This work was supported by &#39;&#39;Grant-in-Aid for Scientific Research on Innovative Areas (Brain Protein Aging and Dementia Control)(15H01552) from MEXT and Grant-in-Aid for Young Scientists (B) (16K20969). The author thanks Dr. David M. Holtzman and Dr. John R. Cirrito for the technical advices during the development of this method.

All animal studies were reviewed and approved by the Institutional Animal Care and Use Committee of the Graduate School of Medicine at the University of Tokyo.
1. Pre-surgical Procedure
<ol>
	<li>Before starting surgery, wipe everything with 70% ethanol to maintain sterile conditions.&#160;Thermal support using a heating pad is recommended.</li>
	<li>Anesthetize the mice by intraperitoneal injection of chloral hydrate (400 mg/kg). Confirm anesthetization by performing a toe pinch.&#160;Use of meloxicam SR at induction and buprenorphine upon recovery BID for at least 24 h&#160;is recommended.</li>
	<li>Shave the hair with a surgical clipper. Fix a mouse in the mouse and neonatal rat adaptor using ear bars and a nose clamp. 
	NOTE: It is critical to make sure that mouse head is secured at this stage and does not move side-by-side.</li>
	<li>Apply vet ointment on eyes to prevent dryness while under anesthesia.</li>
</ol>
2. Stereotaxic Surgery for Guide Cannula Implantation
<ol>
	<li>Set the mouse and neonatal rat adaptor on the stereotaxic apparatus. Make an incision sagittally on the skin over the skull using a scalpel.&#12288;Wipe off blood and the connective tissue on the skull using a damp cotton swab.</li>
	<li>Determine the coordinate for brain region of interest using brain atlas. Before starting measurements, make sure that midline is straight so that the drill bit can be moved A-P and remain on the midline suture the entire time. 
	NOTE: This article uses the coordinate (A/P: -3.1 mm, M/L: -2.5 mm, D/V: -1.2 mm, 12 degrees) to target posterior hippocampus.</li>
	<li>Level skull A-P
	<ol>
		<li>Attach a drill on a manipulator of stereotaxic frame.Lower the drill until it gently touches lambda and record its ventral coordinate. Repeat this procedure for bregma. 
		NOTE: When the skull is leveled, the vertical measurement of bregma is equal to that of lambda. If not, adjust the height of nose clamp accordingly. After the skull gets leveled, record the anterior/posterior, lateral coordinate of bregma.</li>
	</ol>
	</li>
	<li>Level skull left-right
	<ol>
		<li>Move the drill from bregma to the coordinate (A/P: -3.1 mm, M/L: +2.0 mm), lower the drill to the skull and record the vertical coordinate. Then repeat this procedure for the coordinate (A/P: -3.1 mm, M/L: -2.0 mm). 
		NOTE: If the skull is leveled, these vertical measurements of two equidistant points from the midline are equal. If not, adjust the height of the ear bars.</li>
	</ol>
	</li>
	<li>Drill a burr hole carefully at the target coordinate (A/P: -3.1 mm, M/L: -2.5 mm) to implant a guide cannula. If the diameter of a burr hole is not large enough for a guide cannula implantation, drill another hole that overlaps with the first one. Drill another hole on the right (contralateral side) parietal bone and insert a bone screw, which helps to secure dental cement in 1.10 (See Figure 1B).</li>
	<li>Cut a circular locking piece from the back side of lid of a 1.5 mL centrifuge tube by a razor blade and make a &#39;&#39;crown&#39;&#39;. This crown is used to prevent dental cement from spreading to the skin. Place it on the skull so that the burr holes made in step 2.5 stay within the circle (See Figure 1).</li>
	<li>Set up a stereotaxic assembly by putting a guide cannula on the shorter arm of a stereotaxic adaptor and fasten it using a cap nut. Set the longer arm of the stereotaxic adaptor on the electrode clamp. Attach it on the manipulator of the stereotaxic apparatus (See Figure 1A).</li>
	<li>Rotate the D-V stereotax assembly on the manipulator arm by 12 degrees (See Figure 1B). Move the guide cannula to the burr hole made in 1.6. Insert the guide cannula slowly into the brain by lowering it by 1.2 mm. 
	NOTE: The angle of the probe is specific to the hippocampus; other regions may require other angles or no angle at all. Consult a brain atlas for precise coordinates. Dry the surface of the skull, because if not the cement will not stick and cement cap can become dislodged</li>
	<li>Add the dental cement within the crown to fully cover both the metal part of the guide cannula and the bone screw enough to secure them. Apply additional dental cement if there is a part of skull exposed.</li>
	<li>Wait until dental cement is completely dried (~12-20 min). Remove the stereotaxic adaptor from the electrode clamp. Remove the cap nut and replace the stereotaxic adaptor with a dummy probe and fasten the cap nut.</li>
	<li>Release the mouse from the stereotaxic apparatus and house the mouse alone in an individual cage. 
	NOTE: The mouse should not be left unattended until it has regained sufficient consciousness to maintain sternal recumbency. Check the mouse daily until the day of microdialysis. The mouse receives NSAIDs such as carprofen if it appears to be in pain. Waiting 2 weeks is necessary for sleep-wake studies so the mouse habituates to the new environment10, but other types of studies may require shorter recovery periods (e.g., 1-2 days).</li>
</ol>
3. Microdialysis Setup
<ol>
	<li>Quality-check of probes: Fill a disposable 1ml syringe with distilled waterand connect it to the outlet (shorter port) of a probe using a byton tube. Cover the vent holes with the fingers and depress the syringe plunger gently to infuse water to the probe. Check that water appears from the probe inlet and there is no leakage on the surface of a microdialysis membrane.
	<ol>
		<li>Activation of probes: Submerge the membranes of a probe in ethanol (70-100%) for two seconds. Then, infuse distilled water into the probe again with a syringe again.</li>
	</ol>
	</li>
	<li>Preparation of perfusion buffer: In order to avoid adhesion of target molecules to the tubings,add BSA by diluting 30% BSA solution to 4% with artificial CSF (1.3 mM CaCl2, 1.2 mM MgSO4, 3 mM KCl, 0.4 mM KH2PO4, 25 mM NaHCO3, 122 mM NaCl, pH=7.35), which closely matches electrolyte concentration in CSF, immediately prior to use. Filter the perfusion buffer through a syringe filter unit with 0.1 &#181;m pore size . 
	NOTE: 4% BSA improves recovery for sticking proteins but can severely limit delivery of compounds, especially for compounds that have high BSA-binding. This is one advantage of using lower concentration of BSA (such as 0.15%) in certain instances3. Note that BSA can aggregate very easily when agitated by vortex or stir plate. These aggregates can clog probes or membrane pores. Use caution when preparing a BSA solution to limit this aggregation</li>
	<li>Prepare two separate lines for inlet and outlet (See Figure 1C) and connect both lines with a connection needle. Fill a disposable 3 mL syringe filled with perfusion buffer and connect it with the inlet end of the tubing using a blunt-end needle. Fill the entire tubing with perfusion buffer by running the syringe pump.</li>
	<li>Stop the syringe pump and replace the connection needle between inlet line and outlet line with an activated microdialysis probe from step 3.3 (See Figure 1C). Before this replacement, put the cap nut on the probe.</li>
	<li>Mount the roller tube in the outlet tubing on the roller pump. Start the syringe pump at 10 &#181;L/min and then the roller pump at the slightly slower flow rate (9.5-9.8 &#181;L/min). Make sure to remove all air bubbles in the entire tubing, which may influence the recovery when they enter the probe.</li>
	<li>Anesthetize the mouse from step 1.12 in the same way as in step 1.2. Put the mouse collar around its neck. Remove the cap nut and dummy probe and slowly insert a microdialysis probe from 3.4 through the guide cannula and fasten the cap nut.</li>
	<li>Place the mouse in the cage connected to a free-moving system and tether the mouse with the collar. Keep running both syringe pump and roller pump at the indicated flow rate in step 3.5 for at least 1 h. 
	NOTE: To achieve ISF collection from awake animals, this article uses a free-moving system, where the cage itself responds to an animal&#39;s movement to keep tubings from twisting. Alternatively, liquid swivels available from various companies can be also used.</li>
	<li>Stop the roller pump first and then the syringe pump. Set the desired flow rate. Run the syringe pump 20% faster than the roller pump. 
	NOTE: For instance, if you run at 1 &#181;L/min, operate the syringe pump at 1.2 &#181;L/min. Optimal flow rate should be determined empirically for each molecule.</li>
	<li>Collecting ISF samples: place the free end of outlet tubing on the refrigerated fraction collector. 
	NOTE: Appropriate sample volume varies depending on assays used for analysis.</li>
	<li>After the completion of the experiment, remove the probe.&#160;(Anesthetize the mouse as needed.)&#160; Handle mouse recovery the same way as in step 2.11. Analyze the collected ISF by methods such as HPLC or ELISA.</li>
	<li>To wash the entire tubing after microdialysis, connect inlet and outlet tubings again by replacing the probe with the connection needle and run the diluted bleach in the entire tubing and then flush it with water. Dry and store it for repeated use. 
	NOTE: Other types of tubings are acceptable, however, BSA in perfusion buffer can clog the tubings with small diameter, thus these tubings are considered as single-use. The tubings can be worn down or clogged after multiple uses, so make sure that the flow rate is consistent every time before use.</li>
</ol>

<ol>
	<li>Lei, Y., Han, H., Yuan, F., Javeed, A., Zhao, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+brain+interstitial+system:+Anatomy,+modeling,+in+vivo+measurement,+and+applications.">The brain interstitial system: Anatomy, modeling, in vivo measurement, and applications.</a> Progress in Neurobiology. 157, 230-246 (2017).</li><li>Kushikata, T., Hirota, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuropeptide+microdialysis+in+free-moving+animals.">Neuropeptide microdialysis in free-moving animals.</a> Methods in Molecular Biology. 789, 261-269 (2011).</li><li>Cirrito, J. R., 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=In+vivo+assessment+of+brain+interstitial+fluid+with+microdialysis+reveals+plaque-associated+changes+in+amyloid-beta+metabolism+and+half-life.">In vivo assessment of brain interstitial fluid with microdialysis reveals plaque-associated changes in amyloid-beta metabolism and half-life.</a> The Journal of Neuroscience. 23 (26), 8844-8853 (2003).</li><li>Emmanouilidou, E., 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=Assessment+of+&#945;-synuclein+secretion+in+mouse+and+human+brain+parenchyma.">Assessment of &#945;-synuclein secretion in mouse and human brain parenchyma.</a> PLoS One. 6 (7), 1-9 (2011).</li><li>Yamada, K., 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=In+vivo+microdialysis+reveals+age-dependent+decrease+of+brain+interstitial+fluid+tau+levels+in+P301S+human+tau+transgenic+mice.">In vivo microdialysis reveals age-dependent decrease of brain interstitial fluid tau levels in P301S human tau transgenic mice.</a> The Journal of Neuroscience. 31 (37), 13110-13117 (2011).</li><li>Ulrich, J. D., 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=In+vivo+measurement+of+apolipoprotein+E+from+the+brain+interstitial+fluid+using+microdialysis.">In vivo measurement of apolipoprotein E from the brain interstitial fluid using microdialysis.</a> Molecular Neurodegeneration. 8 (1), 13 (2013).</li><li>Emmanouilidou, E., 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=GABA+transmission+via+ATP-dependent+K++channels+regulates+&#945;-synuclein+secretion+in+mouse+striatum.">GABA transmission via ATP-dependent K+ channels regulates &#945;-synuclein secretion in mouse striatum.</a> Brain. 139 (3), 871-890 (2016).</li><li>Takeda, S., 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=Seed-competent+high-molecular-weight+tau+species+accumulates+in+the+cerebrospinal+fluid+of+Alzheimer's+disease+mouse+model+and+human+patients.">Seed-competent high-molecular-weight tau species accumulates in the cerebrospinal fluid of Alzheimer's disease mouse model and human patients.</a> Annals of Neurology. 80 (3), 355-367 (2016).</li><li>Yamada, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+Microdialysis+of+brain+interstitial+fluid+for+the+determination+of+extracellular+tau+levels.">In vivo Microdialysis of brain interstitial fluid for the determination of extracellular tau levels.</a> Methods in Molecular Biology. 1523, 285-296 (2017).</li><li>Kang, J. -. E., 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=Amyloid-&#946;+dynamics+are+regulated+by+orexin+and+the+sleep-wake+cycle.">Amyloid-&#946; dynamics are regulated by orexin and the sleep-wake cycle.</a> Science. 326 (November), 1005-1008 (2009).</li><li>Cirrito, J. R., 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=Synaptic+activity+regulates+interstitial+fluid+amyloid-beta+levels+in+vivo.">Synaptic activity regulates interstitial fluid amyloid-beta levels in vivo.</a> Neuron. 48 (6), 913-922 (2005).</li><li>Bero, A. W., 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=Neuronal+activity+regulates+the+regional+vulnerability+to+amyloid-&#946;+deposition.">Neuronal activity regulates the regional vulnerability to amyloid-&#946; deposition.</a> Nature Neuroscience. 14 (6), 750-756 (2011).</li><li>Yamada, K., 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=Neuronal+activity+regulates+extracellular+tau+in+vivo.">Neuronal activity regulates extracellular tau in vivo.</a> Journal of Experimental Medicine. 211 (3), 387-393 (2014).</li><li>Pooler, A. M., Phillips, E. C., Lau, D. H. W., Noble, W., Hanger, D. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physiological+release+of+endogenous+tau+is+stimulated+by+neuronal+activity.">Physiological release of endogenous tau is stimulated by neuronal activity.</a> EMBO Reports. 14 (4), 389-394 (2013).</li><li>Castellano, J. M., 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=Human+apoE+isoforms+differentially+regulate+brain+amyloid-&#946;+peptide+clearance.">Human apoE isoforms differentially regulate brain amyloid-&#946; peptide clearance.</a> Science Translational Medicine. 3 (89), 89ra57 (2011).</li><li>Yamada, K., 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=Analysis+of+in+vivo+turnover+of+tau+in+a+mouse+model+of+tauopathy.">Analysis of in vivo turnover of tau in a mouse model of tauopathy.</a> Molecular Neurodegeneration. 10 (1), 55 (2015).</li><li>Taylor, H., 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=Investigating+local+and+long-range+neuronal+network+dynamics+by+simultaneous+optogenetics,+reverse+microdialysis+and+silicon+probe+recordings+in+vivo.">Investigating local and long-range neuronal network dynamics by simultaneous optogenetics, reverse microdialysis and silicon probe recordings in vivo.</a> Journal of Neuroscience Methods. 235, 83-91 (2014).</li></ol>

The author has nothing to disclose.

Microdialysis with high molecular weight cut off membranes has to be operated by a push-pull mode, thus it is critical that the flow rate is accurate and constant. The inaccuracy in the flow rates can be the cause of air bubble generation and inconsistency in the sample concentration. If the flow is inconsistent, check all connections for leakage. If the problem still persists, it may be necessary to re-start with new probes and tubings.
Microdilaysis probes are continuously perfused by the pe...

ISF comprises 15-20% of total brain volume and offers a microenvironment critical for signal transduction, substrate transport and waste clearance1. Therefore, the ability of collecting ISF from living animals will provide greater implications for various biological processes as well as disease mechanism. In vivo microdialysis is one of the few methods that sample and quantify extracellular molecules from ISF from awake, freely moving animals and thereby serves as a useful tool in neuroscience research field2,3. In this method, microdialysis probes with semipermeable membranes are inserted in the brain and perfused with perfusion buffer at the relatively slow flow rate (0.1-5 &#181;L/min). During this perfusion, extracellular molecules in ISF passively diffuse into the probe according to the concentration gradient and collect as a dialysate. Although this article focuses on the method to sample ISF in the brain, both the principle and the method can be applied to other organs by appropriate modification if necessary.
Microdialysis was first employed in the early 1960s, and since then it has been extensively used to collect small molecules including amino acids or neurotransmitters in brain. However, recent commercial availability of microdialysis probes with high-molecular weight cut off membranes (100 kDa-3 MDa) has extended its application to relatively larger proteins in ISF as well4,5,6,7. The studies using these probes has led to the finding that proteins such as tau or &#945;-synuclein that were long thought to be exclusive cytoplasmic are also physiologically present in ISF4,5,8.
One of the difficulties using microdialysis probes with large cut off membranes (typically over 1,000 kDa) is that they are more susceptible to ultrafiltration fluid loss due to the inner pressure accumulated in the probes. Microdialysis probes used here have a unique structure to avoid this issue. The pressure will not be built up due to this structure, thus microdialysis with these probes should be operated in a &#34;push-pull&#34; mode using a syringe pump to perfuse the probes (=push) and a roller/peristaltic pump to collect the dialysate coming from the probe outlet (=pull)9 (Although it needs both push and pull pumps, due to pressure cancelling vent holes present in the probes, the system is technically only driven by the pull pump). This article starts with the stereotaxic surgery of a guide cannula implantation and describes how to set up microdialysis lines in order to collect ISF through microdialysis probes with 1,000 kDa cut-off membranes.

<table>
	<tbody>
		<tr>
			<td>The Univentor 820 Microsampler</td>
			<td>Univentor</td>
			<td>8303002</td>
			<td>Refrigerated fraction collector</td>
		</tr>
		<tr>
			<td>Syringe pump</td>
			<td>KD scientific</td>
			<td>KDS-101</td>
			<td></td>
		</tr>
		<tr>
			<td>Roller pump</td>
			<td>Eicom microdialysis</td>
			<td>ERP-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Raturn Stand-Alone System</td>
			<td>BASi</td>
			<td>MD-1409</td>
			<td>Free-moving system</td>
		</tr>
		<tr>
			<td>Dual species cage kit</td>
			<td>BASi</td>
			<td>CX-1600</td>
			<td></td>
		</tr>
		<tr>
			<td>AtmosLM Microdialysis probe (shaft length 8 mm, membrane length 2 mm)</td>
			<td>Eicom microdialysis</td>
			<td>PEP-8-02</td>
			<td>Shaft length for a probe, a guide, a dumy probe and a stereotaxic adaptor should be identical.</td>
		</tr>
		<tr>
			<td>Microdialysis guide (shaft length 8 mm)</td>
			<td>Eicom microdialysis</td>
			<td>PEG-8</td>
			<td></td>
		</tr>
		<tr>
			<td>Microdialysis dummy probe (shaft length 8 mm)</td>
			<td>Eicom microdialysis</td>
			<td>PED-8</td>
			<td></td>
		</tr>
		<tr>
			<td>Bone screw</td>
			<td>BASi</td>
			<td>MD-1310</td>
			<td></td>
		</tr>
		<tr>
			<td>Super bond C&#38;B set</td>
			<td>Sunmedical</td>
			<td></td>
			<td>Dental cement</td>
		</tr>
		<tr>
			<td>Small animal Stereotaxic Instrument with digital display console</td>
			<td>Kopf</td>
			<td>Model 940</td>
			<td>Stereotaxic apparatus</td>
		</tr>
		<tr>
			<td>Mouse and neonatal rat adaptor</td>
			<td>Stoelting</td>
			<td>51625</td>
			<td></td>
		</tr>
		<tr>
			<td>Standard Ear Bars and Rubber Tips for Mouse Stereotaxic</td>
			<td>Stoelting</td>
			<td>51648</td>
			<td></td>
		</tr>
		<tr>
			<td>Albumin solution from bovine serum</td>
			<td>Sigma</td>
			<td>A7284-50ML</td>
			<td>30% BSA solution</td>
		</tr>
		<tr>
			<td>FEP tubing (70 cm)</td>
			<td>Eicom microdialysis</td>
			<td>JF-10-70</td>
			<td>Internal volume = 0.5 &#181;L/cm</td>
		</tr>
		<tr>
			<td>Teflon tubing (50 cm)</td>
			<td>Eicom microdialysis</td>
			<td>JT-10-50</td>
			<td>Internal volume = 0.08 &#181;L/cm</td>
		</tr>
		<tr>
			<td>Byton tube</td>
			<td>Eicom microdialysis</td>
			<td>JB-30</td>
			<td></td>
		</tr>
		<tr>
			<td>Intramedic luer stab adaptor 23G</td>
			<td>BD</td>
			<td>427565</td>
			<td>Blunt end needle</td>
		</tr>
		<tr>
			<td>Roller tube</td>
			<td>Eicom microdialysis</td>
			<td>RT-5S</td>
			<td>Internal volume = 4 &#181;L</td>
		</tr>
		<tr>
			<td>Cap nut</td>
			<td>Eicom microdialysis</td>
			<td>AC-5</td>
			<td></td>
		</tr>
		<tr>
			<td>0.25 mL microcentrifuge tube with cap</td>
			<td>QSP</td>
			<td>503-Q</td>
			<td>Tubes for fraction collector</td>
		</tr>
		<tr>
			<td>Sterotaxic adaptor (shaft length 8 mm)</td>
			<td>Eicom microdialysis</td>
			<td>PESG-8</td>
			<td></td>
		</tr>
		<tr>
			<td>Connection needle</td>
			<td>Eicom microdialysis</td>
			<td>RTJ</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse animal collar</td>
			<td>BASi</td>
			<td>MD-1365</td>
			<td></td>
		</tr>
		<tr>
			<td>High Speed Rotary Micromotor kit</td>
			<td>FOREDOM</td>
			<td>K.1070</td>
			<td>Drill</td>
		</tr>
		<tr>
			<td>Picrotoxin</td>
			<td>Sigma</td>
			<td>P1675</td>
			<td></td>
		</tr>
		<tr>
			<td>Screw driver for bone screws</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Scalpel</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cotton swab</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical clipper</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

in vivo microdialysis method to collect large extracellular proteins from brain interstitial fluid with high-molecular weight cut-off probes

In vivo microdialysis is a powerful technique to collect ISF from awake, freely-behaving animals based on a dialysis principle. While microdialysis is an established method that measures relatively small molecules including amino acids or neurotransmitters, it has been recently used to also assess dynamics of larger molecules in ISF using probes with high molecular weight cut off membranes. Upon using such probes, microdialysis has to be run in a push-pull mode to avoid pressure accumulated inside of the probes. This article provides step-by-step protocols including stereotaxic surgery and how to set up microdialysis lines to collect proteins from ISF. During microdialysis, drugs can be administered either systemically or by direct infusion into ISF. Reverse microdialysis is a technique to directly infuse compounds into ISF. Inclusion of drugs in the microdialysis perfusion buffer allows them to diffuse into ISF through the probes while simultaneously collecting ISF. By measuring tau protein as an example, the author shows how its levels are altered upon stimulating neuronal activity by reverse microdialysis of picrotoxin. Advantages and limitations of microdialysis are described along with the extended application by combining other in vivo methods.

To stimulate or inhibit neuronal activity in reverse microdialysis11,12,13, picrotoxin, GABAA receptor antagonist or tetrodotoxin, Na+ channel blocker have been used. It has been shown that tau release is stimulated by increase of neuronal activity13,14. Consistent with these previous observations, when 50 &#181;M pi...

Watch this Scientific Journal Video about In Vivo Microdialysis Method to Collect Large Extracellular Proteins from Brain Interstitial Fluid with High-molecular Weight Cut-off Probes at JoVE.com

In Vivo Microdialysis Method to Collect Large Extracellular Proteins from Brain Interstitial Fluid with High-molecular Weight Cut-off Probes

In vivo microdialysis has enabled collection of molecules present in brain interstitial fluid (ISF) from awake, freely-behaving animals. In order to analyze relatively large molecules in ISF, the current article specifically focuses on the microdialysis protocol using probes with high molecular weight cut off membranes.

In Vivo Microdialysis Method to Collect Large Extracellular Proteins from Brain Interstitial Fluid with High-molecular Weight Cut-off Probes

In vivo microdialysis is a powerful technique to collect ISF from awake, freely-behaving animals based on a dialysis principle. While microdialysis is an ...

in-vivo-microdialysis-method-to-collect-large-extracellular-proteins

Research

JoVE Journal

Neuroscience

14.5K Views.  University of Tokyo. In vivo microdialysis has enabled collection of molecules present in brain interstitial fluid (ISF) from awake, freely-behaving animals. In order to analyze relatively large molecules in ISF, the current article specifically focuses on the microdialysis protocol using probes with high molecular weight cut off membranes.

Video: In Vivo Microdialysis Method to Collect Large Extracellular Proteins from Brain Interstitial Fluid with High-molecular Weight Cut-off Probes

Recording Large-scale Neuronal Ensembles with Silicon Probes in the Anesthetized Rat

Large scale electrophysiological recordings from neuronal ensembles offer the opportunity to investigate how the brain orchestrates the wide variety of behaviors from the spiking activity of its neurons. One of the most effective methods to monitor spiking activity from a large number of neurons in multiple local neuronal circuits simultaneously is by using silicon electrode arrays1-3.
Action potentials produce large transmembrane voltage changes in the vicinity of cell somata. These output signals can be measured by placing a conductor in close proximity of a neuron. If there are many active (spiking) neurons in the vicinity of the tip, the electrode records combined signal from all of them, where contribution of a single neuron is weighted by its 'electrical distance'. Silicon probes are ideal recording electrodes to monitor multiple neurons because of a large number of recording sites (+64) and a small volume. Furthermore, multiple sites can be arranged over a distance of millimeters, thus allowing for the simultaneous recordings of neuronal activity in the various cortical layers or in multiple cortical columns (Fig. 1). Importantly, the geometrically precise distribution of the recording sites also allows for the determination of the spatial relationship of the isolated single neurons4. Here, we describe an acute, large-scale neuronal recording from the left and right forelimb somatosensory cortex simultaneously in an anesthetized rat with silicon probes (Fig. 2).

Extracellular recordings of neuronal activity using silicon probes in the anesthetized rat will be described. This technique allows information to be obtained across multiple brain areas from more than 100 neurons simultaneously. It provides information with single cell resolution about neuronal ensembles dynamics in multiple local circuits.

Large scale electrophysiological recordings from neuronal ensembles offer the opportunity to investigate how the brain orchestrates the wide variety of ...

Large-scale Recording of Neurons by Movable Silicon Probes in Behaving Rodents

A major challenge in neuroscience is linking behavior to the collective activity of neural assemblies. Understanding of input-output relationships of neurons and circuits requires methods with the spatial selectivity and temporal resolution appropriate for mechanistic analysis of neural ensembles in the behaving animal, i.e. recording of representatively large samples of isolated single neurons. Ensemble monitoring of neuronal activity has progressed remarkably in the past decade in both small and large-brained animals, including human subjects1-11. Multiple-site recording with silicon-based devices are particularly effective because of their scalability, small volume and geometric design.
Here, we describe methods for recording multiple single neurons and local field potential in behaving rodents, using commercially available micro-machined silicon probes with custom-made accessory components. There are two basic options for interfacing silicon probes to preamplifiers: printed circuit boards and flexible cables. Probe supplying companies (<a href="http://www.neuronexustech.com/" >http://www.neuronexustech.com/</a>; <a href="http://www.sbmicrosystems.com/">http://www.sbmicrosystems.com/</a>; <a href="http://www.acreo.se/">http://www.acreo.se/</a>) usually provide the bonding service and deliver probes bonded to printed circuit boards or flexible cables. Here, we describe the implantation of a 4-shank, 32-site probe attached to flexible polyimide cable, and mounted on a movable microdrive. Each step of the probe preparation, microdrive construction and surgery is illustrated so that the end user can easily replicate the process.

We describe methods for large-scale recording of multiple single units and local field potential in behaving rodents with silicon probes. Drive fabrication, probe attachment to the drive and probe implantation processes are illustrated in sufficient details for easy replication.

A major challenge in neuroscience is linking behavior to the collective activity of neural assemblies. Understanding of input-output relationships of ...

Retrograde Fluorescent Labeling Allows for Targeted Extracellular Single-unit Recording from Identified Neurons In vivo

The overall goal of this method is to record single-unit responses from an identified population of neurons. In vivo electrophysiological recordings from individual neurons are critical for understanding how neural circuits function under natural conditions. Traditionally, these recordings have been performed 'blind', meaning the identity of the recorded cell is unknown at the start of the recording. Cellular identity can be subsequently determined via intracellular1, juxtacellular2 or loose-patch3 iontophoresis of dye, but these recordings cannot be pre-targeted to specific neurons in regions with functionally heterogeneous cell types. Fluorescent proteins can be expressed in a cell-type specific manner permitting visually-guided single-cell electrophysiology4-6. However, there are many model systems for which these genetic tools are not available. Even in genetically accessible model systems, the desired promoter may be unknown or genetically homogenous neurons may have varying projection patterns. Similarly, viral vectors have been used to label specific subgroups of projection neurons7, but use of this method is limited by toxicity and lack of trans-synaptic specificity. Thus, additional techniques that offer specific pre-visualization to record from identified single neurons in vivo are needed. Pre-visualization of the target neuron is particularly useful for challenging recording conditions, for which classical single-cell recordings are often prohibitively difficult8-11. The novel technique described in this paper uses retrograde transport of a fluorescent dye applied using tungsten needles to rapidly and selectively label a specific subset of cells within a particular brain region based on their unique axonal projections, thereby providing a visual cue to obtain targeted electrophysiological recordings from identified neurons in an intact circuit within a vertebrate CNS.
The most significant novel advancement of our method is the use of fluorescent labeling to target specific cell types in a non-genetically accessible model system. Weakly electric fish are an excellent model system for studying neural circuits in awake, behaving animals12. We utilized this technique to study sensory processing by "small cells" in the anterior exterolateral nucleus (ELa) of weakly electric mormyrid fish. "Small cells" are hypothesized to be time comparator neurons important for detecting submillisecond differences in the arrival times of presynaptic spikes13. However, anatomical features such as dense myelin, engulfing synapses, and small cell bodies have made it extremely difficult to record from these cells using traditional methods11, 14. Here we demonstrate that our novel method selectively labels these cells in 28% of preparations, allowing for reliable, robust recordings and characterization of responses to electrosensory stimulation.

Retrograde Fluorescent Labeling Allows for Targeted Extracellular Single-unit Recording from Identified Neurons In vivo

Retrograde transport of fluorescent dye labels a sub-population of neurons based on anatomical projection. Labeled axons can be visually targeted in vivo, permitting extracellular recording from identified axons. This technique facilitates recording when neurons cannot be labeled through genetic manipulation or are difficult to isolate using 'blind' in vivo approaches.

The overall goal of this method is to record single-unit responses from an identified population of neurons. In vivo electrophysiological recordings from ...

Functional Neuroimaging Using Ultrasonic Blood-brain Barrier Disruption and Manganese-enhanced MRI

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains technically challenging. One approach, Activation-Induced Manganese-enhanced MRI (AIM MRI), has been used successfully to map neuronal activity in rodents 1-5. In AIM MRI, Mn2+ acts a calcium analog and accumulates in depolarized neurons 6,7. Because Mn2+ shortens the T1 tissue property, regions of elevated neuronal activity will enhance in MRI. Furthermore, Mn2+ clears slowly from the activated regions; therefore, stimulation can be performed outside the magnet prior to imaging, enabling greater experimental flexibility. However, because Mn2+ does not readily cross the blood-brain barrier (BBB), the need to open the BBB has limited the use of AIM MRI, especially in mice.
One tool for opening the BBB is ultrasound. Though potentially damaging, if ultrasound is administered in combination with gas-filled microbubbles (i.e., ultrasound contrast agents), the acoustic pressure required for BBB opening is considerably lower. This combination of ultrasound and microbubbles can be used to reliably open the BBB without causing tissue damage 8-11.
Here, a method is presented for performing AIM MRI by using microbubbles and ultrasound to open the BBB. After an intravenous injection of perflutren microbubbles, an unfocused pulsed ultrasound beam is applied to the shaved mouse head for 3 minutes. For simplicity, we refer to this technique of BBB Opening with Microbubbles and UltraSound as BOMUS 12. Using BOMUS to open the BBB throughout both cerebral hemispheres, manganese is administered to the whole mouse brain. After experimental stimulation of the lightly sedated mice, AIM MRI is used to map the neuronal response.
To demonstrate this approach, herein BOMUS and AIM MRI are used to map unilateral mechanical stimulation of the vibrissae in lightly sedated mice 13. Because BOMUS can open the BBB throughout both hemispheres, the unstimulated side of the brain is used to control for nonspecific background stimulation. The resultant 3D activation map agrees well with published representations of the vibrissae regions of the barrel field cortex 14. The ultrasonic opening of the BBB is fast, noninvasive, and reversible; and thus this approach is suitable for high-throughput and/or longitudinal studies in awake mice.

A technique is described for broadly opening the blood-brain barrier in the mouse using microbubbles and ultrasound. Using this technique, manganese can be administered to the mouse brain. Because manganese is an MRI contrast agent that accumulates in depolarized neurons, this approach enables imaging of neuronal activity.

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains ...

Hippocampal Insulin Microinjection and In vivo Microdialysis During Spatial Memory Testing

Glucose metabolism is a useful marker for local neural activity, forming the basis of methods such as 2-deoxyglucose and functional magnetic resonance imaging. However, use of such methods in animal models requires anesthesia and hence both alters the brain state and prevents behavioral measures. An alternative method is the use of in vivo microdialysis to take continuous measurement of brain extracellular fluid concentrations of glucose, lactate, and related metabolites in awake, unrestrained animals. This technique is especially useful when combined with tasks designed to rely on specific brain regions and/or acute pharmacological manipulation; for example, hippocampal measurements during a spatial working memory task (spontaneous alternation) show a dip in extracellular glucose and rise in lactate that are suggestive of enhanced glycolysis1-3,4-5, and intrahippocampal insulin administration both improves memory and increases hippocampal glycolysis6. Substances such as insulin can be delivered to the hippocampus via the same microdialysis probe used to measure metabolites. The use of spontaneous alternation as a measure of hippocampal function is designed to avoid any confound from stressful motivators (e.g. footshock), restraint, or rewards (e.g. food), all of which can alter both task performance and metabolism; this task also provides a measure of motor activity that permits control for nonspecific effects of treatment. Combined, these methods permit direct measurement of the neurochemical and metabolic variables regulating behavior.

Hippocampal Insulin Microinjection and In vivo Microdialysis During Spatial Memory Testing

Modulation of hippocampally-dependent spatial working memory by direct intrahippocampal microinjection, accompanied and followed by in vivo microdialysis for metabolites in conscious, behaving animals.

Glucose metabolism is a useful marker for local neural activity, forming the basis of methods such as 2-deoxyglucose and functional magnetic resonance ...

Design and Fabrication of Ultralight Weight, Adjustable Multi-electrode Probes for Electrophysiological Recordings in Mice

The number of physiological investigations in the mouse, mus musculus, has experienced a recent surge, paralleling the growth in methods of genetic targeting for microcircuit dissection and disease modeling. The introduction of optogenetics, for example, has allowed for bidirectional manipulation of genetically-identified neurons, at an unprecedented temporal resolution. To capitalize on these tools and gain insight into dynamic interactions among brain microcircuits, it is essential that one has the ability to record from ensembles of neurons deep within the brain of this small rodent, in both head-fixed and freely behaving preparations. To record from deep structures and distinct cell layers requires a preparation that allows precise advancement of electrodes towards desired brain regions. To record neural ensembles, it is necessary that each electrode be independently movable, allowing the experimenter to resolve individual cells while leaving neighboring electrodes undisturbed. To do both in a freely behaving mouse requires an electrode drive that is lightweight, resilient, and highly customizable for targeting specific brain structures.
A technique for designing and fabricating miniature, ultralight weight, microdrive electrode arrays that are individually customizable and easily assembled from commercially available parts is presented. These devices are easily scalable and can be customized to the structure being targeted; it has been used successfully to record from thalamic and cortical regions in a freely behaving animal during natural behavior.

Understanding the neural substrates of behavior requires brain circuit ensemble recording. Because of its genetic tractability, the mouse offers a model for circuit dissection and disease mimicry. Here, a method of designing and fabricating miniaturized probes is described that is suitable for targeting deep brain structure in the mouse.

The number of physiological investigations in the mouse, mus musculus, has experienced a recent surge, paralleling the growth in methods of genetic ...

Rapid In Situ Hybridization using Oligonucleotide Probes on Paraformaldehyde-prefixed Brain of Rats with Serotonin Syndrome

3,4-Methylenedioxymethamphetamine (MDMA; ecstasy) toxicity may cause region-specific changes in serotonergic mRNA expression due to acute serotonin (5-hydroxytryptamine; 5-HT) syndrome. This hypothesis can be tested using in situ hybridization to detect the serotonin 5-HT2A receptor gene htr2a. In the past, such procedures, utilizing radioactive riboprobe, were difficult because of the complicated workflow that needs several days to perform and the added difficulty that the technique required the use of fresh frozen tissues maintained in an RNase-free environment. Recently, the development of short oligonucleotide probes has simplified in situ hybridization procedures and allowed the use of paraformaldehyde-prefixed brain sections, which are more widely available in laboratories. Here, we describe a detailed protocol using non-radioactive oligonucleotide probes on the prefixed brain tissues. Hybridization probes used for this study include dapB (a bacterial gene coding for dihydrodipicolinate reductase), ppiB (a housekeeping gene coding for peptidylprolyl isomerase B), and htr2a (a serotonin gene coding for 5-HT2A receptors). This method is relatively simply, cheap, reproducible and requires less than two days to complete.

Rapid In Situ Hybridization using Oligonucleotide Probes on Paraformaldehyde-prefixed Brain of Rats with Serotonin Syndrome

This protocol describes a rapid and simplified in situ hybridization method ideal forparaformaldehyde-prefixed brain, thus reducing the need for prolonged complex steps while using fresh frozen tissues. The method is validated using the identification of the serotonin 5-HT2A receptor gene htr2a in rats.

3,4-Methylenedioxymethamphetamine (MDMA; ecstasy) toxicity may cause region-specific changes in serotonergic mRNA expression due to acute serotonin ...

Real-time Iontophoresis with Tetramethylammonium to Quantify Volume Fraction and Tortuosity of Brain Extracellular Space

This review describes the basic concepts and protocol to perform the real-time iontophoresis (RTI) method, the gold-standard to explore and quantify the extracellular space (ECS) of the living brain. The ECS surrounds all brain cells and contains both interstitial fluid and extracellular matrix. The transport of many substances required for brain activity, including neurotransmitters, hormones, and nutrients, occurs by diffusion through the ECS. Changes in the volume and geometry of this space occur during normal brain processes, like sleep, and pathological conditions, like ischemia. However, the structure and regulation of brain ECS, particularly in diseased states, remains largely unexplored. The RTI method measures two physical parameters of living brain: volume fraction and tortuosity. Volume fraction is the proportion of tissue volume occupied by ECS. Tortuosity is a measure of the relative hindrance a substance encounters when diffusing through a brain region as compared to a medium with no obstructions. In RTI, an inert molecule is pulsed from a source microelectrode into the brain ECS. As molecules diffuse away from this source, the changing concentration of the ion is measured over time using an ion-selective microelectrode positioned roughly 100 &#181;m away. From the resulting diffusion curve, both volume fraction and tortuosity can be calculated. This technique has been used in brain slices from multiple species (including humans) and in vivo to study acute and chronic changes to ECS. Unlike other methods, RTI can be used to examine both reversible and irreversible changes to the brain ECS in real time.

This protocol describes real-time iontophoresis, a method that measures physical parameters of the extracellular space (ECS) of living brains. The diffusion of an inert molecule released into the ECS is used to calculate the ECS volume fraction and tortuosity. It is ideal for studying acute reversible changes to brain ECS.

This review describes the basic concepts and protocol to perform the real-time iontophoresis (RTI) method, the gold-standard to explore and quantify the ...

Improving the Application of High Molecular Weight Biotinylated Dextran Amine for Thalamocortical Projection Tracing in the Rat

High molecular weight biotinylated dextran amine (BDA) has been used as a highly sensitive neuroanatomical tracer for many decades. Since the quality of its labeling was affected by various factors, here, we provide a refined protocol for the application of high molecular weight BDA for studying optimal neural labeling in the central nervous system. After stereotactic injection of BDA into the ventral posteromedial nucleus (VPM) of the thalamus in the rat through a delicate glass pipette, BDA was stained with fluorescent streptavidin-Alexa (AF) 594 and counterstained with fluorescent Nissl stain AF500/525. On the background of green Nissl staining, the red BDA labeling, including neuronal cell bodies and axonal terminals, was more distinctly demonstrated in the somatosensory cortex. Furthermore, double fluorescent staining for BDA and the calcium-binding protein parvalbumin (PV) was carried out to observe the correlation of BDA labeling and PV-positive interneurons in the cortical target, providing the opportunity to study the local neural circuits and their chemical characteristics. Thus, this refined method is not only suitable for visualizing high quality neural labeling with the high molecular weight BDA through reciprocal neural pathways between the thalamus and cerebral cortex, but also will permit the simultaneous demonstration of other neural markers with fluorescent histochemistry or immunochemistry.

Here, we present a refined protocol to effectively reveal biotinylated dextran amine (BDA) labeling with a fluorescent staining method through a reciprocal neural pathway. It is suitable for analyzing the fine structure of BDA labeling and distinguishing it from other neural elements under a confocal laser scanning microscope.

High molecular weight biotinylated dextran amine (BDA) has been used as a highly sensitive neuroanatomical tracer for many decades. Since the quality of ...

An Improved Method for Collection of Cerebrospinal Fluid from Anesthetized Mice

The cerebrospinal fluid (CSF) is a valuable body fluid for analysis in neuroscience research. It is one of the fluids in closest contact with the central nervous system and thus, can be used to analyze the diseased state of the brain or spinal cord without directly accessing these tissues. However, in mice it is difficult to obtain from the cisterna magna due to its closeness to blood vessels, which often contaminate samples. The area for CSF collection in mice is also difficult to dissect to and often only small samples are obtained (maximum of 5-7 &#181;L or less). This protocol describes in detail a technique that improves on current methods of collection to minimize contamination from blood and allow for the abundant collection of CSF (on average 10-15 &#181;L can be collected). This technique can be used with other dissection methods for tissue collection from mice, as it does not impact any tissues during CSF extraction. Thus, the brain and spinal cord are not affected with this technique and remain intact. With greater CSF sample collection and purity, more analyses can be used with this fluid to further aid neuroscience research and better understand diseases affecting the brain and spinal cord.

This protocol describes an improved technique for the abundant collection of cerebrospinal fluid (CSF) with no contamination from blood. With greater sample collection and purity, more analyses can be performed using CSF to further our understanding of diseases that affect the brain and spinal cord.

The cerebrospinal fluid (CSF) is a valuable body fluid for analysis in neuroscience research. It is one of the fluids in closest contact with the central ...