Topical cannabinoid agonist, WIN55,212-2, reduces cornea-evoked trigeminal brainstem activity in the rat

MAM-2201 acute administration impairs motor, sensorimotor, prepulse inhibition, and memory functions in mice: a comparison with its analogue AM-2201

RATIONALE

1-[(5-fluoropentyl)-1H-indol-3-yl](4-methyl-1-naphthalenyl) methanone (MAM-2201) is a potent synthetic cannabinoid receptor agonist illegally marketed in "spice" products and as "synthacaine" for its psychoactive effects. It is a naphthoyl-indole derivative which differs from its analogue 1-[(5-Fluoropentyl)-1H-indol-3-yl](1-naphthylenyl) methanone (AM-2201) by the presence of a methyl substituent on carbon 4 (C-4) of the naphthoyl moiety. Multiple cases of intoxication and impaired driving have been linked to AM-2201 and MAM-2201 consumption.

OBJECTIVES

This study aims to investigate the in vitro (murine and human cannabinoid receptors) and in vivo (CD-1 male mice) pharmacodynamic activity of MAM-2201 and compare its effects with those induced by its desmethylated analogue, AM-2201.

RESULTS

In vitro competition binding studies confirmed that MAM-2201 and AM-2201 possess nanomolar affinity for both CD-1 murine and human CB₁ and CB₂ receptors, with preference for the CB₁ receptor. In agreement with the in vitro binding data, in vivo studies showed that MAM-2201 induces visual, acoustic, and tactile impairments that were fully prevented by pretreatment with CB₁ receptor antagonist/partial agonist AM-251, indicating a CB₁ receptor mediated mechanism of action. Administration of MAM-2201 also altered locomotor activity and PPI responses of mice, pointing out its detrimental effect on motor and sensory gating functions and confirming its potential use liability. MAM-2201 and AM-2201 also caused deficits in short- and long-term working memory.

CONCLUSION

These findings point to the potential public health burden that these synthetic cannabinoids may pose, with particular emphasis on impaired driving and workplace performance.

Ethanol enhances JWH-018-induced impairment of sensorimotor and memory functions in mice: From preclinical evidence to forensic implication in Driving Under the Influence of Drugs

BACKGROUND

Several new Synthetic Cannabinoids have appeared each year since their introduction into the illicit drug market as recreational drugs. Among these, naphtalen-1-yl-(1-pentylindol-3-yl) methanone (JWH-018) is one of the most detected compounds in biological samples from patients involved in intoxication or death cases. Furthermore, consumption of JWH-018 has been linked to several cases of Driving Under the Influence of Drugs (DUID) suggesting that effects induced by this compound can affect individuals' ability to drive.

METHODS

Given the high spread of polydrug consumption and the wide number of alcohol-related traffic accidents, this study aims to investigate the acute effects induced by co-administration of JWH-018 with ethanol on sensorimotor and motor responses, grip strength and memory functions in CD-1 male mice. Acute impairments induced by JWH-018 and ethanol alone have also been investigated, in order to compare their effects with that induced by their concurrent administration.

RESULTS

In vivo behavioral experiments revealed a worsening of the cognitive and sensorimotor disruption after the co-administration of JWH-018 with ethanol compared to single compounds.

CONCLUSIONS

These animal-based findings suggest a potential increased impairment on psychomotor performances which could be related to driving abilities posed by poly-drug consumption involving SCs and ethanol.

Neuroprotection of Retinal Ganglion Cells In Vivo Using the Activation of the Endogenous Cannabinoid Signaling System in Mammalian Eyes

Cannabinoid and glutamatergic signaling systems in the human retina coexist and greatly influence one another. Under glaucomatous conditions, excess levels of glutamate accrete in the retinal ganglion cell (RGC) layer. The present study tests the putative neuroprotective effect mediated by cannabinoids at the CB1 and CB2 receptors. In the first experiment, mice were given intravitreal injections of 160 nmol N-methyl-d-aspartic acid (NMDA) in one eye and saline in the paired eye. In the second experiment, both eyes were given NMDA, while one of the two was additionally given the cannabinoid agonist WIN 55,212-2. Ten days later, animals were perfused and the retinae were dissected as wholemounts and stained with Cresyl Violet. Quantitative analysis revealed that 70% of the neurons in the retinal ganglion cell (RGC) layer exposed to NMDA underwent cell death. The addition of the cannabinoid CB1/CB2 agonist doubled the number of neurons surviving the NMDA treatment. These data provide evidence that cannabinoids, either exogenous or endogenous, may be harnessed to provide protection from neurodegenerative diseases, including glaucoma, and from glutamate-induced, and potentially other forms of neurotoxicity, under chronic or acute conditions.

Is there a rational basis for cannabinoids research and development in ocular pain therapy? A systematic review of preclinical evidence

BACKGROUND

Purpose of the present systematic review is to investigate preclinical evidence in favor of the working hypothesis of efficacy of cannabinoids in ocular pain treatment.

METHODS

Literature search includes the most relevant repositories for medical scientific literature from inception until November, 24 2021. Data collection and selection of retrieved records adhere to PRISMA criteria.

RESULTS

In agreement with a priori established protocol the search retrieved 2471 records leaving 479 results after duplicates removal. Eleven records result from title and abstract screening to meet the inclusion criteria; only 4 results are eligible for inclusion in the qualitative synthesis impeding meta-analysis. The qualitative analysis highlights the antinociceptive and anti-inflammatory efficacy of Δ8-tetrahydrocannabinol, cannabidiol and its derivative HU-308 and of new racemic CB1 allosteric ligand GAT211 and its enantiomers GAT228 and GAT229. Moreover, CB2R agonists RO6871304 and RO6871085 and CB2R ligand HU910 provide evidence of anti-inflammatory efficacy. CB2 agonist HU308 reduces of 241% uveitis-induced leukocyte adhesion and changes lipidome profile. Methodological and design issues raise concern of risk of bias and the amount of studies is too small for generalization. Furthermore, the ocular pain model used can resemble only inflammatory but not neuropathic pain.

CONCLUSIONS

The role of the endocannabinoid system in ocular pain is underinvestigated, since only two studies assessing the effects of cannabinoid receptors modulators on pain behavior and other two on pain-related inflammatory processes are found. Preclinical studies investigating the efficacy of cannabinoids in ocular inflammatory and neuropathic pain models are needed to pave the way for clinical translation.

Anandamide Concentration-Dependently Modulates Toll-Like Receptor 3 Agonism or UVB-Induced Inflammatory Response of Human Corneal Epithelial Cells

Photodamage-induced and viral keratitis could benefit from treatment with novel nonsteroid anti-inflammatory agents. Therefore, we determined whether human corneal epithelial cells (HCECs) express members of the endocannabinoid system (ECS), and examined how the endocannabinoid anandamide (AEA, N-arachidonoyl ethanolamine) influences the Toll-like receptor 3 (TLR3) agonism- or UVB irradiation-induced inflammatory response of these cells. Other than confirming the presence of cannabinoid receptors, we show that endocannabinoid synthesizing and catabolizing enzymes are also expressed in HCECs in vitro, as well as in the epithelial layer of the human cornea in situ, proving that they are one possible source of endocannabinoids. p(I:C) and UVB irradiation was effective in promoting the transcription and secretion of inflammatory cytokines. Surprisingly, when applied alone in 100 nM and 10 μM, AEA also resulted in increased pro-inflammatory cytokine production. Importantly, AEA further increased levels of these cytokines in the UVB model, whereas its lower concentration partially prevented the transcriptional effect of p(I:C), while not decreasing the p(I:C)-induced cytokine release. HCECs express the enzymatic machinery required to produce endocannabinoids both in vitro and in situ. Moreover, our data show that, despite earlier reports about the anti-inflammatory potential of AEA in murine cornea, its effects on the immune phenotype of human corneal epithelium may be more complex and context dependent.

CannabinEYEds: The Endocannabinoid System as a Regulator of the Ocular Surface Nociception, Inflammatory Response, Neovascularization and Wound Healing

The endocannabinoid system (ECS) is a complex regulatory system, highly conserved among vertebrates. It has been widely described in nearly all human tissues. In the conjunctiva and cornea, the ECS is believed to play a pivotal role in the modulation of the local inflammatory state as well as in the regulation of tissue repair and fibrosis, neo-angiogenesis and pain perception. This review aims to summarize all the available data on ECS expression and its function in ocular surface structures to provide a specific insight concerning its modulation in dry eye disease, and to propose directions for future research.

Cannabis and the Cornea

Purpose: While cannabis has the potential to reduce corneal pain, cannabinoids might induce side effects. This review article examines the effects of cannabinoids on the cornea. As more states and countries consider the legalization of adult cannabis use, health-care providers will need to identify ocular effects of cannabis consumption.Methods: Studies included in this review examined the connection between cannabis and the cornea, more specifically anti-nociceptive and anti-inflammatory actions of cannabinoids. NCBI Databases from 1781 up to December 2019 were consulted.Results: Five studies examined corneal dysfunctions caused by cannabis consumption (opacification, decreased endothelial cell density). Twelve studies observed a reduction in corneal pain and inflammation (less lymphocytes, decreased corneal neovascularization, increased cell proliferation and migration).Conclusion: More than half of the studies examined the therapeutic effects of cannabinoids on the cornea. As the field is still young, more studies should be conducted to develop safe cannabinoid treatments for corneal diseases.

Potential for endocannabinoid system modulation in ocular pain and inflammation: filling the gaps in current pharmacological options

Challenges in the management of ocular pain are an underappreciated topic. Currently available therapeutics lack both efficacy and clear guidelines for their use, with many also possessing unacceptable side effects. Promising novel agents would offer analgesic, anti-inflammatory, and possibly neuroprotective actions; have favorable ocular safety profiles; and show potential in managing neuropathic pain. Growing evidence supports a link between the endocannabinoid system (ECS) and a range of physiological and disease processes, notably those involving inflammation and pain. Both preclinical and clinical data suggest analgesic and anti-inflammatory actions of cannabinoids and ECS-modifying drugs in chronic pain conditions, including those of neuropathic origin. This review will examine existing evidence for the anatomical and physiological basis of ocular pain, specifically, ocular surface disease and the development of chronic ocular pain. The mechanism of action, efficacy, and limitations of currently available treatments will be discussed, and current knowledge related to ECS-modulation of ocular pain and inflammatory disease will be summarized. A perspective will be provided on the future directions of ECS research in terms of developing cannabinoid therapeutics for ocular pain.

Topical Medical Cannabis: A New Treatment for Wound Pain-Three Cases of Pyoderma Gangrenosum

Pain associated with integumentary wounds is highly prevalent, yet it remains an area of significant unmet need within health care. Currently, systemically administered opioids are the mainstay of treatment. However, recent publications are casting opioids in a negative light given their high side effect profile, inhibition of wound healing, and association with accidental overdose, incidents that are frequently fatal. Thus, novel analgesic strategies for wound-related pain need to be investigated. The ideal methods of pain relief for wound patients are modalities that are topical, lack systemic side effects, noninvasive, self-administered, and display rapid onset of analgesia. Extracts derived from the cannabis plant have been applied to wounds for thousands of years. The discovery of the human endocannabinoid system and its dominant presence throughout the integumentary system provides a valid and logical scientific platform to consider the use of topical cannabinoids for wounds. We are reporting a prospective case series of three patients with pyoderma gangrenosum that were treated with topical medical cannabis compounded in nongenetically modified organic sunflower oil. Clinically significant analgesia that was associated with reduced opioid utilization was noted in all three cases. Topical medical cannabis has the potential to improve pain management in patients suffering from wounds of all classes.

Pharmaco-toxicological effects of the novel third-generation fluorinate synthetic cannabinoids, 5F-ADBINACA, AB-FUBINACA, and STS-135 in mice. In vitro and in vivo studies

INTRODUCTION

5F-ADBINACA, AB-FUBINACA, and STS-135 are 3 novel third-generation fluorinate synthetic cannabinoids that are illegally marketed as incense, herbal preparations, or research chemicals for their psychoactive cannabis-like effects.

METHODS

The present study aims at investigating the in vitro and in vivo pharmacological activity of 5F-ADBINACA, AB-FUBINACA, and STS-135 in male CD-1 mice, comparing their in vivo effects with those caused by the administration of Δ⁹ -THC and JWH-018. In vitro competition binding experiments revealed a nanomolar affinity and potency of the 5F-ADBINACA, AB-FUBINACA, and STS-135 on mouse and human CB₁ and CB₂ receptors. Moreover, these synthetic cannabinoids induced neurotoxicity in murine neuro-2a cells.

RESULTS

In vivo studies showed that 5F-ADBINACA, AB-FUBINACA, and STS-135 induced hypothermia; increased pain threshold to both noxious mechanical and thermal stimuli; caused catalepsy; reduced motor activity; impaired sensorimotor responses (visual, acoustic, and tactile); caused seizures, myoclonia, and hyperreflexia; and promoted aggressiveness in mice. Behavioral and neurological effects were fully prevented by the selective CB₁ receptor antagonist/inverse agonist AM 251. Differently, the visual sensory response induced by STS-135 was only partly prevented by the AM 251, suggesting a CB₁ -independent mechanism.

CONCLUSIONS

For the first time, the present study demonstrates the pharmaco-toxicological effects induced by the administration of 5F-ADBINACA, AB-FUBINACA, and STS-135 in mice and suggests their possible detrimental effects on human health.

Seeing over the horizon - targeting the endocannabinoid system for the treatment of ocular disease

The observation that marijuana reduces intraocular pressure was made by Hepler and Frank in the 1970s. Since then, there has been a significant body of work investigating cannabinoids for their potential use as therapeutics. To date, no endocannabinoid system (ECS)-modulating drug has been approved for clinical use in the eye; however, recent advances in our understanding of the ECS, as well as new pharmacological tools, has renewed interest in the development of ocular ECS-based therapeutics. This review summarizes the current state-of-affairs for the use of ECS-modulating drugs for the treatment of glaucoma and ocular inflammatory and ischemic disease.

Effect of the novel synthetic cannabinoids AKB48 and 5F-AKB48 on "tetrad", sensorimotor, neurological and neurochemical responses in mice. In vitro and in vivo pharmacological studies

RATIONALE

AKB48 and its fluorinate derivate 5F-AKB48 are two novel synthetic cannabinoids belonging to a structural class with an indazole core structure. They are marketed as incense, herbal preparations or chemical supply for their psychoactive Cannabis-like effects.

OBJECTIVES

The present study was aimed at investigating the in vitro and in vivo pharmacological activity of AKB48 and 5F-AKB48 in male CD-1 mice and comparing their in vivo effects with those caused by the administration of Δ⁹-THC and JWH-018.

RESULTS

In vitro competition binding experiments performed on mouse and human CB₁ and CB₂ receptors revealed a nanomolar affinity and potency of the AKB48 and 5F-AKB48. In vivo studies showed that AKB48 and 5F-AKB48, induced hypothermia, increased pain threshold to both noxious mechanical and thermal stimuli, caused catalepsy, reduced motor activity, impaired sensorimotor responses (visual, acoustic and tactile), caused seizures, myoclonia, hyperreflexia and promoted aggressiveness in mice. Moreover, microdialysis study in freely moving mice showed that systemic administration of AKB48 and 5F-AKB48 stimulated dopamine release in the nucleus accumbens. Behavioural, neurological and neurochemical effects were fully prevented by the selective CB₁ receptor antagonist/inverse agonist AM 251.

CONCLUSIONS

For the first time, the present study demonstrates the overall pharmacological effects induced by the administration of AKB48 and 5F-AKB48 in mice and suggests that the fluorination can increase the power and/or effectiveness of SCBs. Furthermore, this study outlines the potential detrimental effects of SCBs on human health.

Turning Down the Thermostat: Modulating the Endocannabinoid System in Ocular Inflammation and Pain

The endocannabinoid system (ECS) has emerged as an important regulator of both physiological and pathological processes. Notably, this endogenous system plays a key role in the modulation of pain and inflammation in a number of tissues. The components of the ECS, including endocannabinoids, their cognate enzymes and cannabinoid receptors, are localized in the eye, and evidence indicates that ECS modulation plays a role in ocular disease states. Of these diseases, ocular inflammation presents a significant medical problem, given that current clinical treatments can be ineffective or are associated with intolerable side-effects. Furthermore, a prominent comorbidity of ocular inflammation is pain, including neuropathic pain, for which therapeutic options remain limited. Recent evidence supports the use of drugs targeting the ECS for the treatment of ocular inflammation and pain in animal models; however, the potential for therapeutic use of cannabinoid drugs in the eye has not been thoroughly investigated at this time. This review will highlight evidence from experimental studies identifying components of the ocular ECS and discuss the functional role of the ECS during different ocular inflammatory disease states, including uveitis and corneal keratitis. Candidate ECS targeted therapies will be discussed, drawing on experimental results obtained from both ocular and non-ocular tissue(s), together with their potential application for the treatment of ocular inflammation and pain.

Effect of JWH-250, JWH-073 and their interaction on "tetrad", sensorimotor, neurological and neurochemical responses in mice

JWH-250 and JWH-073 are two synthetic cannabinoid agonists with nanomolar affinity at CB1 and CB2 receptors. They are illegally marketed within "herbal blend" for theirs psychoactive effects greater than those produced by Cannabis. Recently, we analyzed an "herbal" preparation containing a mixture of both JWH-250 and JWH-073. The present study was aimed at investigating the in vitro and in vivo pharmacological activity of JWH-250 and JWH-073 in male CD-1 mice. In vitro competition binding experiments performed on mouse and human CB1 and CB2 receptors revealed a nanomolar affinity and potency of the JWH-250 and JWH-073. In vivo studies showed that JWH-250 and JWH-073, administered separately, induced a marked hypothermia, increased pain threshold to both noxious mechanical and thermal stimuli, caused catalepsy, reduced motor activity, impaired sensorimotor responses (visual, acoustic and tactile), caused seizures, myoclonia, hyperreflexia and promote aggressiveness in mice. Moreover, microdialysis study in freely moving mice showed that systemic administration of JWH-250 and JWH-073 stimulated dopamine release in the nucleus accumbens in a dose-dependent manner. Behavioral, neurological and neurochemical effects were fully prevented by the selective CB1 receptor antagonist/inverse agonist AM 251. Co-administration of ineffective doses of JWH-250 and JWH-073 impaired visual sensorimotor responses, improved mechanical pain threshold and stimulated mesolimbic DA transmission in mice, living unchanged all other behavioral and physiological parameters. For the first time the present study demonstrates the overall pharmacological effects induced by the administration of JWH-250 and JWH-073 in mice and it reveals their potentially synergistic action suggesting that co-administration of different synthetic cannabinoids may potentiate the detrimental effects of individual compounds increasing their dangerousness and abuse potential.

Anatomical evidence of pruriceptive trigeminothalamic and trigeminoparabrachial projection neurons in mice

Itch is relayed to higher centers by projection neurons in the spinal and medullary dorsal horn. We employed a double-label method to map the ascending projections of pruriceptive and nociceptive trigeminal and spinal neurons. The retrograde tracer fluorogold (FG) was stereotaxically injected into the right thalamus or lateral parabrachial area (LPb) in mice. Seven days later, mice received intradermal (id) microinjection of histamine, chloroquine, capsaicin, or vehicle into the left cheek. Histamine, chloroquine, and capsaicin intradermally elicited similar distributions of Fos-positive neurons in the medial aspect of the superficial medullary and spinal dorsal horn from the trigeminal subnucleus caudalis to C2. Among neurons retrogradely labeled from the thalamus, 43%, 8%, and 22% were Fos-positive following id histamine, chloroquine, or capsaicin. Among the Fos-positive neurons following pruritic or capsaicin stimuli, ∼1-2% were retrogradely labeled with FG. Trigeminoparabrachial projection neurons exhibited a higher incidence of double labeling in the superficial dorsal horn. Among the neurons retrogradely labeled from LPb, 36%, 29%, and 33% were Fos positive following id injection of histamine, chloroquine, and capsaicin, respectively. Among Fos-positive neurons elicited by id histamine, chloroquine, and capsaicin, respectively, 3.7%, 4.3%, and 4.1% were retrogradely labeled from LPb. The present results indicate that, overall, relatively small subpopulations of pruriceptive and/or nociceptive neurons innervating the cheek project to thalamus or LPb. These results imply that the vast majority of pruritogen- and algogen-responsive spinal neurons are likely to function as interneurons relaying information to projection neurons and/or participating in segmental nocifensive circuits.

Identification of prostamides, fatty acyl ethanolamines, and their biosynthetic precursors in rabbit cornea

Arachidonoyl ethanolamine (anandamide) and pros-taglandin ethanolamines (prostamides) are biologically active derivatives of arachidonic acid. Although available through different precursor phospholipids, there is considerable overlap between the biosynthetic pathways of arachidonic acid-derived eicosanoids and anandamide-derived prostamides. Prostamides exhibit physiological actions and are involved in ocular hypotension, smooth muscle contraction, and inflammatory pain. Although topical application of bimatoprost, a structural analog of prostaglandin F2α ethanolamide (PGF2α-EA), is currently a first-line treatment for ocular hypertension, the endogenous production of prostamides and their biochemical precursors in corneal tissue has not yet been reported. In this study, we report the presence of anandamide, palmitoyl-, stearoyl-, α-linolenoyl docosahexaenoyl-, linoleoyl-, and oleoyl-ethanolamines in rabbit cornea, and following treatment with anandamide, the formation of PGF2α-EA, PGE2-EA, PGD2-EA by corneal extracts (all analyzed by LC/ESI-MS/MS). A number of N-acyl phosphatidylethanolamines, precursors of anandamide and other fatty acyl ethanolamines, were also identified in corneal lipid extracts using ESI-MS/MS. These findings suggest that the prostamide and fatty acid ethanolamine pathways are operational in the cornea and may provide valuable insight into corneal physiology and their potential influence on adjacent tissues and the aqueous humor.

JWH-018 impairs sensorimotor functions in mice

Naphthalen-1-yl-(1-pentylindol-3-yl)methanone (JWH-018) is a synthetic cannabinoid agonist illegally marketed in "Spice" and "herbal blend" for its psychoactive effect greater than those produced by cannabis. In rodents JWH-018 reproduces typical effects of (-)-Δ(9)-THC or Dronabinol® (Δ(9)-THC) such as hypothermia, analgesia, hypolocomotion and akinesia, while its effects on sensorimotor functions are still unknown. Therefore, the aim of the present study is to investigate the effect of acute administration of JWH-018 (0.01-6mg/kg i.p.) on sensorimotor functions in male CD-1 mice and to compare its effects with those caused by the administration of Δ(9)-THC (0.01-6mg/kg i.p.). A specific battery of behavioral tests were adopted to investigate effects of cannabinoid agonists on sensorimotor functions (visual, auditory, tactile) and neurological changes (convulsion, myoclonia, hyperreflexia) while video-tracking analysis was used to study spontaneous locomotion. JWH-018 administration inhibited sensorimotor responses at lower doses (0.01-0.1mg/kg), reduced spontaneous locomotion at intermediate/high doses (1-6mg/kg) and induced convulsions, myoclonia and hyperreflexia at high doses (6mg/kg). Similarly, administration of Δ(9)-THC reduced sensorimotor responses in mice but it did not inhibit spontaneous locomotion and it did not induce neurological alterations. All behavioral effects and neurological alterations were prevented by the administration of the selective CB1 receptor antagonist/inverse agonist 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-(piperidin-1-yl)-1H-pyrazole-3-carboxamide (AM 251). For the first time these data demonstrate that JWH-018 impairs sensorimotor responses in mice. This aspect should be carefully evaluated to better understand the potential danger that JWH-018 may pose to public health, with particular reference to decreased performance in driving and hazardous works.

Small intestinal cannabinoid receptor changes following a single colonic insult with oil of mustard in mice

Cannabinoids are known to be clinically beneficial for control of appetite disorders and nausea/vomiting, with emerging data that they can impact other GI disorders, such as inflammation. Post-inflammatory irritable bowel syndrome (PI-IBS) is a condition of perturbed intestinal function that occurs subsequent to earlier periods of intestinal inflammation. Cannabinoid 1 receptor (CB1R) and CB2R alterations in GI inflammation have been demonstrated in both animal models and clinically, but their continuing role in the post-inflammatory period has only been implicated to date. Therefore, to provide direct evidence for CBR involvement in altered GI functions in the absence of overt inflammation, we used a model of enhanced upper GI transit that persists for up to 4 weeks after a single insult by intracolonic 0.5% oil of mustard (OM) in mice. In mice administered OM, CB1R immunostaining in the myenteric plexus was reduced at day 7, when colonic inflammation is subsiding, and then increased at 28 days, compared to tissue from age-matched vehicle-treated mice. In the lamina propria CB2R immunostaining density was also increased at day 28. In mice tested 28 day after OM, either a CB1R-selective agonist, ACEA (1 and 3 mg/kg, s.c.) or a CB2R-selective agonist, JWH-133 (3 and 10 mg/kg, s.c.) reduced the enhanced small intestinal transit in a dose-related manner. Doses of ACEA and JWH-133 (1 mg/kg), alone or combined, reduced small intestinal transit of OM-treated mice to a greater extent than control mice. Thus, in this post-colonic inflammation model, both CBR subtypes are up-regulated and there is increased efficacy of both CB1R and CB2R agonists. We conclude that CBR remodeling occurs not only during GI inflammation but continues during the recovery phase. Thus, either CB1R- or CB2-selective agonists could be efficacious for modulating GI motility in individuals experiencing diarrhea-predominant PI-IBS.

Bright light produces Fos-positive neurons in caudal trigeminal brainstem

Excessive discomfort after exposure to bright light often occurs after ocular injury and during headache. Although the trigeminal nerve is necessary for light-evoked discomfort, the mechanisms underlying this phenomenon, often referred to generally as photophobia, are not well defined. Quantitative Fos-like immunoreactivity (Fos-LI) was used to determine the pattern of neuronal activation in the caudal brainstem after bright light stimulation and, secondly, whether a neurovascular mechanism within the eye contributes to this response. Under barbiturate anesthesia, male rats were exposed to low (1 x 10(4) lx) or high intensity (2 x 10(4) lx) light delivered from a thermal neutral source for 30 min (30 s ON, 30 s OFF) and allowed to survive for 90 min. Intensity-dependent increases in Fos-LI were seen in laminae I-II at the trigeminal caudalis/cervical cord junction region (Vc/C1) and nucleus tractus solitarius (NTS). Fos-LI also increased at the trigeminal interpolaris/caudalis transition (Vi/Vc(vl)) and dorsal paratrigeminal (dPa5) regions independent of intensity. Intravitreal injection of norepinephrine greatly reduced light-evoked Fos-LI at the Vc/C1, dPa5 and NTS, but not at the Vi/Vc transition. Lidocaine applied to the ocular surface had no effect on Fos-LI produced in trigeminal brainstem regions. These results suggested that multiple regions of the caudal trigeminal brainstem complex integrate light-related sensory information. Fos-LI produced at the dPa5 and NTS, coupled with norepinephrine-induced inhibition, was consistent with the hypothesis that light-evoked activation of trigeminal brainstem neurons involves an intraocular neurovascular mechanism with little contribution from neurons that supply the ocular surface.

Effects of WIN55,212-2 on voltage-gated sodium channels in trigeminal ganglion neurons of rats

OBJECTIVES

This study was carried out to investigate the effects of WIN55,212-2, a potential cannabinoid receptor agonist, on voltage-gated sodium currents I(Na) in cultured trigeminal ganglion neurons of rats, and to investigate whether the anti-nociceptive effects of cannabinoid receptor subtype 1 (CB1) were produced through its modulation on I(Na).

METHODS

Whole cell patch clamp techniques were used to record I(Na) before and after WIN55,212-2 was perfused in cultured trigeminal ganglion neurons of rats.

RESULTS

WIN55,212-2 (0.01 micromol/l) could enhance I(Na) slightly by 11.5 +/- 4.7% (n=7, p<0.05), and this effect could not be blocked by AM251, the CB1 receptor antagonist. However, WIN55,212-2 could inhibit I(Na) in concentration dependent manner at concentrations from 0.1 to 100 micromol/l. The inhibitory rates were 17.4 +/- 6.0, 22.5 +/- 7.8, 43.9 +/- 9.4 and 73.9 +/- 6.7% respectively by 0.1, 1, 10, 100 micromol/l WIN55,212-2, and the EC(50) was 17.8 micromol/l (n=7, p<0.05 or p<0.01). This inhibitory effect could be blocked partly by 1 micromol/l AM251 (n=7, p<0.05). WIN55,212-2 (0.01 micromol/l) shifted the active curve of I(Na) leftward slightly (n=7, p<0.05), but had no effect on its stable inactive curve (n=7, p>0.05). WIN55,212-2 (10 micromol/l) did not affect the active and stable inactive curves of I(Na) (n=7, p>0.05).

CONCLUSION

WIN55,212-2 had bidirectional (two phases) effects on I(Na) in trigeminal ganglion neurons. It might act on different receptors, and the CB1 receptor participated in its modulation on I(Na).

Stimulation of neuronal receptors, neuropeptides and cytokines during experimental oil of mustard colitis

Oil of mustard (OM), administered intracolonically, produces severe colitis in mice that is maximized within 3 days. The purpose of this study was to characterize the cytokine response, and to establish expression patterns of enteric neuronal mediators and neuronal receptors affected during active colitis. We measured the changes in the mRNA levels for neuronal receptors and mediators by real-time PCR, and cytokine and chemokine protein levels in the affected tissue. Significant increases in neuronal receptors, such as transient receptor potential A1 (TRPA1), cannabinoid type 1 receptor, neurokinin 1 receptor (NK1R) and delta-opioid receptor; prokineticin-1 receptor; and soluble mediators, such as prodynorphin, proenkephalin1, NK1, prokineticin-1 and secretory leukocyte protease inhibitor, occurred. Significant increases in cytokines, such as interleukin (IL)-1beta, IL-6 and granulocyte macrophage colony stimulating factor (GM-CSF), and in chemokines, such as macrophage chemotactic protein 1 (MCP-1), macrophage inflammatory protein 1 (MIP-1alpha) and Kupffer cell derived chemokine (KC), were detected, with no changes in T-cell-derived cytokines. Furthermore, immunodeficient C57Bl/6 RAG2(-/-) mice exhibited OM colitis of equal severity as seen in wt C57Bl/6 and CD-1 mice. The results demonstrate rapidly increased levels of mRNA for neuronal receptors and soluble mediators associated with pain and inflammation, and increases in cytokines associated with macrophage and neutrophil activation and recruitment. Collectively, the data support a neurogenic component in OM colitis coupled with a myeloid cell-related, T- and B-cell-independent inflammatory component.

Continuous infusion of the cannabinoid WIN 55,212-2 to the site of a peripheral nerve injury reduces mechanical and cold hypersensitivity

BACKGROUND AND PURPOSE

Cannabinoids have analgesic and anti-inflammatory properties but their use is limited by psychotropic activity at CNS receptors. Restricting cannabinoid delivery to peripheral tissues at systemically inactive doses offers a potential solution to this problem.

EXPERIMENTAL APPROACH

WIN 55,212-2 was continuously delivered to the site of a partial ligation injury to the sciatic nerve via a perineural catheter connected to a mini-osmotic pump implanted at the time of injury. Bilateral reflex limb withdrawal behaviour was measured in adult male Wistar rats in response to mechanical and cooling stimulation of the hind paw.

KEY RESULTS

Compared with vehicle treatment, WIN 55,212-2 (1.4 microg microl(-1) hr(-1)) reduced hypersensitivity to stimuli applied to the injured limb at 2, 4 and 6 days after injury. The effects of WIN 55,212-2 (0.6-2.8 microg microl(-1) hr(-1)) were dose-dependent. Estimated EC(50) values for reduction in mean responses to mechanical and cooling stimulation (day 4 post-surgery) were 1.55 (95% C.I, [1.11-2.16]) microg microl(-1) hr(-1) and 1.52 (95% C.I, [1.07-2.18]) microg microl(-1) hr(-1), respectively. When delivered to the contralateral side to injury, WIN 55,212-2 (1.4 or 2.8 microg microl(-1) hr(-1)) did not significantly affect nerve injury-associated hypersensitivity. Co-perineural application of a CB(1) receptor antagonist SR141716a and WIN 55,212-2 prevented the effects of WIN 55,212-2 on hypersensitivity. Co-application of CB(2) receptor antagonist SR144528 reversed WIN 55,212-2's effect on mechanical hypersensitivity on day 2 only.

CONCLUSIONS AND IMPLICATIONS

These data support a peripheral antihyperalgesic effect of WIN 55,212-2 when delivered directly to the site of a nerve injury at systemically inactive doses.

Cannabinoid (CB1) receptor activation inhibits trigeminovascular neurons

Migraine is a common and disabling neurological disorder that involves activation or the perception of activation of the trigeminovascular system. Cannabinoid (CB) receptors are present in brain and have been suggested to be antinociceptive. Here we determined the effect of cannabinoid receptor activation on neurons with trigeminovascular nociceptive input in the rat. Neurons in the trigeminocervical complex (TCC) were studied using extracellular electrophysiological techniques. Responses to both dural electrical stimulation and cutaneous facial receptive field activation of the ophthalmic division of the trigeminal nerve and the effect of cannabinoid agonists and antagonists were studied. Nonselective CB receptor activation with R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2, 3-de]-1,4-benzoxazin-yl]-(1-naphthalenyl) (WIN55,212; 1 mg kg(-1)) inhibited neuronal responses to A-(by 52%) and C-fiber (by 44%) afferents, an effect blocked by the CB(1) receptor antagonist SR141716 [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide; 3 mg kg(-1)] but not the CB2 receptor antagonist AM630 (6-iodopravadoline; 3 mg kg(-1)). Anandamide (10 mg kg(-1)) was able to inhibit both A- and C-fiber-elicited TCC firing, only after transient receptor potential vanilloid 1 receptor inhibition. Activation of cannabinoid receptors had no effect on cutaneous receptive fields when recorded from TCC neurons. The data show that manipulation of CB1 receptors can affect the responses of trigeminal neurons with A- and C-fiber inputs from the dura mater. This may be a direct effect on neurons in the TCC itself or an effect in discrete areas of the brain that innervate these neurons. The data suggest that CB receptors may have therapeutic potential in migraine, cluster headache, or other primary headaches, although the potential hazards of psychoactive side effects that accompany cannabinoid treatments may be complex to overcome.

Agonists of cannabinoid receptor 1 and 2 inhibit experimental colitis induced by oil of mustard and by dextran sulfate sodium

Oil of mustard (OM) is a potent neuronal activator that is known to elicit visceral hyperalgesia when given intracolonically, but the full extent to which OM is also proinflammatory in the gastrointestinal tract is not known. We have previously shown that male CD-1 mice given a single administration of 0.5% OM develop a severe colitis that is maximum at day 3 and that gradually lessens until essentially absent by day 14. OM-induced neuronal stimulation is reported to be reduced by cannabinoid agonists, and cannabinoid receptor 1 (CB1R)-/- mice have exacerbated experimental colitis. Therefore, we examined the role of cannabinoids in this OM-induced 3-day model of colitis in CD-1 mice and in a 7-day dextran sulfate sodium (DSS) colitis model in BALB/c mice. In OM colitis, the CB1R-selective agonist ACEA and the CB2R-selective agonist JWH-133 reduced (P < 0.05) colon weight gain (means +/- SE; 82 +/- 13% and 47 +/- 15% inhibition, respectively), colon shrinkage (98 +/- 24% and 42 +/- 12%, respectively), colon inflammatory damage score (49 +/- 11% and 40 +/- 12%, respectively), and diarrhea (58 +/- 12% and 43 +/- 11%, respectively). Histological damage was similarly reduced by these treatments. Likewise, CBR agonists attenuated DSS colitis, albeit at higher doses; ACEA at 10 mg/kg, twice daily, inhibited (P < 0.05) macroscopic and microscopic scores (46 +/- 9% and 63 +/- 7%, respectively); whereas 20 mg/kg, twice daily, of JWH-133 was required to diminish (P < 0.05) macroscopic and microscopic scores (29 +/- 7% and 43 +/- 5%, respectively). CB1R and CB2R immunostaining of colon sections revealed that CB1R in enteric neurons was more intense in colitic vs. control mice; however, CB1R was also increased in the endothelial layer in OM colitis only. CB2R immunostaining was more marked in infiltrated immune cells in OM colitis. These findings validate the OM colitis model with respect to the DSS model and provide strong support to the emerging idea that cannabinoid receptor activation mediates protective mechanisms in experimental colitis. The demonstration of CB1R agonist effects in colitis support the neurogenic nature of the OM-induced colitis model and reinforce the importance of neuronal activation in intestinal inflammation.

Cannabinoid mechanisms of pain suppression

A large body of literature indicates that cannabinoids suppress behavioral responses to acute and persistent noxious stimulation in animals. This review examines neuroanatomical, behavioral, and neurophysiological evidence supporting a role for cannabinoids in suppressing pain at spinal, supraspinal, and peripheral levels. Localization studies employing receptor binding and quantitative autoradiography, immunocytochemistry, and in situ hybridization are reviewed to examine the distribution of cannabinoid receptors at these levels and provide a neuroanatomical framework with which to understand the roles of endogenous cannabinoids in sensory processing. Pharmacological and transgenic approaches that have been used to study cannabinoid antinociceptive mechanisms are described. These studies provide insight into the functional roles of cannabinoid CB1 (CB1R) and CB2 (CB2R) receptor subtypes in cannabinoid antinociceptive mechanisms, as revealed in animal models of acute and persistent pain. The role of endocannabinoids and related fatty acid amides that are implicated in endogenous mechanisms for pain suppression are discussed. Human studies evaluating therapeutic potential of cannabinoid pharmacotherapies in experimental and clinical pain syndromes are evaluated. The potential of exploiting cannabinoid antinociceptive mechanisms in novel pharmacotherapies for pain is discussed.

Acute colitis induction by oil of mustard results in later development of an IBS-like accelerated upper GI transit in mice

Oil of mustard (OM) is a potent neuronal activator that promotes allodynia and hyperalgesia within minutes of application. In this study, OM was used to induce an acute colitis. We also investigated whether intracolonic OM-induced inflammation alters gastrointestinal (GI) function over a longer time frame as a model of postinflammatory irritable bowel syndrome (PI-IBS). Mice given a single administration of 0.5% OM developed a severe colitis that peaked at day 3, was reduced at day 7, and was absent by day 14. At the peak response, there was body weight loss, colon shrinkage, thickening and weight increases, distension of the proximal colon, and diarrhea. Macroscopic inspection of the distal colon revealed a discontinuous pattern of inflammatory damage and occasional transmural ulceration. Histological examination showed loss of epithelium, an inflammatory infiltrate, destruction of mucosal architecture, edema, and loss of circular smooth muscle architecture. OM administration increased transit of a carmine dye bolus from 58% of the total length of the upper GI tract in untreated age-matched controls to as high as 74% when tested at day 28 post-OM. Mice in the latter group demonstrated a significantly more sensitive response to inhibition of upper GI transit by the mu-opioid receptor agonist loperamide compared with normal mice. OM induces a rapid, acute, and transient colitis and, in the longer term, functional changes in motility that are observed when there is no gross inflammation and thereby is a model of functional bowel disorders that mimic aspects of PI-IBS in humans.

Cannabinoid receptor-independent actions of the aminoalkylindole WIN 55,212-2 on trigeminal sensory neurons

The prototypical aminoalkylindole cannabinoid WIN 55,212-2 (WIN-2) has been shown to produce antihyperalgesia through a peripheral mechanism of action. However, it is not known whether WIN-2 exerts this action directly via cannabinoid receptors located on primary afferents or if other, perhaps indirect or noncannabinoid, mechanisms are involved. To address this question, we have examined the specific actions of WIN-2 on trigeminal ganglion (TG) neurons in vitro by quantifying its ability to modulate the evoked secretion of the proinflammatory neuropeptide CGRP as well as the inflammatory mediator-induced generation of cAMP. WIN-2 evoked CGRP release from TG neurons in vitro (EC(50)=26 microm) in a concentration- and calcium-dependent manner, which was mimicked by the cannabinoid receptor-inactive enantiomer WIN 55,212-3 (WIN-3). Moreover, WIN-2-evoked CGRP release was attenuated by the nonselective cation channel blocker ruthenium red but not by the vanilloid receptor type 1 (TRPV1) antagonist capsazepine, suggesting that, unlike certain endogenous and synthetic cannabinoids, WIN-2 is not a TRPV1 agonist but rather acts at an as yet unidentified cation channel. The inhibitory effects of WIN-2 on TG neurons were also examined. WIN-2 neither inhibited capsaicin-evoked CGRP release nor did it inhibit forskolin-, isoproteranol- or prostaglandin E(2)-stimulated cAMP accumulation. On the other hand, WIN-2 significantly inhibited (EC(50)=1.7 microm) 50 mm K(+)-evoked CGRP release by approximately 70%. WIN-2 inhibition of 50 mm K(+)-evoked CGRP release was not reversed by antagonists of cannabinoid type 1 (CB1) receptor, but was mimicked in magnitude and potency (EC(50)=2.7 microm) by its cannabinoid-inactive enantiomer WIN-3. These findings indicate that WIN-2 exerts both excitatory and inhibitory effects on TG neurons, neither of which appear to be mediated by CB1, CB2 or TRPV1 receptors, but by a novel calcium-dependent mechanism. The ramifications of these results are discussed in relation to our current understanding of cannabinoid/vanilloid interactions with primary sensory neurons.

A novel class of neurons at the trigeminal subnucleus interpolaris/caudalis transition region monitors ocular surface fluid status and modulates tear production

Reflex tears are produced by many conditions, one of which is drying of the ocular surface. Although peripheral neural control of the lacrimal gland is well established, the afferent pathways and properties of central premotor neurons necessary for this reflex are not known. Male rats under barbiturate anesthesia were used to determine whether neurons at the ventral trigeminal subnucleus interpolaris- caudalis (Vi/Vc) transition or the trigeminal subnucleus caudalis-cervical cord (Vc/C1) junction region in the lower brainstem were necessary for tears evoked by noxious chemical stimulation (CO2 pulses) or drying of the ocular surface. Both the Vi/Vc transition and Vc/C1 junction regions receive a dense direct projection from corneal nociceptors. Synaptic blockade of the Vi/Vc transition, but not the Vc/C1 junction, by the GABA(A) receptor agonist muscimol inhibited CO2-evoked tears. Glutamate excitation of the Vi/Vc transition, but not the Vc/C1 junction, increased tear volume. Single units recorded at the Vi/Vc transition, but not at the Vc/C1 junction, were inhibited by wetting and excited by drying the ocular surface. Nearly all moisture-sensitive Vi/Vc units displayed an initial inhibitory phase to noxious concentrations of CO2 followed by delayed excitation and displayed an inhibitory surround receptive field from periorbital facial skin. Drying of the ocular surface produced many Fos-positive neurons at the Vi/Vc transition, but not at the Vc/C1 junction. This is the first report of a unique class of moisture-sensitive neurons that exist only at the ventral Vi/Vc transition, and not at more caudal portions of Vc, that may underlie fluid homeostasis of the ocular surface.

Activation of peripheral cannabinoid receptors attenuates cutaneous hyperalgesia produced by a heat injury

Accumulating evidence suggests that cannabinoids can produce antinociception through peripheral mechanisms. In the present study, we determined whether cannabinoids attenuated existing hyperalgesia produced by a mild heat injury to the glabrous hindpaw and whether the antihyperalgesia was receptor-mediated. Anesthetized rats received a mild heat injury (55 degrees C for 30 s) to one hindpaw. Fifteen minutes after injury, animals exhibited hyperalgesia as evidenced by lowered withdrawal latency to radiant heat and increased withdrawal frequency to a von Frey monofilament (200 mN force) delivered to the injured hindpaw. Separate groups of animals were then treated with an intraplantar (i.pl.) injection of vehicle or the cannabinoid receptor agonist WIN 55,212-2 at doses of 1, 10, or 30 microg in 100 microl. WIN 55,212-2 attenuated both heat and mechanical hyperalgesia dose-dependently. The inactive enantiomer WIN 55,212-3 did not alter mechanical or heat hyperalgesia, suggesting the effects of WIN 55,212-2 were receptor-mediated. The CB1 receptor antagonist AM 251 (30 microg) co-injected with WIN 55,212-2 (30 microg) attenuated the antihyperalgesic effects of WIN 55,212-2. The CB2 receptor antagonist AM 630 (30 microg) co-injected with WIN 55,212-2 attenuated only the early antihyperalgesic effects of WIN 55,212-2. I.pl. injection of WIN 55,212-2 into the contralateral paw did not alter the heat-injury induced hyperalgesia, suggesting that the antihyperalgesia occurred through a peripheral mechanism. These data demonstrate that cannabinoids primarily activate peripheral CB1 receptors to attenuate hyperalgesia. Activation of this receptor in the periphery may attenuate pain without causing unwanted side effects mediated by central CB1 receptors.

Local application of the cannabinoid receptor agonist, WIN 55,212–2, to spinal trigeminal nucleus caudalis differentially affects nociceptive and non-nociceptive neurons

Cannabinoid receptor agonists produce analgesia for pains of non-cranial origin. However, their effectiveness for craniofacial pains is currently unclear. In the present study, the cannabinoid CB1/CB2 receptor agonist, WIN 55,212-2 (WIN), was bath applied to the brainstem while activity of spinal trigeminal nucleus caudalis (Vc) neurons evoked by transcutaneous electrical stimulation was recorded in isoflurane anesthetized rats. Neurons were characterized using mechanical and electrical stimulation of the face, and were classified as either low-threshold mechanoreceptive (LTM) or wide dynamic range (WDR). LTM neurons responded to light brushing of the receptive field and received only Abeta primary afferent fiber input. WDR neurons showed a graded response to mechanical stimulation, responding maximally to noxious stimuli, and demonstrated both A- and C-fiber evoked activity. In addition, WDR neurons displayed longer latency, C-fiber mediated post-discharge (PDC) activity after repetitive stimulation. Local bath application of 2.0 mg/ml WIN significantly reduced PDC activity (3+/-1% control, P<0.01), C-fiber evoked activity (58+/-9% control, P<0.01), and Abeta evoked activity (57+/-10% control, P<0.01) in WDR neurons. In contrast, LTM Abeta-fiber evoked activity increased after local administration of WIN (204+/-52% control, P<0.01). SR141716A, a CB1 receptor antagonist, prevented the effects of WIN on WDR PDC and LTM Abeta evoked activity. These results indicate that cannabinoid receptor agonists may be effective agents for craniofacial pain. Furthermore, the particular sensitivity of PDC activity, a measure of neuronal hyperexcitability, to cannabinoid receptor agonists may be relevant to the treatment of persistent craniofacial pain.

Effect of morphine sulphate eye drops on hyperalgesia in the rat cornea

In addition to their traditional role in centrally mediated analgesia, opiate compounds produce significant effects when administered peripherally. Using a recently characterized model of acute chemical injury to the rat cornea, we assessed the effects of morphine sulphate eye drops on corneal inflammation and hyperalgesia. Topical application of a 5 microM morphine sulphate eye drop preparation attenuated capsaicin-induced blinking in a concentration-dependent manner. However, morphine had no effect on capsaicin-induced blinking when applied to healthy, non-inflamed rat cornea. In addition, 5 microM morphine given every 2 h following cauterization retarded the development of both stromal edema and the infiltration of immune cells. Both the analgesic and anti-inflammatory effects of morphine were prevented by the opioid receptor antagonists naloxone, CTAP, and naltrindole. We conclude that morphine acts on mu and delta opioid receptors located in the rat cornea to attenuate inflammation and hyperalgesia.