From the Microbiome to the Electrome: Implications for the Microbiota-Gut-Brain Axis.

The gut microbiome plays a fundamental role in metabolism, as well as the immune and nervous systems. Microbial imbalance (dysbiosis) can contribute to subsequent physical and mental pathologies. As such, interest has been growing in the microbiota-gut-brain brain axis and the bioelectrical communication that could exist between bacterial and nervous cells. The aim of this study was to investigate the bioelectrical profile (electrome) of two bacterial species characteristic of the gut microbiome: a Proteobacteria Gram-negative bacillus Escherichia coli (E. coli), and a Firmicutes Gram-positive coccus Enterococcus faecalis (E. faecalis). We analyzed both bacterial strains to (i) validate the fluorescent probe bis-(1,3-dibutylbarbituric acid) trimethine oxonol, DiBAC4(3), as a reliable reporter of the changes in membrane potential (Vmem) for both bacteria; (ii) assess the evolution of the bioelectric profile throughout the growth of both strains; (iii) investigate the effects of two neural-type stimuli on Vmem changes: the excitatory neurotransmitter glutamate (Glu) and the inhibitory neurotransmitter γ-aminobutyric acid (GABA); (iv) examine the impact of the bioelectrical changes induced by neurotransmitters on bacterial growth, viability, and cultivability using absorbance, live/dead fluorescent probes, and viable counts, respectively. Our findings reveal distinct bioelectrical profiles characteristic of each bacterial species and growth phase. Importantly, neural-type stimuli induce Vmem changes without affecting bacterial growth, viability, or cultivability, suggesting a specific bioelectrical response in bacterial cells to neurotransmitter cues. These results contribute to understanding the bacterial response to external stimuli, with potential implications for modulating bacterial bioelectricity as a novel therapeutic target.

Bioelectrical State of Bacteria Is Linked to Growth Dynamics and Response to Neurotransmitters: Perspectives for the Investigation of the Microbiota-Brain Axis.

Inter-cellular communication is mediated by a sum of biochemical, biophysical, and bioelectrical signals. This might occur not only between cells belonging to the same tissue and/or animal species but also between cells that are, from an evolutionary point of view, far away. The possibility that bioelectrical communication takes place between bacteria and nerve cells has opened exciting perspectives in the study of the gut microbiota-brain axis. The aim of this paper is (i) to establish a reliable method for the assessment of the bioelectrical state of two bacterial strains: Bacillus subtilis (B. subtilis) and Limosilactobacillus reuteri (L. reuteri); (ii) to monitor the bacterial bioelectrical profile throughout its growth dynamics; and (iii) to evaluate the effects of two neurotransmitters (glutamate and γ-aminobutyric acid-GABA) on the bioelectrical signature of bacteria. Our results show that membrane potential (Vmem) and the proliferative capacity of the population are functionally linked in B. subtilis in each phase of the cell cycle. Remarkably, we demonstrate that bacteria respond to neural signals by changing Vmem properties. Finally, we show that Vmem changes in response to neural stimuli are present also in a microbiota-related strain L. reuteri. Our proof-of-principle data reveal a new methodological approach for the better understanding of the relation between bacteria and the brain, with a special focus on gut microbiota. Likewise, this approach will open exciting perspectives in the study of the inter-cellular mechanisms which regulate the bi-directional communication between bacteria and neurons and, ultimately, for designing gut microbiota-brain axis-targeted treatments for neuropsychiatric diseases.

Long-term effect of intravitreal ranibizumab therapy on retinal nerve fiber layer in eyes with exudative age-related macular degeneration.

PURPOSE: To investigate long-term effect (96 months) of intravitreal ranibizumab administered for exudative age-related macular degeneration (AMD) on retinal nerve fiber layer (RNFL) thickness when used following a pro re nata regimen. METHODS: In this prospective study, 20 eyes of 20 patients diagnosed with exudative AMD were included. Contralateral non-exudative AMD eyes of nine of these patients were included as controls. Data on intraocular pressure (IOP) and number of injections were recorded. Spectralis optic coherence tomography (OCT) of the circumpapillary RNFL was performed under dilation when diagnosis was made and before the three loading injections. "Follow-up" software was selected to accurately compare baseline with subsequent images through the 8 years of the study. RESULTS: Baseline IOP was 14.1 mmHg both in study (standard deviation, SD: 0.8) and control eyes (SD: 0.9) and remained unchanged during the study. Mean number of injections was 21 (SD: 2.8) at the end of the study. Mean average thickness of RNFL in the study eye group at the end of the study was 96.5 µm (SD: 2.1). Mean loss for the study period was 5.3 µm (SD: 0.7; p < 0.0001). Corresponding RNFL values for controls were 92.9 (SD: 3.2) and 5.8 µm (SD: 1.2; p < 0.001). Superior temporal sector had the greatest loss in both groups, followed by inferior and nasal sectors. No statistically significant differences were found when comparing losses in injected eyes versus control eyes. CONCLUSIONS: RNFL thickness decreased both equally in injected eyes and control eyes. Thus, no long-term effects of intravitreal ranibizumab were observed on the retinal nerve fiber layer thickness.

Long-Term Consequences of COVID-19 Lockdown in Neovascular AMD Patients in Spain: Structural and Functional Outcomes after 1 Year of Standard Follow-Up and Treatment.

Consequences of the COVID-19 pandemic on medical care have been extensively analyzed. Specifically, in ophthalmology practice, patients suffering age-related macular degeneration (AMD) represent one of the most affected subgroups. After reporting the acute consequences of treatment suspension in neovascular AMD, we have now evaluated these same 242 patients (270 eyes) to assess if prior functional and anatomical situations can be restored after twelve months of regular follow-up and treatment. We compared data from visits before COVID-19 outbreak and the first visit after lockdown with data obtained in subsequent visits, until one year of follow-up was achieved. For each patient, rate of visual loss per year before COVID-19 pandemic, considered "natural history of treated AMD", was calculated. This rate of visual loss significantly increased during the lockdown period and now, after twelve months of regular follow-up, is still higher than before COVID outbreak (3.1 vs. 1.6 ETDRS letters/year, p < 0.01). Percentage of OCT images showing active disease is now lower than before the lockdown period (51% vs. 65.3%, p = 0.0017). Although anatomic deterioration, regarding signs of active disease, can be apparently fully restored, our results suggest that functional consequences of temporary anti-VEGF treatment suspension are not entirely reversible after 12 months of treatment, as BCVA remains lower and visual loss rate is still higher than before the COVID-19 pandemic.

Effect of COVID-19 Lockdown in Spain on Structural and Functional Outcomes of Neovascular AMD Patients.

This is a retrospective single-center study of patients with neovascular age-related macular degeneration whose follow-up was delayed due to COVID-19 pandemic with at least three months between visits in Madrid, Spain. The purpose of the study was to evaluate best corrected visual acuity (BCVA) changes and try to identify features in optical coherence tomography (OCT) that could be related to more profound visual loss. It included 270 eyes. The two last visits before lockdown were used for comparison with the visit after lockdown. BCVA changed from 60.2 ± 18.2 to 55.9 ± 20.5 ETDRS letters. 29% of the eyes lost more than 5 letters. OCT was active in 67% of eyes before lockdown and in 80.4% after lockdown. Multiple lineal analysis showed that patients whose OCT before lockdown presented with a combination of intra and subretinal fluid were more likely to suffer a greater visual loss (p = 0.002). These patients should be encouraged to not miss any visits in case a new lockdown is imposed.

Pupillary behavior in relation to wavelength and age.

Pupil light reflex can be used as a non-invasive ocular predictor of cephalic autonomic nervous system integrity. Spectral sensitivity of the pupil's response to light has, for some time, been an interesting issue. It has generally, however, only been investigated with the use of white light and studies with monochromatic wavelengths are scarce. This study investigates the effects of wavelength and age within three parameters of the pupil light reflex (amplitude of response, latency, and velocity of constriction) in a large sample of younger and older adults (N = 97), in mesopic conditions. Subjects were exposed to a single light stimulus at four different wavelengths: white (5600°K), blue (450 nm), green (510 nm), and red (600 nm). Data was analyzed appropriately, and, when applicable, using the General Linear Model (GLM), Randomized Complete Block Design (RCBD), Student's t-test and/or ANCOVA. Across all subjects, pupillary response to light had the greatest amplitude and shortest latency in white and green light conditions. In regards to age, older subjects (46-78 years) showed an increased latency in white light and decreased velocity of constriction in green light compared to younger subjects (18-45 years old). This study provides data patterns on parameters of wavelength-dependent pupil reflexes to light in adults and it contributes to the large body of pupillometric research. It is hoped that this study will add to the overall evaluation of cephalic autonomic nervous system integrity.