JC would like to acknowledge the David Hay Memorial Fund, The University of Melbourne for financial support in writing this manuscript. Funding for this project was provided by an ARC Linkage grant 100200129 (BVB, AJV, CTON).

Ethics statement: Animal experiments were conducted in accordance with the Australian Code for the Care and Use of Animals for Scientific Purposes (2013). Animal ethics approval was obtained from the Animal Ethics Committee, University of Melbourne.&#160;The materials herein are for laboratory experiments only, and not intended for medical or veterinary use.
1. Preparing Electrodes
Note: A three channel transmitter is used for surgical implantation which enables 2 ERG and 1 VEP recording to b...

<ol>
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B., Wader, T., Hovdal, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evoked+potential+tests+in+clinical+diagnosis.">Evoked potential tests in clinical diagnosis.</a> Tidsskr Nor Laegeforen. 133, 960-965 (2013).</li><li>Brankack, J., Schober, W., Klingberg, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Different+laminar+distribution+of+flash+evoked+potentials+in+cortical+areas+17+and+18+b+of+freely+moving+rats.">Different laminar distribution of flash evoked potentials in cortical areas 17 and 18 b of freely moving rats.</a> J Hirnforsch. 31, 525-533 (1990).</li><li>Creel, D., Dustman, R. E., Beck, E. 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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+rate+of+functional+recovery+from+acute+IOP+elevation.">The rate of functional recovery from acute IOP elevation.</a> Invest Ophthalmol Vis Sci. 47, 4872-4880 (2006).</li><li>Lamb, T. D., Pugh, E. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+quantitative+account+of+the+activation+steps+involved+in+phototransduction+in+amphibian+photoreceptors.">A quantitative account of the activation steps involved in phototransduction in amphibian photoreceptors.</a> J Physiol. 449, 719-758 (1992).</li><li>Hood, D. C., Birch, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rod+phototransduction+in+retinitis+pigmentosa:+estimation+and+interpretation+of+parameters+derived+from+the+rod+a-wave.">Rod phototransduction in retinitis pigmentosa: estimation and interpretation of parameters derived from the rod a-wave.</a> Invest Ophthalmol Vis Sci. 35, 2948-2961 (1994).</li><li>Charng, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conscious+wireless+electroretinogram+and+visual+evoked+potentials+in+rats.">Conscious wireless electroretinogram and visual evoked potentials in rats.</a> PLoS Onez. 8, e74172 (2013).</li><li>Galambos, R., Szabo-Salfay, O., Szatmari, E., Szilagyi, N., Juhasz, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sleep+modifies+retinal+ganglion+cell+responses+in+the+normal+rat.">Sleep modifies retinal ganglion cell responses in the normal rat.</a> Proc Natl Acad Sci U S A. 98, 2083-2088 (2001).</li><li>Meeren, H. K., Van Luijtelaar, E. L., Coenen, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cortical+and+thalamic+visual+evoked+potentials+during+sleep-wake+states+and+spike-wave+discharges+in+the+rat.">Cortical and thalamic visual evoked potentials during sleep-wake states and spike-wave discharges in the rat.</a> Electroencephalogr Clin Neurophysiol. 108, 306-319 (1998).</li><li>Nair, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+common+anesthetics+on+eye+movement+and+electroretinogram.">Effects of common anesthetics on eye movement and electroretinogram.</a> Doc Ophthalmol. 122, 163-176 (2011).</li><li>Amouzadeh, H. R., Sangiah, S., Qualls, C. W., Cowell, R. L., Mauromoustakos, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Xylazine-induced+pulmonary+edema+in+rats.">Xylazine-induced pulmonary edema in rats.</a> Toxicol Appl Pharmacol. 108, 417-427 (1991).</li><li>Charng, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retinal+electrophysiology+is+a+viable+preclinical+biomarker+for+drug+penetrance+into+the+central+nervous+system.">Retinal electrophysiology is a viable preclinical biomarker for drug penetrance into the central nervous system.</a> J Ophthalmol. , (2016).</li></ol>

RG and RF are employees to the commercial funder of this research (Pfizer Neusentis and Pfizer Global Research). MI was an employee of Pfizer Global Research during this research and is currently an employee of Proteostasis Therapeutics (Cambridge, USA).

Due to the minimally invasive nature of visual electrophysiology, ERG and VEP recordings in human patients are conducted under conscious conditions and only require the use of topical anesthetics for electrode placement. In contrast, visual electrophysiology in animal models is conventionally conducted under general anesthesia to enable stable electrode placement by eliminating voluntary eye and body movements. However, commonly used general anesthetics alter the ERG and VEP responses as shown by our previous publication...

The ERG and VEP are minimally invasive in vivo tools to assess the integrity of retinal and visual pathways respectively in both the laboratory and clinic. The full-field ERG yields a characteristic waveform which can be broken down into different components, with each element representing different cell classes of the retinal pathway1,2. The classic full-field ERG waveform consists of an initial negative slope (a-wave), which has been shown to represent photoreceptor activity post light exposure2-4. The a-wave is followed by a substantial positive waveform (b-wave) which reflects electrical activity of middle retina, predominantly the ON-bipolar cells5-7. Furthermore, one can vary luminous energy and inter-stimulus-interval to isolate cone from rod responses8.
The flash VEP represents electrical potentials of the visual cortex and brain stem in response to retinal light stimulation9,10. This waveform can be broken down into early and late components, with the early component reflecting activity of neurons of the retino-geniculo-striate pathway11-13 and the late component representing cortical processing performed in various V1 laminae in rats11,13. Therefore simultaneous measurement of the ERG and VEP returns comprehensive assessment of the structures involved in the visual pathway.
Currently, in order to record electrophysiology in animals, anesthesia is employed to enable stable placement of electrodes. There have been attempts to measure ERG and VEP in conscious rats14-16 but these studies employed a wired setup, which can be cumbersome and may lead to animal stress by restricting animal movement and natural behavior17. With recent advances in wireless technology including improved miniaturization and battery life, it is now possible to implement a telemetry approach for ERG and VEP recording, decreasing the stress associated with wired recordings and improving long term viability. Fully internalized stable implantations of telemetry probes have proven to be successful for chronic monitoring of temperature, blood pressure18, activity19 as well as electroencephalography20. Such advances in technology will also assist with repeatability and stability of conscious recordings, increasing the platform&#39;s utility for chronic studies.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Bioamplifier</td>
			<td>ADInstruments</td>
			<td>ML 135</td>
			<td>Amplifies ERG and VEP signals</td>
		</tr>
		<tr>
			<td>Carboxymethylcellulose sodium 1.0%</td>
			<td>Allergan</td>
			<td>CAS 0009000-11-7</td>
			<td>Maintain corneal hydration during surgery</td>
		</tr>
		<tr>
			<td>Carprofen 0.5%</td>
			<td>Pfizer Animal Health Group</td>
			<td>CAS 53716-49-7</td>
			<td>Post-surgery analgesia, given with injectable saline for fluid replenishment</td>
		</tr>
		<tr>
			<td>Chlorhexadine 0.5%</td>
			<td>Orion Laboratories</td>
			<td>27411, 80085</td>
			<td>Disinfection of surgical instrument</td>
		</tr>
		<tr>
			<td>Cyanoacrylate gel activator</td>
			<td>RS components</td>
			<td>473-439</td>
			<td>Quickly dries cyanoacrylate gel</td>
		</tr>
		<tr>
			<td>Cyanocrylate gel&#160;</td>
			<td>RS components</td>
			<td>473-423</td>
			<td>Fix stainless screws to skull</td>
		</tr>
		<tr>
			<td>Dental burr</td>
			<td>Storz Instruments, Bausch and Lomb</td>
			<td>E0824A</td>
			<td>Miniature drill head of ~0.7mm diameter for making a small hole in the skull over each hemisphere to implant VEP screws</td>
		</tr>
		<tr>
			<td>Drill</td>
			<td>Bosch</td>
			<td>Dremel 300 series</td>
			<td>Automatic drill for trepanning</td>
		</tr>
		<tr>
			<td>Enrofloxin</td>
			<td>Troy Laboratories</td>
			<td></td>
			<td>Prophylactic antibiotic post surgey</td>
		</tr>
		<tr>
			<td>Ganzfeld integrating sphere</td>
			<td>Photometric Solutions International</td>
			<td></td>
			<td>Custom designed light stimulator: 36 mm diameter, 13 cm aperture size</td>
		</tr>
		<tr>
			<td>Gauze swabs</td>
			<td>Multigate Medical Products Pty Ltd</td>
			<td>57-100B</td>
			<td>Dries surgical incision and exposed skull surface during surgery</td>
		</tr>
		<tr>
			<td>Isoflurane 99.9%</td>
			<td>Abbott Australasia Pty Ltd</td>
			<td>CAS 26675-46-7</td>
			<td>Proprietory Name: Isoflo(TM) Inhalation anaaesthetic. Pharmaceutical-grade inhalation anesthetic mixed with oxygen gas for VEP electrode implant surgery</td>
		</tr>
		<tr>
			<td>Kenacomb ointment</td>
			<td>Aspen Pharma Pty Ltd</td>
			<td></td>
			<td>To reduce skin irritation and itching after surgery</td>
		</tr>
		<tr>
			<td>Luxeon LEDs</td>
			<td>Phillips Lighting Co.</td>
			<td></td>
			<td>For light stimulation, twenty 5 watt and one 1 watt LEDs, controlled by Scope software</td>
		</tr>
		<tr>
			<td>Needle (macrosurgery)</td>
			<td>World Precision Instruments</td>
			<td>501959</td>
			<td>for suturing abdominal and head surgery, used with 3-0 suture, eye needle, cutting edge 5/16 circle Size 1, 15mm</td>
		</tr>
		<tr>
			<td>Needle holder (macrosurgery)</td>
			<td>World Precision Instruments</td>
			<td>500224</td>
			<td>To hold needle during abdominal and head surgery</td>
		</tr>
		<tr>
			<td>Needle holder (microsurgery)</td>
			<td>World Precision Instruments</td>
			<td>555419NT</td>
			<td>To hold needle during ocular surgery</td>
		</tr>
		<tr>
			<td>Optiva catheter</td>
			<td>Smiths Medical International LTD</td>
			<td>16 or 21 G</td>
			<td>Guide corneal active electrodes from skull to conjunctiva</td>
		</tr>
		<tr>
			<td>Povidone iodine 10%</td>
			<td>Sanofi-Aventis</td>
			<td>CAS 25655-41-8</td>
			<td>Proprietory name: Betadine, Antiseptic to prepare the shaved skin for surgery 10%, 500 mL</td>
		</tr>
		<tr>
			<td>Powerlab data acquisition system</td>
			<td>ADInstruments</td>
			<td>ML 785</td>
			<td>Acquire signal from telemetry transmitter, paired to telemetry data converter</td>
		</tr>
		<tr>
			<td>Proxymetacaine 0.5%</td>
			<td>Alcon Laboratories&#160;</td>
			<td>CAS 5875-06-9</td>
			<td>Topical ocular analgesia</td>
		</tr>
		<tr>
			<td>Restrainer</td>
			<td>cutom made</td>
			<td></td>
			<td>Front of the restrainer is tapered to minimize head movement, length can be adjusted to accommodate different rat length, overall diameter is 60 mm.&#160;</td>
		</tr>
		<tr>
			<td>Scapel blade</td>
			<td>R.G. Medical Supplies</td>
			<td>SNSM0206</td>
			<td>For surgical incision</td>
		</tr>
		<tr>
			<td>Scissors (macrosurgery)</td>
			<td>World Precision Instruments</td>
			<td>501225</td>
			<td>for cutting tissue on the abodmen and forhead</td>
		</tr>
		<tr>
			<td>Scissors (microsurgery)</td>
			<td>World Precision Instruments</td>
			<td>501232</td>
			<td>To dissect the conjunctiva for electrode attachment</td>
		</tr>
		<tr>
			<td>Scope Software</td>
			<td>ADInstruments</td>
			<td>version 3.7.6</td>
			<td>Simultaneously triggers the stimulus via the ADI Powerlab system and collects data</td>
		</tr>
		<tr>
			<td>Shaver</td>
			<td>Oster</td>
			<td>Golden A5</td>
			<td>Shave fur from surgical areas</td>
		</tr>
		<tr>
			<td>Stainless streel screws&#160;</td>
			<td>MicroFasteners</td>
			<td>L001.003CS304</td>
			<td>0.7 mm shaft diameter, 3 mm in length&#160;</td>
		</tr>
		<tr>
			<td>Stereotaxic frame</td>
			<td>David Kopf</td>
			<td>Model 900</td>
			<td>A small animal stereotaxic instrument for locating the implantation landmarks on the skull</td>
		</tr>
		<tr>
			<td>Surgical drape</td>
			<td>Vital Medical Supplies</td>
			<td>GM29-612EE</td>
			<td>Ensure sterile enviornment during surgery</td>
		</tr>
		<tr>
			<td>Suture (macrosurgery)</td>
			<td>Ninbo medical needles</td>
			<td>3-0</td>
			<td>for suturing abdominal and head surgery, sterile silk braided, 60cm</td>
		</tr>
		<tr>
			<td>Suture needle (microsurgery)</td>
			<td>Ninbo medical needles</td>
			<td>8-0 or 9-0</td>
			<td>for ocular surgery including, suturing electrode to sclera and closing conjunctival wound, nylon suture, 3/8 circle 1&#215;5, 30cm</td>
		</tr>
		<tr>
			<td>Telemetry data converter&#160;</td>
			<td>DataSciences International</td>
			<td>R08</td>
			<td>allows telemetry signal to interface with data collection software</td>
		</tr>
		<tr>
			<td>Telemetry Data Exchange Matrix</td>
			<td>DataSciences International</td>
			<td></td>
			<td>Gathers data from transmitters, pair with receiver</td>
		</tr>
		<tr>
			<td>Telemetry data receiver</td>
			<td>DataSciences International</td>
			<td>RPC-1</td>
			<td>Receives telemetry data from transmitter</td>
		</tr>
		<tr>
			<td>Telemetry transmitter</td>
			<td>DataSciences International</td>
			<td>F50-EEE</td>
			<td>3 channel telemetry transmitter</td>
		</tr>
		<tr>
			<td>Tropicamide 0.5%</td>
			<td>Alcon Laboratories&#160;</td>
			<td></td>
			<td>Iris dilation</td>
		</tr>
		<tr>
			<td>Tweezers (macrosurgery)</td>
			<td>World Precision Instruments</td>
			<td>500092</td>
			<td>Manipulate tissues during abdominal and head surgery</td>
		</tr>
		<tr>
			<td>Tweezers (microsurgery)</td>
			<td>World Precision Instruments</td>
			<td>500342</td>
			<td>Manipulate tissues during ocular surgery</td>
		</tr>
	</tbody>
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implantation and recording of wireless electroretinogram and visual evoked potential in conscious rats

The full-field electroretinogram (ERG) and visual evoked potential (VEP) are useful tools to assess retinal and visual pathway integrity in both laboratory and clinical settings. Currently, preclinical ERG and VEP measurements are performed with anesthesia to ensure stable electrode placements. However, the very presence of anesthesia has been shown to contaminate normal physiological responses. To overcome these anesthesia confounds, we develop a novel platform to assay ERG and VEP in conscious rats. Electrodes are surgically implanted sub-conjunctivally on the eye to assay the ERG and epidurally over the visual cortex to measure the VEP. A range of amplitude and sensitivity/timing parameters are assayed for both the ERG and VEP at increasing luminous energies. The ERG and VEP signals are shown to be stable and repeatable for at least 4 weeks post surgical implantation. This ability to record ERG and VEP signals without anesthesia confounds in the preclinical setting should provide superior translation to clinical data.

The photoreceptor response is analyzed by fitting a delayed Gaussian to the leading edge of the initial descending limb of the ERG response at the top 2 luminous energies (1.20, 1.52 log c.s.m-2) for each animal, based on the model of Lamb and Pugh22, formulated by Hood and Birch23. This formula returns an amplitude and a sensitivity parameter, (Figure 1C and 1D, respectively). A hyperbolic function was fitted to the lumin...

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Implantation and Recording of Wireless Electroretinogram and Visual Evoked Potential in Conscious Rats

We show surgical implantation and Recording procedures to measure visual electrophysiological signals from the eye (electroretinogram) and brain (visual evoked potential) in conscious rats, which is more analogous to the human condition where recordings are conducted without anesthesia confounds.

The full-field electroretinogram (ERG) and visual evoked potential (VEP) are useful tools to assess retinal and visual pathway integrity in both ...

The overall goal of this procedure is to measure conscious ERG and VEP signals following surgical implantation of wireless telemetry probes. This technique can help answer key questions in the region of neuroscience field, such as how neurons behave without the limitation of general anesthesia under both healthy conditions and diseased state. The main advantage of this technique is that it allows simultaneous recording of the electro physiology for the retina and for the visual cortex in conscious animal.To begin this procedure prepare the electrodes under a microscope. To do so untwist a double stranded, stainless steel electrode with two fine tipped pliers. Trim one of the stainless steel strands at approximately one centimeter from the tip, leaving a single longer, straight strand to shape the ring electrode.Then, fold the single stainless steel strand back into it self and twist to form a smooth ring at the tip of the electrode. Next shape an ERG active electrode by twisting the base of the loop to form a circle with a diameter of point two to point five millimeters. For the two ERG inactive and one VEP inactive electrodes make the loop diameter to point eight millimeters.In this example, prepare one active ERG and three inactive electrodes. After that, hook the circular VEP active electrode around a stainless steel screw so the electrode rests against the screw head. Then, hook the three inactive electrodes around a second stainless steel screw.The ground electrode will go directly into the peritoneal cavity and there is no need to make a loop at the tip. After shaving and disinfecting the surgical site of an anesthetized animal, make a 10 millimeter incision on the head along he mid line between the ears with a surgical scalpel. Then, make a five millimeter incision on the abdomen through the skin layer, along the mid line below the sternum.After that, tunnel a cannula of five millimeter diameter subcutaneously, from the abdomen incision to the head incision. Feed the electrode wires of the tansmitter through the cannula from the abdomen to the head. Leave the reference electrode with the transmitter base.Then, cover all the electrode tips with aseptic gauze. Next, secure the rat's head to a stereotaxic platform. Extend the forehead incision to 30 millimeters with surgical scissors.Then, expose a surgical area by retracting the skin with two sutures. Scrape off the periosteum overlying the skull to expose the bregma, lambda and mid line sutures. Subsequently, drill two holes through the skull at the VEP active and ERG, VEP inactive stereotaxic coordinates.Attach the active and inactive electrodes with stainless steel screws to the skull to about one millimeter in depth. To implant the ERG active electrodes, use a suture to temporarily retract the upper eye lid. Then, insert a 16 to 21 gauge cannula subcutaneously from behind the eye through the superior conjunctival fornix to the forehead.Subsequently, remove the guiding needle. Next, feed the active electrode through plastic catheter from the forehead towards the eye. Then, remove the plastic catheter.Use a temporary suture, which is threaded through the electrode loop to prevent the electrode from retracting back into the tunnel. After that, make a point five millimeter incision on the superior conjunctiva one millimeter behind the limbus. Use blunt dissection to expose the underlying sclera.Then, implant a suture immediately behind the limbus at half scleral thickness and be careful not to puncture the eyeball. Subsequently, remove the temporary suture from the ERG active electrode. Anchor the ERG active electrode to the half scleral thickness suture by tying three consecutive knots and ensure the electrode tip is situated close to the limbus for good signal to noise ratio.If necessary pull back the excess electrode lead so the active electrode doesn't impinge on the cornea. Then, close the conjuntival flap using one to two interrupted sutures to completely cover the ERG electrode. Afterward, remove the eyelid retracting suture.Repeat the procedure for the contralateral eye. Now, apply cyanoacrylate gel over the skull to secure all the stainless steel screws and electrode wires. Ensure the ERG active electrodes are not tightly pulled before being secured to enable eye movements.Next, close the incision using interrupted sutures. Then, rotate the rodent to expose the abdominal area. Extend the abdominal dermal incision to 40 millimeters along the linea alba with surgical scissors.After that, make a 35 millimeter incision through the inner muscle wall, to expose the inner abdominal cavity. Using two sutures, attach the transmitter body to the animal's inner abdominal wall at the right and avoid contacting the liver. Fold the ground electrode by securing it in a loop with two sutures and place it, free floating, in the abdominal cavity along with the other electrode leads.Subsequently, close the peritoneum using a continuous suture. Then close the skin incision using interrupted sutures. For recording dark adapted signals animals are dark adapted for 12 hours and all procedures are preformed in a dark room with the aide of dim red light.For illustration purposes recordings will be conducted under normal room lighting conditions here. Before recording, apply topical anesthesia and dilating drops to the cornea of the rat. Next, guide the conscious animal into a custom made, clear restrainer.Place the rat in front of the Ganzfeld bowl with it's eyes aligned with the opening of the bowl. Turn on the indwelling transmitter by passing a magnet within five centimeters of it. Verify that the transmitter is on by checking the LED status light on the receiver base.Close the Faraday cage which house's the receiver pad to improve the signal to noise ratio. Then, collect signals over a range of luminous energies. This figure shows the ERG wave forms in conscious rats on day seven post surgery.ERG responses were recorded to range of stimulus energy with the response to the dim flash shown at the bottom and the brightest flash at the top. On day 28 post surgery, these wave forms remained similar to those on day seven. Over four weeks there was no significant time effect for photo receptor amplitude and sensitivity.Rod bi polar cell amplitude and sensitivity. Cone bi polar cell amplitude. And implicit time.Similarly, VEP wave forms appear to be comparable seven and 28 days post surgery. With amplitude and timing parameters showing no significant time effect. These results indicated robust ERG and VEP signal stability.Once mastered, the surgical component of the technique will be completed in one and half to two hours. The conscious recording component, if preformed properly can be completed in 45 minutes. Following this procedure, other methods like pharmacological or disease manipulation can also be preformed.This will answer additional questions in drug discovery as well as chronicle longitudinal experiments. Additionally this procedure can also be preformed in other animals if required. After watching this video, you should have a good understanding of how to surgically implant and subsequently measure conscious ERG and VEP telemetry signals.

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8.6K visualizações.  University of Melbourne. The overall goal of this procedure is to measure conscious ERG and VEP signals following surgical implantation of wireless telemetry probes. This technique can help answer key questions in the region of neuroscience field, such as how neurons behave without the limitation of general anesthesia under both healthy conditions and diseased state. The main advantage of this technique is that it allows simultaneous recording of the electro physiology for the retina and for the visual cortex in cons...