Cannabinoid tetrad effects of oral Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) in male and female rats: sex, dose-effects and time course evaluations

A critical assessment of the abuse, dependence and associated safety risks of naturally occurring and synthetic cannabinoids

Various countries and US States have legalized cannabis, and the use of the psychoactive1 and non-psychoactive cannabinoids is steadily increasing. In this review, we have collated evidence from published non-clinical and clinical sources to evaluate the abuse, dependence and associated safety risks of the individual cannabinoids present in cannabis. As context, we also evaluated various synthetic cannabinoids. The evidence shows that delta-9 tetrahydrocannabinol (Δ9-THC) and other psychoactive cannabinoids in cannabis have moderate reinforcing effects. Although they rapidly induce pharmacological tolerance, the withdrawal syndrome produced by the psychoactive cannabinoids in cannabis is of moderate severity and lasts from 2 to 6 days. The evidence overwhelmingly shows that non-psychoactive cannabinoids do not produce intoxicating, cognitive or rewarding properties in humans. There has been much speculation whether cannabidiol (CBD) influences the psychoactive and potentially harmful effects of Δ9-THC. Although most non-clinical and clinical investigations have shown that CBD does not attenuate the CNS effects of Δ9-THC or synthetic psychoactive cannabinoids, there is sufficient uncertainty to warrant further research. Based on the analysis, our assessment is cannabis has moderate levels of abuse and dependence risk. While the risks and harms are substantially lower than those posed by many illegal and legal substances of abuse, including tobacco and alcohol, they are far from negligible. In contrast, potent synthetic cannabinoid (CB1/CB2) receptor agonists are more reinforcing and highly intoxicating and pose a substantial risk for abuse and harm. 1 "Psychoactive" is defined as a substance that when taken or administered affects mental processes, e.g., perception, consciousness, cognition or mood and emotions.

Effectiveness of cannabidiol (CBD) on histopathological changes and gene expression in hepatocellular carcinoma (HCC) model in male rats: the role of Hedgehog (Hh) signaling pathway

The third most prevalent malignancy to cause mortality is hepatocellular carcinoma (HCC). The Hedgehog (Hh) signaling pathway is activated by binding to the transmembrane receptor Patched-1 (PTCH-1), which depresses the transmembrane G protein-coupled receptor Smoothened (SMO). This study was performed to examine the preventative and therapeutic effects of cannabidiol in adult rats exposed to diethyl nitrosamine (DENA)-induced HCC.A total of 50 male rats were divided into five groups of 10 rats each. Group I was the control group. Group II received intraperitoneal (IP) injections of DENA for 14 weeks. Group III included rats that received cannabidiol (CBD) orally (3-30 mg/kg) for 2 weeks and DENA injections for 14 weeks. Group IV rats received oral CBD for 2 weeks before 14 weeks of DENA injections. Group V included rats that received CBD orally for 2 weeks after their last injection of DENA. Measurements were made for alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma glutamyl transferase (GGT), superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and alpha fetoprotein (AFP). Following total RNA extraction, Smo, Hhip, Ptch-1, and Gli-1 expressions were measured using quantitative real-time polymerase chain reaction (qRT-PCR). A histopathological analysis of liver tissues was performed.The liver enzymes, oxidant-antioxidant state, morphological, and molecular parameters of the adult male rat model of DENA-induced HCC showed a beneficial improvement after CBD administration. In conclusion, by focusing on the Hh signaling system, administration of CBD showed a beneficial improvement in the liver enzymes, oxidant-antioxidant status, morphological, and molecular parameters in the DENA-induced HCC in adult male rats.

Cannabinoid treatments in epilepsy and seizure disorders

Cannabis has been used to treat convulsions and other disorders since ancient times. In the last few decades, preclinical animal studies and clinical investigations have established the role of cannabidiol (CBD) in treating epilepsy and seizures and support potential therapeutic benefits for cannabinoids in other neurological and psychiatric disorders. Here, we comprehensively review the role of cannabinoids in epilepsy. We briefly review the diverse physiological processes mediating the central nervous system response to cannabinoids, including Δ9-tetrahydrocannabinol (Δ9-THC), cannabidiol, and terpenes. Next, we characterize the anti- and proconvulsive effects of cannabinoids from animal studies of acute seizures and chronic epileptogenesis. We then review the clinical literature on using cannabinoids to treat epilepsy, including anecdotal evidence and case studies as well as the more recent randomized controlled clinical trials that led to US Food and Drug Administration approval of CBD for some types of epilepsy. Overall, we seek to evaluate our current understanding of cannabinoids in epilepsy and focus future research on unanswered questions.

The potential protective and therapeutic effects of cannabidiol oil on experimental Leukemia induced by DMBA in male rats

BACKGROUND

7,12-Dimethylbenzanthracene (DMBA) is a member of the polycyclic aromatic hydrocarbon family. It is a member of the polycyclic aromatic hydrocarbon family. It is a mutagenic, carcinogenic, and immunosuppressor agent. Cannabidiol (CBD) is a phytocannabinoid. It has anticonvulsant, anti-inflammatory, anti-anxiety, antioxidant, and anti-cancer properties. The purpose of this study was to investigate the possible protective and therapeutic benefits of CBD oil in DMBA-induced leukemia in rats.

METHOD

Experimental animals were divided into six groups of five rats each. Group 1 (normal control) included healthy rats. Group 2 included normal rats that received olive oil. Group 3 included normal rats that received CBD. Group 4 included the DMBA-induced leukemic group. Group 5 (prophylactic group) included rats that received CBD as a prophylaxis before IV injection with DMBA. Group 6 (treated group) included DMBA-induced leukemic rats that received CBD as treatment. Liver functions (total, direct and indirect bilirubin, alkaline phosphatase (ALP), alanine transaminase (ALT), aspartate aminotransferase (AST), albumin, globulin, and albumin globulin ratio) were measured. Superoxide dismutase (SOD) and catalase (CAT) were also measured. Total RNA extraction followed by-real time qRT-PCR gene expression of LC3-II, Beclin, mTOR, and P62 was performed. Histopathological examination of liver and spleen tissues was performed.

RESULTS

Administration of CBD in groups 5 and 6 resulted in a significant improvement of the levels of liver functions compared to the leukemic untreated rats. Also, the levels of catalase and SOD significantly increased after treatment with CBD compared to the leukemic group. After treatment with CBD in groups 5 and 6, there were downregulations in the expression of all studied genes compared to leukemic untreated rats. Treatment with CBD was more statistically effective than prophylactic use.

CONCLUSION

Administration of CBD resulted in a significant improvement in the biochemical, antioxidant status, morphological, and molecular measures in DMBA-induced leukemia in adult male rats. The therapeutic use was more effective than the prophylactic one.

CB 1 Cannabinoid Receptor Agonists Induce Acute Respiratory Depression in Awake Mice

Recreational use of synthetic cannabinoid agonists (i.e., "Spice" compounds) that target the Cannabinoid Type 1 receptor (CB 1 ) can cause respiratory depression in humans. However, Δ 9 -tetrahydrocannabinol (THC), the major psychoactive phytocannabinoid in cannabis, is not traditionally thought to interact with CNS control of respiration, based largely upon sparse labeling of CB1 receptors in the medulla and few reports of clinically significant respiratory depression following cannabis overdose. The respiratory effects of CB 1 agonists have rarely been studied in vivo , suggesting that additional inquiry is required to reconcile the conflict between conventional wisdom and human data. Here we used whole body plethysmography to examine the respiratory effects of the synthetic high efficacy CB 1 agonist CP55,940, and the low efficacy CB 1 agonist Δ 9 -tetrahydrocannabinol in male and female mice. CP55,940 and THC, administered systemically, both robustly suppressed minute ventilation. Both cannabinoids also produced sizable reductions in tidal volume, decreasing both peak inspiratory and expiratory flow - measures of respiratory effort. Similarly, both drugs reduced respiratory frequency, decreasing both inspiratory and expiratory time while markedly increasing expiratory pause, and to a lesser extent, inspiratory pause. Respiratory suppressive effects occurred at lower doses in females than in males, and at many of the same doses shown to produce cardinal behavioral signs of CB 1 activation. We next used RNAscope in situ hybridization to localize CB 1 mRNA to glutamatergic neurons in the medullary pre-Bötzinger Complex, a critical nucleus in controlling respiration. Our results show that, contrary to previous conventional wisdom, CB 1 mRNA is expressed in glutamatergic neurons in a brain region essential for breathing and CB 1 agonists can cause significant respiratory depression.

Roadmap for the expression of canonical and extended endocannabinoid system receptors and metabolic enzymes in peripheral organs of preclinical animal models

The endocannabinoid system is widely expressed throughout the body and is comprised of receptors, ligands, and enzymes that maintain metabolic, immune, and reproductive homeostasis. Increasing interest in the endocannabinoid system has arisen due to these physiologic roles, policy changes leading to more widespread recreational use, and the therapeutic potential of Cannabis and phytocannabinoids. Rodents have been the primary preclinical model of focus due to their relative low cost, short gestational period, genetic manipulation strategies, and gold-standard behavioral tests. However, the potential for lack of clinical translation to non-human primates and humans is high as cross-species comparisons of the endocannabinoid system have not been evaluated. To bridge this gap in knowledge, we evaluate the relative gene expression of 14 canonical and extended endocannabinoid receptors in seven peripheral organs of C57/BL6 mice, Sprague-Dawley rats, and non-human primate rhesus macaques. Notably, we identify species- and organ-specific heterogeneity in endocannabinoid receptor distribution where there is surprisingly limited overlap among the preclinical models. Importantly, we determined there were no receptors with identical expression patterns among mice (three males and two females), rats (six females), and rhesus macaques (four males). Our findings demonstrate a critical, yet previously unappreciated, contributor to challenges of rigor and reproducibility in the cannabinoid field, which has implications in hampering progress in understanding the complexity of the endocannabinoid system and development of cannabinoid-based therapies.

Distinct antinociceptive and conditioned behavioral effects are produced by individual cannabinoids and a cannabis-derived mixture

Cannabinoids have been proposed as therapeutics for pain mitigation. Therefore, the antihyperalgesic effects of a proprietary cannabis-derived mixture, Non-Euphoric Phytocannabinoid Elixir #14 (NEPE14), were examined in a persistent Complete Freund's Adjuvant (CFA)-induced model of inflammatory pain. The acute antinociceptive and operant behavioral effects of NEPE14 were then compared with single cannabinoid preparations of Δ9-tetrahydrocannabinol (Δ9-THC), Δ8-THC, the synthetic cannabinoid (-)-CP 55,940 (CP), and cannabidiol (CBD). The THC isomers and CP were also administered with cannabinoid-type-1 receptor (CB1R) antagonist, AM251, and NEPE14 was administered in combination with THC or CP. To induce inflammation, CFA or saline was administered into the paw of male and female Wistar rats. After injections, mechanical hypersensitivity was assessed with Von Frey filaments, and thermal hyperalgesia with a thermal probe. Nine Sprague Dawley rats were also trained to respond under a fixed-ratio 30 schedule for food reinforcers during a 60-min session. Response rates were recorded during the session and warm-water tail-withdrawal latency post session. In CFA-administered rats, mechanical and thermal paw-withdrawal thresholds significantly decreased compared to vehicle, indicating hyperalgesia. Both i.p. (6.6-20.7 ml/kg) and o.m. (30-300 μL) NEPE14 significantly reduced the mechanical and thermal hyperalgesia. In contrast, neither NEPE14 (3.7-20.7 mL/kg i.p., 100-1000 μL o.m.) nor CBD (10-100 mg/kg) significantly decreased response rates or increased tail-withdrawal latency. Acute Δ9-THC, Δ8-THC (1-5.6 mg/kg), and CP (0.032-0.18 mg/kg) significantly and dose-dependently decreased overall response rate and increased tail-withdrawal latency compared to vehicle. AM251 significantly antagonized the rate-decreasing effects of THC, and CP, as well as the antinociceptive effects of CP. Combinations of NEPE14 with Δ9-THC or CP were not significantly different from these cannabinoids alone. In summary, while NEPE14 significantly reduced CFA-induced hyperalgesia, it was more similar to CBD than Δ9-THC, Δ8-THC, and CP for significantly reducing thermal nociception and disrupting conditioned behavior.

Advice to People with Parkinson's in My Clinic: Cannabis

Cannabis (in all the varied methods of delivery) continues to garner significant attention as a potential therapeutic intervention for neurodegenerative disorders, including Parkinson's disease (PD). The recent legalization of personal use of cannabis products in some parts of the world has increased this interest and with it, potential availability to many more people. However, such access has led to more questions than answers for both patients and health care professionals. These include what symptom(s) of PD will cannabis products treat; what dose; what type of cannabis product to use and what are the side effects?

Characterization of cannabinoid plasma concentration, maternal health, and cytokine levels in a rat model of prenatal Cannabis smoke exposure

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-Δ9-tetrahydrocannabinol (THC) (18% THC, 0.1% cannabidiol [CBD]) smoke, inhaled high-CBD (0.7% THC, 13% 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.

Sex Differences in Plasma, Adipose Tissue, and Central Accumulation of Cannabinoids, and Behavioral Effects of Oral Cannabis Consumption in Male and Female C57BL/6 Mice

BACKGROUND

Cannabis edibles are an increasingly popular form of cannabis consumption. Oral consumption of cannabis has distinct physiological and behavioral effects compared with 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.

METHODS

Adult male and female C57BL/6 mice received a single dose of commercially available cannabis oil (5 mg/kg Δ⁹-tetrahydrocannabinol [THC]) by oral gavage. At 0.5, 1, 2, 3, and 6 hours post exposure, plasma, hippocampus, and adipose tissue were collected for THC, 11-OH-THC, and THC-COOH measures.

RESULTS

We 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 3 hours post exposure; and (4) male mice displayed a longer-lasting antinociceptive effect of oral cannabis.

CONCLUSIONS

Oral 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.

Effects of oral Δ9-tetrahydrocannabinol and cannabidiol combinations on a sustained attention task in rats

A well-documented side effect of cannabis and Δ9-tetrahydrocannabinol (THC) acute administration is deficits in cognition and attention. Cannabidiol (CBD), a nonintoxicating constituent of cannabis, may modulate THC's impairing effects. A goal of this study was to determine the effects of THC and CBD, alone and in combination, on performance in the rodent Psychomotor Vigilance Test (rPVT), a translational paradigm used to quantify sustained attention. Outcome measures in the rPVT include motor speed, premature responding, and lapses in attention. Sprague Dawley rats were trained to perform the rPVT to the acquisition criteria and then received oral doses (mg/kg) of THC (1-17.6), CBD (1-100), and combinations of THC + CBD in sesame oil prior to rPVT sessions, administered in a within-subject randomized design. Blood was collected from rats receiving selected doses of THC alone or THC + CBD for analysis of THC and its metabolites. THC alone produced significant decreases in accuracy and increases in lapses in attention at higher doses (10 mg/kg; ps < .05). The coadministration of CBD (10 mg/kg) with THC (3 or 10 mg/kg) caused greater impairments to sustained attention compared with administration of THC alone (ps < .05). The rPVT is a translational platform sensitive to detect impairments in attention associated with THC and other cannabis constituents. Further work is necessary to determine the mechanism of THC and CBD interactions on impairments in sustained attention. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Sex differences in acute delta-9-tetrahydrocannabinol (Δ9-THC) response and tolerance as a function of mouse strain

Cannabinoids are increasingly used to alleviate pain; however, tolerance to their antinociceptive effects, including those of delta-9-tetrahydrocannabinol (Δ9-THC), may limit their therapeutic utility. With more women than men using medical cannabis for pain relief, it is crucial to understand how sex influences cannabinoid-mediated antinociception and tolerance. Though studies in rats consistently find females are more sensitive to the acute antinociceptive effects of cannabinoids, our work with mice consistently finds the converse. The present study examined whether our observed sex differences in Δ9-THC-induced antinociception and tolerance are consistent across multiple mouse strains or are strain-dependent. Male and female C57BL/6J (B6), DBA/2, AKR, and CBA/J mice were assessed for differences in acute Δ9-THC-induced antinociception and hypothermia prior to and following seven days of once-daily Δ9-THC administration. Consistent with our previous findings, male B6 mice were more sensitive to the acute antinociceptive effects of Δ9-THC than female littermates, an effect which dissipated with age. B6 males had decreased cannabinoid expression in the PAG compared to females. While DBA and CBA female mice showed increased Δ9-THC-antinociception compared to male littermates at 30 and 10 mg/kg Δ9-THC, respectively, these differences were less pronounced at higher doses, revealing that dose of Δ9-THC may also be important. Overall, CBA mice were more sensitive to Δ9-THC-induced antinociception while AKR mice were less responsive. These studies highlight the therapeutic potential of Δ9-THC in pain management and underscore the importance of considering not only Δ9-THC dose as a function of sex, but potentially genetic differences when evaluating their clinical utility.

Toxicological Evaluation and Pain Assessment of Four Minor Cannabinoids Following 14-Day Oral Administration in Rats

Introduction: Despite growing consumer interest and market availability, the safety of minor cannabinoids, generally present in low concentrations in Cannabis sativa L., is not well understood. Materials and Methods: Cannabichromene (CBC; 3.2, 10, 17, 22, 32, or 100 mg/kg-bw/day), cannabinol (CBN; 1, 3.2, 10, 17, 32, or 100 mg/kg-bw/day), delta-8-tetrahydrocannabinol (D8-THC; 0.32, 1, 3.2, or 10 mg/kg-bw/day), tetrahydrocannabivarin (THCV; 3.2, 10, 17, 22, 32, or 100 mg/kg-bw/day), and vehicle (medium-chain triglyceride oil) preparations were administered via oral gavage once daily for 14 days to Sprague Dawley rats. Changes in behavior, body weight, food consumption, clinical pathology, organ weights, body temperature, and thermal pain sensitivity (tail flick assay) were assessed. Select organ tissues were collected at terminal necropsy and fixed for histopathological examination. Results: No treatment-related deaths were observed throughout the study, and cannabinoids were generally well tolerated. While some significant trends in body weight differences from controls (increases and decreases) were observed, these occurred independently of food consumption. Overall, differences in serum chemistry and hematology parameters between cannabinoid groups and their respective control groups were considered to occur due to biological variation among rats. No treatment-related gross abnormalities were observed in examined organs. Significant changes in absolute and relative organ weights occurred primarily in males and were generally of negligible magnitude. There were no biologically significant histopathological observations. While pain tolerance was significantly improved in animals treated with D8-THC (3.2 and 10 mg/kg-bw/day, day 14), results across minor cannabinoids were inconsistent and warrant further study. Conclusion: Minor cannabinoids were well tolerated across 14 days of daily oral administration at the doses assessed. Modest, dose-dependent trends in relative organ weights and serum chemistry parameters warrant exploration at higher oral doses. These data will assist in dose selection for future studies investigating the long-term safety and effects of CBC, CBN, D8-THC, and THCV.

Mechanisms of cannabinoid tolerance

Cannabis has been used recreationally and medically for centuries, yet research into understanding the mechanisms of its therapeutic effects has only recently garnered more attention. There is evidence to support the use of cannabinoids for the treatment of chronic pain, muscle spasticity, nausea and vomiting due to chemotherapy, improving weight gain in HIV-related cachexia, emesis, sleep disorders, managing symptoms in Tourette syndrome, and patient-reported muscle spasticity from multiple sclerosis. However, tolerance and the risk for cannabis use disorder are two significant disadvantages for cannabinoid-based therapies in humans. Recent work has revealed prominent sex differences in the acute response and tolerance to cannabinoids in both humans and animal models. This review will discuss evidence demonstrating cannabinoid tolerance in rodents, non-human primates, and humans and our current understanding of the neuroadaptations occurring at the cannabinoid type 1 receptor (CB1R) that are responsible tolerance. CB1R expression is downregulated in tolerant animals and humans while there is strong evidence of CB1R desensitization in cannabinoid tolerant rodent models. Throughout the review, critical knowledge gaps are indicated and discussed, such as the lack of a neuroimaging probe to assess CB1R desensitization in humans. The review discusses the intracellular signaling pathways that are responsible for mediating CB1R desensitization and downregulation including the action of G protein-coupled receptor kinases, β-arrestin2 recruitment, c-Jun N-terminal kinases, protein kinase A, and the intracellular trafficking of CB1R. Finally, the review discusses approaches to reduce cannabinoid tolerance in humans based on our current understanding of the neuroadaptations and mechanisms responsible for this process.

Roadmap For The Expression Of Canonical and Extended Endocannabinoid System Receptors and Proteins in Peripheral Organs of Preclinical Animal Models

The endocannabinoid system is widely expressed throughout the body and is comprised of receptors, ligands, and enzymes that maintain metabolic, immune, and reproductive homeostasis. Increasing interest in the endocannabinoid system has arisen due to these physiologic roles, policy changes leading to more widespread recreational use, and the therapeutic potential of Cannabis and phytocannabinoids. Rodents have been the primary preclinical model of focus due to their relative low cost, short gestational period, genetic manipulation strategies, and gold-standard behavioral tests. However, the potential for lack of clinical translation to non-human primates and humans is high as cross-species comparisons of the endocannabinoid system has not been evaluated. To bridge this gap in knowledge, we evaluate the relative gene expression of 14 canonical and extended endocannabinoid receptors in seven peripheral organs of C57/BL6 mice, Sprague-Dawley rats, and non-human primate rhesus macaques. Notably, we identify species- and organ-specific heterogeneity in endocannabinoid receptor distribution where there is surprisingly limited overlap among the preclinical models. Importantly, we determined there were only five receptors (CB2, GPR18, GPR55, TRPV2, and FAAH) that had identical expression patterns in mice, rats, and rhesus macaques. Our findings demonstrate a critical, yet previously unappreciated, contributor to challenges of rigor and reproducibility in the cannabinoid field, which has profound implications in hampering progress in understanding the complexity of the endocannabinoid system and development of cannabinoid-based therapies.

Chronic Δ9-tetrahydrocannabinol treatment has dose-dependent effects on open field exploratory behavior and [3H] SR141716A receptor binding in the rat brain

AIMS

Acute and chronic Δ⁹-THC exposure paradigms affect the body differently. More must be known about the impact of chronic Δ⁹-THC on cannabinoid-1 (CB1R) and mu-opioid (MOR) receptor levels in the brain. The present study examined chronic Δ⁹-THC's effects on CB1R and MOR levels and locomotor activity.

MAIN METHODS

Adolescent Sprague-Dawley rats were given daily intraperitoneal injections of Δ⁹-THC [0.75mg/kg (low dose or LD) or 2.0 mg/kg (high dose or HD)] or vehicle for 24 days, and locomotion in the open field was tested after the first and fourth weeks of chronic Δ⁹-THC exposure. Brains were harvested at the end of treatment. [³H] SR141716A and [³H] DAMGO autoradiography assessed CB1R and MOR levels, respectively.

KEY FINDINGS

Relative to each other, chronic HD rats showed reduced vertical plane (VP) entries and time, while LD rats had increased VP entries and time for locomotion, as assessed by open-field testing; no effects were found relative to the control. Autoradiography analyses showed that HD Δ⁹-THC significantly decreased CB1R binding relative to LD Δ⁹-THC in the cingulate (33%), primary motor (42%), secondary motor (33%) somatosensory (38%), rhinal (38%), and auditory (50%) cortices; LD Δ⁹-THC rats displayed elevated binding in the primary motor (33% increase) and hypothalamic (33 % increase) regions compared with controls. No significant differences were observed in MOR binding for the LD or HD compared to the control.

SIGNIFICANCE

These results demonstrate that chronic Δ⁹-THC dose-dependently altered CB1R levels throughout the brain and locomotor activity in the open field.

Cannabinoid Tolerance in S426A/S430A x β-Arrestin 2 Knockout Double-Mutant Mice

Tolerance to compounds that target G protein-coupled receptors (GPCRs), such as the cannabinoid type-1 receptor (CB1R), is in part facilitated by receptor desensitization. Processes that mediate CB1R desensitization include phosphorylation of CB1R residues S426 and S430 by a GPCR kinase and subsequent recruitment of the β-arrestin2 scaffolding protein. Tolerance to cannabinoid drugs is reduced in S426A/S430A mutant mice and β-arrestin2 knockout (KO) mice according to previous work in vivo. However, the presence of additional phosphorylatable residues on the CB1R C-terminus made it unclear as to whether recruitment to S426 and S430 accounted for all desensitization and tolerance by β-arrestin2. Therefore, we assessed acute response and tolerance to the cannabinoids delta-9-tetrahydrocannabinol (Δ9-THC) and CP55,940 in S426A/S430A x β-arrestin2 KO double-mutant mice. We observed both delayed tolerance and increased sensitivity to the antinociceptive and hypothermic effects of CP55,940 in male S426A/S430A single- and double-mutant mice compared with wild-type littermates, but not with Δ9-THC. Female S426A/S430A single- and double-mutant mice were more sensitive to acute antinociception (CP55,940 and Δ9-THC) and hypothermia (CP55,940 only) exclusively after chronic dosing and did not differ in the development of tolerance. These results indicate that phosphorylation of S426 and S430 are likely responsible for β-arrestin2-mediated desensitization as double-mutant mice did not differ from the S426A/S430A single-mutant model in respect to cannabinoid tolerance and sensitivity. We also found antinociceptive and hypothermic effects from cannabinoid treatment demonstrated by sex-, agonist-, and duration-dependent features. SIGNIFICANCE STATEMENT: A better understanding of the molecular mechanisms involved in tolerance will improve the therapeutic potential of cannabinoid drugs. This study determined that further deletion of β-arrestin2 does not enhance the delay in cannabinoid tolerance observed in CB1R S426A/S430A mutant mice.

High-CBD Cannabis Vapor Attenuates Opioid Reward and Partially Modulates Nociception in Female Rats

Chronic pain patients report analgesic effects when using cannabidiol (CBD), a phytocannabinoid found in whole-plant cannabis extract (WPE). Several studies suggest that cannabis-derived products may serve as an analgesic adjunct or alternative to opioids, and importantly, CBD may also attenuate the abuse potential of opioids. Vaping is a popular route of administration among people who use cannabis, however both the therapeutic and hazardous effects of vaping are poorly characterized. Despite the fact that chronic pain is more prevalent in women, the ability of inhaled high-CBD WPE to relieve pain and reduce opioid reward has not been studied in females. Here, we present a comprehensive analysis of high-CBD WPE vapor inhalation in female rats. We found that WPE was modestly efficacious in reversing neuropathy-induced cold allodynia in rats with spared nerve injury (SNI). Chronic exposure to WPE did not affect lung cytoarchitecture or estrous cycle, and it did not induce cognitive impairment, social withdrawal or anxiolytic effects. WPE inhalation prevented morphine-induced conditioned place preference and reinstatement. Similarly, WPE exposure reduced fentanyl self-administration in rats with and without neuropathic pain. We also found that WPE vapor lacks of reinforcing effects compared to the standard excipient used in most vapor administration research. Combined, these results suggest that although high-CBD vapor has modest analgesic effects, it has a robust safety profile, no abuse potential, and it significantly reduces opioid reward in females. Clinical studies examining high-CBD WPE as an adjunct treatment during opioid use disorder are highly warranted.

Chronic low-dose Δ9-tetrahydrocannabinol (THC) treatment stabilizes dendritic spines in 18-month-old mice

Cognitive functions decline during aging. This decline could be caused by changes in dendritic spine stability and altered spine dynamics. Previously, we have shown that a low dose chronic THC treatment improves learning abilities in old whereas impairs learning abilities in young mice. The mechanism underlying this age-dependent effect is not known. Dendritic spine stability is a key for memory formation, therefore we hypothesized that THC affects spine dynamics in an age-dependent manner. We applied longitudinal 2-photon in vivo imaging to 3- and 18-month-old mice treated with 3 mg/kg/day of THC for 28 days via an osmotic pump. We imaged the same dendritic segments before, during and after the treatment and assessed changes in spine density and stability. We now show that in old mice THC improved spine stability resulting in a long-lasting increase in spine density. In contrast, in young mice THC transiently increased spine turnover and destabilized the spines.

Decursinol-mediated antinociception and anti-allodynia in acute and neuropathic pain models in male mice: Tolerance and receptor profiling

Korean scientists have shown that oral administration of Angelica gigas Nakai (AGN) root alcoholic extract and the metabolite of its pyranocoumarins, decursinol, have antinociceptive properties across various thermal and acute inflammatory pain models. The objectives of this study were 1) to assess whether tolerance develops to the antinociceptive effects of once-daily intraperitoneally administered decursinol (50 mg/kg) in acute thermal pain models, 2) to establish its anti-allodynic efficacy and potential tolerance development in a model of chemotherapy-evoked neuropathic pain (CENP) and 3) to probe the involvement of select receptors in mediating the pain-relieving effects with antagonists. The results show that decursinol induced antinociception in both the hot plate and tail-flick assays and reversed mechanical allodynia in mice with cisplatin-evoked neuropathic pain. Tolerance was detected to the antinociceptive effects of decursinol in the hot plate and tail-flick assays and to the anti-allodynic effects of decursinol in neuropathic mice. Pretreatment with either the 5-HT2 antagonist methysergide, the 5-HT2A antagonist volinanserin, or the 5-HT2C antagonist SB-242084 failed to attenuate decursinol-induced antinociception in the tail-flick assay. While pretreatment with the cannabinoid inverse agonists rimonabant and SR144528 failed to modify decursinol-induced anti-allodynia, pretreatment with the opioid antagonist naloxone partially attenuated the anti-allodynic effects of decursinol. In conclusion, our data support decursinol as an active phytochemical of AGN having both antinociceptive and anti-allodynic properties. Future work warrants a more critical investigation of potential receptor mechanisms as they are likely more complicated than initially reported.