Pharmacology Biochemistry and Behavior

Opioids are effective medications, but they have several key limitations including the development of tolerance, establishment of dependence, diversion for non-medical use and the development of addiction. Therefore, any drugs which act in an additive or synergistic fashion with opioids to address medical applications have the potential to reduce opioid-related harms. This study was conducted to determine if heroin and {Delta}9-tetrahydrocannabinol (THC) interact in an additive or independent manner to alter nociception, body temperature and spontaneous locomotor activity when inhaled or injected. Groups of male and female rats implanted with radiotelemetry transmitters were exposed to vapor for assessment of effects on temperature and activity. Heroin (50 mg/mL in the propylene glycol; PG) inhalation increased temperature and activity whereas THC (50 mg/mL) inhalation decreased temperature and activity. Effects of combined inhalation were in opposition, and additional experiments found the same outcome for the injection of heroin (0.5 mg/kg, s.c.) and THC (10 mg/kg, i.p.) alone and in combination. In contrast, the co-administration of Heroin and THC by either inhalation or injection produced additive effects on thermal nociception assessed with a warm water tail-withdrawal assay in male and female Sprague-Dawley and Wistar rats. The conclusion of this study is that additive effects of THC with heroin on a medical endpoint such as analgesia may not generalize to other behavioral or physiological effects, which may be a positive outcome for unwanted side effects.

Adolescent drug exposure has been associated with more severe mental health outcomes related to substance abuse and anxiety disorders. The aim of the present study was to contrast the long-term effects of repeated heroin vapor inhalation during adolescence with similar heroin exposure in adulthood. Groups of female Wistar rats underwent twice daily 30-minute sessions of heroin or propylene glycol (control) vapor inhalation from postnatal days (PND) 36-45 or PND 85-94, respectively. Nociception was assessed after vapor inhalation sessions and forty days later, for the Adolescent-Exposed and Adult-Exposed groups. Anxiety-like behavior was assessed with an elevated plus-maze (EPM) and spatial learning was assessed with a Barnes maze. Acute effects of naloxone (0.3 mg/kg, i.p.) and heroin (0.5 and 1.0 mg/kg, s.c.) on thermal nociception were determined on PND 140/189 and PND 149/198, respectively. Repeated heroin vapor inhalation produced anti-nociceptive tolerance across sessions in both adolescent and adult rats, with the adolescents exhibiting more complete tolerance. Heroin vapor inhalation produced anxiolytic effects, regardless of age of exposure. There were no effects of heroin on spatial learning. Naloxone produced acute hyperalgesia in all but the Adolescent-Exposed heroin group, and heroin anti-nociception was blunted in both heroin-exposed groups at the highest heroin dose. Repeated heroin vapor inhalation can produce lasting effects on nociception and anxiety-like behavior that persist for months after the exposure. Importantly, these findings suggest that adolescent exposure to heroin vapor produces specific effects on nociception that are not observed when exposure occurs in adulthood.

BackgroundCannabis edibles are an increasingly popular form of cannabis consumption. Oral consumption of cannabis has distinct physiological and behavioural effects than injection or inhalation. An animal model is needed to understand the pharmacokinetics and physiological effects of oral cannabis consumption in rodents as a model for human cannabis edible use. MethodsAdult male and female C57BL/6 mice received a single dose of commercially available cannabis oil (5 mg/kg THC) by oral gavage. At 0.5-, 1-, 2-, 3-, and 6-hours post-exposure, plasma, hippocampus, and adipose tissue was collected for THC, 11-OH-THC, and THC-COOH measures. ResultsWe report delayed time to peak THC and 11-OH-THC concentrations in plasma, brain and adipose tissue, which is consistent with human pharmacokinetics studies. We also found sex differences in the cannabis tetrad: (1) female mice had a delayed hypothermic effect 6 hours post-consumption, which was not present in males; (2) females had stronger catalepsy than males; (3) males were less mobile following cannabis exposure, whereas female mice showed no difference in locomotion but an anxiogenic effect at 3h post exposure; and (4) male mice displayed a longer lasting antinociceptive effect of oral cannabis. ConclusionsOral cannabis consumption is a translationally relevant form of administration that produces similar physiological effects as injection or vaping administration and thus should be considered as a viable approach for examining the physiological effects of cannabis moving forward. Furthermore, given the strong sex differences in metabolism of oral cannabis, these factors should be carefully considered when designing animal studies on the effects of cannabis. Significance statementOral delivery of cannabis oil in mice is a translational model that increases plasma, hippocampal, and adipose cannabinoids. Furthermore, oral cannabis and produces lasting psychoactive effects including sex dependent effects on hypothermia, cataplexy, locomotor activity and nociception.

The -pyrrolidino-phenone cathinone stimulants first came to widespread attention because of bizarre behavior consequent to the use of -pyrrolidinopentiophenone (-PVP, "flakka") reported in the popular press. As with other designer drugs, diversification of cathiones has been driven by desireable subjective effects, but also by attempts to stay ahead of legal controls of specific molecules. The -pyrrolidinohexiophenone (-PHP) and -pyrrolidinopropiophenone (-PPP) compounds have been relatively under-investigated relative to -PVP and provide a key opportunity to also investigate structure-activity relationships, i.e., how the extension of the alpha carbon chain may affect potency or efficacy. Male and female rats were used to contrast the effects of -PHP and -PPP with those of -PVP in altering wheel activity and effects on spontaneous locomotion and body temperature were assessed in female rats. The -PHP and -PVP compounds (5, 10 mg/kg, i.p.) suppressed wheel activity in female and male rats, whereas -PPP was only effective in female rats. Inhalation of -PHP or -PVP by female rats suppressed wheel activity for an abbreviated duration, compared with the injection route. Spontaneous activity was increased in a dose-dependent manner by all three compounds in female rats, and a small decrements in body temperature were observed after the highest dose of all three compounds. These data show that all three of the -pyrrolidino-phenone cathinones exhibit significant stimulant-like activity in both male and female rats. Differences were minor and were mostly in potency and the duration of activity. Abuse liability is therefore likely to be equivalent for all three pyrrolidino-phenones.

Epidemiological evidence suggests that the legalization of cannabis may reduce opioid-related harms. Preclinical evidence of neuropharmacological interactions of endogenous cannabinoid and opioid systems prompts further investigation of cannabinoids as potential therapeutics for the non-medical use of opioids. In these studies female rats, previously trained to self-administer oxycodone (0.15 mg/kg/infusion) intravenously in 6 h sessions, were allowed to self-administer oxycodone after exposure to cannabidiol (CBD) and {Delta}9-tetrahydrocannabinol (THC) by vapor inhalation and THC by injection (5.0-20 mg/kg, i.p.). Self-administration was characterized under Progressive Ratio (PR) and Fixed Ratio (FR) 1 schedules of reinforcement in 3 h sessions. THC decreased IVSA of oxycodone in a FR procedure but increased reward seeking in a PR procedure. CBD decreased the IVSA of oxycodone in the FR but not the PR procedure. The results are consistent with an anti-reward effect of CBD but suggest THC acts to increase the reinforcing efficacy of oxycodone in this procedure.

The current research on psychedelic compounds such as lysergic amide diethylamide (LSD) is leaning heavily on the notion that psychedelics are not addictive. While much of the literature supports this argument, some of the common use patterns and the descriptions of the subjective effects of these compounds in humans, together with rather lacking and mixed data from non-human animal studies leave room for questions of potentially rewarding or reinforcing stimulus effects. Initiated by a surprising finding in a control study, we investigated these potential rewarding effects of LSD and a selective 5-HT2A agonist 25CN-NBOH using both unbiased and biased designs of conditioned place preference as well as ex vivo patch-clamp electrophysiology measurements of glutamatergic synaptic plasticity on midbrain ventral tegmental area (VTA) dopamine neurons in C57Bl6/J mice. Our results showed no reliable formation of place preference with either compound, agreeing with previous claims of psychedelics having at most weak reinforcing effects. However, we did observe single doses of the drugs, especially LSD, inducing synaptic plasticity in the medially located VTA dopamine neurons, implicating a role for the midbrain dopamine system in the effects of psychedelic drugs. Graphical abstractTreatment with mixed serotonin receptor agonist, psychedelics lysergic acid diethylamide (LSD) or selective serotonin 2A receptor agonist 25CN-NBOH did not cause reliable induction of conditioned place preference in C57Bl/6J mice. However, we did observe single doses of the drugs, especially LSD, inducing synaptic plasticity in the medially located VTA dopamine neurons. These findings challenge some of the previous rodent data but are in general in line with the claims of psychedelics having at most weak reinforcing effects. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=143 SRC="FIGDIR/small/628157v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@57a87org.highwire.dtl.DTLVardef@1af3827org.highwire.dtl.DTLVardef@8fb256org.highwire.dtl.DTLVardef@5504b_HPS_FORMAT_FIGEXP M_FIG C_FIG

Electronic cigarette liquids (e-liquids) often contain flavors and solvents that may influence nicotine addiction. In this study, we characterized the dose-response relationship of commercial unflavored nicotine e-liquids and investigated the impact of vanilla-flavored e-liquids on nicotine vapor self-administration (VSA) and withdrawal in rats. Male adolescent Sprague Dawley rats self-administered aerosols generated from commercial e-liquids containing 0, 3, 6, or 12 mg/ml nicotine in a propylene glycol (PG) and glycerol (G) vehicle. The vehicle (0 mg/ml nicotine) supported robust VSA, indicating the reinforcing effects of PG/G vapor. 3 mg/ml nicotine did not support VSA, while both 6 and 12 mg/ml nicotine concentrations produced significant reinforcement, with 6 mg/ml yielding the most stable responding. The 6 mg/ml concentration was selected for subsequent comparisons with vanilla-flavored e-liquids. Vanilla flavor (0 mg/ml nicotine) led to maintained VSA behavior, confirming its reinforcing effects. However, the combination of vanilla and nicotine (6 mg/ml) did not alter nicotine intake or withdrawal severity, as assessed by mecamylamine-precipitated somatic signs. Blood nicotine and cotinine levels were similar between nicotine and vanilla + nicotine conditions, indicating that vanilla flavor did not affect systemic nicotine metabolism. Additionally, the PG/G vehicle induced significant somatic signs, suggesting that vapor exposure itself, independent of nicotine, contributes to these physiological responses. These findings provide critical insights into the reinforcing and physiological effects of both nicotine and non-nicotine constituents in e-cigarette aerosols, underscoring the need for future studies and regulatory strategies that consider the abuse liability of flavors and solvents, such as PG/G, particularly among adolescents. Significance StatementFlavored electronic nicotine delivery systems raise concern for promoting nicotine use in youth. Using a rat vapor self-administration model, we show nicotine produces concentration-dependent reinforcement, while vanilla flavor is reinforcing but does not enhance nicotine intake or withdrawal.

Chronic neuropathic pain affects 6.9-10% of the U.S. population. While mu opioid receptor (MOR) agonists are not first-line treatments for chronic pain, previous data suggests that [~]70% of chronic neuropathic pain patients receive MOR agonist treatment. Previous studies demonstrated decreased MOR expression and activity in pain states compared with non-injured or sham controls; however, we know little about how chronic pain states may alter the antinociceptive- and antihyperalgesic-like effects of MOR agonists in vivo. Therefore, the goal of this study was to determine if there were significant differences in MOR agonist-induced antinociceptive- or antihyperalgesic-like effects between SNI and sham groups. MOR agonist-induced antinociceptive- and antihyperalgesic-like effects were evaluated in SNI and sham groups repeatedly over 6 months. MOR agonists induced dose-dependent antinociceptive- and antihyperalgesic-like effects in male and female rats in the expected rank order of potency (fentanyl>morphine[≥]nalbuphine). Over time, there were small rightward shifts in fentanyl- and morphine-induced effects; however, these rightward shifts were observed in sham and SNI groups, suggesting this occurred independent of pain state. Interestingly, in sham and SNI groups, nalbuphine-induced effects were more potent 6 months post-operatively than 3 months, suggesting the potency of nalbuphine changed over time, independent of pain state. Other, non-MOR agonist analgesics were evaluated. Collectively, these data indicate that SNI failed to alter MOR agonist-induced antinociceptive- and antihyperalgesic-like effects. Future studies should evaluate if the SNI-independent increase in sensitivity to nalbuphine is related to the partial KOR agonist activity and if SNI-induced hypersensitivity alters tolerance following repeated administration of MOR agonists. Significance StatementMany chronic pain patients are treated with opioids, but we understand relatively little about how chronic pain may alter the in vivo effects of opioid analgesics. This study demonstrates that, compared to sham groups, SNI-induced hypersensitivity did not alter the potency or efficacy of opioid analgesics, opioid-induced tolerance to analgesic-like effects, or opioid-induced rate suppressant effects in either male or female rats.

Opioid addiction and misuse are a serious national crisis that affects public health, as well as social and economic welfare. Mortality due to opioid misuse is further exasperated by the combination of opioids with non-opioid respiratory depressants such as xylazine that are resistant to mu opioid receptor antagonists such as naloxone. This study tested the hypothesis that oxytocin can mitigate the severe opioid induced respiratory depression (OIRD) and mortality induced by high doses of fentanyl or the combination of fentanyl with xylazine. Our results show OXT can improve survival and respiratory function in both male and female rats with opioid induced respiratory depression caused by fentanyl, as well as a combination of fentanyl and xylazine. The improvement in respiratory function by OXT post fentanyl-xylazine was significantly greater than the recovery using only naloxone. Chemogenetic activation of OXT receptor positive neurons in the ventral respiratory group (VRG) provided similar benefits to that of OXT administration in reversing OIRD. These results indicate OXT is a promising therapeutic target for reversing OIRD and the respiratory depression that occurs with the combination of opioids and xylazine, a situation where naloxone is only partially effective. Additional translational benefits of OXT include it can be repurposed as it is already a FDA approved drug for other uses, has a high safety profile, and is unlikely to induce the withdrawal or reversal of analgesia that occurs with naloxone. Key PointsO_LIOxytocin (OXT) improves survival and respiratory function in both male and female rats with opioid induced respiratory depression (OIRD) caused by fentanyl C_LIO_LIOXT also reverses OIRD induced by the combination of fentanyl and xylazine C_LIO_LIThe improvement in respiratory function by OXT post fentanyl-xylazine was significantly greater than the recovery using only naloxone C_LIO_LIChemogenetic activation of OXT receptor positive neurons in the ventral respiratory group (VRG) provided similar benefits to that of OXT administration in reversing OIRD C_LIO_LIThese results indicate OXT is a promising therapeutic target for reversing OIRD and the respiratory depression that occurs with the combination of opioids and xylazine C_LI

RationalePreclinical models of electronic nicotine delivery system (ENDS; "e-cigarette") use have been rare, so there is an urgent need to develop experimental approaches to evaluate their effects. ObjectiveTo contrast the impact of inhaled nicotine across sex. MethodsMale and female Wistar rats were exposed to vapor from a propylene glycol vehicle (PG), nicotine (NIC; 1-30 mg/mL in PG), or were injected with NIC (0.1-0.8 mg/kg, s.c.), and then assessed for changes in temperature and activity. The antagonist mecamylamine (2 mg/kg) was administered prior to NIC to verify pharmacological specificity. Plasma levels of nicotine and cotinine were determined after inhalation and injection. ResultsActivity increased in females for [~]60 minutes after nicotine inhalation, and this was blocked by mecamylamine. A similar magnitude of hyperlocomotion was observed after s.c. administration. Body temperature was reduced after nicotine inhalation by female rats but mecamylamine increased this hypothermia. Increased locomotor activity was observed in male rats if inhalation was extended to 40 minutes or when multiple inhalation epochs were used per session. The temperature of male rats was not altered by nicotine. Plasma nicotine concentrations were slightly lower in male rats than in female rats after 30-minute nicotine vapor inhalation and slightly higher after nicotine injection (1.0 mg/kg, s.c.). ConclusionsNicotine inhalation increases locomotor activity in male and female rats to a similar or greater extent than by subcutaneous injection. Sex differences were observed, which may be related to lower nicotine plasma levels, lower baseline activity and/or a higher vehicle response in males.

Background and PurposeThe 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 ApproachThis 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 ResultsMethylone, 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 ImplicationsThese 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. What is already known"Bath Salts" preparations are associated with a sympathomimetic toxidrome in human users. What this study addsCharacterization of both pharmacokinetic and pharmacodynamic interactions between common "Bath Salts" constituents with regard to cardiovascular and locomotor effects. Clinical SignificanceThe vast majority of drug overdose deaths involve more than one substance. Though these studies focused on combinations of stimulant drugs, they provide direct evidence that the toxidrome resulting from multi-drug overdoses can be significantly different than would be expected for a single drug.

There is significant overlap between chronic pain and opioid use disorder (OUD) patient populations such that approximately 50-65% of chronic pain patients have OUD. However, we understand relatively little about how chronic, long-lasting pain states alter ongoing self-administration of opioid analgesics. Thus, the goal of this study was to determine if chronic neuropathic pain altered the ongoing self-administration of fentanyl, or a non-opioid drug of abuse, cocaine. Animals were trained to self-administer fentanyl or cocaine in a multi-dose self-administration procedure composed of five 25-min components, exposing animals to multiple doses of drug per day. Operant behavior was established prior to induction of chronic pain via the spared nerve injury (SNI). Animals were allowed 72 hours of post-operative recovery and resumed self-administration on post-operative day 4. All animals dose-dependently self-administered fentanyl prior to surgery. On post-operative day 4, both sham and SNI groups showed a significant decrease in fentanyl self-administration. By post-operative day 9, fentanyl intake was no longer significantly different from pre-surgical intake. Over the course of 4 weeks of self-administration, there was an increase in intake of specifically the 10 ug/kg/inf dose of fentanyl. Cocaine self-administration was not altered at any point following either surgery. Collectively, these results suggest that SNI-induced hypersensitivity failed to alter the reinforcing effects of fentanyl, or non-opioid drug of abuse, cocaine. Future studies should evaluate the abuse potential of lower efficacy MOR agonists such as nalbuphine or buprenorphine, as small changes were observed in fentanyl-maintained behavior over time in both SNI and sham groups. Significance statementMOR agonists are excellent analgesics; however, they are not first-line treatments for chronic pain, in part due to abuse potential. This study demonstrates that small, significant rightward shifts in the fentanyl dose response curve were observed following induction of both sham and spared nerve injury (SNI) (chronic neuropathic pain-like) states, suggesting these changes were observed independent of pain state. These data indicate that SNI-induced neuropathic pain failed to alter the ongoing self-administration of highly potent MOR agonist, fentanyl.

Background{beta}-Nicotyrine ({beta}-Nic) is a unique minor alkaloid constituent in electronic nicotine delivery systems (ENDS) that is derived from nicotine (Nic) degradation and can reach 25% of Nic concentrations in ENDS aerosol. {beta}-Nic slows Nic metabolism and prolongs systemic Nic exposure, which may alter the discriminability of Nic. The present study sought to examine {beta}-Nic has interoceptive effects itself, and if it alters the subjective effects ENDS products within a drug-discrimination paradigm. MethodsThe pharmacodynamics of {beta}-Nic were examined in vitro, and a nicotine discrimination paradigm was used to determine if {beta}-Nic (0 - 5.0 mg/kg) shares discriminative stimulus properties with Nic (0.2 mg/kg) in male (n = 13) and female (n = 14) rats after 10- & 60-min {beta}-Nic pretreatment delays. A second group of rats was trained to discriminate {beta}-Nic and Nornicotine (Nornic) from saline to determine if {beta}-Nic alone has interoceptive properties and whether they are similar to Nornic. Results{beta}-Nic had similar binding affinity and efficacy at the 4{beta}2 nicotinic receptor subtype as Nornic, [~]50% of Nic efficacy. However, {beta}-Nic only weakly substituted for Nic during substitution testing in female rats, but not males, whereas Nornic fully substituted for Nic. Combination testing at the 10 and 60-min pretreatment intervals showed that {beta}-Nic dose-dependently increased the duration of nicotines discriminative stimulus effects, especially at the 60-min delay. Drug naive rats could reliably discriminate Nornic, but not {beta}-Nic, from Sal. Conclusion{beta}-Nic increased and prolonged the interoceptive stimulus properties of Nic, suggesting it may alter to the abuse liability of ENDS through its ability to slow Nic metabolism.

Recent data suggest that 3,4-methylenedioxypyrovalerone (MDPV) has neurotoxic effects; however, the cognitive and neurochemical consequences of MDPV self-administration remain largely unexplored. Furthermore, despite the fact that drug preparations that contain MDPV often also contain caffeine, little is known regarding the toxic effects produced by the co-use of these two stimulants. The current study investigated the degree to which self-administered MDPV, or a mixture of MDPV+caffeine can produce deficits in recognition memory and alter neurochemistry relative to prototypical stimulants. Male Sprague-Dawley rats were provided 90-min or 12-h access to MDPV, MDPV+caffeine, methamphetamine, cocaine, or saline for 6 weeks. Novel object recognition (NOR) memory was evaluated prior to any drug self-administration history and 3 weeks after the final self-administration session. Rats that had 12-h access to methamphetamine and those that had 90-min or 12-h access to MDPV+caffeine exhibited significant deficits in NOR, whereas no significant deficits were observed in rats that self-administered cocaine or MDPV. Striatal mono-amine levels were not systematically affected. These data demonstrate synergism between MDPV and caffeine with regard to producing recognition memory deficits and lethality, highlighting the importance of recapitulating the manner in which drugs are used (e.g., in mixtures containing multiple stimulants, binge-like patterns of intake).

Pleasant subjective effects of drugs (e.g., euphoria) have been demonstrated to contribute to their abuse potential. In humans, there is some evidence that acute pain states may decrease the positive subjective effects of opioids; however, no studies have directly tested the impact of a long-lasting pain state. Therefore, the goal of this study was to directly evaluate the discriminative stimulus of mu opioid receptor (MOR) agonist, fentanyl, or the non-opioid drug of abuse, cocaine, in the presence or absence of spared nerve injury (SNI) induced chronic neuropathic pain. Prior to surgery, MOR agonists (fentanyl, morphine, nalbuphine) dose-dependently increased % fentanyl-like responding, as expected; surprisingly, after surgery, we saw small, significant rightward shifts in the fentanyl and morphine dose response curves in both sham and SNI groups suggesting that the observed shifts were not due to chronic pain. In both sham and SNI groups, there was an increase in the generalization of nalbuphine to the fentanyl-discriminative stimulus. There was no change in the discriminative stimulus of cocaine (or amphetamine substitutions) over 4 months of SNI-induced chronic neuropathic pain or sham states, suggesting that the SNI model failed to alter the discriminative stimuli of fentanyl and cocaine. Following induction of chronic neuropathic pain, there was an observed increase in quinpirole-induced generalization to the cocaine discriminative stimulus. In the future, studies should directly examine the abuse potential of low efficacy MOR agonists and dopaminergic agonists in the presence and absence of chronic pain states. Significance StatementSubjective or interoceptive effects of drugs of abuse are known to contribute to the abuse potential. This study demonstrated that long-lasting neuropathic pain failed to alter the discriminative stimulus of mu opioid receptor agonists or cocaine; however, we observed an increase in quinpirole-induced generalization to the cocaine discriminative stimulus, suggesting the abuse potential of direct dopaminergic agonists should be further evaluated in the presence or absence of pain states.

The gold standard pharmacological treatment for opioid use disorder (OUD) consists of maintenance therapy with long-acting opioid agonists such as buprenorphine and methadone. Despite these compounds having demonstrated substantial efficacy, a significant number of patients do not show optimal therapeutic responses. Moreover, the abuse liability of these medications remains a major concern. Cebranopadol, is a new, long-acting pan-opioid agonist that also activates the nociception/orphanin FQ NOP receptor. Here we used rats to explore the therapeutic potential of this agent in OUD. First, in operant intravenous self-administration experiments we compared the potential abuse liability of cebranopadol with the prototypical opioid heroin. Under a fixed ratio 1 (FR1) contingency, rats maintained responding for heroin (1, 7, 20, 60 g/inf) to a larger extent than cebranopadol (0.03, 0.1, 0.3, 1.0, 6.0 g/inf). When the contingency was switched to a progressive ratio (PR) reinforcement schedule, heroin maintained responding at high levels at all except the lowest dose. Conversely, in the cebranopadol groups responding decreased drastically and the break point (BP) did not differ from saline controls. Next, we demonstrated that oral administration of cebranopadol (0, 25, 50 g/kg) significantly attenuated drug self-administration independent of heroin dose (1, 7, 20, 60 g/inf). Cebranopadol also reduced the break point for heroin (20 g/inf). Furthermore, in a heroin self-administration training extinction/reinstatement paradigm, pretreatment with cebranopadol significantly attenuated yohimbine stress-induced reinstatement of drug seeking. Together, these data indicate that cebranopadol has limited abuse liability compared to heroin and is highly efficacious in attenuating opioid self-administration and stress-induced reinstatement, suggesting clinical potential of this compound for OUD treatment.

Dopamine transmission is implicated in aberrant behaviors associated with substance use disorders. Previous research revealed a causal link between excessive drug consumption and the loss of dopamine signaling to stimuli associated with psychostimulant use. The emerging change in dopamine signaling is specific to stimuli associated with the substance rather than the pharmacological properties of the drug itself. Because the change in dopamine signaling was specific to the associated stimuli and not the pharmacological properties of the substance, we examined if treatment with the dopamine precursor, L-DOPA, alters alcohol and opioid self-administration. Therefore, we trained rats to orally self-administer ethanol or the synthetic opioid fentanyl and found that treating animals with L-DOPA significantly reduced consumption of both alcohol and fentanyl. These data suggest dopamine signaling has a vital role in mediating the amount of drug animals will voluntarily take, across multiple classes of drugs. Importantly, these data are preclinical demonstrations of L-DOPA being utilized as a harm reducing treatment in substance use disorders.

Methylglyoxal (MG) is an endogenously produced non-enzymatic side product of glycolysis that acts as a partial agonist at GABAA receptors. MG that is metabolized by the enzyme glyoxalase-1 (GLO1). Inhibition of GLO1 increases methylglyoxal levels, and has been shown to modulate various behaviors, including decreasing seeking of cocaine-paired cues and ethanol consumption. The goal of these studies was to determine if GLO1 inhibition could alter cocaine-or oxycodone-induced locomotor activation and/or conditioned place preference (CPP) to cocaine or oxycodone. We used both pharmacological and genetic manipulations of GLO1 to address this question. Administration of the GLO1 inhibitor s-bromobenzylglutathione cyclopentyl diester (pBBG) did not alter the locomotor response to cocaine or oxycodone. Additionally, pBBG had no significant effect on place preference for cocaine or oxycodone. Genetic knockdown of Glo1, which is conceptually similar to pharmacological inhibition, did not have any significant effects on cocaine place preference, nor did Glo1 overexpression affect locomotor response to cocaine. In summary, our results show that neither pharmacological nor genetic manipulations of GLO1 influence locomotor response or CPP to cocaine or oxycodone.

The opioid epidemic has led to a devastating loss of life nationwide. Of those dependent on opioids, many individuals desire to quit or reduce use, but their efforts are often unsuccessful given the powerful reinforcing properties associated with opioid drugs, especially fentanyl given its high potency and speed of onset. Here, we developed a novel theraputic based on a newly developed artificial intelligence (AI)-based platform, which was rationally designed to identify markers of dysregulation from human drug user postmortem brain tissue. The GATC-021 compound was synthesized and validated with in vitro screening for target specificity. Thereafter, GATC-021 was examined for its effectiveness in modulating opioid dependence with an animal model of addiction. We found that GATC-021 substantially reduced fentanyl intake in both male and female rats, as assessed with intravenous self-administration. However, given drug soluability challenges, additional studies are needed to better develop drug formulations to permit translation into clinical populations more effectively. Taken together, these findings validate our AI-based platform for novel therapeutic development with a polypharmacy approach and further support the effectiveness of such target modulation as a promising therapeutic approach for those suffering from opioid use disorder.

Nicotine and cannabis are two of the most commonly consumed licit and illicit drugs during pregnancy, often consumed together via e-cigarettes. Vaping is assumed to be a safer alternative than traditional routes of consumption, yet the potential consequences of prenatal e-cigarette exposure are largely unknown, particularly when these two drugs are co-consumed. In a novel co-exposure model, pregnant Sprague-Dawley rats received nicotine (36 mg/mL), THC (100 mg/mL), the combination, or the vehicle via e-cigarettes daily from gestational days 5-20, mimicking the first and second human trimesters. Maternal blood samples were collected throughout pregnancy to measure drug and metabolite levels, and core body temperatures before and after exposure were also measured. Pregnant dams exposed to combined nicotine and THC had lower plasma nicotine and cotinine levels than those exposed to nicotine alone; similarly, the combined exposure group also had lower plasma THC and THC metabolite (THC-OH and THC-COOH) levels than those exposed to THC alone. Prenatal nicotine exposure gradually decreased basal core body temperatures each day, with chronic exposure, whereas exposure to THC alone decreased temperatures during the individual sessions. Despite these physiological effects, no changes were observed in food or water intake, weight gain, or basic litter outcomes. These data suggest that combined exposure to nicotine and THC elicits both separate and interactive physiological effects of nicotine and THC on pregnant dams. These data and use of this model can help improve education for pregnant mothers about prenatal e-cigarette use and has important implications for public policy. HIGHLIGHTSO_LIRepeated prenatal nicotine exposure via e-cigarettes gradually decreased temperatures C_LIO_LIPrenatal THC exposure via e-cigarettes decreased temperatures during intoxication C_LIO_LICombined prenatal exposure via e-cigarettes altered plasma drug and metabolite levels C_LIO_LIThis co-exposure model elicits separate and interactive effects of nicotine and THC C_LI