Accelerated aging of senescence accelerated mice R-1 demonstrated by flash visually evoked cortical potentials

Age-related differences in retinal function and structure in C57BL/6J and Thy1-YFPh mice

Age-related neuronal adaptations are known to help maintain function. This study aims to examine gross age-related in vivo retinal functional adaptations (using electroretinography) in young and middle aged C57BL/6J and Thy1-YFPh mice and to relate this to in vivo retinal structure (using optical coherence tomography). Electroretinography responses were generally larger in Thy1-YFPh mice than in C57BL/6J mice, with similar in vivo retinal layer thicknesses except for longer inner/outer photoreceptor segment in Thy1-YFPh mice. Relative to 3-month-old mice, 12-month-old mice showed reduced photoreceptor (C57BL/6J 84.0±2.5 %; Thy1-YFPh 80.2±5.2 %) and bipolar cell (C57BL/6J 75.6±2.3 %; Thy1-YFPh 68.1±5.5 %) function. There was relative preservation of ganglion cell function (C57BL/6J 79.7±3.7 %; Thy1-YFPh 91.7±5.0 %) with age, which was associated with increased b-wave (bipolar cell) sensitivities to light. Ganglion cell function was correlated with both b-wave amplitude and sensitivity. This study shows that there are normal age-related adaptations to preserve functional output. Different mouse strains may have varied age-related adaptation capacity and should be taken into consideration when examining age-related susceptibility to injury.

Dose-dependent effect of myelin oligodendrocyte glycoprotein on visual function and optic nerve damage in experimental autoimmune encephalomyelitis

Female Dark Agouti rats were immunized with increasing doses of myelin oligodendrocyte glycoprotein (MOG) to develop experimental autoimmune encephalomyelitis (EAE), a preclinical model of multiple sclerosis. Typical EAE motor impairments were assessed daily and noninvasive visual evoked potentials (VEPs) were recorded at baseline and 5 weeks after immunization, with final histopathology of optic nerves (ONs). Immunized rats exhibited a relapsing-remitting clinical course. Both VEP and histological abnormalities were detected in a MOG dose-dependent gradient. Increasing MOG dosage augmented visual function impairment in EAE, which could be monitored with VEP recording to assess demyelination and axonal loss along ONs.

Non-invasive visual evoked potentials to assess optic nerve involvement in the dark agouti rat model of experimental autoimmune encephalomyelitis induced by myelin oligodendrocyte glycoprotein

Experimental autoimmune encephalomyelitis (EAE) is the primary disease model of multiple sclerosis (MS), one of the most diffused neurological diseases characterized by fatigue, muscle weakness, vision loss, anxiety and depression. EAE can be induced through injection of myelin peptides to susceptible mouse or rat strains. In particular, EAE elicited by the autoimmune reaction against myelin oligodendrocyte glycoprotein (MOG) presents the common features of human MS: inflammation, demyelination and axonal loss. Optic neuritis affects visual pathways in both MS and in several EAE models. Neurophysiological evaluation through visual evoked potential (VEP) recording is useful to check visual pathway dysfunctions and to test the efficacy of innovative treatments against optic neuritis. For this purpose, we investigate the extent of VEP abnormalities in the dark agouti (DA) rat immunized with MOG, which develops a relapsing-remitting disease course. Together with the detection of motor signs, we acquired VEPs during both early and late stages of EAE, taking advantage of a non-invasive recording procedure that allows long follow-up studies. The validation of VEP outcomes was determined by comparison with ON histopathology, aimed at revealing inflammation, demyelination and nerve fiber loss. Our results indicate that the first VEP latency delay in MOG-EAE DA rats appeared before motor deficits and were mainly related to an inflammatory state. Subsequent VEP delays, detected during relapsing EAE phases, were associated with a combination of inflammation, demyelination and axonal loss. Moreover, DA rats with atypical EAE clinical course tested at extremely late time points, manifested abnormal VEPs although motor signs were mild. Overall, our data demonstrated that non-invasive VEPs are a powerful tool to detect visual involvement at different stages of EAE, prompting their validation as biomarkers to test novel treatments against MS optic neuritis.

Optic nerve involvement in experimental autoimmune encephalomyelitis to homologous spinal cord homogenate immunization in the dark agouti rat

Dark-Agouti rats were immunized with spinal cord homogenate to develop Experimental Autoimmune Encephalomyelitis, a model of multiple sclerosis. We assessed motor signs and recorded VEPs for five or eight weeks with epidural or epidermal electrodes, respectively, with final histopathology of optic nerves (ONs). Injected rats exhibited motor deficits a week after immunization. VEP delays arose from the 2nd to the 5th week, when a recovery occurred in epidermal-recorded rats. ON damage appeared in epidural-, but not in epidermal-recorded rats, probably due to a remyelination process. VEP could be exploited as neurophysiological marker to test novel treatments against neurodegeneration involving ONs.

Visual evoked potentials can be reliably recorded using noninvasive epidermal electrodes in the anesthetized rat

PURPOSE

Visual evoked potentials (VEPs) are a powerful tool to evaluate nervous conduction along the visual pathways, both in humans and in animal models. Traditionally, epidural screw electrodes are used to record VEPs in preclinical research. Here we tested the feasibility in the preclinical setting of the same noninvasive technique used for clinical VEP acquisition, by using epidermal cup electrodes with no surgical procedures.

METHODS

Monocular flash VEPs were recorded bilaterally under sevoflurane anesthesia once a week for 6 weeks in 14 dark Agouti rats, 7 with implanted epidural screws and 7 with epidermal 6 mm Ø Ag/AgCl cups.

RESULTS

VEP traces obtained with the two techniques were morphologically comparable. There were no significant differences in latency of the main visual component between screw-recorded VEPs (sVEPs) and cup-recorded VEPs (cVEPs). Amplitude values with epidermal cups were significantly lower than those with epidural screws. Both techniques provided latencies and amplitudes which were stable over time. Furthermore, with regard to latency both methods ensured highly repeatable measurements over time, with epidermal cups even providing slightly better results. On the other hand, considering amplitudes, cVEPs and sVEPs provided fairly acceptable repeatability.

CONCLUSIONS

Epidermal cup electrodes can provide comparable results to those obtained with the "gold standard" epidural screws, while representing a simpler and less invasive technique to test nervous conduction along the visual pathways in the preclinical setting.

Flash visual evoked potentials in mice can be modulated by transcranial direct current stimulation

Transcranial direct current stimulation (tDCS) in humans has been shown to affect the size of visual evoked potentials (VEPs) in a polarity-dependent way. VEPs have been widely employed in mice to study the visual system in physiological and pathological conditions and are extensively used as animal models of neurological and visual disorders. The present study was performed to evaluate whether mice VEPs could be modulated by tDCS in the same manner as in humans. We describe here the effects of 10 min tDCS (anodal, cathodal or no stimulation) on flash-VEPs in C57BL/6 mice under sevoflurane anesthesia. VEP amplitudes of the first major peak (P1) were analyzed before, at 0, 5 and 10 min after tDCS. Compared with no stimulation condition, anodal tDCS increased P1 amplitude slightly more than 25%, while cathodal stimulation had opposite effects, with a decrease of P1 amplitude by about 30%. After-effects tended to reverse toward basal levels within 10 min after tDCS. These results, suggesting polarity-dependent modulation similar to what described in humans of tDCS effects on VEPs, encourage the use of mice models to study tDCS mechanisms of action and explore therapeutic applications on neurological models of disease.