Search Results (15)

The vertebrate retina is a complex neural tissue composed of a repeating array of distinct cell types that communicate through specialized synaptic connections. The neurochemistry underlying these connections reveals the synaptic chemistry, including the neurotransmitters involved and their corresponding receptors. The basic pattern of communication is that the pathway from photoreceptors to bipolar cells to ganglion cells typically uses glutamate as the signaling transmitter, with three ionotropic and one metabotropic receptor types. In contrast, much of the lateral feedback, performed by horizontal cells and amacrine cells, uses the inhibitory neurotransmitter GABA, while other amacrine cells use glycine or dopamine. This review examines all of these neurotransmitter systems for each retinal cell type, along with how these systems process the visual signals transmitted to the lateral geniculate nucleus and the visual cortex. Full article

Background/Objectives: The loss of retinal ganglion cells (RGCs) is a hallmark of glaucoma, a major cause of blindness. Glial cell activation due to increased intraocular pressure (IOP) significantly contributes to RGC death. Therefore, substances with anti-inflammatory properties could help prevent that process. This study investigated whether combining Citicoline and Coenzyme Q10 (CoQ10) can reduce glial activation in the retina and the rest of the visual pathway, potentially preventing neurodegeneration in a mouse model of unilateral laser-induced ocular hypertension (OHT). Methods: Four groups of mice were used: vehicle (n = 12), CitiQ10 (n = 12), OHT–vehicle (n = 18), and OHT–CitiQ10 (n = 18). The administration of Citicoline and CoQ10 was performed orally once a day, initiated 15 days prior to the laser treatment and maintained post-treatment until sacrifice (3 days for retina or 7 days for the rest of the visual pathway). The retina, dorsolateral geniculate nucleus, superior colliculus, and visual cortex (V1) were immunohistochemically stained and analyzed. Results: In the laser–CitiQ10 group, the Citicoline + CoQ10 compound revealed (1) an IOP decrease at 24 h and 3 days post-laser; and (2) reduced signs of macroglial (decreased GFAP area) and microglial (soma size, arbor area, microglia number, P2RY12 expression) activation in the retina and in the rest of the visual pathway (reduced activated microglial phenotypes and lower GFAP expression). Conclusions: This study shows that oral administration of Citicoline and CoQ10 can reduce glial activation caused by increased IOP in retina and visual pathway in a mouse model of OHT, potentially protecting RGCs from OHT-induced inflammation. Full article

In this study, we designed a biomimetic artificial visual system (AVS) inspired by biological visual system that can process RGB images. Our approach begins by mimicking the photoreceptor cone cells to simulate the initial input processing followed by a learnable dendritic neuron model to replicate ganglion cells that integrate outputs from bipolar and horizontal cell simulations. To handle multi-channel integration, we utilize a nonlearnable dendritic neuron model to simulate the lateral geniculate nucleus (LGN), which consolidates outputs across color channels, an essential function in biological multi-channel processing. Cross-validation experiments show that AVS demonstrates strong generalization across varied object–background configurations, achieving accuracy where traditional models like EfN-B0, ResNet50, and ConvNeXt typically fall short. Additionally, our results across different training-to-testing data ratios reveal that AVS maintains over 96% test accuracy even with limited training data, underscoring its robustness in low-data scenarios. This demonstrates the practical advantage of the AVS model in applications where large-scale annotated datasets are unavailable or expensive to curate. This AVS model not only advances biologically inspired multi-channel processing but also provides a practical framework for efficient, integrated visual processing in computational models. Full article

Glaucoma is a neurodegenerative disease characterized by the loss of retinal ganglion cells (RGCs), with intraocular pressure (IOP) being its primary risk factor. Despite controlling IOP, the neurodegenerative process often continues. Therefore, substances with neuroprotective, antioxidant, and anti-inflammatory properties could protect against RGC death. This study investigated the neuroprotective effects on RGCs and visual pathway neurons of a compound consisting of citicoline and coenzyme Q10 (CoQ10) in a mouse model of unilateral, laser-induced ocular hypertension (OHT). Four groups of mice were used: vehicle group (n = 6), citicoline + CoQ10 group (n = 6), laser–vehicle group (n = 6), and laser–citicoline + CoQ10 group (n = 6). The citicoline + CoQ10 was administered orally once a day starting 15 days before laser treatment, continuing until sacrifice (7 days post-laser). Retinas, the dorsolateral geniculate nucleus (dLGN), the superior colliculus (SC), and the visual cortex (V1) were analyzed. The citicoline + CoQ10 compound used in the laser–citicoline + CoQ10 group demonstrated (1) an ocular hypotensive effect only at 24 h post-laser; (2) prevention of Brn3a+ RGC death in OHT eyes; and (3) no changes in NeuN+ neurons in the dLGN. This study demonstrates that the oral administration of the citicoline + CoQ10 combination may exert a neuroprotective effect against RGC death in an established rodent model of OHT. Full article

Background: The suprageniculate fossa (SGF) is located between the geniculate ganglion, the middle cranial fossa (MCF) and the anterior semicircular canal (ASCC). An endoscopic transcanal approach has been recently proposed to treat the different lesions in this area. The aim of the study is to describe the anatomical pathway of this approach by measuring the dimensions of its boundaries while checking their correlation with the pneumatization of the SGF area. Methods: This is a retrospective anatomical analysis of Cone Beam CT scans of 80 patients, for a total of 160 temporal bones analyzed. Two checkpoints were measured for the SGF route, as an internal and an external window. These are triangles between the MCF dura, the geniculate ganglion and the ASCC on parasagittal and axial planes. The pneumatization of the SGF was also assessed, classified and correlated with the measured dimensions. Results: The depth of the SGF was 7.5 ± 1.8 mm. The width of the external window was 7.5 ± 1.9, 5.6 ± 2.4 and 1.6 ± 1.6 mm for the posterior, middle and anterior points of measurement, respectively. The height of the internal window was 7.6 ± 1.2, 4.5 ± 1.5 and 1.7 ± 1.7 mm for the posterior, middle and anterior points of measurement, respectively. Type A pneumatization was found in 87 cases, type B in 34 and type C in 39. The degree of pneumatization directly correlated to the depth and height of the fossa. Conclusions: The suprageniculate approach route is defined by the internal and external windows which should be evaluated during a pre-surgery imaging assessment. The detailed anatomy of the approach and the novel classification of the pneumatization of the SGF are here described which may be useful to plan a safer procedure with minimal complications. Full article

Mild traumatic brain injury (mTBI) affects millions of people in the U.S. Approximately 20–30% of those individuals develop adverse symptoms lasting at least 3 months. In a rat mTBI study, the closed-head impact model of engineered rotational acceleration (CHIMERA) produced significant axonal injury in the optic tract (OT), indicating white-matter damage. Because retinal ganglion cells project to the lateral geniculate nucleus (LGN) in the thalamus through the OT, we hypothesized that synaptic density may be reduced in the LGN of rats following CHIMERA injury. A modified SEQUIN (synaptic evaluation and quantification by imaging nanostructure) method, combined with immunofluorescent double-labeling of pre-synaptic (synapsin) and post-synaptic (PSD-95) markers, was used to quantify synaptic density in the LGN. Microglial activation at the CHIMERA injury site was determined using Iba-1 immunohistochemistry. Additionally, the effects of ketamine, a potential neuroprotective drug, were evaluated in CHIMERA-induced mTBI. A single-session repetitive (ssr-) CHIMERA (3 impacts, 1.5 joule/impact) produced mild effects on microglial activation at the injury site, which was significantly enhanced by post-injury intravenous ketamine (10 mg/kg) infusion. However, ssr-CHIMERA did not alter synaptic density in the LGN, although ketamine produced a trend of reduction in synaptic density at post-injury day 4. Further research is necessary to characterize the effects of ssr-CHIMERA and subanesthetic doses of intravenous ketamine on different brain regions and multiple time points post-injury. The current study demonstrates the utility of the ssr-CHIMERA as a rodent model of mTBI, which researchers can use to identify biological mechanisms of mTBI and to develop improved treatment strategies for individuals suffering from head trauma. Full article

(1) Background: COVID-19 infection has affected almost 6 million people worldwide. Geniculate Ganglion Zoster resulting in Ramsay Hunt Syndrome (RHS) has been rarely described in this context. (2) Methods: Here, a case of RHS in the context of asymptomatic COVID-19 infection is reported followed by a literature review of the previously published cases (PubMed research combining “COVID-19” and “Ramsay Hunt Syndrome” or their abbreviations/synonyms, searching for data published at any time till October 2023). (3) Results: Five cases have been previously published (age range: 25–67 years; n = 3 males). Three patients were known to be immunocompetent prior to infection, one was receiving corticotherapy for lung disease, and one had an unspecified immune status. RHS predominantly involved both facial and vestibulocochlear nerves, with one case exclusively involving the facial nerve as the presented case. Regarding facial nerve palsy, three were right-sided (like the current report) and two were left-sided. Two cases were asymptomatic to COVID-19 (like the present patient), one had mild fatigue, and two had classical COVID-19 symptoms preceding RHS symptoms. Workup included serological testing against Varicella Zoster Virus and PCR assays that can detect the viral DNA in saliva, blood, tears, exudates, and cerebrospinal fluid. The treatment combined antiviral and corticosteroid therapies which yielded heterogeneous outcomes that might be related to some demographic and clinical data. (4) Conclusions: RHS rarely occurs in the context of COVID-19. Early recognition is important. Management seems to be similar to the classical condition. Some data may help predict facial nerve recovery. Full article

Ramsay Hunt syndrome (RHS) has a poor prognosis because of varicella-zoster virus (VZV) infection. This is most closely related to severe inflammation in the geniculate ganglion of the facial nerve due to VZV infection or reactivation. This study investigated whether there were differences in the prognosis and accompanying symptoms of facial paralysis based on the presence or absence of VZV IgM and IgG antibodies. This study was conducted as a retrospective chart analysis of 105 patients with RHS who were admitted to our hospital between 2015 and 2021. The House–Brackmann (HB) grade and electroneurography (ENoG) was used to evaluate the degree of facial paralysis. Patients’ subjective symptoms were evaluated by dividing them into dizziness, tinnitus, hyperacusis, and hearing loss. No difference was observed in the initial HB grade with or without IgM; however, the final HB grade was significantly higher in IgM-positive patients than in IgM-negative patients (p < 0.05). Further, when IgM was positive, the value of the orbicularis oculi muscle in the ENoG test results was significantly higher (p < 0.05), and symptoms of tinnitus and hyperacusis occurred more frequently (p < 0.05). The initial and final HB grades were significantly higher in IgG-positive patients than in IgG-negative patients (p < 0.05). When IgG was positive, the values of nasalis and oris muscles in the ENoG test results were significantly higher (p < 0.05), and symptoms of dizziness occurred more frequently (p < 0.05). This study confirmed that the more active the immunological action of the VZV in the body, the greater the damage to the facial and vestibulocochlear nerves, which are associated with the degree of facial paralysis and the accompanying otologic symptoms. Full article

Background: To evaluate patients with middle ear cholesteatoma presenting with facial palsy (FP). Material-Methods: A total of 14 subjects (10 males and 4 females), with a mean age of 42.5 years, were included in our study. The majority of patients presented with incomplete FP (House–Brackmann HB II-IV, 11 cases) and the remaining 3 patients had complete facial paralysis (HB V-VI). A canal wall down mastoidectomy was performed in all the patients, followed by partial facial nerve decompression. Results: At the one-year follow-up, eleven (78.5%) patients demonstrated satisfactory recovery to HB I-II. Facial function recovered to HB grade I-II in 9 (100%) patients who were surgically treated within one month, and in 2 (40%) patients who underwent surgery after one month. The tympanic segment of facial nerve was the most common site of involvement (8 patients). The multiple regression analysis showed that a higher preoperative HB grade combined with a gradual than sudden onset of FP more likely resulted in worse postoperative HB grade. Conclusion: Early surgical removal of cholesteatoma associated with FP is more likely to result in good facial nerve recovery (78.5% of cases), when it is performed within one month from the onset of FP. According to the literature, the tympanic segment of the facial nerve was more frequently damaged (77.7%), followed by the mastoid segment (22.9%), labyrinthine segment (11.1%), and geniculate ganglion (11.1%). Labyrinthine fistula, mainly of the lateral semicircular canal, can be expected in cases of facial nerve dehiscence. The canal wall down mastoidectomy combined with partial decompression surgery was the most preferred surgical treatment for the FP secondary to cholesteatoma. Full article

Light exerts powerful biological effects on mood regulation. Whereas the source of photic information affecting mood is well established at least via intrinsically photosensitive retinal ganglion cells (ipRGCs) secreting the melanopsin photopigment, the precise circuits that mediate the impact of light on depressive behaviors are not well understood. This review proposes two distinct retina–brain pathways of light effects on mood: (i) a suprachiasmatic nucleus (SCN)-dependent pathway with light effect on mood via the synchronization of biological rhythms, and (ii) a SCN-independent pathway with light effects on mood through modulation of the homeostatic process of sleep, alertness and emotion regulation: (1) light directly inhibits brain areas promoting sleep such as the ventrolateral preoptic nucleus (VLPO), and activates numerous brain areas involved in alertness such as, monoaminergic areas, thalamic regions and hypothalamic regions including orexin areas; (2) moreover, light seems to modulate mood through orexin-, serotonin- and dopamine-dependent pathways; (3) in addition, light activates brain emotional processing areas including the amygdala, the nucleus accumbens, the perihabenular nucleus, the left hippocampus and pathways such as the retina–ventral lateral geniculate nucleus and intergeniculate leaflet–lateral habenula pathway. This work synthetizes new insights into the neural basis required for light influence mood Full article

During the development of the retina and the nervous system, high levels of energy are required by the axons of retinal ganglion cells (RGCs) to grow towards their brain targets. This energy demand leads to an increase of glycolysis and L-lactate concentrations in the retina. L-lactate is known to be the endogenous ligand of the GPR81 receptor. However, the role of L-lactate and its receptor in the development of the nervous system has not been studied in depth. In the present study, we used immunohistochemistry to show that GPR81 is localized in different retinal layers during development, but is predominantly expressed in the RGC of the adult rodent. Treatment of retinal explants with L-lactate or the exogenous GPR81 agonist 3,5-DHBA altered RGC growth cone (GC) morphology (increasing in size and number of filopodia) and promoted RGC axon growth. These GPR81-mediated modifications of GC morphology and axon growth were mediated by protein kinases A and C, but were absent in explants from gpr81^−/− transgenic mice. Living gpr81^−/− mice showed a decrease in ipsilateral projections of RGCs to the dorsal lateral geniculate nucleus (dLGN). In conclusion, present results suggest that L-lactate and its receptor GPR81 play an important role in the development of the visual nervous system. Full article

Combined administration of N-Methyl-D-Aspartate (NMDA) and kainic acid (KA) on the inner retina was studied as a model of excitotoxicity. The right eye of C57BL6J mice was injected with 1 µL of PBS containing NMDA 30 mM and KA 10 mM. Only PBS was injected in the left eye. One week after intraocular injection, electroretinogram recordings and immunohistochemistry were performed on both eyes. Retinal ganglion cell (RGC) projections were studied by fluorescent-cholerotoxin anterograde labeling. A clear decrease of the retinal “b” wave amplitude, both in scotopic and photopic conditions, was observed in the eyes injected with NMDA/KA. No significant effect on the “a” wave amplitude was observed, indicating the preservation of photoreceptors. Immunocytochemical labeling showed no effects on the outer nuclear layer, but a significant thinning on the inner retinal layers, thus indicating that NMDA and KA induce a deleterious effect on bipolar, amacrine and ganglion cells. Anterograde tracing of the visual pathway after NMDA and KA injection showed the absence of RGC projections to the contralateral superior colliculus and lateral geniculate nucleus. We conclude that glutamate receptor agonists, NMDA and KA, induce a deleterious effect of the inner retina when injected together into the vitreous chamber. Full article

The Hedgehog (Hh) pathway has regulatory roles in maintaining and restoring lingual taste organs, the papillae and taste buds, and taste sensation. Taste buds and taste nerve responses are eliminated if Hh signaling is genetically suppressed or pharmacologically inhibited, but regeneration can occur if signaling is reactivated within the lingual epithelium. Whereas Hh pathway disruption alters taste sensation, tactile and cold responses remain intact, indicating that Hh signaling is modality-specific in regulation of tongue sensation. However, although Hh regulation is essential in taste, the basic biology of pathway controls is not fully understood. With recent demonstrations that sonic hedgehog (Shh) is within both taste buds and the innervating ganglion neurons/nerve fibers, it is compelling to consider Hh signaling throughout the tongue and taste organ cell and tissue compartments. Distinctive signaling centers and niches are reviewed in taste papilla epithelium, taste buds, basal lamina, fibroblasts and lamellipodia, lingual nerves, and sensory ganglia. Several new roles for the innervation in lingual Hh signaling are proposed. Hh signaling within the lingual epithelium and an intact innervation each is necessary, but only together are sufficient to sustain and restore taste buds. Importantly, patients who use Hh pathway inhibiting drugs confront an altered chemosensory world with loss of taste buds and taste responses, intact lingual touch and cold sensation, and taste recovery after drug discontinuation. Full article

Under optimal conditions, just 3–6 ms of visual stimulation suffices for humans to see motion. Motion perception on this timescale implies that the visual system under these conditions reliably encodes, transmits, and processes neural signals with near-millisecond precision. Motivated by in vitro evidence for high temporal precision of motion signals in the primate retina, we investigated how neuronal and perceptual limits of motion encoding relate. Specifically, we examined the correspondence between the time scale at which cat retinal ganglion cells in vivo represent motion information and temporal thresholds for human motion discrimination. The timescale for motion encoding by ganglion cells ranged from 4.6 to 91 ms, and depended non-linearly on temporal frequency, but not on contrast. Human psychophysics revealed that minimal stimulus durations required for perceiving motion direction were similarly brief, 5.6–65 ms, and similarly depended on temporal frequency but, above ~10%, not on contrast. Notably, physiological and psychophysical measurements corresponded closely throughout (r = 0.99), despite more than a 20-fold variation in both human thresholds and optimal timescales for motion encoding in the retina. The match in absolute values of the neurophysiological and psychophysical data may be taken to indicate that from the lateral geniculate nucleus (LGN) through to the level of perception little temporal precision is lost. However, we also show that integrating responses from multiple neurons can improve temporal resolution, and this potential trade-off between spatial and temporal resolution would allow for loss of temporal resolution after the LGN. While the extent of neuronal integration cannot be determined from either our human psychophysical or neurophysiological experiments and its contribution to the measured temporal resolution is unknown, our results demonstrate a striking similarity in stimulus dependence between the temporal fidelity established in the retina and the temporal limits of human motion discrimination. Full article

Conventional imaging methods could not distinguish processes within the ventral and dorsal streams. The application of Fourier time series analysis was helpful to segregate changes in the ventral and dorsal streams of the visual system in male and female mice. The present study measured the accumulation of [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) in the mouse brain using small animal positron emission tomography and magnetic resonance imaging (PET/MRI) during light stimulation with blue and yellow filters, compared to during conditions of darkness. Fourier analysis was performed using mean standardized uptake values (SUV) of [¹⁸F]FDG for each stimulus condition to derive spectral density estimates for each condition. In male mice, luminance opponency occurred by S-peak changes in the sub-cortical retino-geniculate pathways in the dorsal stream supplied by ganglionic arteries in the left visual cortex, while chromatic opponency involved C-peak changes in the cortico-subcortical pathways in the ventral stream perfused by cortical arteries in the left visual cortex. In female mice, there was resonance phenomenon at C-peak in the ventral stream perfused by the cortical arteries in the right visual cortex during luminance processing. Conversely, chromatic opponency caused by S-peak changes in the subcortical retino-geniculate pathways in the dorsal stream supplied by the ganglionic arteries in the right visual cortex. In conclusion, Fourier time series analysis uncovered distinct mechanisms of color processing in the ventral stream in males, while in female mice color processing was in the dorsal stream. It demonstrated that computation of colour processing as a conscious experience could have a wide range of applications in neuroscience, artificial intelligence and quantum mechanics. Full article