Anatomy and Physiology of Visual Evoked Potentials and Electroretinograms

Semi-invasive and non-invasive recording of visual evoked potentials in mice

PURPOSE

Visual evoked potentials (VEPs) are used to assess visual function in preclinical models of neurodegenerative diseases. VEP recording with epidural screw electrodes is a common method to study visual function in rodents, despite being an invasive procedure that can damage the tissue under the skull. The present study was performed to test a semi-invasive (epicranial) and a non-invasive (epidermal) VEP recording technique, comparing them with the classic epidural acquisition method.

METHODS

Flash VEPs were recorded from C57BL/6 mice on three separate days within 2 weeks. Waveforms, latencies and amplitudes of the components were compared between the three different methods, utilizing coefficient of repeatability, coefficient of variation and intersession standard deviation to evaluate reproducibility.

RESULTS

While epidural electrodes succeeded in recording two negative peaks (N1 and N2), epicranial and epidermal electrodes recorded a single peak (N1). Statistical indexes showed a comparable reproducibility between the three techniques, with a greater stability of N1 latency recorded through epicranial electrodes. Moreover, N1 amplitudes recorded with the new less-invasive methods were more reproducible compared to the invasive gold-standard technique.

CONCLUSIONS

These results demonstrate the reliability of semi- and non-invasive VEP recordings, which can be useful to evaluate murine models of neurological diseases.

Cerebral malaria induces electrophysiological and neurochemical impairment in mice retinal tissue: possible effect on glutathione and glutamatergic system

Background

Cerebral malaria (CM) is a severe complication resulting from Plasmodium falciparum infection. This condition has usually been associated with cognitive, behavioural and motor dysfunctions, being the retinopathy the most serious consequence resulting from the disease. The pathophysiological mechanisms underlying this complication remain incompletely understood. Several experimental models of CM have already been developed in order to clarify those mechanisms related to this syndrome. In this context, the present work has been performed to investigate which possible electrophysiological and neurochemistry alterations could be involved in the CM pathology.

Methods

Experimental CM was induced in Plasmodium berghei-infected male and female C57Bl/6 mice. The survival and neurological symptoms of CM were registered. Brains and retina were assayed for TNF levels and NOS2 expression. Electroretinography measurements were recorded to assessed a- and b-wave amplitudes and neurochemicals changes were evaluated by determination of glutamate and glutathione levels by HPLC.

Results

Susceptible C57Bl/6 mice infected with ≈ 10⁶ parasitized red blood cells (P. berghei ANKA strain), showed a low parasitaemia, with evident clinical signs as: respiratory failure, ataxia, hemiplegia, and coma followed by animal death. In parallel to the clinical characterization of CM, the retinal electrophysiological analysis showed an intense decrease of a- and-b-wave amplitude associated to cone photoreceptor response only at the 7 days post-infection. Neurochemical results demonstrated that the disease led to a decrease in the glutathione levels with 2 days post inoculation. It was also demonstrated that the increase in the glutathione levels during the infection was followed by the increase in the ³H-glutamate uptake rate (4 and 7 days post-infection), suggesting that CM condition causes an up-regulation of the transporters systems. Furthermore, these findings also highlighted that the electrophysiological and neurochemical alterations occurs in a manner independent on the establishment of an inflammatory response, once tumour necrosis factor levels and inducible nitric oxide synthase expression were altered only in the cerebral tissue but not in the retina.

Conclusions

In summary, these findings indicate for the first time that CM induces neurochemical and electrophysiological impairment in the mice retinal tissue, in a TNF-independent manner.

VISUAL EVOKED POTENTIAL FINDINGS IN BEHÇET'S DISEASE WITHOUT NEUROLOGICAL MANIFESTATIONS

Behçet's disease (BD) is a chronic, recurrent multisystem inflammatory disorder firstly described by Turkish dermatologist Dr. Hulusi Behçet in 1937. The classic triad consists of recurrent oral and genital ulcerations and uveitis. The article presents the value of visual evoked potential findings of a series of 44 patients with BD without neurological manifestations seen at the Medical Hospital in Neurology and Dermatology clinics over the past 8 years. The mean latency value of positive peak P100 in BD patients was significantly delayed compared to that of control subjects (patients's mean: 105.6 ms in right eye and 107.7 ms in left eye; control subject's mean: 101.4 ms in right eye and 101.7 ms in left eye).

Effect of anoxia on the electroretinogram of three anoxia-tolerant vertebrates

To survive anoxia, neural ATP levels have to be defended. Reducing electrical activity, which accounts for 50% or more of neural energy consumption, should be beneficial for anoxic survival. The retina is a hypoxia sensitive part of the central nervous system. Here, we quantify the in vivo retinal light response (electroretinogram; ERG) in three vertebrates that exhibit varying degrees of anoxia tolerance: freshwater turtle (Trachemys scripta), epaulette shark (Hemiscyllium ocellatum) and leopard frog (Rana pipiens). A virtually total suppression of ERG in anoxia, probably resulting in functional blindness, has previously been seen in the extremely anoxia-tolerant crucian carp (Carassius carassius). Surprisingly, the equally anoxia-tolerant turtle, which strongly depresses brain and whole-body metabolism during anoxia, exhibited a relatively modest anoxic reduction in ERG: the combined amplitude of turtle ERG waves was reduced by approximately 50% after 2 h. In contrast, the shark b-wave amplitude practically disappeared after 30 min of severe hypoxia, and the frog b-wave was decreased by approximately 75% after 40 min in anoxia. The specific A(1) adenosine receptor antagonist CPT significantly delayed the suppression of turtle ERG, while the hypoxic shark ERG was unaffected by the non-specific adenosine receptor antagonist aminophylline, suggesting adenosinergic involvement in turtle but not in shark.

Eletrorretinografia por padrão reverso em pacientes com enxaqueca sem aura

Foram submetidos a eletrorretinografia por padrão reverso (PERG) 17 pacientes com o diagnóstico de enxaqueca sem aura através dos critérios estabelecidos pela Sociedade Internacional de Cefaléia. O estímulo usado em nossos enfermos foi o estruturado produzido por aparelho de televisão de 20 polegadas. A frequência foi de 1 estímulo por segundo e o total de estímulos somados foi de 512. Constatamos as latências das ondas P 50 e N 95 dentro dos limites de normalidade em todos os nossos casos, a exceção de um em que no olho esquerdo não houve ondas detectadas. Será necessário maior número de exames para que no futuro possamos obter dados que nos ajudem a entender a fisiopatologia da enxaqueca.