Rationale
Rapidly evolving e-cigarette technology developed for self-administering nicotine aerosol has the potential to be utilized to self-administer other aerosolized drugs of abuse. Rodent models ...which mirror characteristics of human e-cigarette use are necessary to explore the degree to which this may be a public health concern.
Objectives
Our goal was to develop a highly translational model of discrete nose-only aerosol puff drug delivery to explore the reinforcing effects of fentanyl and sufentanil aerosols in rats.
Methods
Male and female Sprague–Dawley rats were trained to perform a multiple schedule FR1 lever-press, 4-s (second) nose hold operant during which the subject’s orofacial areas were exposed to drug-free glycerol/propylene glycol aerosol produced by a commercial e-cigarette at a power setting of 18 watts. Each completed 4-s drug-free vehicle aerosol exposure resulted in a 3-s presentation of a 0.1-ml dipper of sweetened milk solution. After training, rats were then allowed to self-administer 4-s nose-only puffs of fentanyl (100–6000 µg/ml) or sufentanil (30–500 µg/ml) aerosol in the absence of paired milk dipper reinforcers.
Results
All 31 rats learned the lever-press/nose-poke multiple schedule for milk dippers alone and 25 accepted exposure to 4 s of 18 watts of drug-free vehicle aerosol when paired with milk dipper presentations. In the absence of paired milk dipper presentations, fentanyl aerosol puffs at concentrations of 1000 and 3000 µg/ml as well as 100 µg/ml puffs of sufentanil served as reinforcers compared to both air puffs and drug-free vehicle aerosol puffs. There were no significant differences between males and females in number of fentanyl or sufentanil puffs self-administered.
Conclusions
Discrete nose-only puffs of two potent opioids under exposure conditions comparable to puff durations in human e-cigarette users serve as reinforcers in rats. This outcome suggests that under appropriate conditions e-cigarettes might be a potential alternative delivery mechanism for illicit opioids.
Recent human clinical studies with the NMDA receptor (NMDAR) antagonist ketamine have revealed profound and long-lasting antidepressant effects with rapid onset in several clinical trials, but ...antidepressant effects were preceded by dissociative side effects. Here we show that GLYX-13, a novel NMDAR glycine-site functional partial agonist, produces an antidepressant-like effect in the Porsolt, novelty induced hypophagia, and learned helplessness tests in rats without exhibiting substance abuse-related, gating, and sedative side effects of ketamine in the drug discrimination, conditioned place preference, pre-pulse inhibition and open-field tests. Like ketamine, the GLYX-13-induced antidepressant-like effects required AMPA/kainate receptor activation, as evidenced by the ability of NBQX to abolish the antidepressant-like effect. Both GLYX-13 and ketamine persistently (24 h) enhanced the induction of long-term potentiation of synaptic transmission and the magnitude of NMDAR-NR2B conductance at rat Schaffer collateral-CA1 synapses in vitro. Cell surface biotinylation studies showed that both GLYX-13 and ketamine led to increases in both NR2B and GluR1 protein levels, as measured by Western analysis, whereas no changes were seen in mRNA expression (microarray and qRT-PCR). GLYX-13, unlike ketamine, produced its antidepressant-like effect when injected directly into the medial prefrontal cortex (MPFC). These results suggest that GLYX-13 produces an antidepressant-like effect without the side effects seen with ketamine at least in part by directly modulating NR2B-containing NMDARs in the MPFC. Furthermore, the enhancement of 'metaplasticity' by both GLYX-13 and ketamine may help explain the long-lasting antidepressant effects of these NMDAR modulators. GLYX-13 is currently in a Phase II clinical development program for treatment-resistant depression.
Stroke remains a significant problem despite decades of work on neuroprotective strategies. NMDA receptor (NMDAR) antagonists are neuroprotective in preclinical models, but have been clinically ...unsuccessful, in part due to side effects. Here we describe a prototypical GluN2B-selective antagonist with an IC50 value that is 10-fold more potent at acidic pH 6.9 associated with ischemic tissue compared to pH 7.6, a value close to the pH in healthy brain tissue. This should maximize neuroprotection in ischemic tissue while minimizing on-target side effects associated with NMDAR blockade in noninjured brain regions. We have determined the mechanism underlying pH-dependent inhibition and demonstrate the utility of this approach in vivo. We also identify dicarboxylate dimers as a novel proton sensor in proteins. These results provide insight into the molecular basis of pH-dependent neuroprotective NMDAR block, which could be beneficial in a wide range of neurological insults associated with tissue acidification.
•pH-dependent binding of a GluN2B modulator to the GluN1/GluN2B ATD heterodimer•pH dependence renders a GluN2B modulator more potent at acidic pH during ischemia•pH-dependent GluN2B inhibitors are neuroprotective in vivo with reduced side effects•A novel dicarboxylate pH sensor establishes precedent for proton sensitive domains
Yuan et al. describe a unique structure-activity relationship and the molecular mechanism governing pH sensitivity of GluN2B-selective NMDAR antagonists, which is clinically significant for neuroprotection during neuronal injury. They identify the dicarboxylate dimer as a new pH-sensitive motif within proteins.
Ketamine represents a breakthrough therapy for patients with major depressive disorder (MDD). Unfortunately use‐limiting effects such as sedation, cognitive impairment and risk for abuse negatively ...impact ketamine’s therapeutic utility. What remains unexplored is the relative vulnerability of MDD patients to ketamine’s adverse effects. Thus, we evaluated the effects of ketamine on locomotor activation and the acquisition of intravenous (IV) ketamine self‐administration. These studies were performed in Sprague‐Dawley (SD) rats, a “normal” control strain and Wistar Kyoto (WKY) rats, an inbred strain which demonstrate stress vulnerability and mimics behavioral and physiological aspects of MDD in humans. Male and female rats from each strain were administered saline or a dose of ketamine (3‐ 56 mg/kg, IP) and locomotor activity was recorded for 30 min. Following 2‐4 months during which rats were handled but underwent no experimental procedures, they were surgically implanted with chronic IV catheters. Subjects were then given access to 0.3 mg/kg/infusion IV ketamine under a fixed ratio (FR) 1 schedule during 21 daily 1‐hr sessions. Acquisition criteria required subjects to respond for >15 infusions during 3 consecutive sessions, with responding on the inactive lever < 70% of that on the active lever. To determine the potential impact of learning disparities between strains, separate groups of SD and WKY rats were also assessed for acquisition of food maintained responding under the same schedule of reinforcement. Ketamine produced a biphasic dose‐dependent effect on activity in both strains with intermediate doses producing an increase in locomotion and higher doses suppressing activity. WKY rats displayed significantly less activity than SD rats under vehicle conditions, as well as following ketamine treatments. Ketamine significantly increased distance traveled at 3, 10 and 30 mg/kg in SD rats and at 3 and 10 mg/kg in WKY rats. While distance traveled by WKY rats was lower across all ketamine doses, data normalization relative to vehicle control revealed that ketamine produced a similar level of effect in both strains. Approximately 75% of SD rats acquired ketamine self‐administration within a 21‐day window under our testing conditions; whereas, less than 20% of the WKY rats acquired the behavior. Subsequent exploration of responding for higher and lower ketamine concentrations failed to engender self‐administration behavior in WKY rats. Using active training techniques to promote responding and drug exposure ultimately resulted in approximately 75% of the WKY rats self‐administering ketamine under FR1 conditions versus 100% of the SD rats. In contrast, all subjects from both strains learned to respond for food pellets within 4 sessions. Overall, consistent with previous work, our studies show that WKY rats have lower baseline activity levels. However ketamine‐induced locomotor activation was proportionate to those for our control strain. Similarly, both strains readily acquired and responded for food under a FR schedule suggesting an equivalent capacity to learn an operant task for a natural reinforcer. Yet, obvious differences emerged when operant responding was reinforced with IV ketamine suggesting that ketamine produces lower reinforcing effects in WKY rats relative to SD. Alternatively it is possible that WKY rats are more sensitive to ketamine’s aversive effects.
Despite the increasingly pervasive use of chemogenetic tools in preclinical neuroscience research, the in vivo pharmacology of DREADD agonists remains poorly understood. The pharmacological effects ...of any ligand acting at receptors, engineered or endogenous, are influenced by numerous factors including potency, time course, and receptor selectivity. Thus, rigorous comparison of the potency and time course of available DREADD ligands may provide an empirical foundation for ligand selection.
Compare the behavioral pharmacology of three different DREADD ligands clozapine-N-oxide (CNO), compound 21 (C21), and deschloroclozapine (DCZ) in a locomotor activity assay in tyrosine hydroxylase:cre recombinase (TH:Cre) male and female rats.
Locomotor activity in nine adult TH:Cre Sprague-Dawley rats (5 female, 4 male) was monitored for two hours following administration of d-amphetamine (vehicle, 0.1–3.2 mg/kg, IP), DCZ (vehicle, 0.32–320 µg/kg, IP), CNO (vehicle, 0.32–10 mg/kg), and C21 (vehicle, 0.1–3.2 mg/kg, IP). Behavioral sessions were conducted twice per week prior to and starting three weeks after bilateral intra-VTA hM3Dq DREADD virus injection.
d-Amphetamine significantly increased locomotor activity pre- and post-DREADD virus injection. DCZ, CNO, and C21 did not alter locomotor activity pre-DREADD virus injection. There was no significant effect of DCZ, CNO, and C21 on locomotor activity post-DREADD virus injection; however, large individual differences in both behavioral response and receptor expression were observed.
Large individual variability was observed in both DREADD agonist behavioral effects and receptor expression. These results suggest further basic research would facilitate the utility of these chemogenetic tools for behavioral neuroscience research.
In vitro studies show that the abused inhalant toluene affects a number of ligand-gated ion channels. The two most consistently implicated of these are γ-aminobutyric acid type A (GABAA) receptors ...which are positively modulated by toluene and N-methyl-d-aspartate (NMDA) receptors which are negatively modulated by toluene. Behavioral studies also suggest an interaction of toluene with GABAA and/or NMDA receptors but it is unclear if these receptors underlie the abuse-related intoxicating effects of toluene. Seventeen B6SJLF1/J mice were trained using a two-choice operant drug discrimination procedure to discriminate 10min of exposure to 2000ppm toluene vapor from 10min of exposure to air. The discrimination was acquired in a mean of 65 training sessions. The stimulus effects of 2000ppm toluene vapor were exposure concentration-dependent but rapidly diminished following the cessation of vapor exposure. The stimulus effects of toluene generalized to the chlorinated hydrocarbon vapor perchloroethylene but not 1,1,2-trichloroethane nor the volatile anesthetic isoflurane. The competitive NMDA antagonist CGS-19755, the uncompetitive antagonist dizocilpine and the glycine-site antagonist L701,324 all failed to substitute for toluene. The classical nonselective benzodiazepines midazolam and chlordiazepoxide produced toluene-like stimulus effects but the alpha 1 subunit preferring positive GABAA modulator zaleplon failed to substitute for toluene. The barbiturates pentobarbital and methohexital and the GABAA-positive modulator neurosteroid allopregnanolone did not substitute for toluene. These data suggest that the stimulus effects of toluene may be at least partially mediated by benzodiazepine-like positive allosteric modulation of GABAA receptors containing alpha 2, 3 or 5 subunits.
Drug self-administration procedures are the gold standard for laboratory research to study mechanisms of drug use disorders and evaluate candidate medications. However, preclinical-to-clinical ...translation has been hampered by a lack of coordination. To address this limitation, we previously developed homologous intravenous (IV) cocaine choice self-administration procedures in rhesus monkeys and humans, and then demonstrated their functional equivalence. The present studies sought to determine the sensitivity of these procedures to d-amphetamine maintenance. Three (N = 3) rhesus monkeys with histories of cocaine self-administration and 16 (N = 16) humans with cocaine use disorder completed the studies. Monkeys were maintained on IV d-amphetamine (0, 0.019, 0.037 and 0.074 mg/kg/h), and then completed 7 sessions during each condition in which they completed 9 choice trials to receive 0.14 mg/kg/injection IV cocaine (corresponding to 10 mg/70 kg in humans) or 10 food pellets under independent, concurrent progressive-ratio schedules. Humans were maintained on oral extended release d-amphetamine (0, 30 and 60 mg/day, corresponding to the lowest 3 doses in monkeys) and participated in 12 sessions in which they chose money ($6.00) or IV cocaine (0, 3, 10 and 30 mg/70 kg). Blood samples were taken to compare d-amphetamine plasma levels across species. In monkeys and humans, d-amphetamine reduced the number of cocaine choices and produced comparable blood levels at equivalent daily doses. d-Amphetamine had similar efficacy, though lower potency, at reducing choice for an equivalent cocaine dose in monkeys relative to humans. These coordinated studies support the utility of these procedures as a translational model for cocaine use disorder.
Public Health Significance
The present studies demonstrated that the use of coordinated procedures in monkeys and humans yielded similar decreases in cocaine choice during d-amphetamine maintenance across species. The concordance of these results, and with clinical trials that found reductions in cocaine use in patients treated with d-amphetamine, supports the utility of these procedures as a translational laboratory model of cocaine use disorder.
Highlights • Homologous procedures were established for cocaine choice in monkeys and humans. • Choice was governed by cocaine dose and magnitude of the alternative non-drug reinforcer. • Cocaine ...choice dose-effect curves in monkeys and humans were highly correlated. • Lisdexamfetamine treatment selectively decreased cocaine choice in monkeys. • This platform will be useful for translational testing of candidate medications.
GHB: a new and novel drug of abuse Nicholson, Katherine L.; Balster, Robert L.
Drug and alcohol dependence,
06/2001, Letnik:
63, Številka:
1
Journal Article
Recenzirano
There has been increasing attention in the United States to problems of abuse of
gamma-hydroxybutyrate (GHB), with some evidence for problems in other parts of the world as well. In vitro and animal ...research show that, while GHB shares some properties with abused central nervous system depressant drugs, it has unique aspects of its pharmacology as well, including actions at a specific neural receptor which probably mediates many of its effects. Abuse potential assessment of GHB using standard animal models has not yielded a picture of a highly abusable substance, but little human testing has yet been done. Very little systematic data exist on tolerance and dependence with GHB, but both have been seen in human users. Quantitative data on the prevalence of GHB abuse is incomplete, but various qualitative measures indicate that a mini-epidemic of abuse began in the late 1980s and continues to the present. GHB is often included with the group of ‘club drugs’, and can be used as an intoxicant. It also has been used as a growth promoter and sleep aid and has been implicated in cases of ‘date rape’, usually in combination with alcohol. Undoubtedly the easy availability of GHB and some of its precursors has contributed to its popularity. Recent changes in the control status of GHB in the US may reduce its availability with as yet unknown consequences for the scope of the public health problem. Drug abuse experts need to familiarize themselves with GHB as possibly representing a new type of drug abuse problem with some unique properties.
Mu opioid receptor (MOR) selective antagonists and partial agonists have clinical utility for the treatment of opioid use disorders (OUDs). However, the development of many has suffered due to their ...poor pharmacokinetic properties and/or rapid metabolism. Our recent efforts to identify MOR modulators have provided 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(isoquinoline-3-carboxamido)morphinan (NAQ), a low-efficacy partial agonist, that showed sub-nanomolar binding affinity to the MOR (K i 0.6 nM) with selectivity over the delta opioid receptor (δ/μ 241) and the kappa opioid receptor (κ/μ 48). Its potent inhibition of the analgesic effect of morphine (AD50 0.46 mg/kg) and precipitation of significantly less withdrawal symptoms even at 100-fold greater dose than naloxone represents a promising molecule for further development as a novel OUD therapeutic agent. Therefore, further in vitro and in vivo characterization of its pharmacokinetics and pharmacodynamics properties was conducted to fully understand its pharmaceutical profile. NAQ showed favorable in vitro ADMET properties and no off-target binding to several classes of GPCRs, enzymes, and ion channels. Following intravenous administration, 1 mg/kg dose of NAQ showed a similar in vivo pharmacokinetic profile to naloxone; however, orally administered 10 mg/kg NAQ demonstrated significantly improved oral bioavailability over both naloxone and naltrexone. Abuse liability assessment of NAQ in rats demonstrated that NAQ functioned as a less potent reinforcer than heroin. Chronic 5 day NAQ pretreatment decreased heroin self-administration in a heroin-vs-food choice procedure similar to the clinically used MOR partial agonist buprenorphine. Taken together, these studies provide evidence supporting NAQ as a promising lead to develop novel OUD therapeutics.
PDF
