Published: July 1st, 2016
This protocol describes simultaneous measurement of electroretinogram and visual evoked potentials in anesthetized rats.
The electroretinogram (ERG) and visual evoked potential (VEP) are commonly used to assess the integrity of the visual pathway. The ERG measures the electrical responses of the retina to light stimulation, while the VEP measures the corresponding functional integrity of the visual pathways from the retina to the primary visual cortex following the same light event. The ERG waveform can be broken down into components that reflect responses from different retinal neuronal and glial cell classes. The early components of the VEP waveform represent the integrity of the optic nerve and higher cortical centers. These recordings can be conducted in isolation or together, depending on the application. The methodology described in this paper allows simultaneous assessment of retinal and cortical visual evoked electrophysiology from both eyes and both hemispheres. This is a useful way to more comprehensively assess retinal function and the upstream effects that changes in retinal function can have on visual evoked cortical function.
Measurement of the electroretinogram (ERG) and visual evoked potential (VEP) provide useful quantitative assessments of the integrity of the visual pathway. The ERG measures the electrical responses of the retina to light stimulation, while the VEP measures the corresponding functional integrity of the visual pathways from the retina to the primary visual cortex following the same light event. This manuscript describes a protocol for the recording and analysis of ERG and VEP responses in a commonly used laboratory model, the rat.
The ERG provides an index of the functional integrity of a number of key retinal cell classes by quantifying the....
All experimental procedures were conducted according to the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes, set out by the National Health and Medical Research Council in Australia. Ethics clearance was obtained from the University of Melbourne, Science Faculty, Animal Ethics Committee (approval number 0911322.1).
1. Pre-implantation of Chronic VEP Electrodes
Note: If concurrent ERG and VEP signals are to be collected animals must be surgically implanted with VEP electrode.......
The ERG a-wave (> -1.38 log cd.s.m-2), b-waves (> - 4.99 log cd.s.m-2) STRs (< - 4.99 log cd.s.m-2) and the VEPs (> - 0.52 log cd.s.m-2) were recorded simultaneously (Figure 1 and 3). At very dim flashes, a positive STR (pSTR) is seen at approximately 110 msec after the flash, and a negative STR (nSTR) at approximately 220 msec (Figures 1 and 2). An ERG with a large b-wave, peaks between 50 to 10.......
The ERG and VEP are objective measures of visual function from the retina and cortex, respectively. The advantage of simultaneous recording is that a more comprehensive view of the entire visual pathway is afforded. Specifically, the complementary information from their concurrent assessment could provide a clearer delineation of the site of injury in the visual pathway (e.g., for disorders with overlapping ERG yet distinct VEP manifestations18, when optic neuropathy may co-exist with primary cerebral.......
|Stainless steel 26 mm clip for connecting VEP screw electrodes to cables
|For amplifying ERG and VEP signals
|Carboxymethylcellulose sodium 1.0%
|Viscous fluid for improving signal quality of the active ERG electrode
|Pfizer Animal Health Group
|Proprietary name: Rimadyl injectable (50 mg/mL). For post-surgery analgesia, diluted to 0.5% (5 mg/mL) in normal saline
|For disinfecting surgical instruments
|Circulating water bath
|For maintaining body temperature of the anesthetized animal during surgery and electrophysiological recordings
|For encasing the electrode-skull assembly to make it more robust
|Storz Instruments, Bausch and Lomb
|A miniature drill head of ~0.7mm diameter for making a small hole in the skull over each hemisphere to implant VEP screws
|Dremel 300 series
|An automatic drill for trepanning
|Platinum cables for connecting silver wire electrodes to the amplifier
|Ensures light proof to maintain dark adaptation. Encloses the Ganzfeld setup to improve signal to noise ratio
|Multigate Medical Products Pty Ltd
|For drying the surgical incision and exposed skull surface during surgery
|Ganzfeld integrating sphere
|Photometric Solutions International
|Custom designed light stimulator: 36 mm diameter, 13 cm aperture size
|VELCRO Australia Pty Ltd
|VELCRO Brand Reusable Wrap
|Hook-and-loop fastener to secure the electrodes and the animal on the recording platform
|Abbott Australasia Pty Ltd
|Proprietary Name: Isoflo(TM) Inhalation anaaesthetic. Pharmaceutical-grade inhalation anesthetic mixed with oxygen gas for VEP electrode implant surgery
|Proprietary name: Ketamil Injection, Brand: Ilium. Pharmaceutical-grade anesthetic for electrophysiological recording
|Phillips Lighting Co.
|For light stimulation twenty 5 watt and one 1 watt LEDs.
|Holds the ERG active electrode during recordings
|Subcutaneously inserted in the tail to serve as the ground electrode for both the ERG and VEP
|Phenylephrine 2.5% minims
|Bausch and Lomb
|Instilled with Tropicamide to achieve maximal dilation for ERG recording
|Povidone iodine 10%
|Proprietory name: Betadine, Antiseptic to prepare the shaved skin for surgery 10%, 500 mL
|Powerlab data acquisition system
|Controls the LEDs
|For corneal anaesthesia during ERG recordings
|Non-injectable, for electroplating silver wire electrodes
|Simultaneously triggers the stimulus via the Powerlab system and collects data
|Silver (fine round wire)
|Used to make active and inactive ERG electrodes, and the inactive VEP electrode
|Stainless streel screws
|0.7 mm shaft diameter, 3 mm in length to be implanted over the primary visual cortex and serve as the active VEP electrodes
|A small animal stereotaxic instrument for locating the primary visual cortices according to Paxinos & Watson's 2007 rat brain atlas coordinates
|For incising the area of skin overlaying the primary visual cortex to implant the VEP electrodes
|Shanghai Pudong Jinhuan Medical Products Co.,Ltd
|3-0 silk braided suture non-absorbable, for skin retraction during VEP electrode implantation surgery
|Tobramycine eye ointment 0.3%
|Proprietary name: Tobrex. Prophylactic antibiotic ointment applied around the skin wound after surgery
|Proprietary name: 0.5% Mydriacyl eye drop, Instilled to achieve mydriasis for ERG recording
|Pharmaceutical-grade anesthetic for electrophysiological recording
|Eppendorf Pty Ltd
|Eppendorf epTIPS 100 - 5000 mL, for custom-made electrodes
|Microsoft Office Excel
|spreadsheet software for data analysis
|Lethabarb Euthanazia Injection
|Virbac (Australia) Pty Ltd
|325 mg/mL pentobarbital sodium for rapid euthanazia
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