Biology subjects

Hohmann, A. G.

Publications and source records attributed to Hohmann, A. G..

17 recordsLinked to original sources

bioRxiv2026

Cannabidiol attenuates chemotherapy-induced peripheral neuropathic pain through a mechanism that requires the enzyme N-acylphosphatidylethanolamine-specific phospholipase D (NAPE-PLD)

Cannabidiol (CBD) is a non-psychoactive component of cannabis that has been studied as a potential therapy for chronic pain. CBD attenuates behavioral hypersensitivities in models of neuropathic pain, and promotes production of bioactive lipids (e.g., anandamide), altering lipid signaling. However, a lack of understanding of the mechanisms underlying the therapeutic effects of CBD has hindered development and application of CBD to mechanism-based therapies for pain in people. We asked whether the analgesics effects of CBD were dependent upon the enzyme NAPE-PLD. We used a mouse model of chemotherapy-induced peripheral neuropathy (CIPN) to evaluate the acute and chronic antinociceptive effects of CBD and investigate its mechanisms. Pharmacological specificity was tested with antagonists targeting CB1, CB2, PPAR{gamma}, and PPAR receptors. Mechanisms were further examined using NAPE-PLD and GPR55 knockout mice. We also assessed repeated CBD dosing during both the development and maintenance of paclitaxel-induced CIPN in wild-type, GPR55 KO, and NAPE-PLD KO mice. CBD suppressed paclitaxel-induced behavioral hypersensitivities; these effects were attenuated by a PPAR and PPAR{gamma} antagonists, but not CB1 or CB2 antagonists. CBD reduced both the development and maintenance of neuropathic nociception in a model CIPN in wild-type mice, but these effects were absent in NAPE-PLD KO mice. By contrast, anti-allodynic efficacy of CBD was fully preserved in GPR55 KO mice. Pharmacological blockade of the PPAR receptor and genetic deletion of NAPE-PLD abolished the antinociceptive effects of CBD in a model of CIPN, suggesting a pivotal role for NAPE-PLD and PPAR receptors in CBD-mediated analgesia in chemotherapy-induced neuropathic pain.

neuroscience↗

bioRxiv2025

CB2 cannabinoid receptor-specific therapeutic antibody agonists for treatment of chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a debilitating complication of cancer treatment. CB2 cannabinoid receptor activation reduces inflammation and is an attractive therapeutic target. Antibodies targeting G protein-coupled receptors (GPCRs), like CB2, offer high specificity and peripheral-restriction, thereby minimizing off-target activity. Here, we investigated the efficacy of first-in-class CB2-specific antibody agonists (AB110 and AB120) and an isotype control (AB100) on mechanical and cold hypersensitivity induced by paclitaxel in both tumor-free and mammary (4T1) tumor-bearing female mice. These CB2 antibody agonists exhibit biased G- signaling and also reduce macrophage markers and pro-inflammatory cytokines in vitro. Paclitaxel produced behavioral hypersensitivities to mechanical and cold stimulation, which were reduced by AB110 and AB120 for approximately 48 hours post-injection in female mice. Repeated daily dosing did not lead to tolerance to the anti-allodynic effects. Prophylactic treatment with AB110 and AB120 during paclitaxel treatment delayed, but did not prevent, the development of paclitaxel-induced behavioral hypersensitivities after termination of dosing with antibody agonists. AB100 had no effect under any conditions. The anti-allodynic effects of AB120 were absent in CB2 knockout mice, confirming pharmacological specificity via CB2 receptors. Furthermore, AB120 remained effective in paclitaxel-treated tumor-bearing mice. Neither AB110 nor AB120 affected locomotor activity in otherwise naive mice. The cytotoxic activity of paclitaxel on 4T1 tumor cell line was maintained in the presence of CB2 antibody agonists in vitro. Overall, our results suggest that CB2-specific antibody agonists are promising candidates for treating CIPN, providing lasting pain relief without tolerance, off target effects or unwanted CB1-mediated motor side effects.

neuroscience↗

bioRxiv2025

Assessments of Evoked and Spontaneous Pain Following Administration of Gabapentin and the Cannabinoid CB2 agonist LY2828360 in a Rat Model of Spared Nerve Injury

Cannabinoid CB2 agonists reduce stimulus-evoked behavioral hypersensitivities in preclinical pain models, but their ability to modulate spontaneous pain remains unexplored. Spontaneous pain has been assessed in rodents using the conditioned place preference (CPP) approach, given that the relief of pain is described as rewarding and results in negative reinforcement (i.e. removal of an aversive pain state). LY2828360 is a CB2 agonist that failed in a clinical trial for osteoarthritis pain. We compared impact of LY2828360 on evoked and spontaneous pain using a spared nerve injury (SNI) model in rats. First, we verified that an analgesic dose of gabapentin (100 mg/kg i.p.) produces CPP in rats with SNI, but not in sham-operated rats, consistent with a previous report (Griggs et al. 2015). We then used a within-subjects design to ascertain whether the CB2 agonist LY2828360 (10 mg/kg i.p., chronic) would suppress both evoked and spontaneous pain in rats with SNI. To assess evoked pain behavior, mechanical paw withdrawal thresholds were measured and revealed that LY2828360 reliably suppressed mechanical hypersensitivity in the paw ipsilateral, but not contralateral to SNI. Furthermore, efficacy was sustained across repeated injections without development of tolerance. To assess spontaneous pain behavior, we tested the ability of LY2828360 to prevent gabapentin-induced CPP in the SNI model, as failure to develop CPP to gabapentin following treatment with an analgesic has been considered evidence of suppression of spontaneous pain. The same rats that showed suppression of mechanically-evoked responses following chronic LY282860 treatment did not develop CPP to gabapentin. However, rats that were tested in parallel and treated chronically with vehicle showed robust mechanical hypersensitivity, but also did not develop CPP to gabapentin. These studies document that CB2 agonist-induced suppression of mechanically evoked pain is highly robust and reproducible, whereas CPP, used to assess spontaneous pain, is vulnerable to disruption and requires rigorous controls to rule out alternative explanations (e.g. failure to learn).

pharmacology and toxicology↗

bioRxiv2025

A newly designed GABA-AT inactivator, (S)-MeCPP-115, suppresses paclitaxel-induced neuropathic pain in mice

BackgroundChemotherapy-induced peripheral neuropathy (CIPN) is a common and debilitating side effect of paclitaxel treatment. Pharmacological strategies that enhance inhibitory tone, via inhibition of {gamma}-aminobutyric acid aminotransferase (GABA-AT), the enzyme which degrades endogenous GABA, provides analgesic benefit in preclinical studies. (S)-MeCPP-115 is a novel selective GABA-AT inactivator designed from CPP-115 to minimize off-target activity. Whether (S)-MeCPP-115 shows efficacy in preclinical pain models is unknown. MethodsIn vitro assays of cell viability were conducted to ascertain whether (S)-MeCPP-115 interfered with antitumor activity of paclitaxel or produced cytotoxicity in normal cells. Male mice received paclitaxel to induce chemotherapy-induced peripheral neuropathy in vivo. In mice with established paclitaxel-induced mechanical hypersensitivity, (S)-MeCPP-115 was administered via acute and chronic administration using intraperitoneal (i.p.) or intrathecal (i.t.) dosing strategies. Mechanical sensitivity was assessed in all mice with an electronic von Frey analgesiometer before and after paclitaxel and pharmacological treatments. Locomotor activity was also measured in the same subjects to assess possible motor impairment. ResultsIn MTT assays, (S)-MeCPP-115 did not alter the cytotoxic activity of paclitaxel in 4T1 breast cancer cells and did not produce cytotoxicity in non-tumor HEK293 cells. (S)-MeCPP-115 reduced paclitaxel-induced mechanical hypersensitivity after i.p. and i.t. administration. Therapeutic efficacy was maintained with repeated dosing without development of tolerance. (S)-MeCPP-115 did not alter paw withdrawal thresholds in mice that received the Cremophor-based vehicle in lieu of paclitaxel following acute or chronic dosing. Systemic treatment with (S)-MeCPP-115 was well tolerated, whereas i.t. administration produced only minimal locomotor effects. Conclusion(S)-MeCPP-115 did not interfere with the ability of paclitaxel to produce tumor cell cytotoxicity in vitro and did not produce cytotoxicity in non-tumor cells. Systemic and intrathecal administration of (S)-MeCPP-115 produced robust suppression of mechanical hypersensitivity in a mouse model of paclitaxel-induced CIPN without major adverse effects. Selective GABA-AT inhibition represents a promising therapeutic approach for suppressing paclitaxel-induced mechanical hypersensitivity. Further preclinical characterization of the therapeutic profile of (S)-MeCPP-115 is warranted.

pharmacology and toxicology↗

bioRxiv2025

Xylazine exacerbates fentanyl-induced respiratory depression and prevents rescue by naloxone in mice

Xylazine is a veterinary sedative and widespread adulterant of illicit opioids, where it is commonly combined with the highly potent synthetic {micro} opioid receptor (MOR) agonist fentanyl. Xylazine adulteration of fentanyl is associated with increased risk of lethal overdose and decreased efficacy of reversal by the MOR antagonist naloxone. Here we use whole body plethysmography in mice to show that xylazine produces profound respiratory depression at subanesthetic doses. Xylazine rapidly and dose-dependently suppressed minute ventilation, tidal volume, and respiratory frequency. These effects were dependent on -2 adrenergic receptors and were fully blocked by coadministration of the -2 adrenergic antagonist atipamezole. Atipamezole, administered alone, produced only modest reversal of fentanyl-induced respiratory depression. Xylazine, when combined with a dose of fentanyl with modest respiratory effects, suppressed breathing with greater efficacy than when administered alone. Strikingly, doses of naloxone sufficient to completely reverse fentanyl-induced respiratory depression were ineffective in reversing the respiratory suppression induced by xylazine-adulterated fentanyl. By contrast, combinations of naloxone with atipamezole rapidly and fully reversed the suppression of breathing induced by xylazine-adulterated fentanyl. Our results show that xylazine suppresses breathing via activation of -2 receptors, an effect enhanced by coadministration with the MOR agonist fentanyl. Respiratory suppression inflicted by the mixture of xylazine and fentanyl resisted reversal by naloxone but was fully reversible by subsequent coadministration of both naloxone and atipamezole. These observations have profound implications for the current opioid epidemic.

neuroscience↗

bioRxiv2025

Acetaminophen attenuates pathological pain through a mechanism that requires CB1 cannabinoid receptors and the enzyme diacylglycerol lipase in mice

Acetaminophen (APAP) produces analgesia through mechanisms that remain poorly understood. Here, we tested the hypothesis that APAP-induced suppression of pathological pain is associated with cannabinoid receptors and activity of enzymes regulating endogenous lipids (diacylglycerol lipase, DAGL; monoacylglycerol lipase, MAGL) including endocannabinoids. APAP suppressed mechanical hypersensitivity in mouse models of post-surgical and inflammatory pain and the DAGL inhibitors (RHC-80267, DO34) and MAGL inhibitor JZL184 blocked APAPs analgesic effects. Global (rimonabant, AM251) but not peripherally restricted (AM6545) cannabinoid receptor antagonists prevented APAP-induced analgesia. APAP increased corticosterone levels >2-fold and reduced prostaglandins >5-fold across the brain and in the paw skin. In addition, APAP reduced up to 39% of signaling lipids detected in the targeted screen in CFA-treated subjects in a tissue-dependent manner. These observations suggest that APAP plays a wider role in endogenous lipid signaling than previously hypothesized and provides novel insight into mechanisms of action.

neuroscience↗

bioRxiv2025

MILD TRAUMATIC BRAIN INJURY IMPAIRS EPISODIC MEMORY IN RATS

Mild traumatic brain injury (mTBI) is the most common type of traumatic brain injury. Symptoms following mTBI fall into physical, emotional, sleep, and cognitive categories, with memory deficits being a commonly documented sequelae. Whereas many animal models of mTBI exist, relatively few studies have examined the cognitive deficits of mTBI with human-like cognitive tasks. The Wayne State University Closed Head Weight Drop Model recapitulates critical physical elements of sport-related concussions and trauma-based mTBI. However, until now, this model has not previously been evaluated using a human-like memory task. Rats were trained in an odor-based item-in-context task that dissociates episodic and non-episodic memory (Panoz-Brown et al., Current Biology, 2016). The animals then underwent either a weight drop or a sham procedure. After the manipulation, animals were assessed in the item-in-context task. Episodic memory was significantly impaired in the injured rats by over 10% but not in the sham rats. Non-episodic memory was not impaired in either group. Additionally, a time-course immunohistochemical analysis of the hippocampus was performed to examine possible time-dependent changes in ionized calcium-binding adaptor molecule 1 (iba1), a marker of activated microglia/macrophages and glial fibrillary acidic protein (GFAP), a marker of astrocytes. Concussion injury was associated with time-dependent morphological changes in astrocytes and microglia in injured rats compared to sham rats. This study is the first to document episodic memory impairment in an animal model of mTBI.

neuroscience↗

bioRxiv2025

MILD TRAUMATIC BRAIN INJURY IMPAIRS SPATIAL WORKING MEMORY IN RATS

Mild Traumatic Brain Injury (mTBI), or concussion, is the most common form of traumatic brain injury, which accounts for about 80% of cases. It is a common problem in contact sports and may lead to cognitive impairment. This study used the Wayne State University closed-head weight-drop model in lightly anesthetized and unrestrained Long Evans rats. This model allows for the rapid acceleration and deceleration of the head and torso, similar to the biomechanics in human mTBI. Rats were administered a single weight drop. Sham animals were treated the same as the mTBI group but were not subjected to weight drop. Rats were trained in an 8-arm radial maze to assess spatial working memory before and after weight drop manipulation. We observed that the injured rats spatial working memory performance significantly declined compared to the sham rats (cohens d = 1.88). Specifically, the performance of the sham group continued to improve after the sham procedure, whereas the performance of the injury group decreased. This study suggests the WDM model produces a deficit in spatial working memory in rats.

animal behavior and cognition↗

bioRxiv2025

Mice lacking the endocannabinoid-synthesizing enzyme NAPE-PLD exhibit sex-dependent dysregulations in responsiveness to oxycodone and a natural reward

The endogenous opioid and endogenous cannabinoid (endocannabinoid) systems are highly interconnected in the context of drug reward. Bioactive lipids known as N-acylethanolamines (NAEs), and, specifically, anandamide (AEA), influence several unwanted side effects of opioids, including dependence and tolerance. AEA undergoes degradation by the enzyme fatty-acid amide hydrolase (FAAH), whereas the biosynthesis of AEA in vivo is catalyzed by the enzyme N-acyl phosphatidylethanolamine phospholipase-D (NAPE-PLD). AEA and FAAH are implicated in opioid reward, but the impact of genetic deletion of NAPE-PLD on responsiveness to opioids remains unknown. Here we explored the role of NAPE-PLD in behavioral sensitivity to the opioid analgesic oxycodone. We evaluated NAPE-PLD knockout (KO) and wild type (WT) mice of both sexes in preclinical assays that assess either opioid-induced psychomotor responses or voluntary oral consumption of oxycodone. In our studies, genetic deletion of NAPE-PLD produced a shift in sexually dimorphic responses to oxycodone. Psychomotor response to oxycodone was reduced in female NAPE-PLD KO mice but not in males. Female NAPE-PLD KO mice consumed more oral oxycodone that female WT mice, while no genotypic differences in consumption were observed in males. Oxycodone consumption also increased the number of striatal {Delta}FosB positive cells in female WT mice, but not in male WT mice or NAPE-PLD KO mice of either sex. Additionally, NAPE-PLD KO mice of both sexes consumed more sucrose than WT mice. Together, these findings suggest that NAPE-PLD may regulate responses to opioids in a sexually dimorphic manner as the impact of genetic deletion of NAPE-PLD was greater in females than males.

neuroscience↗

bioRxiv2024

Multiple mechanisms of action of an extremely painful venom

Evolutionary arms races between predator and prey can lead to extremely specific and effective defense mechanisms. Such defenses include venoms that deter predators by targeting nociceptive (pain-sensing) pathways. Through co-evolution, venom toxins can become extremely efficient modulators of their molecular targets. The venom of velvet ants (Hymenoptera: Mutillidae) is notoriously painful. The intensity of a velvet ant sting has been described as "Explosive and long lasting, you sound insane as you scream. Hot oil from the deep fryer spilling over your entire hand." [1] The effectiveness of the velvet ant sting as a deterrent against potential predators has been shown across vertebrate orders, including mammals, amphibians, reptiles, and birds [2-4]. The venoms low toxicity suggests it has a targeted effect on nociceptive sensory mechanisms [5]. This leads to the hypothesis that velvet ant venom targets a conserved nociception mechanism, which we sought to uncover using Drosophila melanogaster as a model system. Drosophila larvae have peripheral sensory neurons that sense potentially damaging (noxious) stimuli such as high temperature, harsh mechanical touch, and noxious chemicals [6-9]. These polymodal nociceptors are called class IV multidendritic dendritic arborizing (cIV da) neurons, and they share many features with vertebrate nociceptors, including conserved sensory receptor channels [10,11]. We found that velvet ant venom strongly activated Drosophila nociceptors through heteromeric Pickpocket/Balboa (Ppk/Bba) ion channels. Furthermore, we found a single venom peptide (Do6a) that activated larval nociceptors at nanomolar concentrations through Ppk/Bba. Drosophila Ppk/Bba is homologous to mammalian Acid Sensing Ion Channels (ASICs) [12]. However, the Do6a peptide did not produce behavioral signs of nociception in mice, which was instead triggered by other non-specific, less potent, peptides within the venom. This suggests that Do6a is an insect-specific venom component that potently activates insect nociceptors. Consistent with this, we showed that the velvet ants defensive sting produced aversive behavior in a predatory praying mantis. Together, our results indicate that velvet ant venom evolved to target nociceptive systems of both vertebrates and invertebrates, but through different molecular mechanisms.

neuroscience↗

bioRxiv2024

Genetic deletion of NAPE-PLD induces context-dependent dysregulation of anxiety-like behaviors, stress responsiveness, and HPA-axis functionality in mice

The endocannabinoid (eCB) system regulates stress responsiveness and hypothalamic-pituitary-adrenal (HPA) axis activity. The enzyme N-acyl phosphatidylethanolamine phospholipase-D (NAPE-PLD) is primarily responsible for the synthesis of the endocannabinoid signaling molecule anandamide (AEA) and other structurally related lipid signaling molecules known as N-acylethanolamines (NAEs). However, little is known about how activity of this enzyme affects behavior. As AEA plays a regulatory role in stress adaptation, we hypothesized that reducing synthesis of AEA and other NAEs would dysregulate stress reactivity. To test this hypothesis, we evaluated wild type (WT) and NAPE-PLD knockout (KO) mice in behavioral assays that assess stress responsiveness and anxiety-like behavior. NAPE-PLD KO mice exhibited anxiety-like behaviors in the open field test and the light-dark box test after a period of single housing. NAPE-PLD KO mice exhibited a heightened freezing response to the testing environment that was further enhanced by exposure to 2,3,5-trimethyl-3-thiazoline (TMT) predator odor. NAPE-PLD KO mice exhibited an exaggerated freezing response at baseline but blunted response to TMT when compared to WT mice. NAPE-PLD KO mice also exhibited a context-dependent dysregulation of HPA axis in response to TMT in the paraventricular hypothalamic nucleus at a neuronal level, as measured by c-Fos immunohistochemstry. Male, but not female, NAPE-PLD knockout mice showed higher levels of circulating corticosterone relative to same-sex wildtype mice in response to TMT exposure, suggesting a sexually-dimorphic dysregulation of the HPA axis at the hormonal level. Together, these findings suggest the enzymatic activity of NAPE-PLD regulates emotional resilience and recovery from both acute and sustained stress. Significance StatementThe endocannabinoid anandamide (AEA) regulates stress responsiveness and activity of the hypothalamic-pituitary-adrenal (HPA) axis. Currently, little is known about how an enzyme (i.e. N-acylphosphatidylethanolamine phospholipase-D (NAPE-PLD)) involved in the synthesis of AEA affects behavior. We hypothesized that genetic deletion of NAPE-PLD would dysregulate responsiveness to stress at a behavioral and neuronal level. Our studies provide insight into potential vulnerabilities to stress and anxiety that may result from dysregulation of the enzyme NAPE-PLD in people.

neuroscience↗

bioRxiv2024

CB1 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 (CB1) can cause respiratory depression in humans. However, {Delta}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 CB1 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 CB1 agonist CP55,940, and the low efficacy CB1 agonist {Delta}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 CB1 activation. We next used RNAscope in situ hybridization to localize CB1 mRNA to glutamatergic neurons in the medullary pre-Botzinger Complex, a critical nucleus in controlling respiration. Our results show that, contrary to previous conventional wisdom, CB1 mRNA is expressed in glutamatergic neurons in a brain region essential for breathing and CB1 agonists can cause significant respiratory depression.

neuroscience↗

bioRxiv2024

Cannabinoid CB2 receptors in primary sensory neurons are implicated in CB2 agonist-mediated suppression of paclitaxel-induced neuropathic nociception and sexually-dimorphic sparing of morphine tolerance

Cannabinoid CB2 agonists show therapeutic efficacy without the unwanted side effects commonly associated with direct activation of CB1 receptors. The G protein-biased CB2 receptor agonist LY2828360 attenuates the maintenance of chemotherapy-induced neuropathic nociception in male mice and blocks the development of morphine tolerance in this model. However, the specific cell types involved in this phenomenon have never been investigated and whether this therapeutic profile is observed in female mice remains poorly understood. We used conditional deletion of CB2 receptors from specific cell populations to determine the population(s) mediating the anti-allodynic and morphine-sparing effects of CB2 agonists. Anti-allodynic effects of structurally distinct CB2 agonists (LY2828360 and AM1710) were present in paclitaxel-treated CB2f/f mice of either sex. The anti-allodynic effect of the CB2 agonists were absent in conditional knockout (KO) mice lacking CB2 receptors in peripheral sensory neurons (AdvillinCRE/+; CB2f/f) but preserved in mice lacking CB2 receptors in CX3CR1 expressing microglia/macrophages (CX3CR1CRE/+; CB2f/f). The morphine-sparing effect of LY28282360 occurred in a sexually-dimorphic manner, being present in male mice but absent in female mice of any genotype. In mice with established paclitaxel-induced neuropathy, prior LY2828360 treatment (3 mg/kg per day i.p. x 12 days) blocked the subsequent development of morphine tolerance in male CB2f/f mice but was absent in male (or female) AdvillinCRE/+; CB2f/f mice. LY2828360-induced sparing of morphine tolerance was preserved in male CX3CR1CRE/+; CB2f/f mice, but this effect was not observed in female CX3CR1CRE/+; CB2f/f mice. Similarly, co-administration of morphine with a low dose of LY2828360 (0.1 mg/kg per day i.p. x 6 days) reversed tolerance to the anti-allodynic efficacy of morphine in paclitaxel-treated male CB2f/f mice, but this effect was absent in female CB2f/f mice and AdvillinCRE/+; CB2f/f mice of either sex. Additionally, LY2828360 (3 mg/kg per day i.p. x 8 days) delayed, but did not prevent, the development of paclitaxel-induced mechanical and cold allodynia in either CB2f/f or CX3CR1CRE/+; CB2f/f mice of either sex. Our studies reveal that CB2 receptors in primary sensory neurons are required for the anti-allodynic effects of CB2 agonists in a mouse model of paclitaxel-induced neuropathic nociception. We also find that CB2 agonists acting on primary sensory neurons produce a sexually-dimorphic sparing of morphine tolerance in males, but not female, paclitaxel-treated mice.

neuroscience↗

bioRxiv2024

Negative allosteric modulation of CB1 cannabinoid receptor signaling decreases intravenous morphine self-administration and relapse in mice

The endocannabinoid system interacts with the reward system to modulate responsiveness to natural reinforcers, as well as drugs of abuse. Previous preclinical studies suggested that direct blockade of CB1 cannabinoid receptors (CB1R) could be leveraged as a potential pharmacological approach to treat substance use disorder, but this strategy failed during clinical trials due to severe psychiatric side effects. Alternative strategies have emerged to circumvent the side effects of direct CB1 binding through the development of allosteric modulators. We hypothesized that pharmacological inhibition of CB1R signaling through negative allosteric modulation (NAM) would reduce the reinforcing properties of morphine and decrease opioid addictive behaviors. By employing i.v. self-administration in mice, we studied the effects of the CB1-biased NAM GAT358 on morphine intake, relapse-like behavior, and motivation to work for morphine infusions. Our data revealed that GAT358 reduced morphine infusion intake during the maintenance phase of morphine self-administration under fixed ratio 1 schedule of reinforcement. GAT358 decreased morphine-seeking behavior after forced abstinence. Moreover, GAT358 dose-dependently decreased the motivation to obtain morphine infusions in a progressive ratio schedule of reinforcement. Strikingly, GAT358 did not affect the motivation to work for food rewards in an identical progressive ratio task, suggesting that the effect of GAT358 in decreasing opioid self-administration is reward specific. Furthermore, GAT58 did not produce motor ataxia in the rota-rod test. Our results suggest that CB1R NAMs reduced the reinforcing properties of morphine and could represent a viable therapeutic route to safely decrease opioid-addicted behaviors.

animal behavior and cognition↗

bioRxiv2024

Negative allosteric modulation of cannabinoid CB1 receptor signaling suppresses opioid-mediated tolerance and withdrawal without blocking opioid antinociception

The direct blockade of CB1 cannabinoid receptors produces therapeutic effects as well as adverse side-effects that limit their clinical potential. CB1 negative allosteric modulators (NAMs) represent an indirect approach to decrease the affinity and/or efficacy of orthosteric cannabinoid ligands or endocannabinoids at CB1. We recently reported that GAT358, a CB1-NAM, blocked opioid-induced mesocorticolimbic dopamine release and reward via a CB1-allosteric mechanism of action. Whether a CB1-NAM dampens opioid-mediated therapeutic effects such as analgesia or alters other unwanted side-effects of opioids remain unknown. Here, we characterized the effects of GAT358 on nociceptive behaviors in the presence and absence of morphine. We examined the impact of GAT358 on formalin-evoked pain behavior and Fos protein expression, a marker of neuronal activation, in the lumbar dorsal horn. We also assessed the impact of GAT358 on morphine-induced slowing of colonic transit, tolerance, and withdrawal behaviors. GAT358 attenuated morphine antinociceptive tolerance without blocking acute antinociception. GAT358 also reduced morphine-induced slowing of colonic motility without impacting fecal boli production. GAT358 produced antinociception in the presence and absence of morphine in the formalin model of inflammatory nociception and reduced the number of formalin-evoked Fos protein-like immunoreactive cells in the lumbar spinal dorsal horn. Finally, GAT358 mitigated the somatic signs of naloxone-precipitated, but not spontaneous, opioid withdrawal following chronic morphine dosing in mice. Our results support the therapeutic potential of CB1-NAMs as novel drug candidates aimed at preserving opioid-mediated analgesia while preventing their unwanted side-effects. Our studies also uncover previously unrecognized antinociceptive properties associated with an arrestin-biased CB1-NAMs. HighlightsO_LICB1 negative allosteric modulator (NAM) GAT358 attenuated morphine tolerance C_LIO_LIGAT358 reduced morphine-induced slowing of colonic motility but not fecal production C_LIO_LIGAT358 was antinociceptive for formalin pain alone and when combined with morphine C_LIO_LIGAT358 reduced formalin-evoked Fos protein expression in the lumbar spinal cord C_LIO_LIGAT358 mitigated naloxone precipitated withdrawal after chronic morphine dosing C_LI

neuroscience↗

bioRxiv2022

Engineering human spinal microphysiological systems to model opioid-induced tolerance

Opioids are commonly used for treating chronic pain. However, with continued use, they may induce tolerance and/or hyperalgesia, which limits therapeutic efficacy. The human mechanisms of opioid-induced hyperalgesia are significantly understudied, in part, because current models cannot fully recapitulate human pathology. Here, we engineered novel human spinal microphysiological systems (MPSs) integrated with plug-and-play neural activity sensing for modeling human nociception and opioid-induced tolerance. Each spinal MPS consists of a flattened human spinal cord organoid derived from human stem cells and a 3D printed organoid holder device for plug-and-play neural activity measurement. We found that the flattened organoid design of MPSs not only reduces hypoxia and necrosis in the organoids, but also promotes their neuron maturation, neural activity, and functional development. We further demonstrated that prolonged opioid exposure resulted in neurochemical correlates of opioid tolerance and hyperalgesia, as measured by altered neural activity, reduced densities of glutamate transporter levels and downregulation of -opioid receptor expression of human spinal MPSs. The MPSs are scalable, cost-effective, easy-to-use, and compatible with commonly-used well-plates, thus allowing plug-and-play measurements of neural activity. We believe the MPSs hold a promising translational potential for studying human pain etiology, screening new treatments, and validating novel therapeutics for human pain medicine.

bioengineering↗

bioRxiv2022

Peripheral sensory neuron CB2 cannabinoid receptors are necessary for both CB2-mediated antinociceptive efficacy and sparing of morphine tolerance in a mouse model of neuropathic pain

Painful peripheral neuropathy is the most common neurological complication associated with human immune deficiency virus (HIV) infection. Currently available treatments fail to provide adequate symptom relief, indicating the need for novel treatment strategies. To address this gap in knowledge, we characterized the impact of cannabinoid CB2 agonists, which lack psychoactivity associated with central CB1 activation, on antiretroviral-induced neuropathic nociception and identified cell types expressing CB2 that mediate the antinociceptive efficacy of CB2 agonists. Two structurally distinct CB2 agonists (AM1710 and LY2828360) alleviated antiretroviral-induced neuropathic pain, benefits which were absent in CB2 knockout mice. Conditional deletion of CB2 from peripheral sensory neurons eliminated the antinociceptive efficacy of CB2 agonists. We also asked whether LY2828360 treatment could reverse established morphine tolerance in the ddC-induced neuropathy model and whether CB2 expression on peripheral sensory neurons is necessary for sparing of morphine tolerance by LY2828360. The present studies suggest that CB2 activation may alleviate HIV-associated antiretroviral neuropathy and identify a previously unreported mechanism through which CB2 activation produces antinociceptive efficacy. Our results also provide the first evidence that a CB2 agonist can reverse established morphine tolerance and demonstrate that CB2 localized to peripheral sensory neurons mediates the opioid tolerance sparing efficacy of CB2 agonists.

neuroscience↗