The Endocannabinoid System in the Retina: From Physiology to Practical and Therapeutic Applications

Cannabinoids Activate Endoplasmic Reticulum Stress Response and Promote the Death of Avian Retinal Müller Cells in Culture

BACKGROUND/OBJECTIVES

Activation of cannabinoid CB1 or CB2 receptors induces the death of glial progenitors from the chick retina in culture. Here, by using an enriched retinal glial cell culture, we characterized some mechanisms underlying glial death promoted by cannabinoids.

METHODS AND RESULTS

Retinal cultures obtained from 8-day-old (E8) chick embryos and maintained for 12-15 days (C12-15) were used. MTT assays revealed that the CB1/CB2 agonist WIN 55,212-2 (WIN) decreased cell viability in the cultures in a time-dependent manner, with a concomitant increase in extracellular LDH activity, suggesting membrane integrity loss. Cell death was also dose-dependently induced by cannabidiol (CBD), Δ9-tetrahydrocannabinol (THC), and CP55940, another CB1/CB2 agonist. In contrast to WIN-induced cell death that was not blocked by either antagonist, the deleterious effect of CBD was blocked by the CB2 receptor antagonist SR144528, but not by PF514273, a CB1 receptor antagonist. WIN-treated cultures showed glial cells with large vacuoles in cytoplasm that were absent in cultures incubated with WIN plus 4-phenyl-butyrate (PBA), a chemical chaperone. Since cannabinoids induced the phosphorylation of eukaryotic initiation factor 2-alfa (eIF2α), these results suggest a process of endoplasmic reticulum (ER) swelling and stress. Incubation of the cultures with WIN for 4 h induced a ~five-fold increase in the number of cells labeled with the ROS indicator CM-H2DCFDA. WIN induced the phosphorylation of JNK but not of p38 in the cultures, and also induced an increase in the number of glial cells expressing cleaved-caspase 3 (c-CASP3). The decrease in cell viability and the expression of c-CASP3 was blocked by salubrinal, an inhibitor of eIF2α dephosphorylation.

CONCLUSIONS

These data suggest that cannabinoids induce the apoptosis of glial cells in culture by promoting ROS production, ER stress, JNK phosphorylation, and caspase-3 processing. The graphical abstract was created at Biorender.com.

The endocannabinoid system and ophthalmic pathologies: a review of molecular mechanisms and its implications for clinical practice

Within the last decade the role of the endocannabinoid system (ECS) has been a significant part of ophthalmic research, including both ocular physiology and the development of eye pathologies. It is known that this widespread cell-signaling system is involved in retinal neurobiological processes, including visual signal processing, as well as neurotransmission. Furthermore, various research indicated the involvement of ECS in the molecular basis of various pathologies, mostly glaucoma, diabetic retinopathy, and age-related macular degeneration (AMD). Therefore, the researchers believe that this biological system, its receptors, pathways, and ligands might be considered as an auxiliary compound to reduce the number of patients suffering from ophthalmic diseases. Despite presented in the literature effects of the endocannabinoid system in the eye, none of the current ECS reviews presented a comprehensive description of the endocannabinoid system, its compounds, and, subsequently ophthalmic disorders. Thus, the aim of this review was to summarize all the major data, including the most up-to-date research, concerning a correlation between the endocannabinoid system and the major ophthalmic pathologies.

Neuroprotective Actions of Cannabinoids in the Bovine Isolated Retina: Role of Hydrogen Sulfide

Both hydrogen sulfide and endocannabinoids can protect the neural retina from toxic insults under in vitro and in vivo conditions. Purpose: The aim of the present study was two-fold: (a) to examine the neuroprotective action of cannabinoids [methanandamide and 2-arachidonyl glycerol (2-AG)] against hydrogen peroxide (H2O2)-induced oxidative damage in the isolated bovine retina and (b) to evaluate the role of endogenously biosynthesized hydrogen sulfide (H2S) in the inhibitory actions of cannabinoids on the oxidative stress in the bovine retina. Methods: Isolated neural retinas from cows were exposed to oxidative damage using H2O2 (100 µM) for 10 min. When used, tissues were pretreated with methanandamide (1 nM-100 nM) and 2-AG (1-10 µM) for 30 min before a 10 min treatment with H2O2 (100 µM). In some experiments, retinas were pretreated with inhibitors of the biosynthesis of H2S [cystathionine β-synthase/cystathionine γ-lyase (CBS/CSE), aminooxyacetic acid, AOAA 30 µM, or 3-mercaptopyruvate sulfurtransferase (3MST), α-keto-butyric acid, KBA 1 mM] and the CB1-receptor antagonist, AM251 (100 nM) for 30 min before treatment with methanandamide (1 nM-100 µM). Enzyme immunoassay measurement of 8-epi PGF2α (8-isoprostane) levels was performed to assess lipid peroxidation in retinal tissues. Results: In the presence of H2O2 (100 µM), methanandamide (1 nM-100 µM) and 2-AG (1-10 µM) significantly (p < 0.001) blocked the H2O2-induced elevation in 8-isoprostane levels in the isolated bovine retina. In the presence of the CB1 antagonist AM251 (100 nM), the effect of methanandamide (1 nM) on the H2O2-induced 8-isoprostane production was significantly (p < 0.001) attenuated. While AOAA (30 µM) had no significant (p > 0.05) effect on the inhibition of H2O2-induced oxidative stress elicited by methanandamide, KBA (1 mM) reversed the neuroprotective action of methanandamide. Conclusions: The cannabinoids, methanandamide and 2-AG can prevent H2O2-induced oxidative stress in the isolated bovine retina. The neuroprotective actions of cannabinoids are partially dependent upon the activation of the CB1 receptors and endogenous production of H2S via the 3-MST/CAT pathway.

Nitric oxide modulates contrast suppression in a subset of mouse retinal ganglion cells

Neuromodulators have major influences on the regulation of neural circuit activity across the nervous system. Nitric oxide (NO) has been shown to be a prominent neuromodulator in many circuits and has been extensively studied in the retina. Here, it has been associated with the regulation of light adaptation, gain control, and gap junctional coupling, but its effect on the retinal output, specifically on the different types of retinal ganglion cells (RGCs), is still poorly understood. In this study, we used two-photon Ca2+ imaging and multi-electrode array (MEA) recordings to measure light-evoked activity of RGCs in the ganglion cell layer in the ex vivo mouse retina. This approach allowed us to investigate the neuromodulatory effects of NO on a cell type-level. Our findings reveal that NO selectively modulates the suppression of temporal responses in a distinct subset of contrast-suppressed RGC types, increasing their activity without altering the spatial properties of their receptive fields. Given that under photopic conditions, NO release is triggered by quick changes in light levels, we propose that these RGC types signal fast contrast changes to higher visual regions. Remarkably, we found that about one-third of the RGC types, recorded using two-photon Ca2+ imaging, exhibited consistent, cell type-specific adaptational response changes throughout an experiment, independent of NO. By employing a sequential-recording paradigm, we could disentangle those additional adaptational response changes from drug-induced modulations. Taken together, our research highlights the selective neuromodulatory effects of NO on RGCs and emphasizes the need of considering non-pharmacological activity changes, like adaptation, in such study designs.

Ocular effects of synthetic cannabinoids: a case-control study

OBJECTIVE

To evaluate the ocular effects of "Bonzai", a synthetic cannabinoid (SC), in seropositive and seronegative users.

METHODS

Sixty eyes of 60 consecutive male patients with a history of "Bonzai" use and 30 eyes of 30 age-matched male healthy controls were enrolled in this case-control study. Patients with past "Bonzai" use were grouped as seropositive (n:30) and seronegative (n:30) according to urine toxicology tests. All groups were compared for blood pressures, intraocular pressure, foveal and parafoveal retinal thicknesses, subfoveal and parafoveal choroidal thicknesses, measurements of the peripapillary retinal nerve fibre layer (RNFL), and macular ganglion cell complex (GCC), subfoveal total choroidal, luminal and stromal areas, and choroidal vascularity index (CVI).

RESULTS

No differences were noted in blood pressures between the groups (p > 0.05). The mean intraocular pressure was significantly lower in the seropositive group than in the other groups (p < 0.001). Foveal and retinal thicknesses, RNFL, and GCC measurements did not differ between the groups (p > 0.05). Subfoveal and parafoveal choroidal thicknesses and areas were lower in the seropositive group than in the other groups (p < 0.001, for all). CVI increased in both groups with "Bonzai" use compared to the control group (p < 0.001, for all).

CONCLUSIONS

This study indicates that intraocular pressure may decrease, and choroidal changes may be observed in SC users. Further clinical studies with a larger sample size, especially using purified SC for therapeutic purposes, are needed to confirm the present findings, and further histopathologic studies are required to clarify the changes in the choroid despite SC seronegativity.

CLINICAL TRIAL ID

NCT06235346.

Postmarketing Surveillance of Full Spectrum Hemp Extract CBD Products: Reported Adverse Events and Serious Adverse Events

BACKGROUND

There is a growing interest in products featuring hemp extracts and a demand for more data regarding their safety. To date, there is a paucity of published data on the safety of these products.

METHODS

A retrospective analysis of postmarketing surveillance data collected in the United States on full spectrum hemp extract (FSHE) products manufactured by Charlotte's Web (CW) was conducted over an 18-month period (January 2019 to July 2020). The frequency of adverse events (AEs) and serious adverse events (SAEs) was assessed by analyzing AE reports against the estimated number of consumers who purchased products and the total number of products sold.

RESULTS

During the 18-month period, approximately 646,391 consumers purchased 1,939,172 products and 431 AEs were reported by 304 individuals. The estimated percentage of consumers who reported at least one adverse event was 0.05%. The percentage of AEs per products sold was 0.02%. Most AEs (98.14%) reported were Grade 1 (i.e., asymptomatic or causing mild symptoms), as classified by the Common Terminology Criteria for Adverse Events. Seven AEs were classified as serious, and the percentage of SAEs per products sold was 0.0004%. None of the reported SAEs were classified as a Grade 4 or Grade 5 (i.e., life threatening or fatal).

CONCLUSIONS

Approximately 0.05% of consumers who purchased the CW FSHE products from January 2019 to July 2020 reported an adverse event. The percentage of AEs and SAEs per products sold was 0.02% and 0.0004%, respectively. These data demonstrate that CW FSHE products appear to be well tolerated at recommended doses.

Palmitoylethanolamide, an endogenous fatty acid amide, and its pleiotropic health benefits: A narrative review

The global nutritional transition has led to high frequency and severity of chronic degenerative diseases worldwide, primarily driven by chronic inflammatory stress. At the mealtimes, various pharmaceutical products aim to prevent such an inflammatory stress, they usually cause various systemic side effects. Therefore, supplementation of natural and safe ingredients is a great strategy to reduce the risk and severity of inflammatory stress-related diseases. As a result, palmitoylethanolamide (PEA), an endocannabinoid-like mediator, has been extensively studied for its myriad of actions, including anti-inflammatory, anti-microbial, immunostimulatory, neuroprotective, and pain-reducing effects with high tolerability and safety of PEA in animals and humans. Because of the multiple molecular targets and mechanisms of action, PEA has shown therapeutic benefits in various diseases, including neurological, psychiatric, ophthalmic, metabolic, oncological, renal, hepatic, immunological, rheumatological, and gastrointestinal conditions. The current review highlights the roles and functions of PEA in various physiological and pathological conditions, further supporting the use of PEA as an important dietary agent.

Dynamic endocannabinoid-mediated neuromodulation of retinal circadian circuitry

Circadian rhythms are biological rhythms that originate from the "master circadian clock," called the suprachiasmatic nucleus (SCN). SCN orchestrates the circadian rhythms using light as a chief zeitgeber, enabling humans to synchronize their daily physio-behavioral activities with the Earth's light-dark cycle. However, chronic/ irregular photic disturbances from the retina via the retinohypothalamic tract (RHT) can disrupt the amplitude and the expression of clock genes, such as the period circadian clock 2, causing circadian rhythm disruption (CRd) and associated neuropathologies. The present review discusses neuromodulation across the RHT originating from retinal photic inputs and modulation offered by endocannabinoids as a function of mitigation of the CRd and associated neuro-dysfunction. Literature indicates that cannabinoid agonists alleviate the SCN's ability to get entrained to light by modulating the activity of its chief neurotransmitter, i.e., γ-aminobutyric acid, thus preventing light-induced disruption of activity rhythms in laboratory animals. In the retina, endocannabinoid signaling modulates the overall gain of the retinal ganglion cells by regulating the membrane currents (Ca2+, K+, and Cl- channels) and glutamatergic neurotransmission of photoreceptors and bipolar cells. Additionally, endocannabinoids signalling also regulate the high-voltage-activated Ca2+ channels to mitigate the retinal ganglion cells and intrinsically photosensitive retinal ganglion cells-mediated glutamate release in the SCN, thus regulating the RHT-mediated light stimulation of SCN neurons to prevent excitotoxicity. As per the literature, cannabinoid receptors 1 and 2 are becoming newer targets in drug discovery paradigms, and the involvement of endocannabinoids in light-induced CRd through the RHT may possibly mitigate severe neuropathologies.

The Metabolism of 2-arachidonoylglycerol in Rod Outer Segments Is Modulated by Proteins Involved in the Phototransduction Process

We previously reported that 2-arachidonoylglycerol (2-AG) synthesis by diacylglycerol lipase (DAGL) and lysophosphatidate phosphohydrolase (LPAP) and hydrolysis by monoacylglycerol lipase (MAGL) in rod outer segments (ROS) from bovine retina were differently modified by light applied to the retina. Based on these findings, the aim of the present research was to evaluate whether 2-AG metabolism could be modulated by proteins involved in the visual process. To this end, ROS kept in darkness (DROS) or obtained in darkness and then subjected to light (BROS) were treated with GTPγS and GDPβS, or with low and moderate ionic strength buffers for detaching soluble and peripheral proteins, or soluble proteins, respectively. Only DAGL activity was stimulated by the application of light to the ROS. GTPγS-stimulated DAGL activity in DROS reached similar values to that observed in BROS. The studies using different ionic strength show that (1) the highest decrease in DROS DAGL activity was observed when both phosphodiesterase (PDE) and transducin α (Tα) are totally membrane-associated; (2) the decrease in BROS DAGL activity does not depend on PDE association to membrane, and that (3) MAGL activity decreases, both in DROS and BROS, when PDE is not associated to the membrane. Our results indicate that the bioavailability of 2-AG under light conditions is favored by G protein-stimulated increase in DAGL activity and hindered principally by Tα/PDE association with the ROS membrane, which decreases DAGL activity.

Formulation and In Vitro-Ex vivo Evaluation of Cannabidiol and Cannabidiol-Valine-Hemisuccinate Loaded Lipid-Based Nanoformulations for Ocular Applications

The goal of this investigation is to develop stable ophthalmic nanoformulations containing cannabidiol (CBD) and its analog cannabidiol-valine-hemisuccinate (CBD-VHS) for improved ocular delivery. Two nanoformulations, nanoemulsion (NE) and nanomicelles (NMC), were developed and evaluated for physicochemical characteristics, drug-excipient compatibility, sterilization, thermal analysis, surface morphology, ex-vivo transcorneal permeation, corneal deposition, and stability. The saturation solubility studies revealed that among the surfactants tested, Cremophor EL had the highest solubilizing capacity for CBD (23.3 ± 0.1 mg/mL) and CBD-VHS (11.2 ± 0.2 mg/mL). The globule size for the lead CBD formulations (NE and NMC) ranged between 205 and 270 nm while CBD-VHS-NMC formulation had a particle size of about 78 nm. The sterilized formulations, except for CBD-VHS-NMC at 40 °C, were stable for three months of storage (last time point tested). Release, in terms of CBD, in the in-vitro release/diffusion studies over 18 h, were faster from the CBD-VHS nanomicelles (38 %) compared to that from the CBD nanoemulsion (16 %) and nanomicelles (33 %). Transcorneal permeation studies revealed improvement in CBD permeability and flux with both formulations; however, a greater improvement was observed with the NMC formulation compared to the NE formulation. In conclusion, the nanoformulations prepared could serve as efficient topical ocular drug delivery platforms for CBD and its analog.

Silva H, P. de Carvalho R, Ventura ALM, Calaza KC, Silveira MS, Kubrusly RCC, de Melo Reis RA. The Healthy and Diseased Retina Seen through Neuron-Glia Interactions

The retina is the sensory tissue responsible for the first stages of visual processing, with a conserved anatomy and functional architecture among vertebrates. To date, retinal eye diseases, such as diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, glaucoma, and others, affect nearly 170 million people worldwide, resulting in vision loss and blindness. To tackle retinal disorders, the developing retina has been explored as a versatile model to study intercellular signaling, as it presents a broad neurochemical repertoire that has been approached in the last decades in terms of signaling and diseases. Retina, dissociated and arranged as typical cultures, as mixed or neuron- and glia-enriched, and/or organized as neurospheres and/or as organoids, are valuable to understand both neuronal and glial compartments, which have contributed to revealing roles and mechanisms between transmitter systems as well as antioxidants, trophic factors, and extracellular matrix proteins. Overall, contributions in understanding neurogenesis, tissue development, differentiation, connectivity, plasticity, and cell death are widely described. A complete access to the genome of several vertebrates, as well as the recent transcriptome at the single cell level at different stages of development, also anticipates future advances in providing cues to target blinding diseases or retinal dysfunctions.

Compare of optic coherence tomography parameters in recreational synthetic tetrahydrocannabinol use and healthy control

PURPOSE

To evaluate retinal thickness (RT), retinal nerve fiber layer thickness (RNFLT), and choroidal thickness (CT) changes in synthetic cannabinoid (SC) users.

METHODS

This prospective study evaluated the RT, RNFLT, and CT values of 56 SC users and 58 healthy controls. The individuals using SCs were referred to us by our hospital's forensic medicine department. Retinal and choroidal images were obtained using spectral-domain optical coherence tomography (OCT). Measurements (one subfoveal, three temporals, three nasal) were taken at 500 μm intervals up to 1500 μm using the caliper system. Only the right eye was used for subsequent analysis.

RESULTS

Mean ages were 27.7 ± 5.7 years in the SC-user group and 25.4 ± 6.7 in the control group. Subfoveal Global RNFLT was in the SCs group 102.3 ± 10.5 μm and 105.6 ± 20.2 μm in the control group (p = 0.271). Subfoveal CT was in the SC group mean of 316.1 ± 100.2 μm and in the control group mean 346.4 ± 81.8 μm (p = 0.065). RT, T500 (283.3 ± 36.7 μm, 296.6 ± 20.5 μm, p = 0.011) and N1500 (355.1 ± 14.3 μm, 349.3 ± 18.1 μm, p = 0.049) were significantly higher in the SC group than in the control group, respectively.

CONCLUSION

Analysis of OCT findings of individuals who had been using SC for more than one year revealed no statistically significant difference between RNFLT and CT, although N1500 was significantly higher in RT. Further studies in the field of OCT are important to explore the pathology of SC.

Therapeutic Potential of Cannabinoids in Glaucoma

Glaucoma is a leading cause of irreversible blindness worldwide. To date, intraocular pressure (IOP) is the only modifiable risk factor in glaucoma treatment, but even in treated patients, the disease can progress. Cannabinoids, which have been known to lower IOP since the 1970s, have been shown to have beneficial effects in glaucoma patients beyond their IOP-lowering properties. In addition to the classical cannabinoid receptors CB1 and CB2, knowledge of non-classical cannabinoid receptors and the endocannabinoid system has increased in recent years. In particular, the CB2 receptor has been shown to mediate anti-inflammatory, anti-apoptotic, and neuroprotective properties, which may represent a promising therapeutic target for neuroprotection in glaucoma patients. Due to their vasodilatory effects, cannabinoids improve blood flow to the optic nerve head, which may suggest a vasoprotective potential and counteract the altered blood flow observed in glaucoma patients. The aim of this review was to assess the available evidence on the effects and therapeutic potential of cannabinoids in glaucoma patients. The pharmacological mechanisms underlying the effects of cannabinoids on IOP, neuroprotection, and ocular hemodynamics have been discussed.

Vitreous Fatty Amides and Acyl Carnitines Are Altered in Intermediate Age-Related Macular Degeneration

Purpose

Age-related macular degeneration (AMD) is the leading cause of visual impairment worldwide. In this study, we aimed to investigate the vitreous humor metabolite profiles of patients with intermediate AMD using untargeted metabolomics.

Methods

We performed metabolomics using high-resolution liquid chromatography mass spectrometry on the vitreous humor of 31 patients with intermediate AMD and 30 controls who underwent vitrectomy for epiretinal membrane with or without cataract surgery. Univariate analyses after false discovery rate correction were performed to discriminate the metabolites and identify the significant metabolites of intermediate AMD. For biologic interpretation, enrichment and pathway analysis were conducted using MetaboAnalyst 5.0.

Results

Of the 858 metabolites analyzed in the vitreous humor, 258 metabolites that distinguished patients with AMD from controls were identified (P values < 0.05). Ascorbic acid and uric acid levels increased in the AMD group (all P values < 0.05). The acyl carnitines, such as acetyl L-carnitine (1.37-fold), and fatty amides, such as anandamide (0.9-fold) and docosanamide (0.67-fold), were higher in patients with intermediate AMD. In contrast, nicotinamide (-0.55-fold), and succinic acid (-1.69-fold) were lower in patients with intermediate AMD. The metabolic pathway related oxidation of branched chain fatty acids and carnitine synthesis showed enrichment.

Conclusions

Multiple metabolites related to fatty amides and acyl carnitine were found to be increased in the vitreous humor of patients with intermediate AMD, whereas succinic acid and nicotinamide were reduced, suggesting that altered metabolites related to fatty amides and acyl carnitines and energy metabolism may be implicated in the etiology of AMD.

Blockade of CB1 or Activation of CB2 Cannabinoid Receptors Is Differentially Efficacious in the Treatment of the Early Pathological Events in Streptozotocin-Induced Diabetic Rats

Oxidative stress, neurodegeneration, neuroinflammation, and vascular leakage are believed to play a key role in the early stage of diabetic retinopathy (ESDR). The aim of this study was to investigate the blockade of cannabinoid receptor 1 (CB1R) and activation of cannabinoid receptor 2 (CB2R) as putative therapeutics for the treatment of the early toxic events in DR. Diabetic rats [streptozotocin (STZ)-induced] were treated topically (20 μL, 10 mg/mL), once daily for fourteen days (early stage DR model), with SR141716 (CB1R antagonist), AM1710 (CB2R agonist), and the dual treatment SR141716/AM1710. Immunohistochemical-histological, ELISA, and Evans-Blue analyses were performed to assess the neuroprotective and vasculoprotective properties of the pharmacological treatments on diabetes-induced retinal toxicity. Activation of CB2R or blockade of CB1R, as well as the dual treatment, attenuated the nitrative stress induced by diabetes. Both single treatments protected neural elements (e.g., RGC axons) and reduced vascular leakage. AM1710 alone reversed all toxic insults. These findings provide new knowledge regarding the differential efficacies of the cannabinoids, when administered topically, in the treatment of ESDR. Cannabinoid neuroprotection of the diabetic retina in ESDR may prove therapeutic in delaying the development of the advanced stage of the disease.

Cannabinoids and terpenes for diabetes mellitus and its complications: from mechanisms to new therapies

The number of people diagnosed with diabetes mellitus and its complications is markedly increasing worldwide, leading to a worldwide epidemic across all age groups, from children to older adults. Diabetes is associated with premature aging. In recent years, it has been found that peripheral overactivation of the endocannabinoid system (ECS), and in particular cannabinoid receptor 1 (CB1R) signaling, plays a crucial role in the progression of insulin resistance, diabetes (especially type 2), and its aging-related comorbidities such as atherosclerosis, nephropathy, neuropathy, and retinopathy. Therefore, it is suggested that peripheral blockade of CB1R may ameliorate diabetes and diabetes-related comorbidities. The use of synthetic CB1R antagonists such as rimonabant has been prohibited because of their psychiatric side effects. In contrast, phytocannabinoids such as cannabidiol (CBD) and tetrahydrocannabivarin (THCV), produced by cannabis, exhibit antagonistic activity on CB1R signaling and do not show any adverse side effects such as psychoactive effects, depression, or anxiety, thereby serving as potential candidates for the treatment of diabetes and its complications. In addition to these phytocannabinoids, cannabis also produces a substantial number of other phytocannabinoids, terpenes, and flavonoids with therapeutic potential against insulin resistance, diabetes, and its complications. In this review, the pathogenesis of diabetes, its complications, and the potential to use cannabinoids, terpenes, and flavonoids for its treatment are discussed.

(Wh)olistic (E)ndocannabinoidome-Microbiome-Axis Modulation through (N)utrition (WHEN) to Curb Obesity and Related Disorders

The discovery of the endocannabinoidome (eCBome) is evolving gradually with yet to be elucidated functional lipid mediators and receptors. The diet modulates these bioactive lipids and the gut microbiome, both working in an entwined alliance. Mounting evidence suggests that, in different ways and with a certain specialisation, lipid signalling mediators such as N-acylethanolamines (NAEs), 2-monoacylglycerols (2-MAGs), and N-acyl-amino acids (NAAs), along with endocannabinoids (eCBs), can modulate physiological mechanisms underpinning appetite, food intake, macronutrient metabolism, pain sensation, blood pressure, mood, cognition, and immunity. This knowledge has been primarily utilised in pharmacology and medicine to develop many drugs targeting the fine and specific molecular pathways orchestrating eCB and eCBome activity. Conversely, the contribution of dietary NAEs, 2-MAGs and eCBs to the biological functions of these molecules has been little studied. In this review, we discuss the importance of (Wh) olistic (E)ndocannabinoidome-Microbiome-Axis Modulation through (N) utrition (WHEN), in the management of obesity and related disorders.

Variations of retinal dysfunctions with the level of cannabis use in regular users: Toward a better understanding of cannabis use pathophysiology

The impact of regular cannabis use on retinal function has already been studied using flash (fERG) and pattern (PERG) electroretinogram. Delayed ganglion and bipolar cells responses were observed as showed by increased peak time of PERG N95 and fERG b-wave recorded in photopic condition. Hypoactivity of amacrine cells was also showed by decreased amplitudes of oscillatory potentials (OPs). However, it is unknown how these retinal anomalies evolve according to the level of cannabis use in cannabis users. The aim of this study was to longitudinally assess the retinal function during a treatment aiming to reduce cannabis use. We recorded PERG and fERG in 40 regular cannabis users receiving either an 8 weeks mindfulness-based relapse prevention program or an 8 weeks treatment-as-usual therapy. ERGs were recorded before treatment, at the end of it, and 4 weeks afterward. We found reduced peak times in PERG N95 and fERG b-wave (p = 0.032 and p = 0.024: Dunn's post-hoc test) recorded at week 8 and increased amplitudes in OP2 and OP3 (p = 0.012 and p = 0.030: Dunn's post-hoc test) recorded at week 12 in users with decreased cannabis use. These results support variations of retinal anomalies with the level of cannabis use, implying that reduction of cannabis use could restore retinal function in regular users.

Topical application of cannabinoid-ligands ameliorates experimental dry-eye disease

PURPOSE

Dry eye disease (DED) is a multifactorial disease, with limitations regarding efficacy and tolerability of applied substances. Among several candidates, the endocannabinoid system with its receptors (CB1R and CB2R) were reported to modulate inflammation, wound healing and pain, which are also core DED pathomechanisms. This study is to investigate the therapeutic responses of Δ-9 tetrahydrocannabinol (a non-selective agonist) and two selective antagonists, SR141716A (CB1R antagonist) and SR144528 (CB2R antagonist), as a topical application using a DED mouse model.

METHOD

Experimental DED was induced in naïve C57BL/6 mice. Expression of CBR at the ocular surface of naïve and DED mice was determined by qPCR and in-situ hybridization. Either THC or CBR antagonists were compounded in an aqueous solution and dosed during the induction of DED. Tear production, cornea sensitivity, and cornea fluorescence staining were tested. At the end of each experiment, corneas were stained with β3-tubulin for analysis of corneal nerve morphology. Conjunctiva was analyzed for CD4⁺ and CD8⁺ infiltration.

RESULTS

CB1R and CB2R are present at the ocular surface, and desiccating stress increased CBR expressions (p < 0.05). After 10 days of DED induction, treated groups demonstrated a reduced CBR expression in the cornea, which was concurrent with improvements in the DED phenotype including fluorescence staining & inflammation. Applying THC protected corneal nerve morphology, thus maintained corneal sensitivity and reduced CD4⁺ T-cell infiltration. The CB1R antagonist maintained cornea sensitivity without changing nerve morphology.

CONCLUSIONS

Endocannabinoid receptor modulation presents a potential multi-functional therapeutic approach for DED.

The Vertical and Horizontal Pathways in the Monkey Retina Are Modulated by Typical and Atypical Cannabinoid Receptors

The endocannabinoid (eCB) system has been found in all visual parts of the central ner-vous system and plays a role in the processing of visual information in many species, including monkeys and humans. Using anatomical methods, cannabinoid receptors are present in the monkey retina, particularly in the vertical glutamatergic pathway, and also in the horizontal GABAergic pathway. Modulating the eCB system regulates normal retinal function as demonstrated by electrophysiological recordings. The characterization of the expression patterns of all types of cannabinoid receptors in the retina is progressing, and further research is needed to elucidate their exact role in processing visual information. Typical cannabinoid receptors include G-protein coupled receptor CB1R and CB2R, and atypical cannabinoid receptors include the G-protein coupled receptor 55 (GPR55) and the ion channel transient receptor potential vanilloid 1 (TRPV1). This review focuses on the expression and localization studies carried out in monkeys, but some data on other animal species and humans will also be reported. Furthermore, the role of the endogenous cannabinoid receptors in retinal function will also be presented using intraocular injections of known modulators (agonists and antagonists) on electroretinographic patterns in monkeys. The effects of the natural bioactive lipid lysophosphatidylglucoside and synthetic FAAH inhibitor URB597 on retinal function, will also be described. Finally, the potential of typical and atypical cannabinoid receptor acti-vity regulation in retinal diseases, such as age-related macular degeneration, diabetic retinopathy, glaucoma, and retinitis pigmentosa will be briefly explored.

The Inhibition of the Degrading Enzyme Fatty Acid Amide Hydrolase Alters the Activity of the Cone System in the Vervet Monkey Retina

Recent studies using full-field electroretinography (ffERG) that triggers a non-specific mass response generated by several retinal sources have attributed an important role for cannabinoid receptors in mediating vision in primates. Specific cone-mediated responses evoked through the photopic flicker ERG appear to be a better way to validate the assumption that endogenous cannabinoids modulate the cone pathway, since FAAH is mainly expressed in the vervet monkey cone photoreceptors. The aim of this study is two-fold: (1) to use the photopic flicker ERG to target the cone pathway specifically, and (2) use URB597 as a selective inhibitor of the endocannabinoid degrading enzyme Fatty Acid Amide Hydrolase (FAAH) to enhance the levels of fatty acid amides, particularly anandamide. We recorded ERGs under four different flicker frequencies (15, 20, 25, and 30 Hz) in light-adapted conditions after intravitreal injections of URB597. Our results show that intravitreal injections of URB597, compared to the vehicle DMSO, increased significantly ffERG amplitudes at 30 Hz, a frequency that solely recruits cone activity. However, at 15 Hz, a frequency that activates both rods and cones, no significant difference was found in the ERG response amplitude. Additionally, we found no differences in implicit times after URB597 injections compared to DMSO vehicle. These results support the role of molecules degraded by FAAH in cone-mediated vision in non-human primates.

Dynamics of the accommodative response after smoking cannabis

PURPOSE

Cannabis is the most widely consumed illicit drug worldwide. It has been suggested that cannabis could generate blurred vision during reading tasks. The goal of this study was to objectively assess the acute effects of smoking cannabis on the dynamics of ocular accommodation. The influence of other factors, including target distance and the direction of accommodation, as well as personal characteristics, were also analysed.

METHODS

Nineteen young people who were occasional cannabis users participated in the study (mean age 22.53 [3.12] years). Their usage profiles were evaluated by means of the Cannabis Use Disorders Identification Test-revised (CUDIT-r). The dynamics of the accommodative response were evaluated using an open-field auto refractor (Grand Seiko WAM-5500). The participants completed two different experimental sessions, one week apart, and in random order (baseline session and after smoking cannabis). During these sessions, the amplitude of the response (D), mean velocity (D/s), peak velocity (D/s), response time (s), accommodative lag (D) and accommodation variability (D) were measured.

RESULTS

The results indicated that cannabis use had a significant main effect on the mean accommodation/disaccommodation velocity (F_1,13  = 7.21; p = 0.02; η p 2  = 0.396). Cannabis consumption also interacted significantly with other factors. Response time showed a significant two-way interaction between condition × target distance (F_1,13  = 11.71; p = 0.005; η p 2  = 0.474) and condition × accommodation direction (F_1,13  = 8.71; p = 0.01; η p 2  = 0.401). For mean velocity, two-way interactions were found between condition × age (F_1,13  = 6.03; p = 0.03; η p 2  = 0.354), condition × CUDIT-r score (F_1,13  = 6.03; p = 0.03; η p 2  = 0.356) and condition × target distance (F_1,13  = 7.20; p = 0.02; η p 2  = 0.396).

CONCLUSIONS

These findings suggest that cannabis use can alter the accommodation process, although further studies should be carried out to explore the role of attention deficits. According to these results, certain daily activities that depend on an accurate accommodative function may be affected by cannabis use.

Cannabinoid signaling promotes the de-differentiation and proliferation of Müller glia-derived progenitor cells

Endocannabinoids (eCB) are lipid-based neurotransmitters that are known to influence synaptic function in the visual system. eCBs are also known to suppress neuroinflammation in different pathological states. However, nothing is known about the roles of the eCB system during the transition of Müller glia (MG) into proliferating progenitor-like cells in the retina. Accordingly, we used the chick and mouse model to characterize expression patterns of eCB-related genes and applied pharmacological agents to investigate how the eCB system impacts glial reactivity and the capacity of MG to become Müller glia-derived progenitor cells (MGPCs). We queried single cell RNA-seq libraries to identify eCB-related genes and identify cells with dynamic patterns of expression in damaged retinas. MG and inner retinal neurons expressed the eCB receptor CNR1, as well as enzymes involved in eCB metabolism. In the chick, intraocular injections of cannabinoids, 2-Arachidonoylglycerol (2-AG) and Anandamide (AEA), stimulated the formation of MGPCs. Cannabinoid Receptor 1 (CNR1)-agonists and Monoglyceride Lipase-inhibitor promoted the formation of MGPCs, whereas CNR1-antagonist and inhibitors of eCB synthesis suppressed this process. In damaged mouse retinas where MG activate NFkB-signaling, activation of CNR1 decreased and inhibition of CNR1 increased NFkB, whereas levels of neuronal cell death were unaffected. Surprisingly, retinal microglia were largely unaffected by increases or decreases in eCB-signaling in both chick and mouse retinas. We conclude that the eCB system in the retina influences the reactivity of MG and the formation of proliferating MGPCs, but does not influence the reactivity of immune cells in the retina.

Oscillatory potentials abnormalities in regular cannabis users: Amacrine cells dysfunction as a marker of central dopaminergic modulation

BACKGROUND

Cannabis is a neuromodulating substance that acts on central synaptic transmission. Regular cannabis use induces a decreased capacity for dopamine synthesis in the brain. The retina is considered an easy means of investigating dysfunctions of synaptic transmission in the brain. We have previously studied the impact of regular cannabis use on retinal function. Using the N95 wave of the pattern electroretinogram, we found a 6 ms-delayed ganglion cells response. Using the b-wave of the photopic flash electroretinogram, we found a 1 ms-delayed bipolar cells response. Here, we investigated amacrine cells function because these cells are located between the bipolar cells and the ganglion cells and contribute to amplifying the signal between these two layers of the retina. We tested the effect of regular cannabis use on these retinal dopaminergic cells. We assessed the role of these cells in amplifying the delay observed previously.

METHODS

We recorded dark-adapted 3.0 flash ERG oscillatory potentials in 56 regular cannabis users and 29 healthy controls. The amplitude and implicit time of OP1, OP2, OP3 and OP4 were evaluated.

RESULTS

Cannabis users showed a significant decrease in OP2 amplitude (p = 0.029, Mann-Whitney test) and OP3 amplitude (p = 0.024, Mann-Whitney test). No significant difference was found between the groups for OP1 and OP4 amplitude or for the implicit time of oscillatory potentials.

CONCLUSIONS

These results reflect the impact of regular cannabis use on amacrine cells function. They highlight abnormalities in dopaminergic transmission and are similar to those found in Parkinson's disease. Oscillatory potentials could be used as markers of central dopaminergic modulation.

The Effect of Orally Administered Low-Dose Dronabinol on Retinal Blood Flow and Oxygen Metabolism in Healthy Subjects

Purpose: The present study was performed to investigate the effect of oral dronabinol, a synthetic tetrahydrocannabinol derivate, on retinal hemodynamics in healthy subjects in a randomized, double-masked, placebo-controlled, 2-way crossover design. Methods: Twenty-four subjects received 5 mg dronabinol on 1 study day and placebo on the other study day. Total retinal blood flow (TRBF) was measured using a custom-built Doppler Optical Coherence Tomography system. Oxygen saturation of major retinal vessels was measured with a commercially available Dynamic Vessel Analyzer. Based on these parameters, retinal oxygen extraction was calculated. Measurements were performed before and after drug administration on both study days. Results: Placebo had no effect on TRBF, retinal arterial or venous oxygen content, and retinal oxygen extraction (P > 0.1 each). In contrast, dronabinol induced a significant increase in TRBF from 38.9 ± 6.1 to 40.7 ± 6.7 μL/min (P < 0.001), which was accompanied by a significant increase in retinal venous oxygen content (from 0.129 ± 0.008 to 0.132 ± 0.009 mL O₂/mL, P = 0.02). As no change in retinal arterial oxygen content occurred (P = 0.12), retinal oxygen extraction remained stable (2.2 ± 0.4 μL vs. 2.2 ± 0.4 μL O₂/min, P = 0.29). Conclusions: These results indicate that orally administered dronabinol increases TRBF in healthy subjects without altering retinal oxygen extraction. The drug may therefore be a candidate for improving perfusion in patients with ocular vascular disease.

Cannabidiol Signaling in the Eye and Its Potential as an Ocular Therapeutic Agent

Cannabidiol (CBD), the major non-intoxicating constituent of Cannabis sativa, has gained recent attention due to its putative therapeutic uses for a wide variety of diseases. CBD was discovered in the 1940s and its structure fully characterized in the 1960s. However, for many years most research efforts related to cannabis derived chemicals have focused on D9-tetrahydrocannabinol (THC). In contrast to THC, the lack of intoxicating psychoactivity associated with CBD highlights the potential of this cannabinoid for clinical drug development. This review details in vitro and in vivo studies of CBD related to the eye, the therapeutic potential of cannabidiol for various ocular conditions, and molecular targets and mechanisms for CBD-induced ocular effects. In addition, challenges of CBD applications for clinical ocular therapeutics and future directions are discussed.

Cannabinoids in Glaucoma Patients: The Never-Ending Story

Glaucoma is one of the principal causes of irreversible blindness worldwide. Yet, intraocular pressure (IOP) is the main modifiable risk factor for disease progression. In the never-ending challenge to develop new and effective drugs, several molecules have been tested as anti-glaucoma agents thanks to their pressure-lowering capabilities. Among these molecules, the cannabinoids have been investigated as possible anti-glaucoma drugs since the early 1970s. Cannabinoids are a large class of chemical compounds that exploit their effects by interaction with cannabinoid receptors 1 and 2. These receptors are widely expressed in the human retina where they may influence important functions such as photo-transduction, amacrine cell network maintenance, and IOP regulation. Therefore, in past years several studies have been conducted in order to assess the IOP lowering effects of cannabinoids. PRISMA guidelines have been used to perform a literature search on Pubmed and Scopus aiming to investigate the mechanism of IOP lowering effects and the potential benefits of orally administered, inhaled, topical, and intravenous cannabinoids in the treatment of glaucoma patients.

Cannabinoids and the eye

Cannabis ranks among the most commonly used psychotropic drugs worldwide. In the context of the global movement toward more widespread legalisation, there is a growing need toward developing a better understanding of the physiological and pathological effects. We provide an overview of the current evidence on the effects of cannabinoids on the eye. Of the identified cannabinoids, Δ⁹-tetrahydrocannabinol is recognized to be the primary psychotropic compound, and cannabidiol is the predominant nonpsychoactive ingredient. Despite demonstrating ocular hypotensive and neuroprotective activity, the use of cannabinoids as a treatment for glaucoma is limited by a large number of potential systemic and ophthalmic side effects. Anterior segment effects of cannabinoids are complex, with preliminary evidence showing decreased corneal endothelial density in chronic cannabinoid users. Experiments in rodents, however, have shown potential promise for the treatment of ocular surface injury via antinociceptive and antiinflammatory effects. Electroretinography studies demonstrating adverse effects on photoreceptor, bipolar, and ganglion cell function suggest links between cannabis and neuroretinal dysfunction. Neuro-ophthalmic associations include ocular motility deficits and decrements in smooth pursuit and saccadic eye movements, although potential therapeutic effects for congenital and acquired nystagmus have been observed.

Spatial localization of retinal anomalies in regular cannabis users: The relevance of the multifocal electroretinogram

Widely used in industrialized countries, cannabis is a neuromodulator substance. The cannabinoid system is present at critical stages of retinal processing. We have recently shown a delay in bipolar and ganglion cell responses in regular cannabis users, as observed using flash (fERG) and pattern (PERG) electroretinogram. Although the results obtained during these tests provide information about global retinal responses, they do not give any indication about the spatial localization of the anomalies that were detected. The latter may be analyzed, however, by means of multifocal electroretinogram (mfERG). We recorded the mfERG responses in 49 regular cannabis users and 21 healthy subjects. The amplitudes and implicit times of the mfERG N1, P1 and N2 waves were recorded. The results showed that in regular cannabis users: in the <2° region, a significant increase in the N2 implicit time (p = 0.037); in the 2-5° region, a significant increase in the N2 (p = 0.018) and P1 (p = 0.046) implicit times; in the 5-10° region, a significant increase in the P1 (p = 0.006) and N1 (p = 0.034) implicit times; and in the 10-15° region, a significant increase in the P1 implicit time (p = 0.014). An isolated decrease in the N1 amplitude in the 2-5° region (p = 0.044) was also found. This indicates that there is a delay in the transmission of visual information from the central retina to the near periphery in cannabis users suggesting potential alterations in precise and color vision.

Electroretinography in psychiatry: A systematic literature review

This review aims to consolidate the available information on use of electroretinography as a diagnostic tool in psychiatry. The electroretinogram (ERG) has been found to have diagnostic utility in cocaine withdrawal (reduced light-adapted b-wave response), major depressive disorder (reduced contrast gain in pattern ERG), and schizophrenia (reduced a- and b-wave amplitudes). This review examines these findings as well as the applicability of ERG to substance use disorder, Alzheimer's disease, autism spectrum disorder, panic disorder, eating disorders, attention deficit hyperactivity disorder, and medication use. While there have been promising results, current research suffers from a lack of specificity. Further research that quantifies anomalies in ERG present in psychiatric illness is needed.

Inhibition of GABAergic Neurons and Excitation of Glutamatergic Neurons in the Ventrolateral Periaqueductal Gray Participate in Electroacupuncture Analgesia Mediated by Cannabinoid Receptor

Although electroacupuncture (EA) has become a worldwide practice, little is understood about its precise target in the central nervous system (CNS) and the cell type-specific analgesia mechanism. In the present study, we found that EA has significant antinociceptive effects both in inflammatory and neuropathic pain models. Chemogenetic inhibition of GABAergic neurons in the ventrolateral periaqueductal gray (vlPAG) replicated the effects of EA, whereas the combination of chemogenetic activation of GABAergic neurons and chemogenetic inhibition of glutamatergic neurons in the vlPAG was needed to reverse the effects of EA. Specifically knocking out CB1 receptors on GABAergic neurons in the vlPAG abolished the EA effect on pain hypersensitivity, while specifically knocking out CB1 receptors on glutamatergic neurons attenuated only a small portion of the EA effect. EA synchronously inhibits GABAergic neurons and activates glutamatergic neurons in the vlPAG through CB1 receptors to produce EA-induced analgesia. The CB1 receptors on GABAergic neurons localized in the vlPAG was the basis of the EA effect on pain hypersensitivity. This study provides new experimental evidence that EA can bidirectionally regulate GABAergic neurons and glutamatergic neurons via the CB1 receptors of the vlPAG to produce analgesia effects.

Association between increased retinal background noise and co-occurrent regular cannabis and alcohol use

BACKGROUND

Cannabis consumption is widespread across the world, and the co-occurrence of cannabis use and alcohol consumption is common. The study of background noise - resting-state neural activity, in the absence of stimulation - is an approach that could enable the neurotoxicity of these substances to be explored. Preliminary results have shown that delta-9-tetrahydrocannabinol (Δ9-THC) causes an increase in neural noise in the brain. Neurons in the brain and the retina share a neurotransmission system and have similar anatomical and functional properties. Retinal function, evaluated using an electroretinogram (ERG), may therefore reflect central neurochemistry. This study analyses retinal background noise in a population of regular co-occurrent cannabis and alcohol consumers.

METHODS

We recorded the flash ERGs of 26 healthy controls and 45 regular cannabis consumers, separated into two groups based on their alcohol consumption: less than or equal to 4 glasses per week (CU ≤ 4) or strictly >4 glasses per week (CU >4). In order to extract the background noise, the Fourier transform of the pseudo-periodic and sinusoidal signals of the 3.0 flicker-response sequence was calculated. This sequence represents the vertical transmission of the signal from cones to bipolar cells. The magnitude of the background noise is defined as the average of the magnitudes of the two neighbouring harmonics: harmonic -1 (low frequency noise) and harmonic +1 (high frequency noise).

RESULTS

The magnitude of harmonic -1 was significantly increased between the groups CU > 4 (6.78 (±1.24)) and CU ≤ 4 (5.69 (±1.80)) among regular users of cannabis and alcohol. A significant increase in the average magnitude of the two harmonics was found between the groups CU > 4 (5.12 (±0.92)) and CU ≤ 4 (4.36 (±1.14)). No significant difference was observed with regard to the magnitude of the harmonic +1.

CONCLUSIONS

The increase in background noise may reflect the neurotoxicity of cannabis, potentiated by alcohol consumption, on retinal neurons dynamic. This neural disruption of the response generated by retinal stimulation may be attributable to altered neurotransmitter release.

Cannabis use and human retina: The path for the study of brain synaptic transmission dysfunctions in cannabis users

Owing to the difficulty of obtaining direct access to the functioning brain, new approaches are needed for the indirect exploration of brain disorders in neuroscience research. Due to its embryonic origin, the retina is part of the central nervous system and is well suited to the investigation of neurological functions in psychiatric and addictive disorders. In this review, we focus on cannabis use, which is a crucial public health challenge, since cannabis is one of the most widely used addictive drugs in industrialized countries. We first explain why studying retinal function is relevant when exploring the effects of cannabis use on brain function. Next, we describe both the retinal electrophysiological measurements and retinal dysfunctions observed after acute and regular cannabis use. We then discuss how these retinal dysfunctions may inform brain synaptic transmission abnormalities. Finally, we present various directions for future research on the neurotoxic effects of cannabis use.

The Role of Endogenous Neuroprotective Mechanisms in the Prevention of Retinal Ganglion Cells Degeneration

Retinal neurons are not able to undergo spontaneous regeneration in response to damage. A variety of stressors, i.e., UV radiation, high temperature, ischemia, allergens, and others, induce reactive oxygen species production, resulting in consecutive alteration of stress-response gene expression and finally can lead to cell apoptosis. Neurons have developed their own endogenous cellular protective systems. Some of them are preventing cell death and others are allowing functional recovery after injury. The high efficiency of these mechanisms is crucial for cell survival. In this review we focus on the contribution of the most recently studied endogenous neuroprotective factors involved in retinal ganglion cell (RGC) survival, among which, neurotrophic factors and their signaling pathways, processes regulating the redox status, and different pathways regulating cell death are the most important. Additionally, we summarize currently ongoing clinical trials for therapies for RGC degeneration and optic neuropathies, including glaucoma. Knowledge of the endogenous cellular protective mechanisms may help in the development of effective therapies and potential novel therapeutic targets in order to achieve progress in the treatment of retinal and optic nerve diseases.

Immune regulation in the aging retina

The retina is an immune privileged tissue, which is protected from external and internal insults by its blood-retina barriers and immune suppressive microenvironment. Apart from the avoidance and tolerance strategies, the retina is also protected by its own defense system, i.e., microglia and the complement system. The immune privilege and defense mechanisms work together to maintain retinal homeostasis. During aging, the retina is at an increased risk of developing various degenerative diseases such as age-related macular degeneration, diabetic retinopathy, and glaucomatous retinopathy. Previously, we have shown that aging induces a para-inflammatory response in the retina. In this review, we explore the impact of aging on retinal immune regulation and the connection between homeostatic control of retinal immune privilege and para-inflammation under aging conditions and present a view that may explain why aging puts the retina at risk of developing degenerative diseases.

Delayed bipolar and ganglion cells neuroretinal processing in regular cannabis users: The retina as a relevant site to investigate brain synaptic transmission dysfunctions

Cannabis use is widespread worldwide, but the impact of smoking cannabis regularly on brain synaptic transmission has only been partially elucidated. The retina is considered as an easy means of determining dysfunction in brain synaptic transmission. The endocannabinoid system is involved in regulating retinal synaptic transmission, which might also be affected by tobacco. Previous preliminary results have shown impairments in retinal ganglion cell response in cannabis users. Here, we test the extent to which earlier retinal levels-bipolar cells and photoreceptors-are affected in cannabis users, i.e. by the association of tobacco and cannabis. We recorded pattern (PERG) and flash (fERG) ERG in 53 regular cannabis users and 29 healthy controls. Amplitude and peak time of P50 and N95 (PERG) and of a- and b-waves (fERG) were evaluated. Cannabis users showed a significant increase in PERG N95 peak time and in fERG light-adapted 3.0 b-wave peak time, compared with controls (p = 0.0001 and p = 0.002, respectively; Mann-Whitney U test). No significant difference was found between the groups in terms of wave amplitude (p = 0.525 and p = 0.767 for the N95 and light-adapted 3.0 b-wave amplitude respectively; Mann-Whitney U test). The results demonstrated delayed ganglion and bipolar cell responses in cannabis users. These results reflect a delay in the transmission of visual information from the retina to the brain. This retinal dysfunction may be explained by an effect of cannabis use on retinal synaptic transmission. Main limitations of these results concern tobacco and alcohol use that differed between groups. The consequences of these anomalies on visual perception along with the molecular mechanisms underlying this retinal dysfunction should be explored in future human and animal studies.

Cannabinoid Receptor Type 1 Expression in the Developing Avian Retina: Morphological and Functional Correlation With the Dopaminergic System

The avian retina has been used as a model to study signaling by different neuro- and gliotransmitters. It is unclear how dopaminergic and cannabinoid systems are related in the retina. Here we studied the expression of type 1 and 2 cannabinoid receptors (CB₁ and CB₂), as well as monoacylglycerol lipase (MAGL), the enzyme that degrades 2-arachidonoylglycerol (2-AG), during retina development. Our data show that CB₁ receptor is highly expressed from embryonic day 5 (E5) until post hatched day 7 (PE7), decreasing its levels throughout development. CB₁ is densely found in the ganglion cell layer (GCL) and inner plexiform layer (IPL). CB₂ receptor was also found from E5 until PE7 with a decrease in its contents from E9 afterwards. CB₂ was mainly present in the lamination of the IPL at PE7. MAGL is expressed in all retinal layers, mainly in the IPL and OPL from E9 to PE7 retina. CB₁ and CB₂ were found both in neurons and glia cells, but MAGL was only expressed in Müller glia. Older retinas (PE7) show CB₁ positive cells mainly in the INL and co-expression of CB₁ and tyrosine hydroxylase (TH) are shown in a few cells when both systems are mature. CB₁ co-localized with TH and was heavily associated to D₁ receptor labeling in primary cell cultures. Finally, cyclic AMP (cAMP) was activated by the selective D₁ agonist SKF38393, and inhibited when cultures were treated with WIN55, 212–2 (WIN) in a CB₁ dependent manner. The results suggest a correlation between the endocannabinoid and dopaminergic systems (DSs) during the avian retina development. Activation of CB₁ limits cAMP accumulation via D₁ receptor activation and may influence embryological parameters during avian retina differentiation.

Neuroprotection by (endo)Cannabinoids in Glaucoma and Retinal Neurodegenerative Diseases

BACKGROUND

Emerging neuroprotective strategies are being explored to preserve the retina from degeneration, that occurs in eye pathologies like glaucoma, diabetic retinopathy, age-related macular degeneration, and retinitis pigmentosa. Incidentally, neuroprotection of retina is a defending mechanism designed to prevent or delay neuronal cell death, and to maintain neural function following an initial insult, thus avoiding loss of vision.

METHODS

Numerous studies have investigated potential neuroprotective properties of plant-derived phytocannabinoids, as well as of their endogenous counterparts collectively termed endocannabinoids (eCBs), in several degenerative diseases of the retina. eCBs are a group of neuromodulators that, mainly by activating G protein-coupled type-1 and type-2 cannabinoid (CB1 and CB2) receptors, trigger multiple signal transduction cascades that modulate central and peripheral cell functions. A fine balance between biosynthetic and degrading enzymes that control the right concentration of eCBs has been shown to provide neuroprotection in traumatic, ischemic, inflammatory and neurotoxic damage of the brain.

RESULTS

Since the existence of eCBs and their binding receptors was documented in the retina of numerous species (from fishes to primates), their involvement in the visual processing has been demonstrated, more recently with a focus on retinal neurodegeneration and neuroprotection.

CONCLUSION

The aim of this review is to present a modern view of the endocannabinoid system, in order to discuss in a better perspective available data from preclinical studies on the use of eCBs as new neuroprotective agents, potentially useful to prevent glaucoma and retinal neurodegenerative diseases.

Looking into the brain through the retinal ganglion cells in psychiatric disorders: A review of evidences

Psychiatry and neuroscience research need novel approaches to indirectly investigate brain function. As the retina is an anatomical and developmental extension of the central nervous system (CNS), changes in retinal function may reflect neurological dysfunctions in psychiatric disorders. The last and most integrated retinal relay before visual information transfer to the brain is the ganglion cell layer. Here, based on collected arguments, we argue that these cells offer a crucial site for indirectly investigating brain function. We describe the anatomical and physiological properties of these cells together with measurements of their functional properties named pattern electroretinogram (PERG). Based on ganglion cell dysfunctions measured with PERG in neurological disorders, we argue for the relevance of studying ganglion cell function in psychiatric research. We review studies that have evaluated ganglion cell function in psychiatric and addictive disorders and discuss how changes in PERG measurements could be functional markers of pathophysiological mechanisms of psychiatric disorders.