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

Optical coherence tomography as a potential surrogate marker of dopaminergic modulation across the life span

The retina has been considered a "window to the brain" and shares similar innervation by the dopaminergic system with the cortex in terms of an unequal distribution of D1 and D2 receptors. Here, we provide a comprehensive overview that Optical Coherence Tomography (OCT), a non-invasive imaging technique, which provides an "in vivo" representation of the retina, shows promise to be used as a surrogate marker of dopaminergic neuromodulation in cognition. Overall, most evidence supports reduced retinal thickness in individuals with dopaminergic dysregulation (e.g., patients with Parkinson's Disease, non-demented older adults) and with poor cognitive functioning. By using the theoretical framework of metacontrol, we derive hypotheses that retinal thinning associated to decreased dopamine (DA) levels affecting D1 families, might lead to a decrease in the signal-to-noise ratio (SNR) affecting cognitive persistence (depending on D1-modulated DA activity) but not cognitive flexibility (depending on D2-modulated DA activity). We argue that the use of OCT parameters might not only be an insightful for cognitive neuroscience research, but also a potentially effective tool for individualized medicine with a focus on cognition. As our society progressively ages in the forthcoming years and decades, the preservation of cognitive abilities and promoting healthy aging will hold of crucial significance. OCT has the potential to function as a swift, non-invasive, and economical method for promptly recognizing individuals with a heightened vulnerability to cognitive deterioration throughout all stages of life.

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.

Comparative analysis of electroretinogram with subdermal and invasive recording methods in mice

Electroretinogram (ERG) is the most common clinical and basic visual electrodiagnostic test, which has long been used to evaluate the retinal function through photic stimulation. Despite its wide application, there are still some pitfalls often neglected in ERG recording, such as the recording time point, active electrode location, and the animal strain. In this study, we systematically analyzed and compared the effects of multiple factors on ERG, which would provide an important reference for ERG detection by other investigators. ERG was recorded using the Celeris D430 rodent ERG testing system. The amplitudes and latencies of a wave, b wave and oscillatory potentials (OPs) recorded from different electrode locations (subdermal and invasive), different times of day (day time 8:00 to 13:00 and night time 18:00 to 23:00), bilateral eyes (left and right), and different mouse strains (C57 and CD1) were analyzed and compared. Our results revealed that ERG was affected by active electrode locations and difference between day and night, while OPs seemed not to be influenced. There was no significant difference in the amplitudes or latencies of ERG and OPs between left and right eyes, irrespective of measurements at day or night, or which method was used. Compared to C57 mice, both ERG and OP responses were significantly decreased in Brn3b^AP/AP mice, a model for retinal ganglion cell (RGC) loss. In addition, there were some non-negligible differences in visual responses between C57 and CD1 mouse strains. Our results suggest that the invasive procedure is a reliable method for evaluating the visual function including VEP, ERG and OP responses in mice. Moreover, these comparative analyses provide valuable references for future studies of mammalian visual electrophysiology.

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.