Summary
Abstract
Introduction
Protocol
Representative Results
Discussion
Acknowledgements
Materials
References
Neuroscience
Questo protocollo descrive la iontoforesi in tempo reale, un metodo che misura i parametri fisici dello spazio extracellulare (ECS) dei cervelli viventi. La diffusione di una molecola inerte rilasciata nell'ECS viene usata per calcolare la frazione del volume ECS e la tortuosità. È ideale per studiare cambiamenti reversibili acuti al cervello ECS.
Questa revisione descrive i concetti base e il protocollo per eseguire il metodo in tempo reale di iontoforesi (RTI), lo standard oro per esplorare e quantificare lo spazio extracellulare (ECS) del cervello vivente. L'ECS circonda tutte le cellule del cervello e contiene sia il liquido interstiziale che la matrice extracellulare. Il trasporto di molte sostanze necessarie per l'attività cerebrale, compresi i neurotrasmettitori, gli ormoni e le sostanze nutritive, avviene per diffusione attraverso la ECS. Le variazioni del volume e della geometria di questo spazio si verificano durante i processi normali del cervello, come il sonno e le condizioni patologiche, come l'ischemia. Tuttavia, la struttura e la regolazione della ECS cerebrale, in particolare negli stati malati, rimangono in gran parte inesplorati. Il metodo RTI misura due parametri fisici del cervello vivente: frazione di volume e tortuosità. La frazione di volume è la proporzione del volume di tessuto occupata da ECS. Tortuosità è una misura della relativa impedenza che una sostanza incontra quando si diffonde attraverso un cervelloGion rispetto ad un mezzo senza ostruzioni. In RTI, una molecola inerte viene pulsata da un microelettrodo di origine nel cervello ECS. Mentre le molecole si diffondono da questa sorgente, la variabile concentrazione dello ione viene misurata nel tempo utilizzando un microelettrodo ionico selettivo posizionato a circa 100 μm di distanza. Dalla curva di diffusione risultante, è possibile calcolare sia la frazione di volume sia la tortuosità. Questa tecnica è stata utilizzata in fette cerebrali di molteplici specie (compresi gli esseri umani) e in vivo per studiare cambiamenti acuti e cronici a ECS. A differenza di altri metodi, RTI può essere utilizzato per esaminare sia cambiamenti reversibili che irreversibili nel cervello ECS in tempo reale.
Lo spazio extracellulare (ECS) è la rete di canali interconnessi esterni a tutte le cellule del cervello e contiene sia il liquido interstiziale che la matrice extracellulare ( Figura 1a e Figura 1b ). La distribuzione di molte sostanze necessarie per la funzionalità delle cellule cerebrali, comprese le sostanze nutritive, gli ormoni e i neurotrasmettitori, avviene per diffusione attraverso la ECS. I cambiamenti nei parametri fisici di questo spazio, compresi il volume, la geometria e la matrice extracellulare, possono influenzare drasticamente la diffusione attraverso la ECS e le cellule cerebrali di ....
Tutte le procedure animali, utilizzate per ottenere campioni di tessuto, sono stati approvati dal comitato di etica animale presso il SUNY Downstate Medical Center.
1. Preparazione di soluzioni e attrezzature
L'utilità della tecnica RTI è dimostrata in un esperimento progettato per misurare i cambiamenti in α e durante una sfida ipoosmolare ( Figura 8 e Figura 9 ). È stato precedentemente dimostrato che ridurre l'osmolarità del ECS mediante lavaggio su ACSF ipotonico produrrà una diminuzione di α e un aumento di λ 13 .
Figura 10: Dati non ideali che dimostrano problemi tecnici comuni. (A) Schemi di problemi tecnici comuni con microelettrodi ionoforesi: Confronto tra il normale rilascio di TMA da un microelettrodo funzionamento ionoforesi con tre fonti che dimostrano problemi tecnici. [Elevata ingrandimento, a1] La corrente in una sorgente ionoforica ideale viene trasportata ugualmente da rilascio di TMA e assorbi.......
Name | Company | Catalog Number | Comments |
A/D and D/A converter | National Instruments Corporation | NI USB-6221 DAQ | The NI USB-6221 is still sold as a 'Legacy' device by NI. They recommend using NI USB-6341 X Series DAQs for new installations, however we have not tested the newer units. We describe the use of the NI USB-6221 with MATLAB and Windows 7 (32-bit). Alternatives: the much older PCI-MIO-16E-4 A/D converter (Used under Windows XP or older OS only) with BNC-2090 BNC connector panel and SH68-68-EP cable. As noted in the Wanda Manual, an experimental MATLAB program to use Axon Binary Files is available. |
agarose | Lonza | NuSieve GTG Agarose #50081 | to prepare dilute agarose gel for RTI measurements |
amplifier for ISM | Dagan | Model IX2-700 Dual Intracellular Preamplifier | ion and reference voltage amplifier with N=0.1 (for reference barrel) and N=0.001 (for ion barrel) headstages |
biological compound miscroscope (with 4x and 10x objective) | for chipping the microelectrode tips and inspecting microelectrodes; various suppliers, e.g. AmScope | ||
borosilicate theta capillary glass tubing | Harvard Apparatus | Warner Instruments model TG200-4; order #64-0811 | double-barreled glass tubing for ion-selective microelectrodes and iontophoretic microelectrodes; O.D. 2.0 mm, I.D. 1.4 mm, septum 0.2 mm, length 10 cm |
brush | Winsor & Newton | University Series 233, size 0 | round shoft handle brush, available from Amazon |
bunsen burner | Fisher | ||
camera for visualizing micropipettes | Olympus | OLY-150 | requires monitor, IR filter on substage illuminator is optional |
chart recorder | to record continuously voltages on ion-selective microelectrode during calibration in tetramethylammonium standards and during RTI experiment; e.g. Kipp & Zonen type BD112 dual-cannel chart recorded, available refurbished | ||
chlorotrimethylsilane, puriss., > 99% | Sigma-Aldrich | catalog # 92360 | for silanization; CAUTION: flammable, acute toxicity (oral, dermal, inhalation), skin corrosion, eye damage, reacts violently with water, see Sigma-Aldrich Safety Information for full description |
Commercial Software | The MathWorks | MATLAB, Data acquisition toolbox | for data acquisition and analysis using Wanda and Walter programs. Note that an academic license is available. |
eye protective goggles | Fisher | ||
fixed-stage compound microscope | Olympus | BX51WI | can use other compound microscopes with fixed stages |
forceps | Fine Science Tools | #11251-10 | to chip glass capillary; Dumond #5, preferably used and no longer needed for fine work |
fume hood | for silanization and filling the tip of ion-selective barrel with liquid ion exchanger; various supliers, e.g. Captair with approriate filter sold by Erlab | ||
glass microscope slide | Fisher | #12-550A | to chip microelectrode tips |
heater/stirrer | Fisher | Corning PC-420D | to prepare dilute agarose gel and stir solutions |
iontophoretic unit | Dagan | ION-100 and PS-100 | ION-100 is a single channel iontophoresis unit +/- 130 V compliance; PS-100 is an external power supply; alternatives: e.g. Axoprobe-1A made by Axon Instruments (now Molecular Devices), out of production, check for availability of refurbished units (eBay and other sites) |
liquid ion exchanger (LIX) for tetramethylammonium | World Precision Instruments | IE190 Potassium Ion Exchanger | Note: this is equivalent to the original Corning potassium exchanger 477317 based on tetraphenlyborate - do not confuse with neutral carrier potassium exchanger originating from the laboartory of Dr. Simon, ETH, Zurich, which does not sense tetramethylammonium, and is sold by Fluka. You can also make liquid ion exchanger for tetramethylammonium yourself: 3% by weight potassium tetrakis = (p-chlorophenyl) borate dissolved in 2,3-dimethylnitrobenzene. Buy chemicals from Fluka (now part of Sigma). See Oehme and Simon (1976) Anal. Chim. Acta 86: 21-25; CAUTION: The toxicological properties of this liquid ion exchanger have not been fully determined. Ingestion or contact with the human body may be harmful. Exercise due care! Liquid ion exchangers should be stored in a cool place out of direct sunlight. |
microelectrode holder | WPI | M3301EH | to hold ion-selective microeletrode prefabricate for silanization and filling the tip of ion-selective barrel with liquid ion exchanger; WPI sells two versions of this holder, clear M3301EH and black M3301EH. In our experience, the clear M3301EH appears to be sturdier then the black M3301EH. |
micromanipulator | Narishige | MM-3 | to position ion-selective microelectrode prefabricate during silanization and filling the tip of ion-selective barrel with liquid ion exchanger; can be substituted with any three-axis micromanipulator in good working condition |
micropipette puller | Sutter Instruments | Model P-97 | to pull double-barreled glass tubing; other pullers can be used as long as they can accommodate large diameter double-barreled glass tubing |
microprobe thermometer | Physiotemp | Model BAT-12R | fine probe of this thermometer is placed close to recording site |
needle | BD | Syringes and Needles # 305122 (25 gauge) | for silanization; BD PrecisionGlide needles 25 G x 5/8 in (0.5mm x 16mm) |
objective 5x dry | Olympus | MPlan N | |
objective 10x water immersion | Olympus | UMPlan FL N | 10x objective is water immersion, numerical aperture is 0.3, working distance is 3.3 mm |
plastic containers (with lids) | Fisher | #14-375-148 | to store tetramethylammonium standard solutions and microelectrodes |
platform and x-y translation stage for fixed-stage microscope | EXFO | Gibraltar Burleigh | platform holds slice chamber, micromanipulators and accesorries, x-y translational stage moves microscope without compromising recording stability |
porous minicup | for RTI measurements in a dilute agarose gel; homemade | ||
reusable adhesive | Bostik | Blu-Tack | for securing microelectrodes to holding vessel and other uses; various suppliers, available from Amazon |
robotic micromanipulator with precise x,y,z positioning | Sutter Instruments | MP-285 | two mircomanipulators are needed to hold separately ion-selective microelectrode and iontophoretic microelectrode. Also possible to glue micropipettes in a spaced array (see text). |
signal conditioning unit with low-pass filter | Axon Instruments | CyberAmp 320 or 380 | no longer available from the manufacturer but may be available from E-Bay; alternatives: e.g. FLA-01 Filter/Amplifier from Cygnus Technology. This is a single channel instrument with a minimum cutoff at 10 Hz using a multipole Bessel filter but the company may be willing to modify it for a lower cutoff frequency (2 Hz) if needed. |
silver wire | A-M Systems | #7830 | diameter 0.015", bare (no coating) |
slice chamber | Harvard Apparatus | Warner Model RC-27L | this is submersion slice chamber; do not use interface slice chamber |
stereomicroscope | for silanization and filling the tip of ion-selective barrel with liquid ion exchanger; horizontally mounted; various suppliers | ||
syringe, 10 mL | BD | Syringes and Needles #309604 | to backfill microelectrodes and for silanization; BD Luer-Lok tip |
syringe filter 0.22µm pore | Whatman | #6780-1302 | to filter backfill solutions; available from Fisher |
syringe needle, 28 gauge, 97mm | World Precision Instruments | MicroFil MF28G-5 | to backfill microelectrodes |
Teflon (=PTFE) tubing | Component Supply | STT-28 PTFE tube light wall (28 gauge) | for silanization of ion-selective barrel; fits on BD PrecisionGlide needles 25 G x 5/8 in. Note: Teflon is essential, PVC tubing would melt by hot wax. |
temperature control system | Harvard Apparatus | Warner Models TC-344B and SH-27A | TC-344B is a dual automatic temperature controller, SH-27A is an in-line heater; controller and heater work with Warner slice chambers |
tetramethyammonium (TMA) chloride | Sigma-Aldrich | T-3411 | 5 M solution; CAUTION: acute toxicity (oral, dermal, inhalation), carcinogenicity, hazardous to the aquatic environment, see Sigma-Aldrich Safety Information for full description |
vibrating blade microtome | Leica | VT1000S | to cut brain slices |
xylenes | Fisher | X5-1 | for silanization; CAUTION: flammable, acute toxicity (oral, dermal, inhalation), skin corrosion, eye damage, carcinogenicity, see Fisher Safety Information for full description |
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