EFFECT OF PROTEIN DEPLETION ON THE ELECTRIC RESPONSE OF THE RETINA IN ALBINO RATS

A Ketogenic & Low-Protein Diet Slows Retinal Degeneration in rd10 Mice

Purpose

Treatments that delay retinal cell death regardless of genetic causation are needed for inherited retinal degeneration (IRD) patients. The ketogenic diet is a high-fat, low-carbohydrate diet, used to treat epilepsy, and has beneficial effects for neurodegenerative diseases. This study aimed to determine whether the ketogenic diet could slow retinal degeneration.

Methods

Early weaned, rd10 and wild-type (WT) mice were placed on either standard chow, a ketogenic diet, or a ketogenic & low-protein diet. From postnatal day (PD) 23 to PD50, weight and blood β-hydroxybutyrate levels were recorded. Retinal thickness, retinal function, and visual performance were measured via optical coherence tomography, electroretinography (ERG), and optokinetic tracking (OKT). At PD40, serum albumin, rhodopsin protein, and phototransduction gene expression were measured.

Results

Both ketogenic diets elicited a systemic induction of ketosis. However, rd10 mice on the ketogenic & low-protein diet had significant increases in photoreceptor thickness, ERG amplitudes, and OKT thresholds, whereas rd10 mice on the ketogenic diet showed no photoreceptor preservation. In both rd10 and WT mice, the ketogenic & low-protein diet was associated with abnormal weight gain and decreases in serum albumin levels, 27% and 56%, respectively. In WT mice, the ketogenic & low-protein diet was also associated with an ∼20% to 30% reduction in ERG amplitudes.

Conclusions

The ketogenic & low-protein diet slowed retinal degeneration in a clinically relevant IRD model. In WT mice, the ketogenic & low-protein diet was associated with a decrease in phototransduction and serum albumin, which could serve as a protective mechanism in the rd10 model. Although ketosis was associated with protection, its role remains unclear.

Translational Relevance

Neuroprotective mechanisms associated with the ketogenic & low-protein diet have potential to slow retinal degeneration.

Night vision in a case of vitamin A deficiency due to malabsorption

Night vision was tested electroretinographically and psychophysically in a vitamin A deficient patient before and after therapy. Vitamin A deficiency resulted from malabsorption due to a jeujunoileal bypass operation. Before therapy the patient had severely reduced cone and rod function. After the reversal operation, accompanied by 5 injections of a total of 500,000 units of vitamin A, complete recovery of cone and rod functions was observed within 7 months. Shortly after therapy rod sensitivity reached the normal level, while the time course of rod adaptation remained slower than normal and the dark-adapted electroretinographic (ERG) responses were subnormal. At later stages the ERG responses reached normal amplitudes but rod adaptation stayed slow. Only after 7 months did night vision reach the normal level with regard to the time course of rod adaptation, rod sensitivity, and ERG responses.

Two retinal processes displayed in the cat electroretinogram

Local stimulation of dark adapted cat's retina with spots of light of various intensities elicits a complex b-wave in which four deflections can be consistently identified. An analysis of these wavelets recorded with the low frequency cut off at 80 Hz is made in an attempt to infer their origin. The experimental conditions under which these wavelets were studied were standardized by stimulation with a spot of light at different intensities, frequencies and positions in the visual field. The changes in amplitude and latency by those different conditions of stimulation and by the intravenous (i.v.) injection of additional doses of nembutal, suggests that these peaks are triggered by two retinal excitatory processes related to the scotopic system. It is also pointed out that components 1-2 are mainly determined by the activation of retinal cells which correspond to the area centralis and that components 3-4 represent the activity of retinal cells from the lateral regions (nasal and temporal). The possible clinical use of our results is discussed.

Retinitis pigmentosa

The authors review the symptomatic and genetic aspects of the various entities of isolated retinitis pigmentosa (R.P), both in its typical form and in the forms associated with the affection of other ocular tissues. Syndromes in which R. P. is associated with the affection of other organs and systemic disorders are also cconsidered. Origin, diagnosis and the course of the disease are discussed with regard to electrophysiology, histopathology, fluorescein angiography and biochemistry. Animal research has provided new realizations about the ultrastructure and physiological mechanisms of retinal photoreceptors, and better understanding of abnormal changes. The possible pathogenesis of the human disease, based on research findings, is onsidered. Although R.P. is generally thought to be to be an "untreatable" disease, therapy may be effective in several pathological entities. Methods and results of therapy with vitamins, light deprivation and vision aids are discussed.

Oscillations of potential in the electroretinogram of the lobster

The electroretinogram (ERG) evoked in the lobster by a short flash of light consists of a highly damped, slow oscillation of potential, triggered apparently by a single excitatory process. Near the threshold, only one wave may be evident; but as the intensity of stimulus rises, a prior wave appears, and grows so much more rapidly as to become dominant. Simultaneously third and later waves appear, so that at high intensities the response may include five to seven waves. Dark adaptation favors the second and later waves relative to the first; light adaptation tends to suppress them. On turning on a steady light the oscillations are superimposed on the early stages of development of a maintained, steady-state potential (on-response). Turning off the light causes a rapid fluctuation of potential followed by a similarly damped slow oscillation (off-response). These phenomena resemble in part oscillations recently observed in the b wave of the ERG of many vertebrates including man.