reinstatement tests. We also tested the effects of nicotine (0.4 mg/kg base s.c.) or ethanol (0.7 g/kg i.p.) on the approach to, and reinforcing efficacy of, a food cue., Results: Sign-trackers showed greater reinstatement in response to a nicotine cue. Further, nicotine enhanced sign-tracking but not goal-tracking to a food cue and also enhanced responding for the food cue during the conditioned reinforcement test. Conversely, ethanol reduced sign-tracking and increased goal-tracking, but had no effect on conditioned reinforcement., Conclusions: Our studies demonstrate that the tendency to attribute incentive value to a food cue predicts enhanced cue-induced reinstatement. Additionally, the incentive value of food cues is differentially modulated by nicotine and ethanol, which may be related to the reinforcing effects of these drugs.

Unlabelled: There is considerable individual variation in the extent to which reward cues are attributed with incentive salience. For example, a food-predictive conditioned stimulus (CS; an illuminated lever) becomes attractive, eliciting approach toward it only in some rats ("sign trackers," STs), whereas others ("goal trackers," GTs) approach the food cup during the CS period. The purpose of this study was to determine how individual differences in Pavlovian approach responses are represented in neural firing patterns in the major output structure of the mesolimbic system, the ventral pallidum (VP). Single-unit in vivo electrophysiology was used to record neural activity in the caudal VP during the performance of ST and GT conditioned responses. All rats showed neural responses to both cue onset and reward delivery but, during the CS period, STs showed greater neural activity than GTs both in terms of the percentage of responsive neurons and the magnitude of the change in neural activity. Furthermore, neural activity was positively correlated with the degree of attraction to the cue. Given that the CS had equal predictive value in STs and GTs, we conclude that neural activity in the VP largely reflects the degree to which the CS was attributed with incentive salience., Significance Statement: Cues associated with reward can acquire motivational properties (i.e., incentive salience) that cause them to have a powerful influence on desire and motivated behavior. There are individual differences in sensitivity to reward-paired cues, with some individuals attaching greater motivational value to cues than others. Here, we investigated the neural activity associated with these individual differences in incentive salience. We found that cue-evoked neural firing in the ventral pallidum (VP) reflected the strength of incentive motivation, with the greatest neural responses occurring in individuals that demonstrated the strongest attraction to the cue. This suggests that the VP plays an important role in the process by which cues gain control over motivation and behavior., (Copyright © 2016 the authors 0270-6474/16/367957-14$15.00/0.)

Rationale: Disorders of behavioral regulation, including attention deficit hyperactivity disorder (ADHD) and drug addiction, are in part due to poor inhibitory control, attentional deficits, and hyper-responsivity to reward-associated cues., Objectives: To determine whether these traits are related, we tested genetically variable male and female heterogeneous stock rats in the choice reaction time (CRT) task and Pavlovian conditioned approach (PavCA). Sex differences in the response to methylphenidate during the CRT were also assessed., Methods: In the CRT task, rats were required to withhold responding until one of two lights indicated whether responses into a left or right port would be reinforced with water. Reaction time on correct trials and premature responses were the operational definitions of attention and response inhibition, respectively. Rats were also pretreated with oral methylphenidate (0, 2, 4 mg/kg) during the CRT task to determine whether this drug would improve performance. Subsequently, during PavCA, presentation of an illuminated lever predicted the delivery of a food pellet into a food-cup. Lever-directed approach (sign-tracking) and food-cup approach (goal-tracking) were the primary measures, and rats were categorized as "sign-trackers" and "goal-trackers" using an index based on these measures., Results: Sign-trackers made more premature responses than goal-trackers but showed no differences in reaction time. There were sex differences in both tasks, with females having higher sign-tracking, completing more CRT trials, and making more premature responses after methylphenidate administration., Conclusions: These results indicate that response inhibition is related to reward-cue responsivity, suggesting that these traits are influenced by common genetic factors.

Drug addiction is a syndrome of dysregulated motivation, evidenced by intense drug craving and compulsive drug-seeking behavior. In the search for 'common neurobiological substrates of addiction to different classes of drugs, behavioral neuroscientists have attempted to determine the neural basis for a number of motivational concepts and describe how they are changed by repeated drug use. Here, we describe these concepts and summarize previous work describing three major neural systems that play distinct roles in different conceptual aspects of motivation: (1) a nigrostriatal system that is involved in two forms of instrumental learning, (2) a ventral striatal system that is involved in Pavlovian incentive motivation and negative reinforcement, and (3) frontal cortical areas that regulate decision making and motivational processes. Within striatal systems, drug addiction can involve a transition from goal-oriented, incentive processes to automatic, habit-based responding. In the cortex, weak inhibitory control is a predisposing factor to, as well as a consequence of, repeated drug intake. However, these transitions are not absolute, and addiction can occur without a transition to habit-based responding, occurring as a result of the overvaluation of drug outcomes and hypersensitivity to incentive properties of drug-associated cues. Finally, we point out that addiction is not monolithic and can depend not only on individual differences between addicts, but also on the neurochernical action of specific drug classes.

There is considerable individual variation in the extent to which food- and drug-associated cues (conditioned stimuli, CSs) acquire incentive salience, as indicated by whether they elicit approach towards them, and/or act as conditioned reinforcers. Here we asked whether this variation is influenced by properties of the CS itself. In rats, we assessed both the attractiveness and conditioned reinforcing properties of two CSs: a manipulable lever CS versus an auditory (tone) CS. There was considerable individual variation in the extent to which a lever CS acquired incentive motivational properties, as indicated by whether it became attractive (evoked a sign-tracking or goal-tracking conditioned response) or acted as a conditioned reinforcer. However, with a tone CS all rats learned a goal-tracking response, and the tone CS was an equally effective conditioned reinforcer in sign-trackers and goal-trackers. Even when presented in compound (a lever-tone CS), the two elements of the compound differentially acquired motivational properties. In contrast, amphetamine and stress potentiated the conditioned reinforcing properties of both visual and auditory CSs similarly in rats that primarily sign-tracked or goal-tracked. We conclude that variation in the to the ability of CSs to acquire incentive salience, and thus their ability to act as incentive stimuli capable of motivating behavior, is determined in part by properties of the CS itself.

Even when trained under exactly the same conditions outbred male Sprague-Dawley (SD) rats vary in the form of the Pavlovian conditioned approach response (CR) they acquire. The form of the CR (i.e. sign-tracking vs. goal-tracking) predicts to what degree individuals attribute incentive salience to cues associated with food or drugs. However, we have noticed variation in the incidence of these two phenotypes in rats obtained from different vendors. In this study, we quantified sign- and goal-tracking behavior in a reasonably large sample of SD rats obtained from two vendors (Harlan or Charles River), as well as from individual colonies operated by both vendors. Our sample of rats acquired from Harlan had, on average, more sign-trackers than goal-trackers, and vice versa for our sample of rats acquired from Charles River. Furthermore, there were significant differences among colonies of the same vendor. Although it is impossible to rule out environmental variables, SD rats at different vendors and barriers may have reduced phenotypic heterogeneity as a result of genetic variables, such as random genetic drift or population bottlenecks. Consistent with this hypothesis, we identified marked population structure among colonies from Harlan. Therefore, despite sharing the same name, investigators should be aware that important genetic and phenotypic differences exist among SD rats from different vendors or even from different colonies of the same vendor. If used judiciously this can be an asset to experimental design, but it can also be a pitfall for those unaware of the issue.

Some rats [sign-trackers (STs)] are especially prone to attribute incentive salience to reward cues, relative to others [goal-trackers (GTs)]. Thus, reward cues are more likely to promote maladaptive reward-seeking behavior in STs than GTs. Here, we asked whether STs and GTs differ on another trait that can contribute to poor restraint over behavior evoked by reward cues. We report that, relative to GTs, STs have poor control over attentional performance, due in part to insufficient cholinergic stimulation of cortical circuitry. We found that, relative to GTs, STs showed poor performance on a sustained attention task (SAT). Furthermore, their performance fluctuated rapidly between periods of good to near-chance performance. This finding was reproduced using a separate cohort of rats. As demonstrated earlier, performance on the SAT was associated with increases in extracellular levels of cortical acetylcholine (ACh); however, SAT performance-associated increases in ACh levels were significantly attenuated in STs relative to GTs. Consistent with the view that the modulatory effects of ACh involve stimulation of α4β2* nicotinic ACh receptors (nAChRs), systemic administration of the partial nAChR agonist ABT-089 improved SAT performance in STs and abolished the difference between SAT-associated ACh levels in STs and GTs. Neither the nonselective nAChR agonist nicotine nor the psychostimulant amphetamine improved SAT performance. These findings suggest that individuals who have a propensity to attribute high-incentive salience to reward cues also exhibit relatively poor attentional control. A combination of these traits may render individuals especially vulnerable to disorders, such as obesity and addiction.

Neuroadaptations underlying sensitization to drugs of abuse seem to influence compulsive drug pursuit and relapse associated with addiction. Our previous data support a role for the corticotropin-releasing factor (CRF) type-1 receptor (CRF₁) in ethanol (EtOH)-induced psychomotor sensitization. CRF₁ is endogenously activated by CRF and urocortin-1. Because genetic deletion of urocortin-1 did not affect EtOH sensitization, we hypothesized that CRF is the important ligand underlying EtOH sensitization. To test this hypothesis, we used heterozygous and homozygous knockout (KO) mice, which lack one or both copies of the gene coding for CRF, and their respective wild-type controls. EtOH sensitization was normal in heterozygous, but absent in homozygous, CRF KO mice. Corticosterone (CORT) levels were drastically reduced only in CRF KO mice. Because CRF/CRF₁ initiate EtOH-induced activation of the hypothalamic-pituitary-adrenal axis, we investigated CORT effects on EtOH sensitization. The CORT synthesis inhibitor metyrapone prevented the acquisition, but not the expression, of EtOH sensitization. Exogenous CORT administration sensitized the locomotor response to a subsequent EtOH challenge; we observed, however, that the exogenous CORT levels necessary to induce sensitization to EtOH were significantly higher than those produced by EtOH treatment. Therefore, participation of CORT seems to be necessary, but not sufficient, to explain the role of CRF/CRF₁ in the acquisition of sensitization to EtOH. Extra-hypothalamic CRF/CRF₁ mechanisms are suggested to be involved in the expression of EtOH sensitization. The present results are consistent with current theories proposing a key role for CRF and CRF₁ in drug-induced neuroplasticity, dependence, and addictive behavior.

Rationale: Individuals vary considerably in the extent to which they attribute incentive salience to food-associated cues., Objectives: We asked whether individuals prone to attribute incentive salience to a food cue are also prone to attribute incentive properties to a stimulus associated with a drug of abuse-cocaine., Methods: We first identified those rats that attributed incentive salience to a food cue by quantifying the extent to which they came to approach and engage a food cue. We then used a conditioned place preference procedure to pair an injection of 10 mg/kg cocaine (i.p.) with one distinct floor texture (grid or holes) and saline with another. Following 8 days of conditioning, each rat was given a saline injection and placed into a chamber that had both floors present. We measured the time spent on each floor, and also 50-kHz ultrasonic vocalizations, which have been associated with positive affective states., Results: Rats that vigorously engaged the food cue ("sign trackers") expressed a preference for the cocaine-paired floor compared to those that did not ("goal trackers"). In addition, sign trackers made substantially more frequency-modulated 50-kHz vocalizations when injected with cocaine and when later exposed to the cocaine cue., Conclusions: Rats prone to attribute incentive salience to a food cue are also prone to attribute incentive motivational properties to a tactile cue associated with cocaine. We suggest that individuals prone to attribute incentive salience to reward cues will have difficulty resisting them and, therefore, may be especially vulnerable to develop impulse control disorders, including addiction.

If reward-associated cues acquire the properties of incentive stimuli they can come to powerfully control behavior, and potentially promote maladaptive behavior. Pavlovian incentive stimuli are defined as stimuli that have three fundamental properties: they are attractive, they are themselves desired, and they can spur instrumental actions. We have found, however, that there is considerable individual variation in the extent to which animals attribute Pavlovian incentive motivational properties ("incentive salience") to reward cues. The purpose of this paper was to develop criteria for identifying and classifying individuals based on their propensity to attribute incentive salience to reward cues. To do this, we conducted a meta-analysis of a large sample of rats (N = 1,878) subjected to a classic Pavlovian conditioning procedure. We then used the propensity of animals to approach a cue predictive of reward (one index of the extent to which the cue was attributed with incentive salience), to characterize two behavioral phenotypes in this population: animals that approached the cue ("sign-trackers") vs. others that approached the location of reward delivery ("goal-trackers"). This variation in Pavlovian approach behavior predicted other behavioral indices of the propensity to attribute incentive salience to reward cues. Thus, the procedures reported here should be useful for making comparisons across studies and for assessing individual variation in incentive salience attribution in small samples of the population, or even for classifying single animals.

Little is known about the prevalence and burden of symptoms in patients managed without dialysis. This study was the result of a larger study exploring the experiences of 30 such patients and their trajectories to death. Data were analysed relating to symptoms once the patients had been referred to a Renal Supportive Care Service based in the East End of London, UK. A high symptom prevalence was found with 30 different symptoms reported at first consultation. Widely reported symptoms impacting on daily living included breathlessness, oedema, pruritus, nausea and vomiting and pain. Findings indicate that as symptoms escalate and death approaches, some symptoms, such as fluid overload and lethargy become difficult to treat indicating that death is close. This new knowledge can help staff as they attempt to determine when the end of life is approaching in order to support and care for patients appropriately. This paper highlights a need for effective identification and management of symptoms as they arise and further exploration of the effects of these symptoms on daily living.

Rationale: Morphine relieves pain, in part, by acting on neurons within the periaqueductal gray (PAG). Given that the PAG contains a subpopulation of dopamine neurons, dopamine may contribute to the antinociceptive effects mediated by the PAG., Methods: This hypothesis was tested by measuring the behavioral and electrophysiological effects of administering dopamine agonists and antagonists into the ventrolateral PAG (vPAG). An initial histological experiment verified the existence of dopamine neurons within the vPAG using dopamine transporter and tyrosine hydroxylase antibodies visualized with confocal microscopy., Results: Microinjection of cumulative doses of morphine into the vPAG caused antinociception that was dose-dependently inhibited by the dopamine receptor antagonist alpha-flupenthixol. alpha-Flupenthixol had no effect on nociception when administered alone. Injection of the dopamine receptor agonist (-) apomorphine into the vPAG caused a robust antinociception that was inhibited by the D2 antagonist eticlopride but not the D1 antagonist SCH-23390. The effects of dopamine on GABA(A)-mediated evoked inhibitory post-synaptic potentials (eIPSCs) were measured in PAG slices. Administration of met-enkephalin inhibited peak eIPSCs by 20-50%. Dopamine inhibited eIPSCs by approximately 20-25%. Administration of alpha-flupenthixol (20 muM) attenuated eIPSC inhibition by dopamine but had no effect on met-enkephalin-induced inhibition., Conclusions: These data indicate that PAG dopamine has a direct antinociceptive effect in addition to modulating the antinociceptive effect of morphine. The lack of an effect of alpha-flupenthixol on opioid-inhibition of eIPSCs indicates that this modulation occurs in parallel or subsequent to inhibition of GABA release.

Neuroanatomical research suggests that interactions between dopamine and glutamate within the mesolimbic dopamine system are involved in both drug-induced locomotor stimulation and addiction. Therefore, genetically determined differences in the locomotor responses to ethanol and cocaine may be related to differences in the effects of these drugs on this system. To test this, we measured drug-induced changes in dopamine and glutamate within the nucleus accumbens (NAcc), a major target of mesolimbic dopamine neurons, using in vivo microdialysis in selectively bred FAST and SLOW mouse lines, which were bred for extreme sensitivity (FAST) and insensitivity (SLOW) to the locomotor stimulant effects of ethanol. These mice also show a genetically correlated difference in stimulant response to cocaine (FAST > SLOW). Single injections of ethanol (2 g/kg) or cocaine (40 mg/kg) resulted in larger increases in dopamine within the NAcc in FAST compared with SLOW mice. There was no effect of either drug on NAcc glutamate levels. These experiments indicate that response of the mesolimbic dopamine system is genetically correlated with sensitivity to ethanol- and cocaine-induced locomotion. Because increased sensitivity to the stimulating effects of ethanol appears to be associated with greater risk for alcohol abuse, genetically determined differences in the mesolimbic dopamine response to ethanol may represent a critical underlying mechanism for increased genetic risk for alcoholism.

Rationale: Behavioral sensitization to the locomotor stimulant effects of ethanol may be related to neuroadaptations within glutamatergic systems. Previous research has suggested that the N-methyl-D: -aspartate (NMDA) subclass of glutamate receptors is critical for the development of ethanol sensitization. We hypothesized that sensitization to ethanol would be associated with changes in sensitivity to NMDA receptor ligands., Materials and Methods: DBA/2J and heterogeneous stock (HS) mice were injected with ethanol or saline for 12 days and tested for their acute and sensitized responses to the locomotor effects of ethanol in automated activity monitors. After this treatment phase, mice were challenged with MK-801, ethanol, or ketamine, and locomotor activity was measured for 20 to 60 min. Other ethanol-sensitized and nonsensitized mice were assessed for sensitivity to the effects of NMDA after tail-vein infusions., Results: There was no evidence for cross-sensitization to MK-801 or ketamine, or altered sensitivity to NMDA in ethanol-sensitized animals, in any experiment. In one experiment, previously ethanol-treated HS mice developed tolerance to the locomotor stimulant effects of ketamine., Conclusions: These results indicate that ethanol-induced behavioral sensitization is not associated with increased behavioral sensitivity to NMDA receptor antagonists or altered sensitivity to NMDA receptor agonists. To the extent that changes in sensitivity to these ligands reflect changes in NMDA receptors, these results are inconsistent with the hypothesis that ethanol sensitization is associated with alterations in NMDA receptor-mediated processes.

Repeated administration of the relatively low-efficacy micro-opioid receptor agonist morphine induces tolerance to its antinociceptive effects. High-efficacy agonists such as D-Ala2NMePhe4,Gly-ol5 (DAMGO) have been shown to be less effective at producing tolerance, suggesting that different neural mechanisms underlie tolerance to these agonists. However, the correlation between agonist efficacy and tolerance development has not been examined within the ventrolateral periaqueductal gray (vPAG), a brain area known to be crucial for the development of morphine tolerance. The current studies examined whether tolerance to DAMGO occurs within the vPAG, and whether repeated treatment with DAMGO into the vPAG alters the development of morphine tolerance. The results showed that repeated vPAG microinjections of DAMGO induced robust tolerance and cross-tolerance to morphine. Further, co-administration of a low dose of DAMGO with morphine potentiated morphine tolerance. These findings indicate that similar mechanisms underlie tolerance to morphine and DAMGO within the vPAG.

Rationale: Previous studies suggest that some behavioral effects of ethanol and morphine are genetically correlated. For example, mice bred for sensitivity (FAST) or insensitivity (SLOW) to the locomotor stimulant effects of ethanol differ in their locomotor response to morphine., Objective: To evaluate a possible common mechanism for these traits, we examined the effect of naloxone, an opioid receptor antagonist, on ethanol- and morphine-induced locomotion in FAST and SLOW mice, as well as on ethanol-induced locomotion in two heterogeneous stocks of mice., Method: In experiments 1 and 2, naloxone was given to FAST and SLOW mice 30 min prior to 2 g/kg ethanol or 32 mg/kg morphine, and locomotor activity was measured for 15 min (ethanol) or 30 min (morphine). In experiments 3 and 4, naloxone was administered 30 min prior to 1.25 g/kg ethanol, and locomotor activity was assessed in FAST mice and in a heterogeneous line of mice [Withdrawal Seizure Control (WSC)]. Experiment 5 assessed the effect of naloxone on ethanol-induced stimulation in outbred National Institutes of Health (NIH) Swiss mice., Results: There was no effect of naloxone on the locomotor response to ethanol in FAST, SLOW, WSC, or NIH Swiss mice. However, naloxone did significantly attenuate the locomotor effects of morphine in FAST and SLOW mice., Conclusions: These results suggest that a common opioidergic mechanism is not responsible for the correlated locomotor responses to ethanol and morphine in FAST and SLOW mice, and that activation of the endogenous opioid system is not critical for the induction of ethanol-induced alterations in activity.

Rationale: The ability of ethanol to facilitate GABA(A) receptor-mediated transmission may result in GABA(A) receptor alterations during repeated ethanol administration, and lead to dynamic behavioral changes, including sensitization to the locomotor stimulant effect of ethanol. Since alterations in GABA(A) receptors are likely to alter sensitivity to GABAergic drugs such as 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) and pentobarbital, we determined whether enhanced sensitivity to ethanol was associated with enhanced sensitivity (cross-sensitization) to these drugs. Two procedures that produced differences in the magnitude of expression of ethanol-induced locomotor sensitization were used., Methods: After habituation to testing procedures for 2 days, female DBA/2J mice were injected with ethanol or saline for 12 days. On the following day, locomotion was recorded after a challenge injection of ethanol (2 g/kg), allopregnanolone (10 or 17 mg/kg), or pentobarbital (10 or 20 mg/kg). Due to evidence that exposure to the test chambers influenced sensitization, in some experiments, mice were exposed to the test apparatus on the day prior to challenge., Results: Exposure to the test apparatus prior to drug challenge attenuated the expression of ethanol sensitization, compared with mice without this pre-exposure. Cross-sensitization was not observed to either allopregnanolone or pentobarbital under any condition; however, some groups of repeated ethanol-treated mice displayed tolerance to the initial stimulant effects of allopregnanolone and pentobarbital., Conclusions: These studies indicate that behavioral sensitization to ethanol is not associated with cross-sensitization to pentobarbital or allopregnanolone, and that the expression of ethanol sensitization is influenced by the relative novelty of the test chamber. In addition, these results do not support a mechanism in which alterations in the neurosteroid or barbiturate modulatory sites of the GABA(A) receptor are responsible for the expression of sensitization to the locomotor stimulant effects of ethanol.

Background: Sensitivity to erthanol's locomotor activating and reinforcing effects may be influenced by some common neural mechanisms. Mice selectively bred in replicate for increased (FAST-1 and FAST-2) and decreased (SLOW-1 and SLOW-2) sensitivity to ethanol's locomotor stimulant effects are useful for investigating the neural substrates of ethanol's effects. Previous studies have suggested that differences in N-methyl-d-aspartate (NMDA) receptors may underlie differences in ethanol-induced locomotion in these mice. This study examined the responses of FAST and SLOW mice to ketamine, a fast-acting NMDA antagonist. In addition, reverse-selected lines (r-FAST-1, r-FAST-2, r-SLOW-1, and r-SLOW-2) were tested as a means of verifying correlations detected in the forward-selected lines. Two initial studies characterized ketamine-induced locomotion in DBA/2J (D2) mice, an inbred strain chosen for its high sensitivity to ethanol-induced locomotion., Methods: After a 2- to 3-day period of habituation to test procedures, mice were given intraperitoneal injections of ketamine alone (0, 5, 10, 20, 30, and 60 mg/kg) or in combination with 1 or 2 g/kg ethanol. Locomotor activity was measured for 20 to 30 min in automated activity monitors., Results: When administered alone, ketamine dose-dependently stimulated the locomotor activity of D2 mice and also reduced the amount of ethanol-induced stimulation. Ketamine stimulated locomotion more in FAST mice than in SLOW mice. Reverse selection abolished these differences, because r-FAST and r-SLOW mice did not differ in their responses to ketamine. Ketamine potentiated ethanol's locomotor effects within FAST mice and potentiated ethanol's locomotor depressant effect within one replicate of SLOW mice., Conclusions: We propose that sensitivities to ethanol- and ketamine-induced locomotion are genetically correlated and that the combined effects of ethanol and ketamine in FAST mice reflect a leftward shift in ethanol's biphasic dose-response curve.

The relationship between the effects of the N-methyl-D-aspartate (NMDA) antagonist MK-801 on acute responses to ethanol and its ability to block ethanol sensitization and tolerance was examined in DBA/2J mice. Cross-sensitization between these drugs was also studied. Repeated administration of 0.1 mg/kg MK-801 with ethanol potentiated, whereas 0.25 mg/kg attenuated, sensitization to ethanol's locomotor stimulant effects; rearing was similarly affected. There was evidence for cross-sensitization between ethanol and 0.25 mg/kg MK-801. MK-801 potentiated ethanol's ataxic effects in the grid test, but had no effect on tolerance to this effect. MK-801's effects on ethanol sensitization appeared to be related to its own behavioral effects, rather than NMDA receptor blockade per se. Further, these studies demonstrate dissociation between ethanol sensitization and tolerance.

Rationale: The literature offers many examples of tolerance to ethanol's inhibitory/depressant effects and sensitization to its activating effects. There are also many examples of tolerance to ethanol's aversive effects as measured in the conditioned taste aversion and conditioned place aversion (CPA) procedures. However, there are very few demonstrations of either tolerance or sensitization to ethanol's rewarding or reinforcing effects., Objective: The present studies were designed to examine effects of two forms of ethanol pre-exposure (distal or proximal) on ethanol's rewarding and aversive effects as indexed by the place conditioning procedure., Method: Male inbred (DBA/2J) mice were exposed to ethanol (2 g/kg IP) in an unbiased place conditioning procedure that normally produces either conditioned place preference (CPP) (ethanol injection before CS exposure) or CPA (ethanol injection after CS exposure). In the distal pre-exposure studies (experiments 1 and 2), mice initially received a series of four ethanol injections (0, 2, or 4 g/kg) in the home cage at 48-h intervals during the week before place conditioning. In the proximal pre-exposure studies (experiments 3-4), mice were injected with ethanol 65 min before (experimental groups) or 65 min after (control groups) each paired ethanol injection on CS+ trials., Results: Distal pre-exposure produced a robust sensitization to ethanol's activating effect, whereas proximal pre-exposure generally reduced the activation normally produced by the paired ethanol injection. Both forms of pre-exposure interfered with CPA, but had no effect on CPP., Conclusions: These studies suggest that both forms of pre-exposure reduced ethanol's aversive effect, but had no impact on ethanol's rewarding effect. In general, the detrimental effects of pre-exposure on CPA are explained best in terms of a reduction in ethanol's efficacy as an aversive unconditioned stimulus (i.e. tolerance), although explanations based on other types of associative interference are also possible. The failure to affect CPP with pre-exposure treatments that reduced or eliminated CPA suggests that these behaviors are mediated by independent, motivationally opposite effects of ethanol. Moreover, these results indicate dissociation between sensitization to ethanol's locomotor activating effect and changes in its rewarding effect. To the extent that motivational processes measured by CPP and CPA normally contribute to ethanol drinking, the present findings suggest that increases in ethanol intake seen after chronic ethanol exposure are more likely caused by tolerance to ethanol's aversive effect rather than sensitization to its rewarding or reinforcing effect.

There are mixed results on the effects of opioid antagonists on acute nicotine response in humans. The present study examined the effects of a single dose of 50 mg oral naltrexone relative to placebo on smoking response in 22 chronic smokers during short-term nicotine abstinence, after acute smoking and subsequent smoking deprivation, and on smoking behavior in a choice paradigm. The results showed that naltrexone significantly reduced immediate postcigarette ratings of smoking craving and desire to smoke and increased light-headedness, dizziness, and head rush (ps < 0.05). Reductions in craving and smoking desire persisted during a subsequent 1 h nonsmoking interval. Naltrexone also was found to significantly reduce the total number of cigarettes smoked in the choice interval, which was supported by objective measures of both reduced CO and plasma nicotine levels (ps < 0.01). Exploratory analyses on potential individual difference factors revealed that smokers with the highest levels of craving during abstinence showed the most pronounced naltrexone attenuation of smoking response. The results support the continued exploration of naltrexone as an adjunct to smoking cessation, especially in identified smoker subgroups most sensitive to the effects of opioid antagonism.

An inventory study to the levels of cadmium in the plastic component of household waste was carried out utilizing INAA as the analytical technique. In a 2-h irradiation, 2-d decay, and 1-h measurement, protocol adequate sensitivities could be obtained for Cd, but also for a group of other metals: Cr, Co, Ni, Cu, Sr, Zn, As, Se, Mo, Sn, Sb, Ba, and Hg. Red-, orange-, and yellow-colored plastics either contain Cd at high levels (over 1000 mg/kg) or have relatively low Cd concentrations (less than 50 mg/kg). High concentrations were also occasionally found for Sr, Se, Ba, Sb, and Hg. INAA appeared very well to be routinely usable for such analysis because of the absence of a destruction step, adequate sensitivity, high accuracy, and multielement results.