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Microdialysis of Excitatory Amino Acids During EEG Recordings in Freely Moving Rats

Published: November 8th, 2018



1Department of Medical Sciences, Section of Pharmacology, Neuroscience Center, University of Ferrara and National Institute of Neuroscience

Here, we describe a method for in vivo microdialysis to analyze aspartate and glutamate release in the ventral hippocampus of epileptic and non-epileptic rats, in combination with EEG recordings. Extracellular concentrations of aspartate and glutamate may be correlated with the different phases of the disease.

Microdialysis is a well-established neuroscience technique that correlates the changes of neurologically active substances diffusing into the brain interstitial space with the behavior and/or with the specific outcome of a pathology (e.g., seizures for epilepsy). When studying epilepsy, the microdialysis technique is often combined with short-term or even long-term video-electroencephalography (EEG) monitoring to assess spontaneous seizure frequency, severity, progression and clustering. The combined microdialysis-EEG is based on the use of several methods and instruments. Here, we performed in vivo microdialysis and continuous video-EEG recording to monitor glutamate and aspartate outflow over time, in different phases of the natural history of epilepsy in a rat model. This combined approach allows the pairing of changes in the neurotransmitter release with specific stages of the disease development and progression. The amino acid concentration in the dialysate was determined by liquid chromatography. Here, we describe the methods and outline the principal precautionary measures one should take during in vivo microdialysis-EEG, with particular attention to the stereotaxic surgery, basal and high potassium stimulation during microdialysis, depth electrode EEG recording and high-performance liquid chromatography analysis of aspartate and glutamate in the dialysate. This approach may be adapted to test a variety of drug or disease induced changes of the physiological concentrations of aspartate and glutamate in the brain. Depending on the availability of an appropriate analytical assay, it may be further used to test different soluble molecules when employing EEG recording at the same time.

To provide insight into the functional impairment of glutamate-mediated excitatory and GABAergic inhibitory neurotransmission resulting in spontaneous seizures in temporal lobe epilepsy (TLE),we systematically monitored extracellular concentrations of GABA1 and later the levels of glutamate and aspartate2 by microdialysis in the ventral hippocampus of rats at various time-points of the disease natural course, i.e., during development and progression of epilepsy. We took advantage of the TLE pilocarpine model in rats, which mimics the disease very accurately in terms of behavioral, electrophysiological and histop....

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All experimental procedures have been approved by the University of Ferrara Institutional Animal Care and Use Committee and by the Italian Ministry of Health (authorization: D.M. 246/2012-B) in accordance with guidelines outlined in the European Communities Council Directive of 24 November 1986 (86/609/EEC). This protocol is specifically adjusted for glutamate and aspartate determination in rat brain dialysates obtained under EEG control of microdialysis sessions in epileptic and non-epileptic rats. Many of the materials.......

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Probe recovery

The mean recovery (i.e., the mean amino acid content in the perfusate as a percentage of the content in an equal volume of the vial solution) was 15.49 ± 0.42% at a flow rate of 2 μL/min and 6.32 ± 0.64 at 3 μL/min for glutamate and 14.89 ± 0.36% at a flow rate of 2 μL/min and 10.13 ± 0.51 at 3 μL/min for aspartate when using the cuprophane membrane probe. If using the.......

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In this work, we show how a continuous video-EEG recording coupled with microdialysis can be performed in an experimental model of TLE. Video-EEG recording techniques are used to correctly diagnose the different phases of the disease progression in animals and the microdialysis technique is used to describe the changes in glutamate release that occur in time (no changes have been found for aspartate in a previously published study2). We strongly recommend the use of a single device/implant to perf.......

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The authors wish to thank Anna Binaschi, Paolo Roncon and Eleonora Palma for their contribution to manuscripts published in precedence.


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Name Company Catalog Number Comments
3-channel two-twisted electrode Invivo1, Plastic One, Roanoke, Virginia, USA MS333/3-B/SPC Material
guide cannula Agn Tho's, Lindigö, Sweden MAB 4.15.IC Material
Resin KK2 Plastik Elettra Sport, Lecco, Italy KK2 Material
Super Attack gel Loctite Henkel Italia Srl, Milano, Italy 2047420_71941 Material
Imalgene-Ketamine Merial, Toulouse, France 221300288 (AIC) Solution
Xylazine Sigma, Milano, Italy X1251 Material
Isoflurane-Vet Merial, Toulouse, France 103120022 (AIC) Solution
Altadol 50 mg/ ml - tramadol Formevet, Milano, Italy 103703017 (AIC) Solution
Gentalyn 0.1% crm - gentamycine MSD Italia, Roma, Italy 20891077 (AIC) Material
simplex rapid dental cement Kemdent, Associated Dental Products Ltd, Swindon, United Kingdom ACR811 Material
GlasIonomer CX-Plus Cement Shofu, Kyoto, Japan PN1167 Material
probe clip holder Agn Tho's, Lindigö, Sweden p/n 100 5001 Equipment
Histoacryl® Blue Topical Skin Adhesive TissueSeal, Ann Arbor, Michigan, USA TS1050044FP Material
Valium 10 mg/2 ml - diazepam Roche, Monza, Italy 019995063 (AIC) Material
1 mL syringe with 25G needle Vetrotecnica, Padova, Italy 11.3500.05 Material
rat flexible feeding needle 17G Agn Tho's, Lindigö Sweden 7206 Material
Grass Technology apparatus Grass Technologies, Natus Neurology Incorporated, Pleasanton, California, USA M665G08 Equipment (AS40 amplifier, head box, interconnecting cables, telefactor model RPSA S40)
modular data acquisition and analysis system MP150 Biopac, Goleta, California, USA MP150WSW Equipment
digital video surveillance system AverMedia Technologies, Fremont, California, USA V4.7.0041FD Equipment
microdialysis probe Agn Tho's, Lindigö Sweden MAB 4.15.1.Cu Material
microdialysis probe Synaptech, Colorado Springs, Colorado, USA S-8010 Material
block heater Grant Instruments, Cambridge, England QBD2 Equipment
stirrer Cecchinato A, Aparecchi Scientifici, Mestre, Italy 711 Equipment
infusion pump Univentor, Zejtun, Malta 864 Equipment
fine bore polythene tubing Smiths Medical International Ltd., Keene, New Hampshire, USA 800/100/100/100 Material
blue tubing adapters Agn Tho's, Lindigö Sweden 1002 Material
red tubing adapters Agn Tho's, Lindigö Sweden 1003 Material
2.5 mL syringe with 22G needle Chemil, Padova, Italy S02G22 Material
vial cap Cronus, Labicom, Olomouc, Czech Republic VCA-1004TB-100 Material
septum Thermo Scientific, Rockwoood, Tennessee, USA National C4013-60 8 mm TEF/SIL septum Material
glass insert with bottom spring Supelco, Sigma, Milano, Italy 27400-U Material
autosampler vial National Scientific, Thermo Fisher Scientific, Monza, Italy C4013-2 Material
Smartline manager 5000 system controller and degasser unit Knauer, Berlin, Germany V7602 Equipment
Smartline 1000 quaternary gradient pump Knauer, Berlin, Germany V7603 Equipment
spectrofluorometric detector Shimadzu, Kyoto, Japan RF-551 Equipment
chromatogrphic column Knauer, Berlin, Germany 25EK181EBJ Material
chromatogrphic pre-column Knauer, Berlin, Germany P5DK181EBJ Material
mobile phase solution A 0.1 M sodium phosphate buffer, pH 6.0 Solution
mobile phase solution B 40% 0.1 M sodium phosphate buffer, 30% methanol, 30% acetonitrile, pH 6.5 Solution
Ringer solution composition in mM: MgCl2 0.85, KCl 2.7, NaCl 148, CaCl2 1.2, 0.3% BSA Solution
modified Ringer solution composition in mM: MgCl2 0.85, KCl 100, NaCl 50.7, CaCl2 1.2, 0.3% BSA Solution
saline 0.9% NaCl, ph adjusted to 7.0 Solution
sucrose solution 10% sucrose in distilled water Solution

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