[A procedure for electroretinogram (ERG) recording in mice--effect of monoiodoacetic acid on the ERG in pigmented mice]

Comparisons of α2-Adrenergic Agents, Medetomidine and Xylazine, with Pentobarbital for Anesthesia: Important Pitfalls in Diabetic and Nondiabetic Rats

Purpose: Anesthesia is necessary to conduct rodent electroretinograms (ERGs). We evaluated utility of the α2-agonist medetomidine versus xylazine for ERG studies in nondiabetic and diabetic rats. Pentobarbital was included as a comparator. Methods: Male Sprague-Dawley rats, with and without streptozotocin (STZ)-induced diabetes, were anesthetized with medetomidine (1 mg/kg), xylazine (10 mg/kg) (both with ketamine 75 mg/kg), or pentobarbital (70 mg/kg). The depth of anesthesia was assessed, and if adequate, scotopic ERGs were recorded. Blood glucose was monitored. Results: In nondiabetic rats, all three agents induced satisfactory anesthesia, but with differing durations: medetomidine > pentobarbital > xylazine. ERG responses were similar under medetomidine and xylazine, but relatively reduced under pentobarbital. Both α2-agonists (but not pentobarbital) elicited marked hyperglycemia (peak values 316.1 ± 42.6 and 300.3 ± 29.5 mg/dL, respectively), persisting for 12 h. In diabetic rats, elevated blood glucose concentrations were not affected by any of the agents, but the depth of anesthesia under medetomidine and xylazine was inadequate for ERG recording. Conclusions: In nondiabetic rats, medetomidine and xylazine elicited comparable effects on ERGs that differ from pentobarbital, but both perturbed glucose metabolism, potentially confounding experimental outcomes. In STZ-diabetic rats, neither α2-agent provided adequate anesthesia, while pentobarbital did so. Problems with α2-anesthetic agents, including medetomidine, must be recognized to ensure meaningful interpretation of experimental results.

The effects of iodoacetic acid on the mouse retina

BACKGROUND

To characterize the effects of intravitreal injections of iodoacetic acid (IAA) in comparison to its systemic application as a measure to induce unilateral photoreceptor degeneration.

METHODS

Seven-week-old C57BL/6 J mice received either intravitreal injections of IAA or systemic treatment (intraperitoneal vs intravenous) and were observed in the following 5 weeks using ERG, OCT, and histology.

RESULTS

Systemic treatment with IAA induced high toxic effects and a high mortality in contrast to the intravitreal injection. Intraperitoneal application had no effect on the retina. Intravenous application of 2 × 30 mg/kg BW IAA (time between injections 3.5 h) resulted in an extinction of the ERG and a thinning of the retina, in particular of the outer nuclear layer (ONL) indicating photoreceptor degeneration. Animals receiving intravitreal injections developed cataracts already at low concentrations (up to 100% at 0.25 mg/kg BW). Higher intravitreal IAA doses led to extinguished ERGs. In histology, a thinning of the entire retina was observed that was most prominent in the inner part of the retina.

CONCLUSIONS

In contrast to intraperitoneal administration, intravenous application of IAA led to a selective photoreceptor degeneration. After intravitreal injection, dense cataracts were already observed at concentrations lower than those needed to induce changes in the ERG. ERG results must be interpreted carefully. A thinning of all retinal layers rather than a specific outer retinal degeneration was observed upon intravitreal injection. IAA is not a useful model to induce outer retinal degeneration in mice.

Correlations between ERG, OCT, and Anatomical Findings in the rd10 Mouse

Background. To evaluate the correlation between ERG, OCT, and microscopic findings in the rd10 mouse. Methods. C57BL/6J wild type mice and rd10 mice were compared at the age of 2, 3, 5, 7, 9, 12, 24, and 48 weeks (each age group n = 3) using full-field electroretinography (ERG), spectral domain Optical Coherence Tomography (sd-OCT), fluorescein angiography (FA), Hematoxylin & Eosin histology (HE), and immunohistology (IH). Results. While in wild type mice, the amplitude of a- and b-wave increased with light intensity and with the age of the animals, the rd10 mice showed extinction of the ERG beginning with the age of 5 weeks. In OCT recordings, the thickness of the retina decreased up to 9 weeks of age, mainly based on the degradation of the outer nuclear layer (ONL). Afterwards, the ONL was no longer visible in the OCT. HE staining and immunohistological findings confirmed the in vivo data. Conclusion. ERG and OCT are useful methods to evaluate the retinal function and structure in vivo. The retinal changes seen in the OCT closely match those observed in histological staining.

Visual Electrophysiological Features of Two Naturally Occurring Mouse Models with Retinal Dysfunction

PURPOSE

We developed two strains of mouse with retinal dysfunction, named the ICR-derived retinal dysfunction (IRD)1 and IRD2, from one male ICR mouse with a retinal dysfunction but a normal fundus. The purpose of this study was to describe the features of retinal dysfunction in both mutant mice.

METHODS

Scotopic and photopic electroretinograms (ERGs) were recorded from IRD1 and IRD2 mice at 1 month of age to evaluate retinal function, and then the structures of the retinas in both mutant mice were observed by light microscopy at 1 and 3 months of age. In a mating study, the inheritance pattern and the genetic relation of IRD1 and IRD2 mice were defined.

RESULTS

At 1 month of age, IRD1 mice showed affected scotopic and photopic ERGs, and IRD2 mice exhibited normal photopic but affected scotopic ERGs. The retinal structures of both mutant mice remained normal even at 3 months of age. The IRD1, and IRD2 phenotypes showed an autosomal recessive pattern of inheritance and in the IRD1 backcross offspring some mice that had only cone dysfunction were seen in addition to normal, IRD1, and IRD2 phenotypes. All F1 (IRD1 x IRD2) offspring exhibited IRD2 phenotype, rod dysfunction.

CONCLUSIONS

IRD1 and IRD2 mice had affected rod systems caused by a homozygous mutation in the same rod function-related gene, and additionally IDR1 mice had affected cone systems caused by a homozygous mutation in the cone function-related gene, without apparent anatomical abnormalities in the retinas of either mutant mice even at 3 months of age. We believe that these mice could be new spontaneous animal models for the study of human inherited retinal disorders.