Long-term anesthetic protocol in rats: feasibility in electrophysiology studies in visual prosthesis

Effects of dandelion root on rat heart function and oxidative status

This study aimed to examine the effects of dandelion root on rat heart function and oxidative status. At the beginning of the experimental protocol, Wistar albino rats were randomly classified into two groups (10 rats per group): 1. control group - animals that drank tap water; 2. experimental group - animals that drank dandelion root for four weeks. Every morning for four weeks, the animals received freshly boiled dandelion root in a volume of 250 ml. At the end of the dandelion administration, animals were sacrificed, and their hearts were isolated and retrogradely perfused according to the Langendorff technique at a gradually increasing perfusion pressure between 40 - 120 cm H₂O. The following myocardial function parameters were measured: maximum rate of left ventricular pressure development (dp/dt max), minimum rate of left ventricular pressure development (dp/dt min), systolic left ventricular pressure (SLVP), diastolic left ventricular pressure (DLVP), heart rate (HR). In addition, the coronary flow (CF) was measured flowmetrically. Finally, blood samples were collected after sacrificing to determine oxidative stress biomarkers: nitrite (NO₂^-), superoxide anion radical (O₂^-), hydrogen peroxide (H₂O₂), the index of lipid peroxidation (TBARS), reduced glutathione (GSH), catalase (CAT) and superoxide dismutase (SOD). The present pioneer results indicated that dandelion root did not manifest a negative impact on functional aspects of isolated rat heart. In addition, dandelion consumption was not associated with promising results in terms of maintaining systemic redox balance.

Implications of Neural Plasticity in Retinal Prosthesis

Retinal degenerative diseases such as retinitis pigmentosa cause a progressive loss of photoreceptors that eventually prevents the affected person from perceiving visual sensations. The absence of a visual input produces a neural rewiring cascade that propagates along the visual system. This remodeling occurs first within the retina. Then, subsequent neuroplastic changes take place at higher visual centers in the brain, produced by either the abnormal neural encoding of the visual inputs delivered by the diseased retina or as the result of an adaptation to visual deprivation. While retinal implants can activate the surviving retinal neurons by delivering electric current, the unselective activation patterns of the different neural populations that exist in the retinal layers differ substantially from those in physiologic vision. Therefore, artificially induced neural patterns are being delivered to a brain that has already undergone important neural reconnections. Whether or not the modulation of this neural rewiring can improve the performance for retinal prostheses remains a critical question whose answer may be the enabler of improved functional artificial vision and more personalized neurorehabilitation strategies.

Cross-modal activation of the primary visual cortex by auditory stimulation in RCS rats: considerations in visual prosthesis

An important brain re-wiring, the so-called cross-modal plasticity, occurs during progression of retinal degenerative diseases to compensate for lack of visual input. The visual cortex does not go 'unused', instead it is devoted to processing other sensory modalities. In this study we recorded, in the visual cortex, visual- and auditory-evoked potentials in an anesthetized murine model of retinal degeneration. The latency to the first peak of the recorded local field potentials was used to assess the speed of the response. Visual responses occurred significantly faster in the control group. Conversely, auditory responses appeared significantly faster in animals with retinal degeneration. This suggests the compensatory neural rewiring is optimizing the performance of other sensory modalities, hearing in this case. This phenomenon may play an important role in visual neuro-rehabilitation. Whether or not it can promote or deter the interpretation of artificially encoded neural signals from a visual prosthesis remains to be studied.

Intravenous ketamine for long term anesthesia in rats

Ketamine/xylazine anesthesia has been used primarily for short term procedures in animals, but two prior reports used intravenous ketamine/xylazine for experiments taking many hours. However, there is a discrepancy about the appropriate dose, which is resolved here. Adult Long-Evans rats were used for recording from the retina. Doses of Ketamine/xylazine were adjusted to minimize anesthetic in terminal experiments lasting 10 h. An allometric relation was fitted to the resulting data on doses as a function of body weight, and compared to prior work. The allometric relationship between the continuously infused specific dose and weight was: dose = 9.13 (weight)^−1.213 (r² = 0.73), where dose is in mg-kg⁻¹-hr⁻¹ and rat weight is in kg. The dose of xylazine was 3.3% of the ketamine dose. No attempt was made to explore different relative doses of xylazine and ketamine. Prior work is consistent with this relationship, showing that the earlier discrepancy resulted from using rats of different sizes. Ketamine at the doses used here still depressed the electroretinogram relative to historical controls using urethane. We conclude that intravenous ketamine dosing in rats should not use the same mg-kg⁻¹-hr⁻¹ dose for all rats, but take into account the strong allometric relationship between dose and rat weight. There is an advantage in using smaller doses in order to prevent unnecessary depression of neural responses.