Effects of an ethanol-paired conditioned stimulus on responding for ethanol suppressed by a conditioned-taste-aversion

Ethanol-Paired Conditioned Stimuli (CS) can increase ethanol-responding either in extinction or occurring at low rates late in a session. To examine the generality of CS-induced increases in ethanol-responding, we examined whether a CS could increase responding suppressed by Conditioned-Taste-Aversion (CTA), which presumably suppresses responding by changing ethanol's valence from positive to negative. Rats were trained to respond for ethanol under a Random Interval (RI) schedule. We then removed the lever and paired Random-Time ethanol deliveries with illumination of a stimulus light (i.e., CS) for 10 sessions. Results were compared with a Truly Random Control group, in which the light and ethanol deliveries occurred independently. In a subsequent experiment, rats were treated similarly, except the light served as a discriminative stimulus, as the lever was extended and ethanol deliveries were available under a RI during light presentations. After this training, the lever was returned and rats again responded for ethanol. Subsequently, sessions were followed by LiCl administration. When responding reached low levels, LiCl administration stopped and the light was occasionally illuminated during the session. Responding during the light presentation was compared to responding during the period preceding light presentation. Responding partially recovered across 10 sessions and was greater during light presentations than in the period before it in all three groups. Increases were not reliably different between the groups, indicating that explanations for these increases such as CS-induced increases in motivation or approach toward the light are unlikely to be correct. The most likely explanation for these light-induced increases is that during sessions in which the light had been presented previously, LiCl had never been presented and thus, the light had come to signal that ethanol was safe to drink.

Enhancing massed prolonged exposure with cannabidiol to improve posttraumatic stress disorder: Design and methodology of a pilot randomized clinical trial

Background

The impact of posttraumatic stress disorder (PTSD) is substantial and often results in pervasive functional impairments. Although evidence-based treatments for PTSD are established, there remains room for improvement as many individuals continue to meet diagnostic criteria even after successful treatment completion. Cannabidiol (CBD) has attracted considerable attention based on its potential to treat a myriad of health conditions. CBD may decrease anxiety and facilitate extinction learning processes, two critical targets of trauma-focused psychotherapies. We present the design and methods for a pilot randomized clinical trial to examine the combination of CBD and prolonged exposure for PTSD.

Methods

Participants (n = 24) will be randomized to CBD or placebo for 18 days delivered in combination with ten daily prolonged exposure sessions over two weeks. The study medication will be Epidiolex® (250 mg BID). The PTSD Checklist for DSM-5 will be the primary outcome to assess PTSD severity at baseline, during treatment, and at 1-month follow-up. Blood, saliva, and heart rate will be collected during treatment to assess intervention effects on biological outcomes related to PTSD and the endocannabinoid system.

Results

Consistent with the purpose of a pilot, our goals are to evaluate the feasibility of study procedures, safety of the intervention, and the preliminary effect of CBD to inform a larger trial. Descriptive and inferential statistics will be used to address study aims.

Conclusion

Findings will inform decision making on combining CBD with behavioral interventions for PTSD to enhance outcomes and mitigate the morbidity of this debilitating condition.

Feasibility of a telehealth-based contingency management intervention for alcohol use disorders using the phosphatidylethanol (PEth) 16:0/18:1 alcohol biomarker: a pilot randomized trial

Background: Phosphatidylethanol (PEth) is a blood-based biomarker for alcohol consumption that can be self-collected and has high sensitivity, specificity, and a longer detection window compared to other alcohol biomarkers.Objectives: We evaluated the feasibility and acceptability of a telehealth-based contingency management (CM) intervention for alcohol use disorder (AUD) using the blood-based biomarker PEth to assess alcohol consumption.Methods: Sixteen adults (7 female, 9 male) with AUD were randomized to Control or CM conditions. Control participants received reinforcers regardless of their PEth levels. CM participants received reinforcers for week-to-week decreases in PEth (Phase 1) or maintenance of PEth consistent with abstinence (<20 ng/mL, Phase 2). Blood samples were self-collected using the TASSO-M20 device. Acceptability was assessed by retention in weeks. Satisfaction was assessed with the Client Satisfaction Questionnaire (CSQ-8) and qualitative interviews. The primary efficacy outcome was PEth-defined abstinence. Secondary outcomes included the proportion of visits with PEth-defined heavy alcohol consumption, negative urine ethyl glucuronide results, and self-reported alcohol use.Results: Retention averaged 18.6 ± 8.8 weeks for CM participants. CM participants reported high levels of satisfaction (CSQ-8, Mean = 30.3 ± 1.5). Interview themes included intervention positives, such as staff support, quality of life improvement, and accountability. 72% of PEth samples from CM participants were consistent with abstinence versus 34% for Control participants (OR = 5.0, p = 0.007). PEth-defined heavy alcohol consumption was detected in 28% of CM samples and 52% of Control samples (OR = 0.36, p = 0.159). CM participants averaged 1.9 ± 1.7 drinks/day versus 4.2 ± 6.3 for Control participants (p = 0.304).Conclusion: Results support the acceptability and satisfaction of a telehealth PEth-based CM intervention, though a larger study is needed to assess its efficacy [NCT04038021].

A Rapid Procedure to Assess Shifts in Discriminative Control Over Drinking During Recovery-Like Behavior

BACKGROUND

Previously, we reported that recovery-like behavior decreases stimulus control over drinking, and this likely plays a role in the clinical observation that longer recovery increases relapse resistance. Those studies were conducted using a procedure that required repeated assessment, preventing a longitudinal analysis of the changes in stimulus control over time in each individual. Here we recapitulate those results and extend them to female rats using a more efficient procedure that allows repeated assessment of changes in stimulus control over drinking during recovery.

METHODS

Under a multiple concurrent schedule, rats were trained to reliably respond predominately for ethanol (concurrent Ethanol FR5, Food FR150) in the presence of one stimulus and for food (concurrent Ethanol FR5, Food FR5) in the presence of another stimulus. Stimuli were either lights or tones, depending on the group. After that, a drinking phase in which only the stimulus occasioning ethanol responding was presented (10 or 20 sessions) followed by recovery-like sessions in which only the stimulus occasioning food responding was presented. During these sessions, rats were exposed to the ethanol stimulus under extinction during the first component on sessions 0, 1, 2, 4,8, and 16. The number of food responses during these stimulus exposures prior to the first 5 ethanol responses was the primary measure.

RESULTS

Consistent with the earlier procedure, the number of food responses during ethanol tests increased as a function of the number of recovery sessions completed, regardless of whether the stimuli were visual or auditory. However, there were no significant effects of extended alcohol exposure or sex.

CONCLUSIONS

A rapid procedure consistent with the earlier procedure and clinical evidence was developed in which stimulus control over drinking decreased following longer periods of recovery. Under conditions tested, stimulus type, length of drinking history and sex did not affect this relationship.

Cardiovascular and Locomotor Effects of Binary Mixtures of Common "Bath Salts" Constituents: Studies with Methylone, MDPV, and Caffeine in Rats

Background and Purpose

The use of "Bath Salts" drug preparations has been associated with high rates of toxicity and death. Preparations often contain mixtures of drugs including multiple synthetic cathinones or synthetic cathinones and caffeine; however, little is known about whether interactions among "Bath Salts" constituents contribute to the adverse effects often reported in users.

Experimental Approach

This study used adult male Sprague-Dawley rats to characterize the cardiovascular effects, locomotor effects, and pharmacokinetics of methylone, MDPV, and caffeine, administered alone and as binary mixtures. Dose-addition analyses were used to determine the effect levels predicted for a strictly additive interaction for each dose pair.

Key Results

Methylone, MDPV, and caffeine increased heart rate and locomotion, with methylone producing the largest increase in heart rate, MDPV producing the largest increase in locomotor activity, and caffeine being the least effective in stimulating heart rate and locomotor activity. MDPV and caffeine increased mean arterial pressure, with caffeine being more effective than MDPV. The nature of the interactions between methylone and MDPV tended toward sub-additivity for all endpoints, whereas interactions between MDPV or methylone and caffeine tended to be additive or sub-additive for cardiovascular endpoints, and additive or supra-additive for increases in locomotion. No pharmacokinetic interactions were observed between individual constituents, but methylone displayed non-linear pharmacokinetics at the largest dose evaluated.

Conclusion and Implications

These findings demonstrate that the composition of "Bath Salts" preparations can impact both cardiovascular and locomotor effects and suggest that such interactions among constituent drugs could contribute to the "Bath Salts" toxidrome reported by human users.

Astaxanthin and meclizine extend lifespan in UM-HET3 male mice; fisetin, SG1002 (hydrogen sulfide donor), dimethyl fumarate, mycophenolic acid, and 4-phenylbutyrate do not significantly affect lifespan in either sex at the doses and schedules used

In genetically heterogeneous (UM-HET3) mice produced by the CByB6F1 × C3D2F1 cross, the Nrf2 activator astaxanthin (Asta) extended the median male lifespan by 12% (p = 0.003, log-rank test), while meclizine (Mec), an mTORC1 inhibitor, extended the male lifespan by 8% (p = 0.03). Asta was fed at 1840 ± 520 (9) ppm and Mec at 544 ± 48 (9) ppm, stated as mean ± SE (n) of independent diet preparations. Both were started at 12 months of age. The 90th percentile lifespan for both treatments was extended in absolute value by 6% in males, but neither was significant by the Wang-Allison test. Five other new agents were also tested as follows: fisetin, SG1002 (hydrogen sulfide donor), dimethyl fumarate, mycophenolic acid, and 4-phenylbutyrate. None of these increased lifespan significantly at the dose and method of administration tested in either sex. Amounts of dimethyl fumarate in the diet averaged 35% of the target dose, which may explain the absence of lifespan effects. Body weight was not significantly affected in males by any of the test agents. Late life weights were lower in females fed Asta and Mec, but lifespan was not significantly affected in these females. The male-specific lifespan benefits from Asta and Mec may provide insights into sex-specific aspects of aging.

Shifts in stimulus control over opioid use with increasing periods of recovery

BACKGROUND

Periods of engaging in an alternative behavior diminishes behavioral control by stimuli occasioning alcohol use. This increase in relapse resistance with increasing recovery suggests that changing stimulus control over substance use may be a mechanism responsible for decreased relapse rates with longer recovery. However, the generality of this phenomenon to other drugs of abuse, including opioid self-administration, remains unclear. This study tests the generality of these findings with etonitazene to determine whether the shift in attention represents a behavioral process that generalizes from conditions we previously reported.

METHODS

Five adult male Lewis rats were trained to respond on levers under two stimulus conditions; high-cost food (food FR150 and etonitazene FR5) and low-cost food (both food and etonitazene FR 5). Next, only the high-cost food stimulus (occasioning etonitazene responding) was presented for 20 sessions (Use Phase) followed by 9 sessions in which only the low-cost food stimulus (occasioning food responding) was presented (Recovery Phase). During the Recovery Phase, testing occurred during the first component of sessions 0, 1, 2, 4, and 8 when rats were re-exposed to the high-cost food stimulus. The number of food responses prior to completing the etonitazene response requirement during this stimulus exposure was the primary measure.

RESULTS

Food responses during stimulus re-exposure increased significantly as a function of recovery sessions completed with a slope [95 % CI] of 2.49 responses/recovery session [0.16, 4.81]. The average number of etonitazene deliveries per use session was 32 ± 6.6 or an average daily dose of 48.8 ± 10.1 μg/kg. During Recovery Phase, etonitazene deliveries decreased to 2.4 ± 1 or 3.6 ± 1.5 μg/kg.

CONCLUSION

The decrease in stimulus control observed for ethanol self-administration appears to generalize to opioid self-administration, indicating this change in stimulus control may play a general role in recovery.

Ethanol-paired conditioned stimulus effects on concurrent reinforced responding for ethanol and food

The influence of Pavlovian Conditioned Stimuli (CS) on ethanol self-administration and choice between ethanol and an alternative are potentially important. Ethanol-paired CS might increase ethanol self-administration, especially when it has been reduced during recovery, though the selectivity of these increases has been questioned. To date, one study examined the effects of an ethanol-paired CS on ethanol choice and found that the CS increased ethanol-responding more than food-responding when both were in extinction. However, it remains unclear whether ethanol-paired CS increase ethanol-choice that is not in extinction. Here, we examine the effects of an ethanol-paired CS on ethanol-choice when both food- and ethanol-responding are reinforced. Sixteen adult male Lewis rats were trained on a concurrent schedule to respond for ethanol on one lever and for food on the other lever. Ethanol was available under an FR 5 schedule, and food was available under an FR schedule that was adjusted for each rat to earn an equal number of food and ethanol deliveries. Then, 2-min light presentations were paired with an RT 25-sec schedule of ethanol delivery for 10 sessions in the absence of both levers. After this, subjects were placed back on the concurrent schedule for one session, then five sessions with the CS being present or absent on each trial of the concurrent schedule occurred. Rats learned to respond on one lever for ethanol and on the other for food and earned similar numbers of ethanol and food deliveries. During Pavlovian Conditioning, the number of head entries into the head-entry detector was higher in the presence of the CS than in its absence. In the test sessions, rats made more ethanol responses in the presence of the CS than in its absence. However, this effect was small and did not increase the amount of ethanol earned. Thus, ethanol-paired CS could increase ethanol-responding under a choice procedure but did not increase ethanol consumption meaningfully under the studied conditions.

Acute cannabidiol treatment enhances social interaction in adult male mice

Cannabidiol (CBD) is a non-intoxicating phytochemical from Cannabis sativa that is increasingly used to manage pain. The potential for CBD to ameliorate dimensional behavior symptoms occurring in multiple psychiatric disorders was suggested, including social interaction impairments. To test this hypothesis, adult male BTBRT+Itpr3tf/J (BTBR) mice, a model of idiopathic autism exhibiting social preference deficits and restrictive repetitive behaviors, were acutely treated with vehicle or 0.1, 1, or 10 mg/kg CBD. Social interaction preference was assessed 50 min after treatment, followed by social novelty preference at 60 min, marble burying at 75 min and social dominance at 120 min. CBD (10 mg/kg) enhanced BTBR social interaction but not social novelty preference, marble burying or dominance, with serum levels = 29 ± 11 ng/mg at 3 h post-injection. Next, acute 10 mg/kg CBD was compared to vehicle treatment in male serotonin transporter (SERT) knock-out mice, since SERT deficiency is an autism risk factor, and in their wildtype background strain controls C57BL/6J mice. CBD treatment generally enhanced social interaction preference and attenuated social novelty preference, yet neither marble burying nor dominance was affected. These findings show acute treatment with as little as 10 mg/kg purified CBD can enhance social interaction preference in male mice that are otherwise socially deficient.

Validation of the quantification of phosphatidylethanol 16:0/18:1 concentrations in TASSO-M20 devices

BACKGROUND

Phosphatidylethanol 16:0/18:1 (PEth), found in whole blood, is a biomarker for alcohol consumption with high sensitivity, specificity, and a long detection window. The TASSO-M20 device is used to self-collect capillary blood from the upper arm and has advantages over finger stick methods. The purpose of this study was to (1) validate PEth measurement using the TASSO-M20 device, (2) describe the TASSO-M20 for blood self-collection during a virtual intervention, and (3) characterize PEth, urinary ethyl glucuronide (uEtG) and self-reported alcohol in a single participant over time.

METHODS

PEth levels in blood samples dried on TASSO-M20 plugs were compared to those in (1) liquid whole blood (N = 14) and (2) dried blood spot cards (DBS; N = 23). Additionally, the self-reported drinking, positive or negative uEtG results (dip card cutoff ≥300 ng/mL), and observed self-collection of blood with TASSO-M20 devices for PEth levels were obtained over time during virtual interviews of a single contingency management participant. High-performance liquid chromatography with tandem mass spectrometry detection was used to measure PEth levels for both preparations.

RESULTS

PEth concentrations from dried blood on TASSO-M20 plugs and liquid whole blood were correlated (0 to 1700 ng/mL; N = 14; r2  = 0.988; slope = 0.951) and in a subgroup of samples with lower concentrations (N = 7; 0 to 200 ng/mL; r2  = 0.944, slope = 0.816). PEth concentrations from dried blood on TASSO-M20 plugs and DBS were correlated (0 to 2200 ng/mL; N = 23; r2  = 0.927; slope = 0.667) and in a subgroup of samples with lower concentrations (N = 16; 0 to 180 ng/mL; r2  = 0.978, slope = 0.749). Results of the contingency management participant indicate that changes in PEth levels (TASSO-M20) and uEtG concentrations were consistent with each other and with changes in self-reported alcohol use.

CONCLUSIONS

Our data support the utility, accuracy, and feasibility of using the TASSO-M20 device for blood self-collection during a virtual study. The TASSO-M20 device had multiple advantages over the typical finger stick method, including consistent blood collection, participant acceptability, and less discomfort as indicated by acceptability interviews.

Conditioned stimulus effects on paired or alternative reinforcement depend on presentation duration: Implications for conceptualizations of craving

Conditioned stimuli (CS) associated with alcohol ingestion are thought to play a role in relapse by producing a craving that in turn increases motivation to drink which increases ethanol-seeking and disrupts other ongoing behavior. Alternatively, such CS may provide information indicating a likely increase in the density of the paired unconditioned stimulus and simultaneously elicit behavior that may be incompatible with other ongoing behavior, i.e., approach toward the CS. To explore these possibilities, rats were trained to respond for ethanol or food in two different components of the same session after which a light above the ethanol-lever was lighted twice during each component and each light presentation was followed by ethanol delivery. The duration of this CS was 10 s initially and then increased to 30 s, then to 100 s, and finally returned to 30 s. The change in responding for ethanol or food was compared to a matched period immediately preceding CS presentation. The CS presentation increased responding to ethanol, and this effect increases with longer CS presentations. In contrast, the CS presentation decreased responding to food, and this effect decreases with longer CS presentations. These results appear to support the informational account of CS action rather than simply a change in the motivation to seek and consume ethanol. This suggests that craving as it is commonly understood likely represents multiple behavioral processes, not simply increased desire for alcohol and that reports of craving likely reflect labeling based upon past experiences rather than a cause of future drug-taking.

Neuroprotective effects of Canagliflozin: Lessons from aged genetically diverse UM-HET3 mice

The aging brain is characterized by progressive increases in neuroinflammation and central insulin resistance, which contribute to neurodegenerative diseases and cognitive impairment. Recently, the Interventions Testing Program demonstrated that the anti-diabetes drug, Canagliflozin (Cana), a sodium-glucose transporter 2 inhibitor, led to lower fasting glucose and improved glucose tolerance in both sexes, but extended median lifespan by 14% in male mice only. Here, we show that Cana treatment significantly improved central insulin sensitivity in the hypothalamus and the hippocampus of 30-month-old male mice. Aged males produce more robust neuroimmune responses than aged females. Remarkably, Cana-treated male and female mice showed significant reductions in age-associated hypothalamic gliosis with a decrease in inflammatory cytokine production by microglia. However, in the hippocampus, Cana reduced microgliosis and astrogliosis in males, but not in female mice. The decrease in microgliosis was partially correlated with reduced phosphorylation of S6 kinase in microglia of Cana-treated aged male, but not female mice. Thus, Cana treatment improved insulin responsiveness in aged male mice. Furthermore, Cana treatment improved exploratory and locomotor activity of 30-month-old male but not female mice. Taken together, we demonstrate the sex-specific neuroprotective effects of Cana treatment, suggesting its application for the potential treatment of neurodegenerative diseases.

Age-related changes in CB1 receptor expression and function and the behavioral effects of cannabinoid receptor ligands

Cannabinoid use has increased among aging individuals. However, little information on age-related differences in the behavioral effects of these agents is available. To explore potential differences in the behavioral effects of cannabinoids, we determined effects of Δ⁹-tetrahydrocannabinol (THC, 1-10 mg/kg) or rimonabant (0.3-3.2 mg/kg) on operant fixed-ratio responding (FR10) for food in young adult (6 months) and aged (29 months) rats. THC dose-dependently decreased responding for food. Rimonabant alone had little or no effect on responding up to 1.0 mg/kg, but disrupted responding following a 3.2 mg/kg dose. Rimonabant (1.0 mg/kg) partially antagonized response disruption by THC. These effects were similar in young adult and aged rats. However, aging has been reported to change the neurobiology of cannabinoid CB1 receptors. To confirm our rats exhibited such differences, we assessed CB1 receptor binding sites and function in six subcortical (caudate, nucleus accumbens CA1, and CA2/CA3), and three cortical regions (medial prefrontal, temporal, entorhinal) in young adult (6 months) or aged (26 months) male Lewis rats using quantitative autoradiography. CB1 receptor binding sites were reduced in cortical, but not subcortical brain regions of aged rats. CB1 receptor function, at the level of receptor-G protein interaction, was not different in any region studied. Results indicate that down-regulation of CB1 receptor binding sites observed in cortical regions of aged rats was not accompanied by a commensurate decrease in CB1 receptor-stimulated [³⁵S]GTPγS binding, suggesting a compensatory increase in receptor function in cortical areas. Together, our results provide additional evidence of age-related changes in central CB1 receptor populations. However, the functional compensation for decreased CB1 receptor binding may mitigate changes in behavioral effects of cannabinoids. With the rising use of cannabinoid-based therapeutics among aging populations, further evaluation of age-related changes in the cannabinoid system and the impact of these changes on effects of this class of drugs is warranted.

Beta-guanidinopropionic acid does not extend D rosophila lifespan

Activation of AMP activated protein kinase (AMPK) signaling has been demonstrated to extend lifespan and improve healthspan across multiple species. This suggests pharmaceutical approaches to increase AMPK hold the potential to modify the aging process and promote healthy aging. Beta-guanidinopropionic acid (GPA) is a naturally occurring metabolite structurally similar to creatine. GPA is capable of activating AMPK signaling in mammalian models via competitive inhibition of cytosolic creatine kinase. A previous report suggested that dietary GPA supplementation increased lifespan in Drosophila through its effect on AMPK signaling and regulation of autophagy. However, studies in Caenorhabditis have found no beneficial effect of this compound on worm lifespan and that GPA may actually diminish lifespan in at least one Caenorhabditis species. To confirm previous reports of increased longevity in Drosophila, we tested a wide range of GPA concentrations on lifespan and healthspan in both male and female W¹¹¹⁸ flies. We report here that GPA does not extend lifespan in Drosophila as previously reported. Moreover, high doses of GPA are detrimental to Drosophila lifespan and stress resistance in male flies. These results suggest the lack of a robust effect of GPA on Drosophila lifespan and highlight the importance of replication studies within the field of aging.

Beta-guanidinopropionic acid has age-specific effects on markers of health and function in mice

AMP-activated protein kinase (AMPK) is a central regulator of both lifespan and health across multiple model organisms. β-Guanidinopropionic acid (GPA) is an endogenous AMPK activator previously shown to improve metabolic function in young and obese mice. In this study, we tested whether age of administration significantly affects the physiological outcomes of GPA administration in mice. We report that intervention starting at 7-8 months (young) results in activation of AMPK signaling and a phenotype consisting of lower body mass, improved glucose control, enhanced exercise tolerance, and altered mitochondrial electron transport chain flux similar to previous reports. When GPA treatment is started at 18-19 months (old), the effect of GPA on AMPK signaling is blunted compared to younger mice despite similar accumulation of GPA in skeletal muscle. Even so, GPA administration in older animals delayed age-related declines in lean mass, improved measures of gait performance and circadian rhythm, and increased fat metabolism as measured by respiratory exchange ratio. These results are likely partially driven by the relative difference in basal function and metabolic plasticity between young and old mice. Our results suggest that age-related declines in AMPK sensitivity may limit potential strategies targeting AMPK signaling in older subjects and suggest that further research and development is required for AMPK activators to realize their full potential.

Phosphatidylethanol in whole blood of rhesus monkeys correlates with ethanol consumption

BACKGROUND

Phosphatidylethanol (PEth) homologs are ethanol metabolites used to identify and monitor alcohol drinking in humans. In this study, we measured levels of the 2 most abundant homologs, PEth 16:0/18:1 and PEth 16:0/18:2, in whole blood samples from rhesus macaque monkeys that drank ethanol daily ad libitum to assess the relationship between PEth levels and recent ethanol exposure in this animal model.

METHODS

Blood samples were obtained from The Monkey Alcohol Tissue Research Resource. The monkeys were first induced to consume 4% (w/v) ethanol in water from a panel attached to their home cage. Then, monkeys were allowed to drink ethanol and water ad libitum 22 h daily for 12 months and the daily amount of ethanol each monkey consumed was measured. Whole, uncoagulated blood was collected from each animal at the end of the entire experimental procedure. PEth 16:0/18:1 and PEth 16:0/18:2 levels were analyzed by HPLC with tandem mass spectrometry, and the ethanol consumed during the preceding 14 days was measured. Combined PEth was the sum of the concentrations of both homologs.

RESULTS

Our results show that (1) PEth accumulates in the blood of rhesus monkeys after ethanol consumption; (2) PEth homolog levels were correlated with the daily average ethanol intake during the 14-day period immediately preceding blood collection; (3) the application of established human PEth 16:0/18:1 cutoff concentrations indicative of light social or no ethanol consumption (<20 ng/ml), moderate ethanol consumption (≥ 20 and < 200 ng/ml) and heavy ethanol consumption (≥ 200 ng/ml) predicted significantly different ethanol intake in these animals. PEth homologs were not detected in ethanol-naïve controls.

CONCLUSIONS

This study confirms that PEth is a sensitive biomarker for ethanol consumption in rhesus macaque monkeys. This nonhuman primate model may prove useful in evaluating sources of variability previously shown to exist between ethanol consumption and PEth homolog levels among humans.

Ethanol-paired stimuli can increase reinforced ethanol responding

While ethanol-paired stimuli are frequently postulated to increase drinking motivation and thus increase ethanol responding and precipitate relapse, no study has demonstrated increases in ethanol-reinforced responding following presentation of an ethanol-paired stimulus that had not previously been part of a contingent relationship. Previous studies have shown that food-paired stimuli can increase food responding that is at low rates and increase food consumption in food-sated rats. In Experiment 1, we show that an ethanol-paired stimulus can increase ethanol responding that is at low levels late in the experimental session, presumably due to satiation. However, these increases may have resulted from either associative or non-associative mechanisms. In Experiment 2, we compared the effects of an ethanol-paired stimulus to those of the same stimulus in a Truly-Random-Control group. In a Truly-Random-Control, the stimulus and ethanol each are presented on independent random schedules, and thus any differences between the effects of the stimulus in the experimental and control groups is likely attributable to the association between the stimulus and ethanol. The stimulus increased ethanol-reinforced responding in both the experimental and control groups, but these increases were greater in the experimental than the control group. Thus, both stimulus-change and the pairing of the stimulus with ethanol may result in increases in ethanol-reinforced responding.

Effects of rat strain and method of inducing ethanol drinking on Pavlovian-Instrumental-Transfer with ethanol-paired conditioned stimuli

Ethanol-paired conditioned stimuli (CSs) are widely thought to invigorate ethanol responding, and thus, precipitate relapse to drinking. However, preclinical studies investigating this issue using Pavlovian-Instrumental-Transfer (PIT) procedures have had mixed results, with some studies finding PIT while others did not. The studies failing to show PIT used Lewis rats and induced ethanol drinking using a post-prandial drinking procedure. The present experiments examined whether either of these two variables influenced the magnitude of PIT observed. In the first experiment, ethanol drinking in Lewis rats was induced using either sucrose fading or post-prandial drinking. In the second experiment, ethanol drinking was induced using post-prandial drinking in either Long-Evans Hooded or Lewis rats. In both experiments, rats were trained to respond for ethanol under a random interval schedule. Subsequently with the lever removed, 2-min light presentations were paired with ethanol deliveries. Finally, with the lever returned, the effect of light presentations on responding was tested while responding was in extinction. Light presentations similarly affected responding in Lewis rats regardless of the method of drinking induction. Likewise, light presentations similarly affected responding in both Lewis and Long-Evans Hooded rats. Neither ethanol induction method nor rat strain affected the magnitude of PIT observed, and thus, neither likely explains previous failures to observe PIT with ethanol-maintained behavior.

Frustration stress (unexpected loss of alternative reinforcement) increases opioid self-administration in a model of recovery

PURPOSE

Engaging in alternative activities in the context where opioid use had occurred can constrain opioid use and helps to maintain recovery. However, "frustration stress" that occurs when contingencies on these alternative activities unexpectedly change (e.g., job loss or divorce) is thought to threaten recovery by prompting a return to drug use. Yet it remains unclear whether frustration stress can result in a return to drug use, and if so, whether it returns to prior levels or to even greater levels.

PROCEDURES

We examine the impact of unsignaled extinction of alternative reinforcement on opioid use. Rats were trained to respond for an etonitazene solution (5μg/ml, p.o.), then for food in alternating daily sessions. Subsequently, food and etonitazene were made concurrently available. Under concurrent availability conditions, rats were exposed to 1, 2, or 4 sessions of unsignaled food extinction, and effects on responding for etonitazene and food measured.

FINDINGS

When etonitazene was the only reinforcer available, rats earned 58.3±20.3μg/kg/session (mean±S.E.M.). When food was available in alternating sessions, etonitazene earned was unchanged (65.3±19.2μg/kg/session). Concurrent food availability decreased etonitazene earned (13.5±4.5μg/kg/session). Unsignaled food extinction returned etonitazene earnedto levels similar to (60.5±18.4μg/kg/session), but not greater than, those observed previously when etonitazene alone was available.

CONCLUSIONS

Unsignaled extinction of alternative behavior controlling opioid use can result in increased opioid use, but this use does not rise beyond previous levels observed when opioid use is unconstrained by alternative reinforced behavior.

Nicotine as a discriminative stimulus for ethanol use

Abused drugs reinforce behavior; i.e., they increase the probability of the behavior preceding their administration. Abused drugs can also act as discriminative stimuli; i.e., they can set the occasion for responding reinforced by another event. Thus, one abused drug could come to set the occasion for the use of another and this functional relationship may play a role in polysubstance abuse, where common patterns of use could result in this relationship. Here we establish nicotine (0.4mg/kg, ip 5-min pre-session) as a discriminative stimulus for behavior reinforced by ethanol (0.1ml 8% w/v po, versus food) and determine the ability of nicotine (0.02-0.4mg/kg), varenicline (0.1-3.0mg/kg), and ethanol (250 and 500mg/kg) to control responding for ethanol. We compare these results to those from rats where nicotine signaled food was available (and ethanol was not). Nicotine came to function as a discriminative stimulus. Nicotine and varenicline produced dose-dependent increases in responding on the nicotine-appropriate lever while ethanol produced responding on the vehicle-appropriate lever. Whether this responding occurred on the lever that produced ethanol or food access depended on the training condition. These results demonstrate that a drug can come to set the occasion for use of another and suggest that this behavioral mechanism could play an important role in the maintenance of and recovery from polysubstance abuse, depending on the pattern of use.

Addiction as a BAD, a Behavioral Allocation Disorder

Addiction is continued drug use despite its harm. As one always has alternatives, addiction can be construed as a decision to allocate behavior to drug use. While decision making is commonly discussed and studied as if it resulted from deliberative, evaluative processes, such processes are actually only rarely involved in behavior allocation. These deliberative processes are too slow, effortful and inefficient to guide behavior other than when necessary. Rather, most actions are guided by faster, more automatic processes, often labeled habits. Habits are mostly adaptive, and result from repeated reinforcement leading to over-learned behavior. Habitual behavior occurs rapidly in response to particular contexts, and the behavior occurring first is that which occurs, i.e., the behavior that is decided upon. Thus, as drug use becomes habitual, drug use is likely to be chosen over other available activities in that particular context. However, while drug use becoming habitual is necessary for addiction to develop, it is not sufficient. Typically, constraints limit even habitual drug use to safer levels. These constraints might include limiting occasions for use; and, almost always, constraints on amount consumed. However, in a minority of individuals, drug use is not sufficiently constrained and addiction develops. This review discusses the nature of these constraints, and how they might fail. These failures do not result from abnormal learning processes, but rather unfortunate interactions between a person and their environment over time. These accumulate in the maladaptive allocation of behavior to drug use. This Behavior Allocation Disorder (BAD) can be reversed; occasionally easily when the environment significantly changes, but more often by the arduous application of deliberative processes generally absent from decision making. These deliberative processes must continue until new more adaptive habits become the most probable behavior in the contexts encountered. As alternatives to drug use become the most probable behavior, relapse risk diminishes.

Conditioned Stimulus Form Does Not Explain Failures to See Pavlovian-Instrumental-Transfer With Ethanol-Paired Conditioned Stimuli

BACKGROUND

Pavlovian-Instrumental-Transfer (PIT) examines the effects of associative learning upon instrumental responding. Previous studies examining PIT with ethanol (EtOH)-maintained responding showed increases in responding following presentation of an EtOH-paired conditioned stimulus (CS). Recently, we conducted 2 studies examining PIT with an EtOH-paired CS. One of these found increases in responding, while the other did not. This less robust demonstration of PIT may have resulted from the form of the CS used, as we used a 120-second light stimulus as a CS, while the previous studies used either a 120-second auditory stimulus or a 10-second light stimulus. This study examined whether using conditions similar to our earlier study, but with either a 120-second auditory or a 10-second light stimulus as a CS, resulted in more robust PIT. We also examined the reliability of our previous failure to observe PIT.

METHODS

Three experiments were conducted examining whether PIT was obtained using (i) a 120-second light stimulus, (ii) a 10-second light stimulus, or (iii) a 120-second auditory stimulus as CSs.

RESULTS

We found PIT was not obtained using (i) a 120-second light stimulus as a CS, (ii) a 10-second light stimulus as a CS, or (iii) a 120-second auditory stimulus as a CS.

CONCLUSIONS

These results suggest that CS form does not account for our earlier failure to see PIT. Rather, factors like rat strain or how EtOH drinking is induced may account for when PIT is or is not observed.

Effects of an ethanol-paired CS on responding for ethanol and food: Comparisons with a stimulus in a Truly-Random-Control group and to a food-paired CS on responding for food

Motivational increases due to exposure to alcohol-paired Conditioned Stimuli (CS) are central to some accounts of alcoholism. However, few studies isolate a stimulus's function as a CS from its other potential functions. Pavlovian-Instrumental-Transfer (PIT) procedures isolate a stimulus's function as a CS from its other functions. Though there are several relevant studies using PIT, knowledge gaps exist. Particularly, it is not clear that an alcohol-paired CS will increase alcohol seeking compared to the same stimulus in a Truly-Random-Control group, nor whether such increases are specific to alcohol seeking. To address these knowledge gaps in Experiment 1, rats responded for ethanol (0.1 ml 8% w/v) under an RI 30-sec schedule, then the lever was removed and half the rats had ethanol delivered during occasional 120-sec light presentations, while the remainder had ethanol and the light presented under independent RT schedules. Later the lever was returned and the light was presented during responding in extinction (PIT test). Following this test, levers were again removed and the light was presented without ethanol (light extinction), following again by a PIT test. Responding in the two groups during light presentations did not differ in either PIT test. Experiment 2 repeated Experiment 1 using food instead of ethanol. In Experiment 2, responding during light presentations increased in the paired group. In Experiment 3, rats were trained on a concurrent FR schedule of food and ethanol delivery. Ethanol was delivered following 5 responses and the response requirement for food adjusted so that similar numbers of food and ethanol deliveries were obtained. Subsequently, rats underwent conditioning, control and testing procedures identical to those in Experiment 1. In Experiment 3, the ethanol-paired CS increased ethanol-responding, but not food-responding. These results are most easily interpreted as changes in responding resulting from CS-elicited behavior rather than motivational changes. This interpretation is more compatible with some descriptions of the role of an alcohol-paired CS in alcoholism than others.

Determinants of choice, and vulnerability and recovery in addiction

Addiction may be viewed as choice governed by competing contingencies. One factor impacting choice, particularly as it relates to addiction, is sensitivity to delayed rewards. Discounting of delayed rewards influences addiction vulnerability because of competition between relatively immediate gains of drug use, e.g. intoxication, versus relatively remote gains of abstinence, e.g. family stability. Factors modifying delay sensitivity can be modeled in the laboratory. For instance, increased delay sensitivity can be similarly observed in adolescent humans and non-human animals. Similarly, genetic factors influence delay sensitivity in humans and animals. Recovery from addiction may also be viewed as choice behavior. Thus, reinforcing alternative behavior facilitates recovery because reinforcing alternative behavior decreases the frequency of using drugs. How reinforcing alternative behavior influences recovery can also be modeled in the laboratory. For instance, relapse risk decreases as abstinence duration increases, and this decreasing risk can be modeled in animals using choice procedures. In summary, addiction in many respects can be conceptualized as a problem of choice. Animal models of choice disorders stand to increase our understanding of the core processes that establish and maintain addiction and serve as a proving ground for development of novel treatments.

Drug effects on multiple and concurrent schedules of ethanol- and food-maintained behaviour: context-dependent selectivity

BACKGROUND AND PURPOSE

Drugs that more potently or effectively reduce ethanol-maintained behaviour versus an alternative are considered selective and are considered promising pharmacotherapies for alcoholism. Such results are often obtained using separate groups or multiple schedules where ethanol and the alternative are available alone or sequentially. Recently, we observed that when ethanol and food were available sequentially under a multiple schedule, fluvoxamine and varenicline were selective; yet this selectivity disappeared when ethanol and food were concurrently available.

EXPERIMENTAL APPROACH

We examined the generality of these findings by comparing doses of several drugs required to decrease ethanol- and food-maintained responding under a multiple schedule and under a concurrent schedule. Effects were determined for chlordiazepoxide, 2,5-dimethoxy-4-iodoamphetamine (DOI), meta-chlorophenylpiperazine (mCPP), morphine, naltrexone and d-amphetamine.

KEY RESULTS

Under the multiple schedule, ED50 values for decreases in ethanol-maintained responding were significantly different and lower than ED50 s for decreases in food-maintained responding (demonstrating selectivity) for each drug except for chlordiazepoxide (which was equipotent) and naltrexone (which did not affect responding). However, this selectivity vanished or even inverted under the concurrent schedule, such that ED50 values for decreasing ethanol- and food-maintained responding were not different (or, following DOI, the ED50 for food-maintained responding was lower than for ethanol-maintained responding).

CONCLUSIONS AND IMPLICATIONS

Results are consistent with those seen following fluvoxamine and varenicline administration, and suggest that selectivity is assay-dependent. These results indicate the need for careful interpretation of selective drug effects, especially when obtained in situations where ethanol or the alternative is the only programmed reinforcement available.

Incubation of ethanol reinstatement depends on test conditions and how ethanol consumption is reduced

In reinstatement studies (a common preclinical procedure for studying relapse), incubation occurs (longer abstinence periods result in more responding). This finding is discordant with the clinical literature. Identifying determinants of incubation could aid in interpreting reinstatement and identifying processes involved in relapse. Reinstated responding was examined in rats trained to respond for ethanol and food under a multiple concurrent schedule (Component 1: ethanol FR5, food FR150; Component 2: ethanol FR5, food FR5-alternating across the 30-min session). Ethanol consumption was then reduced for 1 or 16 sessions either by suspending training (rats remained in home cage) or by providing alternative reinforcement (only Component 2 stimuli and contingencies were presented throughout the session). In the next session, stimuli associated with Component 1 were presented and responses recorded but ethanol and food were never delivered. Two test conditions were studied: fixed-ratio completion either produced ethanol- or food-associated stimuli (signaled) or had no programmed consequence (unsignaled). Incubation of ethanol responding was observed only after suspended training during signaled test sessions. Incubation of food responding was also observed after suspended training. These results are most consistent with incubation resulting from a degradation of feedback functions limiting extinction responding, rather than from increased motivation.

Blood levels do not predict behavioral or physiological effects of Δ⁹-tetrahydrocannabinol in rhesus monkeys with different patterns of exposure

BACKGROUND

Recent changes in the legality of cannabis have prompted evaluation of whether blood levels of Δ(9)-tetrahydrocannabinol (THC) or its metabolites could be used to substantiate impairment, particularly related to behavioral tasks such as driving. However, because marked tolerance develops to behavioral effects of THC, the applicability of a particular threshold of blood THC as an index of impairment in people with different patterns of use remains unclear. Studies relevant to this issue are difficult to accomplish in humans, as prior drug exposure is difficult to control.

METHODS

Here, effects of THC to decrease rectal temperature and operant response rate compared to levels of THC and its metabolites were studied in blood in two groups of monkeys: one received intermittent treatment with THC (0.1 mg/kg i.v. every 3-4 days) and another received chronic THC (1 mg/kg/12 h s.c.) for several years.

RESULTS

In monkeys with intermittent THC exposure, a single dose of THC (3.2 mg/kg s.c.) decreased rectal temperature and response rate. The same dose did not affect response rate or rectal temperature in chronically exposed monkeys, indicative of greater tolerance. In both groups, blood levels of THC peaked 20-60 min post-injection and had a similar half-life of elimination, indicating no tolerance to the pharmacokinetics of THC. Notably, in both groups, the behavioral effects of THC were not apparent when blood levels were maximal (20-min post-administration).

CONCLUSION

These data indicate that thresholds for blood levels of THC do not provide a consistent index of behavioral impairment across individuals with different patterns of THC exposure.

Relative potency of varenicline or fluvoxamine to reduce responding for ethanol versus food depends on the presence or absence of concurrently earned food

BACKGROUND

Varenicline, a nicotinic partial agonist, selectively reduces ethanol (EtOH)- versus sucrose-maintained behavior when tested in separate groups, yet like the indirect agonist fluvoxamine, this selectively inverts when EtOH and food are concurrently available.

METHODS

Here, we extend these findings by examining varenicline and fluvoxamine effects under a multiple concurrent schedule where food and EtOH are concurrently available in different components: Component 1 where the food fixed-ratio was 25 and Component 2 where the food fixed-ratio was 75. The EtOH fixed-ratio was always 5. Food-maintained responding predominated in Component 1, while EtOH-maintained responding predominated in Component 2. In a second experiment, varenicline effects were assessed under a multiple schedule where food, then EtOH, then again food were available in separate 5-minute components with fixed-ratios of 5 for each reinforcement.

RESULTS

In the multiple concurrent schedule, varenicline was more potent at reducing food- versus EtOH-maintained responding in both components and reduced EtOH-maintained responding more potently during Component 1 (when food was almost never earned) than in Component 2 (where food was often earned). Fluvoxamine was similarly potent at reducing food- and EtOH-maintained responding. Under the multiple schedule, varenicline, like fluvoxamine, more potently decreases EtOH- versus food maintained responding when only food or EtOH is available in separate components.

CONCLUSIONS

These results demonstrate that selective effects on drug- versus alternative-maintained behavior depend on the schedule arrangement, and assays in which EtOH or an alternative is the only programmed reinforcement may overestimate the selectivity of treatments to decrease EtOH self-administration. Thus selective effects obtained under one assay may not generalize to another. Better understanding the behavioral mechanisms responsible for these results may help to guide pharmaco-therapeutic development for substance use disorders.

A history of alternative reinforcement reduces stimulus generalization of ethanol-seeking in a rat recovery model

BACKGROUND

Longer periods of recovery reduce the likelihood of relapse, which may be due to a reduced ability of various stimuli to occasion alcohol or drug seeking. However, this hypothesis remains largely uninvestigated.

METHODS

Here we assessed the ability of intermediate stimuli to occasion responding for ethanol in rats trained to discriminate an 8 kHz tone signaling a food fixed-ratio (FR) of 5 and an ethanol FR5, from a 16 kHz tone signaling a food FR150 and ethanol FR5. In the presence of the 8 kHz tone responding for food predominates, and in the presence of the 16 kHz tone, responding for ethanol predominates.

RESULTS

In the context of alternation between these conditions, varying the tone from 8 to 16 kHz produces a graded increase in ethanol (versus food) responding, consistent with a stimulus generalization function. A recent history of responding under food-predominant choice conditions, either during the test session or in the four sessions that precede it shifts the generalization function downwards. Extending this history to nine sessions shifts the curve further downwards. The stimulus generalization function was similar in a separate group, trained with different relative ratios for food and ethanol, but with similar behavioral allocation under each discriminative stimulus. Finally, withholding access to food and ethanol for 4 or 16 sessions did not affect the stimulus generalization gradient.

CONCLUSION

These results suggest that longer histories of reinforced alternative behavior might reduce the likelihood of relapse by decreasing the control exerted over alcohol- or drug-seeking by stimuli similar to those that previously occasioned alcohol- or drug-seeking.

Effects of varenicline on ethanol- and food-maintained responding in a concurrent access procedure

BACKGROUND

Varenicline has been reported to reduce drinking in smokers and to selectively decrease responding for ethanol (EtOH) versus alternatives in preclinical studies. Such selectivity may reflect potential therapeutic effects and the involvement of nicotinic receptors in EtOH reinforcement. However, these studies have been conducted with EtOH and an alternative available in isolation or in separate groups, and selectivity can depend on the context in which reinforcement occurs. Whether varenicline selectivity is maintained when EtOH and an alternative are concurrently available has not been reported. To examine the effects of varenicline on EtOH self-administration when an alternative is concurrently available, male Lewis rats (n = 5) were trained to respond for EtOH and food under a concurrent FR5 FRX schedule where the fixed ratio (FR) for food was adjusted (FR = 25 or 35 for each subject) to provide similar numbers of EtOH and food deliveries during a 30-minute session.

METHODS

Doses of varenicline (0.56 to 5.6 mg/kg, i.p.) or vehicle were administered 30 minutes before sessions. Effects of varenicline on responding across the session and during each tenth of the session were compared to responding following vehicle treatment.

RESULTS

Lower doses (0.56 to 1.0 mg/kg) of varenicline increased responding for EtOH without affecting responding for food. Higher doses disrupted responding for EtOH and food similarly.

CONCLUSIONS

Previous reports of varenicline selectivity on EtOH-maintained responding do not generalize to other experimental conditions such as a concurrent schedule. The increase in responding for EtOH following lower doses might be due to enhanced EtOH reinforcement, decreased food reinforcement, rate dependency, or greater perseverance on the initial, EtOH response.

Reinforcement of an alternative behavior as a model of recovery and relapse in the rat

A preclinical model that includes measures of alternative behavior and drug-seeking could improve our understanding of the processes involved in successful recovery; however current preclinical models of relapse do not measure alternative behavior. We assessed the persistence of food-maintained responding and the resumption of ethanol-maintained responding after ethanol-maintained responding was reduced by changing the response requirement for concurrently available food. Ethanol (10%, w/v) was always available following 5 responses (FR5). A 16 kHz tone indicating food delivery followed 150 responses (FR150) resulted in ethanol-predominate responding and substantial amounts of ethanol were earned (0.47 g/kg per 30-min session) and consumed. An 8 kHz tone indicating food delivery followed 5 responses (FR5) for 1, 2, 4, or 16 consecutive sessions reduced ethanol-maintained responding despite unchanged ethanol availability. Ethanol-maintained responding resumed upon subsequent presentation of the 16 kHz tone. However, more responses occurred on the food lever before 5 responses occurred on the ethanol lever as the number of preceding FR5 food sessions increased. These results suggest that alternative reinforcement may reduce control by discriminative stimuli that occasion ethanol-seeking and is consistent with the risk of relapse declining with longer periods of recovery because of the strengthening of alternative behavior.

Shifts in discriminative control with increasing periods of recovery in the rat

BACKGROUND

During recovery from alcoholism, other behavior likely increases. The development of alternative behavior may reduce attention to alcohol-associated stimuli. This could result in greater persistence of the alternative behavior when individuals again encounter alcohol-associated stimuli that might precipitate relapse. Developing animal models of this process could facilitate a better understanding of the mechanisms involved in relapse and recovery. However, current preclinical models of recovery and relapse rarely measure alternative behavior. Thus, our objective was to establish a procedure in rats in which an increase in alternative behavior (responding for food) reduced responding for ethanol (EtOH). The amount of responding for food and EtOH was then assessed after re-exposure to the alcohol-associated stimulus after varying the number of preceding sessions of increased responding for food and reduced responding for EtOH. These results were compared with those from a parallel group responding for saccharin solution instead of EtOH.

METHODS

The solution (EtOH or saccharin) was always available following 5 responses. Presentation of flashing stimulus lights indicated food delivery followed 150 responses and resulted in responding predominately for the solution (84 to 86% of total responses). Presentation of solid stimulus lights indicated food delivery followed 5 responses and resulted in responding predominately for food (1 to 3% of total responses were for the solution). Rats were exposed to solid light conditions for 0, 1, 2, 4, or 16 consecutive sessions before being re-exposed to the flashing stimulus lights in extinction.

RESULTS

Responding for either solution resumed when rats were re-exposed to the flashing stimulus lights (associated with solution-predominate responding). However, more responses occurred on the food lever with longer recent histories of responding for food instead of the solution.

CONCLUSIONS

These results suggest that the longer alternative behavior replaces drinking, the more that attention to stimuli associated with drinking decreases. These results are consistent with the notion that the risk of relapse declines with longer periods of recovery because alternative behavior comes to predominate even in the presence of stimuli associated with drinking.

Apparent inverse relationship between cannabinoid agonist efficacy and tolerance/cross-tolerance produced by Δ⁹-tetrahydrocannabinol treatment in rhesus monkeys

Synthetic cannabinoids (CBs) [naphthalen-1-yl-(1-pentylindol-3-yl) methanone (JWH-018) and naphthalen-1-yl-(1-butylindol-3-yl) methanone (JWH-073)] are marketed, sold, and used as alternatives to cannabis. Synthetic CBs appear to have effects similar to those of Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the drug primarily responsible for the behavioral effects of cannabis. However, synthetic CB products produce atypical effects (e.g., hypertension, seizures, and panic attacks). One potential explanation for atypical effects is CB₁ receptor agonist efficacy, which is reportedly higher for JWH-018 and JWH-073 compared with Δ⁹-THC. The goal of this study was to test a prediction from receptor theory that tolerance/cross-tolerance (i.e., resulting from daily Δ⁹-THC treatment) is greater for a low-efficacy agonist compared with a high-efficacy agonist. Rhesus monkeys discriminated 0.1 mg/kg Δ⁹-THC i.v. from vehicle, and sensitivity to CB(1) agonists was determined before and after 3 and 14 days of Δ⁹-THC treatment (1 mg/kg per day s.c.). (1R,3R,4R)-3-[2-Hydroxy-4-(1,1-dimethylheptyl) phenyl]-4-(3-hydroxypropyl)cyclohexan-1-ol (CP-55,940), a prototype high-efficacy CB₁ receptor agonist, JWH-018, and JWH-073 substituted for the discriminative stimulus effects of Δ⁹-THC. Three days of Δ⁹-THC treatment produced less tolerance/cross-tolerance than 14 days of Δ⁹-THC treatment. Three days of Δ⁹-THC did not result in cross-tolerance to CP-55,940, JWH-073, and JWH-018; in contrast, as reported previously, 3 days of Δ⁹-THC treatment decreased sensitivity to Δ⁹-THC 3-fold. Fourteen days of Δ⁹-THC decreased sensitivity to Δ⁹-THC, CP-55,940, JWH-018, and JWH-073 9.2-fold, 3.6-fold, 4.3-fold, and 5.6-fold, respectively. The greater loss of sensitivity to Δ⁹-THC relative to CP-55,940 and JWH-018 suggests that differences in CB₁ receptor agonist efficacy are important in vivo and might underlie differences in the dependence liability and adverse effects of synthetic CBs versus cannabis.

Purity of synthetic cannabinoids sold online for recreational use

The recreational use of synthetic cannabinoids has recently increased. This increase is due, in part, to the recent availability of inexpensive compound sold legally online in bulk. In particular, JWH-018 (1-pentyl-3-(1-naphthoyl)indole) and JWH-073 (1-butyl-3-(1-naphthoyl)indole) have been found in herbal blends marketed as alternatives to cannabis. Although these particular compounds have recently been emergency scheduled in the United States, online suppliers have shifted sales to other, similar compounds that are not currently scheduled. However, the purity of the drugs obtained from online suppliers is not known. Relative purity of JWH-018 and JWH-073 from three different online suppliers was determined using high-performance liquid chromatography with ultraviolet detection and validated standards obtained from a traditional research chemical supplier. Our results show that JWH-018 and JWH-073 obtained from online vendors was of comparable purity to validated standards, even though the physical properties varied in color, texture, and odor. It is concluded that adverse events following consumption of synthetic cannabinoid preparations is unlikely to be due to impurities or residue from the manufacturing process, but rather to effects of the active drug or interactions with other psychoactive chemicals from herbs blended into products marketed as cannabis alternatives.

JWH-018 and JWH-073: Δ⁹-tetrahydrocannabinol-like discriminative stimulus effects in monkeys

Products containing naphthalen-1-yl-(1-pentylindol-3-yl) methanone (JWH-018) and naphthalen-1-yl-(1-butylindol-3-yl) methanone (JWH-073) are emerging drugs of abuse. Here, the behavioral effects of JWH-018 and JWH-073 were examined in one behavioral assay selective for cannabinoid agonism, rhesus monkeys (n = 4) discriminating Δ⁹-tetrahydrocannabinol (Δ⁹-THC; 0.1 mg/kg i.v.), and another assay sensitive to cannabinoid withdrawal, i.e., monkeys (n = 3) discriminating the cannabinoid antagonist rimonabant (1 mg/kg i.v.) during chronic Δ⁹-THC (1 mg/kg s.c. 12 h) treatment. Δ⁹-THC, JWH-018, and JWH-073 increased drug-lever responding in monkeys discriminating Δ⁹-THC; the ED₅₀ values were 0.044, 0.013, and 0.058 mg/kg, respectively and the duration of action was 4, 2, and 1 h, respectively. Rimonabant (0.32-3.2 mg/kg) produced surmountable antagonism of Δ⁹-THC, JWH-018, and JWH-073. Schild analyses and single-dose apparent affinity estimates yielded apparent pA₂/pK(B) values of 6.65, 6.68, and 6.79 in the presence of Δ⁹-THC, JWH-018, and JWH-073, respectively. In Δ⁹-THC-treated monkeys discriminating rimonabant, the training drug increased responding on the rimonabant lever; the ED₅₀ value of rimonabant was 0.20 mg/kg. Δ⁹-THC (1-10 mg/kg), JWH-018 (0.32-3.2 mg/kg), and JWH-073 (3.2-32 mg/kg) dose-dependently attenuated the rimonabant-discriminative stimulus (i.e., withdrawal). These results suggest that Δ⁹-THC, JWH-018, and JWH-073 act through the same receptors to produce Δ⁹-THC-like subjective effects and attenuate Δ⁹-THC withdrawal. The relatively short duration of action of JWH-018 and JWH-073 might lead to more frequent use, which could strengthen habitual use by increasing the frequency of stimulus-outcome pairings. This coupled with the possible greater efficacy of JWH-018 at cannabinoid 1 receptors could be associated with greater dependence liability than Δ⁹-THC.

Reinforcement magnitude modulation of rate dependent effects in pigeons and rats

Response rate can influence the behavioral effects of many drugs. Reinforcement magnitude may also influence drug effects. Further, reinforcement magnitude can influence rate-dependent effects. For example, in an earlier report, we showed that rate-dependent effects of two antidepressants depended on reinforcement magnitude. The ability of reinforcement magnitude to interact with rate-dependency has not been well characterized. It is not known whether our previous results are specific to antidepressants or generalize to other drug classes. Here, we further examine rate-magnitude interactions by studying effects of two stimulants (d-amphetamine [0.32-5.6 mg/kg] and cocaine [0.32-10 mg/kg]) and two sedatives (chlordiazepoxide [1.78-32 mg/kg] and pentobarbital [1.0-17.8 mg/kg]) in pigeons responding under a 3-component multiple fixed-interval (FI) 300-s schedule maintained by 2-, 4-, or 8-s of food access. We also examine the effects of d-amphetamine [0.32-3.2 mg/kg] and pentobarbital [1.8-10 mg/kg] in rats responding under a similar multiple FI300-s schedule maintained by 2- or 10- food pellet (45 mg) delivery. In pigeons, cocaine and, to a lesser extent, chlordiazepoxide exerted rate-dependent effects that were diminished by increasing durations of food access. The relationship was less apparent for pentobarbital, and not present for d-amphetamine. In rats, rate-dependent effects of pentobarbital and d-amphetamine were not modulated by reinforcement magnitude. In conclusion, some drugs appear to exert rate-dependent effect which are diminished when reinforcement magnitude is relatively high. Subsequent analysis of the rate-dependency data suggest the effects of reinforcement magnitude may be due to a diminution of drug-induced increases in low-rate behavior that occurs early in the fixed-interval.

Examination of reinforcement magnitude on the pharmacological disruption of fixed-ratio performance

Behavioral momentum theory proposes that operant behavior is the product of two separable processes: its rate of occurrence and its resistance to change. Generally speaking, operant situations providing more densely spaced or greater magnitudes of reinforcement should be more resistant to disruption. Attempts to disrupt ongoing behavior by manipulating the availability of food or deprivation level typically have supported the predictions of behavioral momentum. Tests with pharmacological disruptors, however, have yielded mixed results. Most investigations of pharmacological disruption of operant behavior have evaluated momentum across situations that differ in rate of reinforcement. The present experiment was an attempt to systematically replicate prior work, but under conditions of differing reinforcement magnitudes. Pigeons were trained to key peck on a multiple fixed-ratio 30 schedule of food presentation, where different components programmed 2-, 4-, or 8-s access to grain. Resistance to rate-decreasing effects of drugs was evaluated with several compounds drawn from distinct pharmacological classes: chlordiazepoxide, cocaine, clonidine, haloperidol, morphine, and ethanol were tested. Additionally, disruption by prefeeding and extinction was examined. Generally, resistance to change by drug administration was not modulated by reinforcement magnitude. Prefeeding and extinction tests, however, replicated previous work, indicating that our procedure was sensitive to more common disruptors. The results give additional support to the notion that pharmacological disruptors may not behave in the manner predicted by behavioral momentum theory.

Mouse breathalyzer

BACKGROUND

The development of a relatively simple, noninvasive method for estimating blood ethanol concentrations in mice will be useful in behavioral studies related to alcoholism. This study validated such a method.

METHODS

The apparatus consists of a body chamber fitted with a head stock through which the mouse head protrudes. This was fitted against a water-jacketed head-space chamber surrounding the mouse's head. Rebreathed air maintained at 37 degrees C in the head-space chamber was removed using a peristaltic pump and loaded into a 1-ml injection loop. Ethanol in the sample was quantified using gas chromatography. To validate this method, ethanol levels in breath samples were compared against those in tail blood samples collected immediately after the breath samples. Breath samples were collected at 5, 10, 20, 40, 80, 120, and 160 minutes after ethanol (0.4, 0.8, 1.2, 1.6, 2.4, and 3.2 g/kg) was administered to male C57BL/6J mice.

RESULTS

Breath and blood ethanol levels were well correlated (r(2) = 0.96) across time points on the descending ethanol-time curve at doses below 2.4 g/kg. Correlation for these doses on the ascending portion of the curve had greater variance, but was still well correlated (r(2) = 0.92).

CONCLUSIONS

The mouse breathalyzer is an accurate, convenient, noninvasive and well-tolerated method for estimating blood ethanol concentrations in mice across a range of behaviorally relevant concentrations below 2.4 g/kg, especially on the descending limb of the ethanol-time curve. Although this procedure requires a gas chromatograph in the animal facility, the ability to estimate ethanol concentrations quickly and easily will be especially useful in behavioral studies where repeated blood sampling is not feasible.

Cannabinoid agonists differentially substitute for the discriminative stimulus effects of Delta(9)-tetrahydrocannabinol in C57BL/6J mice

RATIONALE

A variety of behavioral procedures have been developed to assess cannabinoid activity in mice; however, the feasibility of establishing Delta(9)-THC as a discriminative stimulus in mice has not been documented.

OBJECTIVE

One goal was to establish Delta(9)-THC as a discriminative stimulus in mice; after having done so, another goal was to examine the in vivo mechanism of action of Delta(9)-THC with other cannabinoids and noncannabinoids.

MATERIALS AND METHODS

C57BL/6J mice (n = 8) were trained to discriminate Delta(9)-THC (10 mg/kg i.p.) from vehicle while responding under a fixed ratio 30 schedule of food presentation.

RESULTS

Mice satisfied the discrimination criteria in 18-98 (median = 67) sessions and the discriminative stimulus effects of Delta(9)-THC were dose-dependent (ED(50) = 2.6 mg/kg). CP 55940 and WIN 55212-2 dose-dependently increased Delta(9)-THC-appropriate responding to 100% (ED(50) = 0.032 and 0.45 mg/kg, respectively), whereas methanandamide and a variety of noncannabinoids (cocaine, ethanol, and ketamine) produced a maximum of 34% Delta(9)-THC-appropriate responding. The cannabinoid CB(1) antagonist SR 141716A (rimonabant) surmountably antagonized the discriminative effects of Delta(9)-THC, CP 55940, and WIN 55212-2; methanandamide did not significantly modify the Delta(9)-THC discriminative stimulus.

CONCLUSIONS

The discriminative stimulus effects of Delta(9)-THC, CP 55940, and WIN 55212-2 are mediated by the same (i.e., CB(1)) receptors, whereas the effects of methanandamide or a metabolite of methanandamide are mediated at least in part by non-CB(1) receptors. The discriminative stimulus effects of Delta(9)-THC in mice could be used to evaluate mechanisms of cannabinoid activity with approaches (e.g., inducible knockouts) currently unavailable in nonmurine species.

Acute tolerance to rate-decreasing effects of single doses of ethanol

Acute tolerance occurs when behavioral impairment is greater at a given blood ethanol concentration (BAC) on the ascending versus descending limb of the BAC-time curve following administration of a single dose of ethanol, however studies utilizing learned behaviors have not been widely reported. We assessed acute tolerance to single doses of ethanol in five Lewis rats responding under a fixed-ratio (FR8) schedule of food presentation. Response rates for food during 1-min components (ending 2, 4, 11, 18, 33, and 57 min after ethanol administration) were determined, and BAC was measured immediately after each component using a rat breathalyzer. Ethanol (0.4, 0.6, 0.8, and 1.2 g/kg, i.p.) produced dose-related decreases in responding for food that tended to recover over time for all but the highest dose tested. Similarly, dose-related increases in BAC were also observed. Using either an analysis that expressed impairment per unit BAC on the ascending limb versus the descending limb (by assessing the area under the curve (AUC) for behavior and BAC on each limb), the slope of the function that relates the behavioral effect to BAC (each expressed as percent maximum effect), or a variant of the Mellanby method (hysteresis), acute tolerance was observed following a dose of 0.4 g/kg ethanol. Though behavior appeared to recover on the descending limb following higher doses (especially 0.6 and 0.8 g/kg), acute tolerance to these doses was not present.

Taurine and ethanol interactions: behavioral effects in mice

Taurine is an abundant amino acid in the brain that shares pharmacological effects and similar potency with ethanol. Recently, taurine-containing beverages have been reported to enhance the euphoric effects of ethanol, though the extent of this effect and the role of taurine remain speculative. The present study was designed to explore interactions between taurine and ethanol on several behaviors including locomotion, ataxia, and loss of righting. Two strains of mice, C57BL/6J and DBA/2J mice, were used to examine potential strain differences. In the first experiment, effects of various doses of taurine (0.3-3.0 g/kg), ethanol (1.0-4.2 g/kg), or taurine in combination with ethanol were assessed in a within-subjects design. Although taurine did not appear to alter effects of ethanol on any measure in either strain, the development of tolerance to locomotor effects and sensitization to ataxic effects of ethanol in DBA/2J mice complicated interpretation of these results. In a second experiment, drug-naïve mice were assigned to one of four treatment groups: saline+saline, saline+ethanol (1.78 g/kg), taurine (1.78 g/kg)+saline, or ethanol+taurine. In this experiment, taurine pretreatment significantly attenuated the locomotor-stimulating effect of ethanol in both strains (but to a greater extent in C57BL/6J mice) and appeared to reduce the ataxic effects of ethanol in C57BL/6J mice. In conclusion, the interaction between taurine and ethanol is subtle. Further, results are inconsistent with the notion that taurine plays a major role in the locomotor, ataxic, or loss of righting effects of ethanol.

Fluvoxamine effects on concurrent ethanol- and food-maintained behaviors

In previous studies, the selective serotonin reuptake inhibitor fluvoxamine preferentially reduced responding for ethanol compared with responding for food under conditions in which each was available alone in separate groups or in the same subjects under a multiple schedule in which baseline response rates were matched. The impact of providing concurrent access to food on pharmacological effects on ethanol self-administration remains largely unexplored. In this study, acute doses of fluvoxamine (3.0-17.8 mg/kg) were administered 30 min before the experimental session to Lewis rats responding under a concurrent fixed-ratio, fixed-ratio schedule of ethanol and food presentation. Ratios for food were adjusted for each subject to provide matched rates of food and ethanol reinforcement across the 30-min session. Although the number of ethanol and food deliveries did not significantly differ under baseline conditions, response rates did differ. Following fluvoxamine administration, responding for food was decreased more than responding for ethanol. This differential effect did not appear to be related to response rate or fixed-ratio size. Thus, the selectivity of fluvoxamine on ethanol- versus food-maintained responding depends on the context in which the behavior occurs. Such results may help explain inconsistencies between preclinical results and those in humans, and could provide insight into the behavioral determinants of pharmacological effects on ethanol self-administration.

Cannabinoid effects on behaviors maintained by ethanol or food: a within-subjects comparison

The cannabinoid CB1 antagonist rimonabant (SR141716A) has been proposed as a therapeutic agent for several addictive disorders, including alcoholism. Rimonabant may selectively reduce responding for an ethanol solution compared with an alternative. While this could represent a specific effect of CB1 inhibition on ethanol reinforcement, this could also result from differences in the baseline rates of behavior or experiences between comparison groups. We developed a procedure in rats that allows a within-subject comparison of ethanol and food-maintained responding and provides well matched baseline response rates. We determined the effects of acute doses of rimonabant (0.3-5.6 mg/kg, intraperitoneal) and the CB1 agonist Delta-9-tetrahydrocannabinol (1.0-5.6 mg/kg, intraperitoneal) on responding for food and ethanol under a multiple fixed-ratio schedule. To confirm that rimonabant blocked cannabinoid receptors, the ability of rimonabant to antagonize Delta-9-tetrahydrocannabinol effects in the same subjects under the same reinforcement schedule was also determined. In contrast with previous reports, rimonabant did not significantly alter responding for ethanol or food. The effects of Delta-9-tetrahydrocannabinol on responding for food were completely antagonized by rimonabant, whereas Delta-9-tetrahydrocannabinol effects on responding for ethanol were not. These results suggest that there may be neuroadaptation of the cannabinoid system following aging or chronic self-administration of ethanol.

Effects of chronic fluvoxamine on ethanol- and food-maintained behaviors

Acute treatment with fluvoxamine reduces responding for ethanol more than responding for food. However, pharmacotherapy for alcoholism is likely to require chronic treatment. These experiments were performed to assess the effects of chronic fluvoxamine on ethanol- and food-maintained behaviors. Effects of chronic fluvoxamine (10 and 17.8 mg/kg/dayx30 days) on ethanol- and food-maintained responding were compared to responding during saline treatment in four Sprague-Dawley rats responding for ethanol and food under a multiple fixed-ratio 5, fixed-ratio 5 schedule. In two subjects, chronic fluvoxamine reduced ethanol-maintained responding more than food-maintained responding; however this effect was transient. In another subject, treatment persistently decreased food-maintained responding relative to ethanol-maintained responding. Finally, in one subject, fluvoxamine nonspecifically disrupted responding for food and ethanol. Similar to results in humans, outbred Sprague-Dawley rats had differential responses to chronic fluvoxamine. The effect was transient in rats that responded favorably (greater reduction of ethanol relative to food responding), while response reductions persisted throughout treatment in rats that responded unfavorably (greater reduction of food relative to ethanol or nonspecific reductions).