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

Association between alcohol use and retinal dysfunctions in patients with alcohol use disorder: A window on GABA, glutamate, and dopamine modulations

BACKGROUND

Alcohol is the most widely consumed addictive substance around the world and have deleterious effect on the central nervous system. Alcohol consumption affect the balance of certain neurotransmitters like GABA, glutamate and dopamine. The retina provides an easy means of investigating dysfunctions of synaptic transmission in the brain. The purpose of this study is to assess the impact of alcohol consumption on retinal function using pattern electroretinogram (PERG) and flash electroretinogram (fERG).

METHODS

We recorded PERG and fERG under scotopic and photopic condition in 20 patients with alcohol use disorder and 20 controls. Implicit time and amplitude of numerous parameters were evaluated: a- and b-waves for fERG, OP3 and OP4 for dark-adapted 3.0 oscillatory potentials fERG, P50 and N95 for PERG.

RESULTS

Patients with alcohol use disorder showed a significant increase in N95 implicit time without a significant change in the amplitudes of oscillatory potentials.

CONCLUSION

The results of our study reflect the impact of alcohol use on ganglion cell function and could highlight alterations in glutamatergic neurotransmission inside the retina. We believe that ERG could be used as an early marker of alcohol consumption.

Perceived Safety, Not Perceived Legality, Mediates the Relationship Between Cannabis Legalization and Drugged Driving

Cannabis legalization has rapidly spread throughout the United States and is associated with multiple public health outcomes, including driving under the influence of cannabis (DUIC). To improve understanding of the relationship between legalization and DUIC, we tested two potential mediators of this relationship: perceived safety and perceived legality of driving high. We analyzed data from 1,236 current (past 30-day) cannabis users who were recruited from states with recreational, medical only, or no legal cannabis between 2016 and 2017 using address-based and social media samples. Using a generalized linear model and adjusting for cannabis legalization, demographics, living in a state with a cannabis-specific drugged driving law, frequency of cannabis use, and weights, we found that perceived safety (risk ratio [RR] = 2.60, 95% CI [1.88, 3.58]), but not perceived legality (RR = 0.96, 95% CI [0.67, 1.37]), was significantly associated with DUIC. Perceived safety mediated the relationship between legalization and DUIC (Coeff: -0.12, 95% CI [-0.23, -0.01]). Models stratified by frequency of cannabis use yielded results consistent with those of pooled models except that, for frequent users, cannabis-specific driving laws were associated with a significantly lower risk of DUIC (RR = 0.64, 95% CI [0.44, 0.92]). Agencies developing cannabis-focused drugged driving educational campaigns should consider the potential role of perceived safety of driving high in DUIC campaigns.

Full-field electroretinogram recorded with skin electrodes in 6- to 12-year-old children

PURPOSE

To determine the full-field electroretinogram (ffERG) parameters, including the light-adapted (LA) 3 ERG and the photopic negative response (PhNR), in 6- to 12-year-old children.

METHODS

ffERG data were obtained from 214 eyes of 214 healthy subjects. The amplitudes and peak time of the ffERG responses were obtained from children divided into 6- to 8-year-old and 9- to 12-year-old groups. Using a skin electrode, electrical signals were measured in response to white stimulating light and white background light (LA 3 ERG). A blue background light and red flashes were then used to elicit the PhNR.

RESULTS

The a-wave amplitude ranged from 0.40 to 9.20 μV, the b-wave ranged from 4.70 to 30.80 μV, and the PhNR ranged from 1.30 to 39.90 μV. The b-wave peak time (33.20 ms) of 6- to 8-year-old groups was slightly shorter than that of the 9- to 12-year-old groups (33.60 ms, P = 0.01), but no differences in amplitudes or in peak time of other components. There were significant correlations between the amplitudes (a-wave and b-wave: r = 0.43, p < 0.001; a-wave and PhNR: r = 0.25, p < 0.001; b-wave and PhNR: r = 0.45, p < 0.001). There was a moderate correlation between the a-wave and b-wave peak time (r = 0.31, P < 0.001).

CONCLUSIONS

We determined the largest dataset of the LA 3 ERG and PhNR parameters in a population of healthy children, aged 6-12 years, which may provide a useful reference value when evaluating children with potential retinal defects.

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.

Tonic Endocannabinoid Levels Modulate Retinal Signaling

The endocannabinoid (eCB) system is critically involved in the modulation of synaptic transmission in the central nervous system, playing an important role in the control of emotional responses, neurodevelopment and synaptic plasticity among other functions. The eCB system is also present in the retina, with studies indicating changes in function after application of cannabinoid receptor agonists, antagonists and in knockout models. Whether eCBs are tonically released in the retina and their physiological functions is, however, still unknown. We investigated the role of the eCB system in the modulation of response strength of retinal ganglion cells (RGCs) to light stimulation, their receptive field organization, contrast sensitivity and excitability properties by performing whole-cell patch-clamp recordings in mouse RGCs before and after bath application of URB597, an inhibitor of the enzyme that degrades the eCB anandamide. Our results show that URB597 application leads to a reduction in the strength of synaptic inputs onto RGCs but paradoxically increases RGC excitability. In addition, URB597 was shown to modulate receptive field organization and contrast sensitivity of RGCs. We conclude that tonically released eCBs modulate retinal signaling by acting on traditional cannabinoid receptors (CB1R/CB2R) as well as on non-cannabinoid receptor targets. Thus, a thorough understanding of the effects of drugs that alter the endogenous cannabinoid levels and of exogenous cannabinoids is necessary to fully comprehend the impact of their medical as well as recreational use on vision.

Retinal electroretinogram features can detect depression state and treatment response in adults: A machine learning approach

BACKGROUND

Major depressive disorder (MDD) is a major public health problem. The retina is a relevant site to indirectly study brain functioning. Alterations in retinal processing were demonstrated in MDD with the pattern electroretinogram (PERG). Here, the relevance of signal processing and machine learning tools applied on PERG was studied.

METHODS

PERG - whose stimulation is reversible checkerboards - was performed according to the International Society for Clinical Electrophysiology of Vision (ISCEV) standards in 24 MDD patients and 29 controls at the inclusion. PERG was recorded every 4 weeks for 3 months in patients. Amplitude and implicit time of P50 and N95 were evaluated. Then, time/frequency features were extracted from the PERG time series based on wavelet analysis. A statistical model has been learned in this feature space and a metric aiming at quantifying the state of the MDD patient has been derived, based on minimum covariance determinant (MCD) mahalanobis distance.

RESULTS

MDD patients showed significant increase in P50 and N95 implicit time (p = 0,006 and p = 0,0004, respectively, Mann-Whitney U test) at the inclusion. The proposed metric extracted from the raw PERG provided discrimination between patients and controls at the inclusion (p = 0,0001). At the end of the follow-up at week 12, the difference between the metrics extracted on controls and patients was not significant (p = 0,07), reflecting the efficacy of the treatment.

CONCLUSIONS

Signal processing and machine learning tools applied on PERG could help clinical decision in the diagnosis and the follow-up of MDD in measuring treatment response.

Impaired P100 among regular cannabis users in response to magnocellular biased visual stimuli

Regular cannabis using causes vision impairment by affecting human retinal neurotransmission. However, studies less considered its impact on the subsequent visual cortical processing, key feature for the integration of the visual signal in brain. We aimed at investigating this purpose in regular cannabis users using spatial frequencies and temporal frequencies filtered visual stimuli. We recruited 45 regular cannabis users and 25 age-matched controls. We recorded visual evoked potentials during the projection of low spatial frequency (0.5 cycles/degree) or high spatial frequency gratings (15 cycles/degree), which were presented statically (0 Hz) or dynamically (8 Hz). We analyzed the amplitude, latency, and area under the curve of both P100 and N170, best EEG markers for early visual processing. Data were compared between groups by repeated measures ANCOVA. Results showed a significant decrease in P100 amplitude among regular cannabis users in low spatial frequency (F(1,67) = 4.43; p = 0.04) and in dynamic condition (F(1,67) = 4.35; p = 0.04). Analysis also reported a decrease in P100 area under the curve in regular cannabis users to low spatial frequency (F(1,67) = 4.31; p = 0.04) and in dynamic condition (F(1,67) = 7.65; p < 0.01). No effect was found on P100 latency, N170 amplitude, latency, or area under the curve. We found alteration of P100 responses to low spatial frequency and dynamic stimuli in regular cannabis users. This result could be interpreted as a preferential magnocellular impairment where such deficit could be linked to glutamatergic dysfunction. As mentioned in the literature, visual and electrophysiological anomalies in schizophrenia are related to a magnocellular dysfunction. Further studies are needed to clarify electrophysiological deficits in both populations. CLINICAL TRIALS REGISTRATION: Electrophysiological Study of the Functioning of Magnocellular Visual Pathway in Regular Cannabis Users (CAUSA MAP). [NCT02864680; ID 2013-A00097-38]. https://clinicaltrials.gov/ct2/show/NCT02864680?cond=Cannabis&cntry=FR&draw=2&rank=1.

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.

Altered central vision and amacrine cells dysfunction as marker of hypodopaminergic activity in treated patients with schizophrenia

BACKGROUND

Retinal dysfunction is widely documented in schizophrenia using flash (fERG) and pattern electroretinograms (PERG), but the role of dopamine transmission has seldom been explored.

METHODS

We explored the role of dopamine transmission by evaluating the spatial location of retinal anomalies using multifocal ERG (mfERG) in photopic condition and the oscillatory potentials (OPs) extracted from fERG measured in scotopic condition in 29 patients with schizophrenia and 29 healthy controls.

RESULTS

With the mfERG, our main results revealed reduced amplitudes in the center of the retina: P1 (p < .005) and N2 amplitudes (p < .01) in the <2° region, N1 (p < .0005) and P1 amplitudes (p < .001) in the 2-5° region and P1 amplitude (p < .05) in the 5-10° region. For OPs, our results showed a decrease in the O1 (p < .005), O2 (p < .005), O3 (p < .05) and overall O1, O2, O3 index amplitudes (p < .005) in patients with schizophrenia.

CONCLUSIONS

Both the central location of retinal dysfunctions of the mfERG and OPs results could reflect a hypodopaminergic effect in patients with schizophrenia. In future studies, OPs should be considered as a measure to evaluate the hypodopaminergy in patients.

Complete evaluation of retinal function in Major Depressive Disorder: From central slowdown to hyperactive periphery

BACKGROUND

Developing easy-to-access biomarkers is crucial in Major Depressive Disorder. The retina has already been suggested as relevant. However, there is a need for a global and local assessment of whole retinal function using a reproducible, standardized protocol allowing for comparison across studies. Our aim is to assess whole retinal function in patients with actual unipolar Major Depressive Episode (MDE) using pattern, flash and multifocal electroretinogram (ERG) according to the International Society for Clinical Electrophysiology of Vision standardized protocols.

METHODS

We assessed retinal function in 14 males and females with MDE, diagnosed based on the Diagnostic and Statistical Manual of Mental Disorders, and in age- and sex-matched healthy controls.

RESULTS

Comparing the patients with the controls, we observed the following using multifocal ERG: a significant increase in N1 peak time in ring 3 and a decrease in P1 amplitude in ring 2; using pattern ERG: a significant increase in P50 peak time; using flash ERG: a decrease in a- and b-wave peak time and an increase in the b-wave amplitude in dark-adapted 3.0, a decrease in a- and b-wave peak time and an increase in both wave amplitudes in light-adapted 3.0, and a decrease in the b-wave peak time in light-adapted flicker.

LIMITATIONS

Sample size. Contribution of pharmacological treatments to the outcomes cannot be formally excluded.

CONCLUSIONS

Patients with MDE exhibit delayed signaling in the central retina and hyperreactivity to light in the periphery. Central retinal function may be a marker of psychomotor retardation and cognitive impairment in MDE.

Retinal dysfunctions in a patient with a clinical high risk for psychosis and severe visual disturbances: A single case report

AIM

Psychosis can be preceded by a clinical high risk for psychosis (CHR) and visual anomalies are predictors of transition to psychosis. Visual retinal processing is altered in psychosis, but no study has explored the links between visual symptoms and retinal functions in CHR patients. We report here the case of NR, an antipsychotic-naive young adult with CHR and severe visual symptoms in whom we explored the retinal function.

METHODS

A flash electroretinogram (fERG) and a pattern electroretinogram (pERG) protocol were conducted and we compared NR results to a group of patients with schizophrenia and a group of healthy controls.

RESULTS

Despites an overlap between the measures of NR and the two groups, visual analyses revealed that NR showed increased b-wave implicit time (rod response) compared to the control group and NR's response was at an intermediate level between two subgroups of schizophrenia patients regarding presence or absence of visual hallucinations.

DISCUSSION

The relevance of retinal dysfunctions as a marker of vulnerability for psychosis is discussed.

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.

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.

Retinal dysfunctions in regular tobacco users: The retina as a window to the reward circuit in addictive disorders

The nicotine contained in tobacco is a neuromodulator which affects neurotransmission within the brain. The retina is an easy way to study central synaptic transmission dysfunctions in neuropsychiatric disorders. The purpose of this study is to assess the impact of regular tobacco use on retinal function using pattern (PERG), flash (fERG) and multifocal (mfERG) electroretinogram (ERG). We recorded PERG, fERG and mfERG for 24 regular tobacco users and 30 healthy non-smoking subjects. The protocol was compliant with International Society for Clinical Electrophysiology of Vision standards. The amplitudes and peak times (PT) of P50, N95 waves (PERG), a-, b- and oscillatory potentials (fERG), and N1, P1, N2 (mfERG) were evaluated. Compared to non-smokers, the results (Mann-Whitney U test, Bonferroni correction) for tobacco users suggested a significant increase of ~ 1 ms in the PT of light-adapted 3.0 fERG b-wave (p = 0.002). Using mfERG, we observed the following increases in tobacco users: in ring 3 for P1 PT of ~1,5 ms and in ring 5 for P1 PT of ~ 1 ms and for N2 PT of ~ 1 ms (p = 0.002, p = 0.002 and p = 0.006). It is our hypothesis that these results reflect the consequences of regular tobacco use on retinal synaptic transmission, and more specifically on dopaminergic and cholinergic transmission. We deduce that the retina may provide a crucial site of investigation for neurotransmission modulation of the reward circuit in regular tobacco users.

Delayed on- and off-retinal responses of cones pathways in regular cannabis users: An On-Off flash electroretinogram case-control study

The retina is considered a useful area for investigating synaptic transmission abnormalities in neuropsychiatric disorders, including as a result of using cannabis, the most widely consumed illicit substance in the developed world. The impact of regular cannabis use on retinal function has already been evaluated, using pattern and flash electroretinogram (ERG) to demonstrate a delay in ganglion and bipolar cell response. Using multifocal ERG, it was showed that the delay to be preferentially located in the central retina. ERG tests do not separately examine the impact of cannabis on the On and Off pathways. The purpose of this study is to assess On and Off pathway function using On-Off ERG. We conducted an On-Off ERG test in 42 regular cannabis users and 26 healthy controls. The protocol was compliant with the International Society for Clinical Electrophysiology of Vision (ISCEV) standards. Amplitude and peak time were measured for the a-, b- and d-waves. Results in the regular cannabis users showed a significant increase in the latencies of both the b- and the d-wave (p = 0.020, p = 0.022, respectively, Mann-Whitney U test), with no change in the wave amplitudes. A-wave peak time and amplitude were unchanged. These findings are reflective of an effect of regular cannabis use on the On and Off pathways and are consistent with previous findings which also identified increases in retinal neuron response times. We confirm here that regular cannabis use impacts the post-receptoral cones pathway at the level of bipolar cells, affecting the On and Off pathways.

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.

Schizophrenia and the retina: Towards a 2020 perspective

BACKGROUND

Differences between people with schizophrenia and psychiatrically healthy controls have been consistently demonstrated on measures of retinal function such as electroretinography (ERG), and measures of retinal structure such as optical coherence tomography (OCT). Since our 2015 review of this literature, multiple new studies have been published using these techniques. At the same time, the accumulation of data has highlighted the "fault lines" in these fields, suggesting methodological considerations that need greater attention in future studies.

METHODS

We reviewed studies of ERG and OCT in schizophrenia, as well as data from studies whose findings are relevant to interpreting these papers, such as those on effects of the following on ERG and OCT data: comorbid medical conditions that are over-represented in schizophrenia, smoking, antipsychotic medication, substance abuse, sex and gender, obesity, attention, motivation, and influences of brain activity on retinal function.

RESULTS

Recent ERG and OCT studies continue to support the hypothesis of retinal structural and functional abnormalities in schizophrenia, and suggest that these are relevant to understanding broader aspects of pathophysiology, neurodevelopment, and neurodegeneration in this disorder. However, there are differences in findings which suggest that the effects of multiple variables on ERG and OCT data need further clarification.

CONCLUSIONS

The retina, as the only component of the CNS that can be imaged directly in live humans, has potential to clarify important aspects of schizophrenia. With greater attention to specific methodological issues, the true potential of ERG and OCT as biomarkers for important clinical phenomena in schizophrenia should become apparent.

Retinal ganglion cells dysfunctions in schizophrenia patients with or without visual hallucinations

The electroretinogram has revealed photoreceptor, bipolar cell, and, in one prior study, retinal ganglion cell (RGC) dysfunction in schizophrenia. The structural abnormalities of the RGC are well documented in schizophrenia and such abnormalities have been associated with visual hallucinations (VH) in neurological disorders. The goals of this study were: 1) to examine the functional responses of photoreceptors and RGC in schizophrenia patients in comparison with healthy controls; and 2) to compare the extent of retinal dysfunction in schizophrenia patients with or without VH. We recorded the flash electroretinogram in scotopic and photopic conditions, and the pattern electroretinogram, in schizophrenia patients (n = 29) and healthy controls (n = 29). Schizophrenia patients were divided in two groups: schizophrenia patients with VH (VH group, n = 12) and schizophrenia patients with auditory hallucinations or no hallucinations (AHNH group, n = 17). Our results replicate previous findings regarding photoreceptor dysfunction in schizophrenia. PERG results showed a significant increase of the P50 implicit time in schizophrenia patients compared with controls (t(55) = 2.1, p < .05, d = 0.55) and a significant increase of the N95 implicit time in schizophrenia patients compared with controls (t(55) = 4.2; p < .001, d = 0.66). We found an increased rod b-wave implicit time (dark-adapted 0.01 ERG) in the VH group compared to the AHNH group and to the control group, which was associated with lifetime VH score. Our results demonstrate a slowing of RGC signaling in schizophrenia patients, which could affect the quality of visual information reaching the visual cortex. The implications of the data for understanding VH in schizophrenia are discussed.

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.