Pharmacology Biochemistry and Behavior

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.

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).

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.

Rationale Synthetic opioids pose a significant public health risk due to their rapid synthesis and potentially lethal potency. New compounds are emerging continuously, meaning current testing platforms struggle to keep pace. Objectives Consequently, there is a critical need for simple, rapid, translatable models to provide a scalable screening platform to identify and hazard-assess emerging synthetic opioids, and test potential intervention strategies. Methods Here, we exposed 4 days post-fertilization (dpf) larval zebrafish to a range of concentrations of the prototypical class representative, fentanyl, to investigate behavioral and neural responses. Results Fentanyl caused low concentration hyperactivity, and high concentration hypolocomotion (sedation) which was reversed by the opioid antagonist naloxone. We confirmed predictive validity by replicating the behavioral responses with other class representatives (diacetylmorphine [heroin] and remifentanil). We also confirmed, pharmacologically, that low concentration hyperlocomotion was mediated by dopamine D2 receptors, replicating effects observed in mammals. Further mechanistic investigation using whole-brain in vivo imaging revealed disrupted connectivity in opioid-related circuits, such as the habenulae and dorsal thalamus, alongside novel pathways, including circuits associated with the pineal gland, torus semicircularis and eminentia granularis, potentially highlighting previously uncharacterized sensory and cerebellar neuronal networks. Conclusions These findings support the use of the larval zebrafish as a scalable model for assessment of synthetic opioids to provide novel insights into opioid-induced behaviors and mechanisms of action that may aid strategies in the growing challenge of interventive treatments for synthetic opioid intoxication. Impact StatementLarval zebrafish reveal neurobehavioral pathways affected by synthetic opioids, offering a valuable tool for rapid hazard assessment.

The use of non-drug alternative reinforcers has long been utilized as a component of therapeutic interventions for the management of substance use disorder; however, the conditions under which alternative reinforcers are most effective are not well characterized. This study evaluated the impact of varying the magnitude of an alternative reinforcer on oxycodone self-administration and reinstatement in male and female squirrel monkeys. Subjects (n=4/sex) were trained under concurrent second-order schedules of reinforcement for intravenous oxycodone (0.001-0.1mg/kg/inj) on one lever, and sweetened condensed milk (5, 10, 20, 30% in water) on another. Oxycodone-primed reinstatement was evaluated by administering 0.32mg/kg oxycodone prior to sessions in which saline was available on the drug-paired lever. During oxycodone self-administration sessions, milk availability decreased oxycodone self-administration and preference in a concentration-dependent manner; low milk concentrations were more effective at decreasing oxycodones reinforcing potency in males. During reinstatement tests, milk significantly attenuated oxycodone-primed responding in both males and females; low milk concentrations were more effective at decreasing the priming effects of oxycodone in females. That alternative reinforcers differentially impacted self-administration and reinstatement in a sex-dependent manner suggests that treatment strategies that utilize alternative reinforcers may be more effective in males or females depending on when they are implemented.

Oxycodone is commonly prescribed for moderate to severe pain disorders. While efficacious, long-term use can result in tolerance, physical dependence, and the development of opioid use disorder. Cannabis and its derivatives such as {Delta}9-Tetrahydrocannabinol ({Delta}9-THC) have been reported to enhance oxycodone analgesia in animal models and in humans. However, it remains unclear if {Delta}9-THC may facilitate unwanted aspects of oxycodone intake, such as tolerance, dependence, and reward at analgesic doses. This study sought to evaluate the impact of co-administration of {Delta}9-THC and oxycodone across behavioral measures related to antinociception, dependence, circadian activity, and reward in both male and female mice. Oxycodone and {Delta}9-THC produced dose-dependent antinociceptive effects in the hotplate assay that were similar between sexes. Repeated treatment (twice daily for 5 days) resulted in antinociceptive tolerance. Combination treatment of oxycodone and {Delta}9-THC produced a greater antinociceptive effect than either administered alone, and delayed the development of antinociceptive tolerance. Repeated treatment with oxycodone produced physical dependence and alterations in circadian activity, neither of which were exacerbated by co-treatment with {Delta}9-THC. Combination treatment of oxycodone and {Delta}9-THC produced CPP when co-administered at doses that did not produce preference when administered alone. These data indicate that {Delta}9-THC may facilitate oxycodone-induced antinociception without augmenting certain unwanted features of opioid intake (e.g. dependence, circadian rhythm alterations). However, our findings also indicate that {Delta}9-THC may facilitate rewarding properties of oxycodone at therapeutically relevant doses which warrant consideration when evaluating this combination for its potential therapeutic utility.

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.

Cocaine use disorder (CUD) is a continuing threat to public health that lacks a Food and Drug Administration approved pharmacotherapy. However, there is evidence to suggest that muscarinic receptor activation may lead to reductions in cocaine taking, acquisition, and choice. Therefore, we use a cocaine-vs-food choice procedure in male and female Sprague-Dawley rats to evaluate the effectiveness of the bitopic M1/M4 preferring muscarinic agonist xanomeline and the M1 muscarinic agonist/positive allosteric modulator VU0364572 (VU72). We found that repeated xanomeline did significantly attenuate cocaine choice while VU72 failed to meaningfully alter cocaine choice across subjects. These results suggest that the mechanism by which muscarinic receptors modulate cocaine reinforcement may be mediated either by M4 muscarinic receptors specifically or a combination of both M1 and M4 muscarinic receptors acting in concert. Furthermore, there is evidence that xanomeline may prove a viable pharmacotherapy for treating CUD.

Prescription and illicit opioid use are a public health crisis, with the landscape shifting to fentanyl use. Since fentanyl is 100-fold more potent than morphine, its use is associated with a higher risk of fatal overdose that can be remediated through naloxone (Narcan) administration. However, recent reports indicate that xylazine, an anesthetic, is increasingly detected in accidental fentanyl overdose deaths. Anecdotal reports suggest that xylazine may prolong the fentanyl "high", alter the onset of fentanyl withdrawal, and increase resistance to naloxone-induced reversal of overdose. To date no preclinical studies have evaluated the impacts of xylazine on fentanyl self-administration (SA; 2.5 g/kg/infusion) or withdrawal to our knowledge. We established a rat model of xylazine/fentanyl co-SA and withdrawal and evaluated outcomes as a function of biological sex. When administered alone, chronic xylazine (2.5 mg/kg, IP) induced unique sex-specific withdrawal symptomatology whereby females showed delayed onset of signs and a possible enhancement of sensitivity to the motor-suppressing effects of xylazine. Xylazine reduced fentanyl consumption both male and female rats regardless of whether it was experimenter-administered or added to the intravenous fentanyl product (0.05. 0.10, and 0.5 mg/kg/infusion) when compared to fentanyl SA alone. Interestingly, this effect was dose-dependent when self-administered intravenously. Naloxone (0.1 mg/kg, SC) did not increase somatic signs of fentanyl withdrawal, regardless of the inclusion of xylazine in the fentanyl infusion in either sex; however, somatic signs of withdrawal were higher across timepoints in females after xylazine/fentanyl co-SA regardless of naloxone exposure as compared to females following fentanyl SA alone. Together, these results indicate that xylazine/fentanyl co-SA dose-dependently suppressed fentanyl intake in both sexes, and induced a unique withdrawal syndrome in females which was not altered by acute naloxone treatment.

Cannabis sativa has gained popularity as a "natural substance", leading many to falsely assume that it is not harmful. This assumption has been documented amongst pregnant mothers, many of whom consider Cannabis use during pregnancy as benign. The purpose of this study was to validate a Cannabis smoke exposure model in pregnant rats by determining the plasma levels of cannabinoids and associated metabolites in the dams after exposure to either Cannabis smoke or injected cannabinoids. Maternal and fetal cytokine and chemokine profiles were also assessed after exposure. Pregnant Sprague-Dawley rats were treated daily from gestational day 6 - 20 with either room air, i.p. vehicle, inhaled high-{Delta}9-tetrahydrocannabinol (THC) (17.98% THC, 0.1% cannabidiol [CBD]) smoke, inhaled high-CBD (0.1% THC, 12.83% CBD) smoke, 3 mg/kg i.p. THC, or 10 mg/kg i.p. CBD. Our data reveal that THC and CBD, but not their metabolites, accumulate in maternal plasma after repeated exposures. Injection of THC or CBD was associated with fewer offspring and increased uterine reabsorption events. For cytokines and chemokines, injection of THC or CBD up-regulated several pro-inflammatory cytokines compared to control or high-THC smoke or high-CBD smoke in placental and fetal brain tissue, whereas smoke exposure was generally associated with reduced cytokine and chemokine concentrations in placental and fetal brain tissue compared to controls. These results support existing, but limited, knowledge on how different routes of administration contribute to inconsistent manifestations of cannabinoid-mediated effects on pregnancy. Smoked Cannabis is still the most common means of human consumption, and more preclinical investigation is needed to determine the effects of smoke inhalation on developmental and behavioural trajectories.

Synthetic cannabinoid receptor agonists (SCRAs) are new psychoactive substances associated with acute intoxication and even death. However, the molecular mechanisms through which SCRAs may exert their toxic effects remain unclear - including the potential differential activation of G protein subtypes by CB1, a major target of SCRA. We measured CB1-mediated activation of Gs and Gi/o proteins by SCRAs by examining stimulation (PTX-treated) as well as inhibition (non-PTX treated) of forskolin-induced cAMP accumulation in HEK cells stably expressing CB1. Real-time measurements of stimulation and inhibition of cAMP levels were made using a BRET biosensor. We found that the maximum concentration of SCRAs tested (10 M), increased cAMP levels 12 to 45% above that produced by forskolin alone, while the phytocannabinoid THC did not significantly alter cAMP levels in PTX-treated HEK-CB1 cells. All SCRAs had greater potency to inhibit of forskolin-induced cAMP levels than to stimulate cAMP levels. The rank order of potencies for SCRA stimulation of cAMP (Gs) was PB-22 > 5F-MDMB-PICA > JWH-018 > AB-FUBINACA > XLR-11. By contrast, the potency of SCRAs for inhibition of cAMP (Gi/o) was 5F-MDMB-PICA > AB-FUBINACA > PB-22 > JWH-018 > XLR-11. The different rank order of potency of the SCRAs to stimulate Gs-like signalling compared to Gi/o signalling suggests differences in G protein preference between SCRAs. Understanding the apparent differences among these drugs may contribute to unravelling their complex effects in humans.

The increasing prevalence of cannabis use, including among pregnant women, highlights the critical need for a deeper understanding of prenatal cannabis exposure. This study aimed to develop a standardized cross-species inhalation exposure protocol to administer the principal psychoactive component of cannabis, {Delta}9-tetrahydrocannabinol (THC), to prairie voles (Microtus ochrogaster) and laboratory rats (Rattus norvegicus), and to investigate the distribution of THC in maternal and fetal tissues following prenatal exposure. Using an established e-cigarette system for delivering vaporized THC, we administered THC to pregnant prairie voles and rats. THC concentrations were measured in maternal plasma and fetal brain tissue using LC-MS/MS (Liquid Chromatography coupled with Tandem Mass Spectrometry). In both species, THC levels were compared across groups to evaluate the impact of fetal position on THC uptake. We found that THC readily crossed the placental barrier in both species, resulting in significantly higher concentrations of THC in the fetal brain within the THC-exposed groups compared to the vehicle controls. Interspecies comparison revealed higher THC concentrations in rat fetal brain tissue compared to prairie voles. No significant effects of fetal position on THC levels were found for either species. The findings confirm placental transfer of THC and reveal species-specific patterns of THC distribution. Additional studies were then carried out in voles to compare plasma and brain THC levels in maternal and virgin adult prairie voles. Maternal brain THC concentrations were significantly higher than fetal brain concentrations in prairie voles. Strong positive correlations were observed between plasma and brain THC concentrations in both maternal and virgin adult prairie voles. This study establishes a translational model for investigating prenatal cannabis exposure using an aerosolized administration method in voles compared to established methods in rats. The standardized protocol and results provide a foundation for future research into the developmental consequences of prenatal cannabis exposure and offer crucial insights for informing public health policies and clinical practices in response to the global increase in cannabis use.

BackgroundSynthetic Cannabinoids Receptor Agonists (SCRAs) are the largest group of new psychoactive substances monitored worldwide. 5F-MDMB-PICA is a recent SCRA classified as a potent full agonist at CB1/CB2 receptors able to activate the mesolimbic dopamine (DA) transmission in adolescent but not in adult mice. Here, we have studied its reinforcing effects in adolescent mice and characterized the neurochemical and behavioral effects induced in the same animals in adulthood. MethodsWe utilized an intravenous self-administration (IVSA) protocol in adolescent (PND 40-56) CD-1 male mice. In adulthood (PND 66-78), we conducted several behavioral and neurobiological assessments including: Sucrose Preference Test (SPT); Resident Intruder Test (RIT); Olfactory Reactivity Test (ORT); brain microdialysis to quantify DA levels in the medial Prefrontal Cortex (mPFC); and fiber photometry analysis using the GCaMP calcium sensor to monitor excitatory neural dynamics in the mPFC after exposure to an aversive odorant. ResultsWe found that 5F-MDMB-PICA, administered through IVSA in adolescent mice, produced an inverted U-shaped dose-response curve. The dose of 2.5 g/kg/25ul elicited behavior consistent with drug seeking. Adult mice exposed to 5F-MDMB-PICA during adolescence exhibited significant behavioral and neurochemical changes in adulthood compared to control mice. These behaviors included increased aggression, reduced social interaction, an anhedonic state, and an abolishment of mPFC DA response to an aversive odorant, as measured by in vivo brain microdialysis. Moreover, fiber photometry analysis of excitatory neuronal activity in the mPFC showed diminished calcium activity in response to the same aversive odorant in 5F-MDMB-PICA-exposed mice compared to controls. ConclusionsNotably, this study is the first to demonstrate that adolescent mice can acquire and sustain IVSA of 5F-MDMB-PICA. Furthermore, it highlights the long-term behavioral and neurochemical changes associated with adolescent exposure to 5F-MDMB-PICA, underscoring the potential detrimental effects of its use during this critical developmental period.

IntroductionThe opioid epidemic has seen an increase in drug use among women of reproductive age. It is well established that Opioid Use Disorder (OUD) can have many negative consequences for the health of mothers and their babies, both during pregnancy and after delivery, but our understanding of the impact of fetal opioid exposure on behavior during adolescence and adulthood is less understood. Preclinical studies have unveiled some of the long-term effects of in utero morphine exposure primarily using injections as the route of drug delivery. Our study utilized a model for oral, voluntary morphine self-administration to investigate neonate, adolescent, and adult offsprings behavioral phenotypes and subsequent ethanol misuse liability. MethodsWe first validated a paradigm for maternal oral intake of morphine, where female mice became morphine dependent pre-pregnancy, and continued to voluntarily consume morphine in the continuous two-bottle choice (C2BC) paradigm during pregnancy and up to offspring postnatal day 7 (PND 7). Offspring were cross-fostered to a drug-naive dam at PND 7, to model first and second trimester in utero exposure in humans and to mimic the stress associated with NOWS. Bodyweight and ultrasonic vocalizations were assessed to determine alterations in the neonates. Offspring from control and morphine-exposed dams were then tested during adolescence and adulthood in a battery of behavioral tests to assess baseline behavioral phenotypes. We also computed a global behavioral score (GBS) to integrate offsprings multiple behavioral outcomes into a composite score that could be used to identify potential vulnerable and resilient populations in offspring exposed prenatally to morphine. Offspring that were tested during adolescence were also evaluated during adulthood in the ethanol intermittent 2BC to assess ethanol misuse risk. ResultsUsing an oral maternal morphine C2BC protocol, we demonstrated that morphine dams display signs of dependence, measured by somatic signs during withdrawal, and voluntarily drink morphine throughout gestation. Neonate cross-fostered offspring display changes in spontaneous activity, body weight, and ultrasonic vocalization parameters. During adolescence, offspring display both increased baseline anxiety-like/compulsive-like behavior, while in adulthood they display increased anxiety-like behavior. No changes were found for baseline physical signs, locomotion, and depressive-like behavior during adolescence or adulthood. In addition, a greater percentage of adult male offspring exposed to maternal morphine fell into moderate and high GBS classifications, signaling a more severe behavioral phenotype, compared to male control offspring. These effects were not observed in adult female offspring exposed to morphine in utero. Additionally, male adult offspring exposed to maternal morphine reduced their 2-hour ethanol intake in the intermittent two-bottle choice (I2BC) paradigm, although no changes in 24-hour ethanol intake and preference were found. No changes were observed in female offspring of morphine-exposed dams. ConclusionOverall, maternal morphine exposure leads to sex-specific changes in neonate, adolescent, and adult behavior, including ethanol intake.

Prevailing preclinical models of cocaine use have not resulted in an FDA-approved treatment for cocaine use disorder, potentially due to a focus on cocaine use in isolation, which may not translate well to polysubstance use in clinical populations. Clinically, nicotine has been shown to increase cocaines potency and reinforcing efficacy, but some preclinical studies suggest that non-contingent nicotine exposure is not sufficient to alter cocaine self-administration in rats; therefore, this experiment examined if the addition of nicotine to the cocaine solution would alter self-administration behavior. Male Sprague Dawley rats (N=7) were trained to self-administer cocaine (0.75mg/kg/inf), and tested on a long access, fixed ratio 1 schedule of reinforcement (6 hour sessions, unlimited inf, 5 days), for cocaine alone (0.75mg/kg/inf), followed by cocaine and nicotine (0.75mg/kg/inf cocaine+0.03mg/kg/inf nicotine). Finally, rats responded on a progressive ratio schedule for varied doses of cocaine with and without concurrent nicotine at a consistent dose (1.5, 0.75, 0.375, 0.19mg/kg/inf cocaine{+/-} 0.03mg/kg/inf nicotine). Unexpectedly, under long access conditions, rats self-administering cocaine and nicotine responded less than for cocaine alone, and did not escalate responding. However, under progressive ratio conditions, responding for cocaine and nicotine was greater than responding for cocaine alone across low and moderate cocaine doses, and decreased at high cocaine doses, indicating a leftward shift in the dose response curve. Together, these data highlight the importance of evaluating multiple outcome measures in nicotine + cocaine paradigms, and suggest that concurrent self-administration of cocaine and nicotine results in greater motivated responding than for cocaine alone.

Continued drug-taking despite adverse consequences is hypothesized to be an insidious behavioral hallmark of drug addiction. Although most preclinical research has focused on drug self-administration in the presence of positive punishment, another source of potential adverse consequences is behavioral allocation away from negative reinforcers (i.e., escape/avoid electric shock) and towards drug reinforcers. The goals of the present study were to establish a discrete-trial cocaine-vs-negative reinforcer choice procedure in male and female rats and determine sensitivity of choice behavior to environmental and pharmacological manipulations. Rats could make up to nine discrete choices between an intravenous cocaine infusion (0.32 - 1.8 mg/kg/inf) under a fixed-ratio (FR) 3 schedule and a negative reinforcer (escape or avoidance of electric shock, 0.1 - 0.7 mA) under an FR1 schedule. The negative reinforcer was consistently chosen over all cocaine doses. Lowering shock magnitude decreased negative reinforcer trials, increased omitted trials, and failed to promote behavioral reallocation towards cocaine. Increasing the negative reinforcement response requirement between sessions only increased omitted trials. Introduction of 12-hr extended access cocaine self-administration sessions across two weeks resulted in high daily cocaine intakes but failed to significantly increase cocaine choice. Acute diazepam pretreatment also did not impact choice behavior up to doses that produced behavioral depression. Overall, the lack of behavioral allocation between cocaine infusions and a negative reinforcer suggests these two reinforcers may be economic independents. Additionally, the failure of extended cocaine access to increase cocaine choice highlights the importance of alternative reinforcers and environmental context in preclinical models of drug addiction.

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

Opioid use disorder (OUD) is a public health problem that includes symptoms such as withdrawal syndrome and opioid-induced hyperalgesia (OIH). Currently, drugs to treat side effects of opioids also have undesirable effects, which lead to limitations. This study investigated the effect of a treatment with cannabidiol (CBD) in morphine-induced hyperalgesia and withdrawal signs in morphine-dependent rats. Male and female rats were submitted to morphine-induced physical dependence protocol consisting of a twice daily treatment with morphine (7.89 mg/kg, 1ml/kg, s.c.) for 10 days. Nociception was measured using the hot plate test and morphine-induced thermal hyperalgesia was equally achieved following 7-10 days of morphine administration in male and female rats. Repeated treatment with CBD (30 mg/kg) was sufficient to prevent thermal hyperalgesia in male and female rats. Subsequently, rats received an acute administration of naloxone (2 mg/kg. s.c.), 90 minutes after the morphine treatment on day 11, the number of withdrawal signs was scored. Rats that received treatment exclusively with morphine presented significant withdrawal signs compared to control (Water). Morphine-dependent female rats showed a prevalent stereotyped behavior of rearing, whereas male rats had the sign of teeth chattering as the most preeminent. Treatment with CBD on day 11 partially attenuated the withdrawal signs in morphine-dependent male rats, but not female rats. Altogether, our data provide evidence of an anti-hyperalgesic effect of CBD in rats. Male and female rats treated chronically with morphine exhibited withdrawal signs in different ratios, indicating sex-differences in withdrawal behavior and CBD attenuated withdrawal signs in a sex-dependent manner.

BackgroundCannabis may reduce the nonmedical use of prescription opioids. Causality of polydrug use is difficult to establish from epidemiological data, and thus controlled laboratory models can test whether cannabinoid co-use with opioids can modulate opioid intake. MethodsMale and female rats were trained to intravenously self-administer (IVSA) oxycodone (0.15 mg/kg/infusion) during 6 h sessions. Separate groups were injected with the vehicle or with THC (5 mg/kg, i.p.; N=10) 30 minutes before sessions for the first three weeks. Treatments were swapped in the fourth week. One male group was trained in the intracranial self-stimulation (ICSS) procedure and assessed for brain reward thresholds prior to each IVSA session. ResultsTHC treated animals self-administered less oxycodone during acquisition, with a larger differential expressed in the female group. Tolerance to the THC effect developed over the initial weeks, and increasing the dose of THC (10 mg/kg, i.p.) prolonged the suppressing effect on IVSA. While ICSS thresholds increased with sequential IVSA sessions, no differences between THC- and Vehicle-treated groups were observed. Oxycodone IVSA was increased following the first 60 h abstinence interval in THC-treated, but not vehicle-treated, rats. Acute injection of THC, when all animals had been THC abstinent for several weeks, increased breakpoints in a Progressive Ratio procedure. ConclusionThese data support the interpretation that THC enhances the reinforcing efficacy of a given dose of oxycodone and may therefore increase the addiction liability.

Opioid Use Disorder (OUD) is a chronic and relapsing psychiatric condition which is currently the leading cause of accidental death in the US. Symptoms of acute opioid withdrawal resemble a flu-like illness which is accompanied by a dysphoric state. Psychological comorbidities such as anxiety, depression, and disordered sleep can persist for months or years, well into the abstinence period. These symptoms are thought to drive further opioid intake in order to alleviate this unpleasant internal state. Many differences in OUD have been documented between male and female patients, with females at higher risk for relapse and overdose. This study sets out to characterize sex differences in symptoms and behavioral adaptations in mice during early withdrawal. Using our moderate dose, three-day precipitated withdrawal paradigm, we discovered significant effects of sex, time, and drug treatment on early withdrawal behaviors, locomotor activity, and gut motility in C57BL/6J mice. Here I will discuss previous methods of condensing behavioral phenotypes into one global withdrawal score, and propose a new methodology. This method increases the ability to detect nuanced effects and allows for more accurate translation across strain, sex, paradigm, and experimental context. Classification of opioid withdrawal-induced behavioral adaptations will allow for improved behavioral analysis of pharmacological manipulations, and investigations of brain circuitry involved in opioid withdrawal, as well as future screening of compounds with potential therapeutic benefit for the treatment of OUD.