Name: stereotaxic infusion of oligomeric amyloid-beta into the mouse hippocampus
Uploaded: 2015-06-17T15:00:00
Description: Watch this Scientific Journal Video about Stereotaxic Infusion of Oligomeric Amyloid-beta into the Mouse Hippocampus at JoVE.com

This work was supported by National Institute of Neurological Disorders and Stroke grant NS081333 (to CMT), Alzheimer&#8217;s Association grant NIRG-10-171721 and National Institute of Mental Health grant MH096702 (to UH), and National Institute on Aging-funded Alzheimer&#8217;s Disease Research Center at Columbia University pilot grant AG008702 (to YYJ and JB).

Note: For all animal experimentation, Institutional and National guidelines for the care and use of laboratory animals were followed.
1. Prepare Surgical Instruments and Solutions for Surgery
<ol>
	<li>Autoclave all stainless steel surgical instruments.</li>
	<li>Prepare 70% ethanol by diluting 200 proof absolute ethanol with sterile molecular grade deionized distilled water.</li>
	<li>Attach the 29 G needle to the Hamilton syringe. Clean the interior of Hamilton syringe and needle by drawin...

<ol>
	<li>Baleriola, 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=Axonally+Synthesized+ATF4+Transmits+a+Neurodegenerative+Signal+across+Brain+Regions.">Axonally Synthesized ATF4 Transmits a Neurodegenerative Signal across Brain Regions.</a> Cell. 158 (5), 1159-1172 (2014).</li><li>Haass, C., Selkoe, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Soluble+protein+oligomers+in+neurodegeneration:+lessons+from+the+Alzheimer's+amyloid+beta-peptide.+Nature+reviews.">Soluble protein oligomers in neurodegeneration: lessons from the Alzheimer's amyloid beta-peptide. Nature reviews.</a> Molecular cell biology. 8 (2), 101-112 (2007).</li><li>Knowles, J. 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=The+p75+neurotrophin+receptor+promotes+amyloid-beta(1-42)-induced+neuritic+dystrophy+in+vitro+and+in+vivo.">The p75 neurotrophin receptor promotes amyloid-beta(1-42)-induced neuritic dystrophy in vitro and in vivo.</a> The Journal of neuroscience : the official journal of the Society for Neuroscience. 29 (34), 10627-10637 (2009).</li><li>Troy, C. 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=beta-Amyloid-induced+neuronal+apoptosis+requires+c-Jun+N-terminal+kinase+activation.">beta-Amyloid-induced neuronal apoptosis requires c-Jun N-terminal kinase activation.</a> Journal of neurochemistry. 77 (1), 157-164 (2001).</li><li>Crews, L., Rockenstein, E., Masliah, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=APP+transgenic+modeling+of+Alzheimer's+disease:+mechanisms+of+neurodegeneration+and+aberrant+neurogenesis.">APP transgenic modeling of Alzheimer's disease: mechanisms of neurodegeneration and aberrant neurogenesis.</a> Brain structure &amp; function. 214 (2-3), 111-126 (2010).</li><li>Gotz, J., Ittner, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Animal+models+of+Alzheimer's+disease+and+frontotemporal+dementia.">Animal models of Alzheimer's disease and frontotemporal dementia.</a> Nature reviews. Neuroscience. 9 (7), 532-544 (2008).</li><li>Calhoun, M. 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=Neuron+loss+in+APP+transgenic+mice.">Neuron loss in APP transgenic mice.</a> Nature. 395 (6704), 755-756 (1998).</li><li>Oakley, 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=Intraneuronal+beta-amyloid+aggregates,+neurodegeneration,+and+neuron+loss+in+transgenic+mice+with+five+familial+Alzheimer's+disease+mutations:+potential+factors+in+amyloid+plaque+formation.">Intraneuronal beta-amyloid aggregates, neurodegeneration, and neuron loss in transgenic mice with five familial Alzheimer's disease mutations: potential factors in amyloid plaque formation.</a> The Journal of neuroscience : the official journal of the Society for Neuroscience. 26 (40), 10129-10140 (2006).</li><li>Jean, Y. Y., 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=Caspase-2+is+essential+for+c-Jun+transcriptional+activation+and+Bim+induction+in+neuron+death.">Caspase-2 is essential for c-Jun transcriptional activation and Bim induction in neuron death.</a> The Biochemical journal. 455 (1), 15-25 (2013).</li><li>Sotthibundhu, A., 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=Beta-amyloid(1-42)+induces+neuronal+death+through+the+p75+neurotrophin+receptor.">Beta-amyloid(1-42) induces neuronal death through the p75 neurotrophin receptor.</a> The Journal of neuroscience : the official journal of the Society for Neuroscience. 28 (15), 3941-3946 (2008).</li><li>Kar, S., Quirion, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amyloid+beta+peptides+and+central+cholinergic+neurons:+functional+interrelationship+and+relevance+to+Alzheimer's+disease+pathology.">Amyloid beta peptides and central cholinergic neurons: functional interrelationship and relevance to Alzheimer's disease pathology.</a> Progress in brain research. 145, 261-274 (2004).</li><li>Leranth, C., Frotscher, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Organization+of+the+septal+region+in+the+rat+brain:+cholinergic-GABAergic+interconnections+and+the+termination+of+hippocampo-septal+fibers.">Organization of the septal region in the rat brain: cholinergic-GABAergic interconnections and the termination of hippocampo-septal fibers.</a> The Journal of comparative neurology. 289 (2), 304-314 (1989).</li><li>Fa, 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=Preparation+of+oligomeric+beta-amyloid+1-42+and+induction+of+synaptic+plasticity+impairment+on+hippocampal+slices.">Preparation of oligomeric beta-amyloid 1-42 and induction of synaptic plasticity impairment on hippocampal slices.</a> Journal of visualized experiments : JoVE. (41), (2010).</li><li>Paxinos, G., Franklin, K. B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Mouse Brain in Stereotaxic Coordinates. , (2001).</li><li>Gage, G. J., Kipke, D. R., Shain, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Whole+animal+perfusion+fixation+for+rodents.">Whole animal perfusion fixation for rodents.</a> Journal of visualized experiments : JoVE. (65), (2012).</li><li>Currle, D. S., Monuki, E. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flash+freezing+and+cryosectioning+E12.5+mouse+brain.">Flash freezing and cryosectioning E12.5 mouse brain.</a> Journal of visualized experiments : JoVE. (4), (2007).</li><li>Jin, 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=Soluble+amyloid+beta-protein+dimers+isolated+from+Alzheimer+cortex+directly+induce+Tau+hyperphosphorylation+and+neuritic+degeneration.">Soluble amyloid beta-protein dimers isolated from Alzheimer cortex directly induce Tau hyperphosphorylation and neuritic degeneration.</a> Proceedings of the National Academy of Sciences of the United States of America. 108 (14), 5819-5824 (2011).</li><li>Lambert, M. P., 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=Diffusible,+nonfibrillar+ligands+derived+from+Abeta1-42+are+potent+central+nervous+system+neurotoxins.">Diffusible, nonfibrillar ligands derived from Abeta1-42 are potent central nervous system neurotoxins.</a> Proceedings of the National Academy of Sciences of the United States of America. 95 (11), 6448-6453 (1998).</li><li>Masters, C. L., Selkoe, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biochemistry+of+amyloid+beta-protein+and+amyloid+deposits+in+Alzheimer+disease.">Biochemistry of amyloid beta-protein and amyloid deposits in Alzheimer disease.</a> Cold Spring Harbor perspectives in medicine. 2 (6), a006262 (2012).</li><li>Chakrabarti, 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=Estrogen+receptor+agonists+for+attenuation+of+neuroinflammation+and+neurodegeneration.">Estrogen receptor agonists for attenuation of neuroinflammation and neurodegeneration.</a> Brain research bulletin. 109C, 22-31 (2014).</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 : the official journal of the Society for Neuroscience. 23 (26), 8844-8853 (2003).</li><li>Puzzo, 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=Picomolar+amyloid-beta+positively+modulates+synaptic+plasticity+and+memory+in+hippocampus.">Picomolar amyloid-beta positively modulates synaptic plasticity and memory in hippocampus.</a> The Journal of neuroscience : the official journal of the Society for Neuroscience. 28 (53), 14537-14545 (2008).</li><li>Puzzo, 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=Endogenous+amyloid-beta+is+necessary+for+hippocampal+synaptic+plasticity+and+memory.">Endogenous amyloid-beta is necessary for hippocampal synaptic plasticity and memory.</a> Annals of. 69 (5), 819-830 (2011).</li><li>Akpan, N., 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=Intranasal+delivery+of+caspase-9+inhibitor+reduces+caspase-6-dependent+axon/neuron+loss+and+improves+neurological+function+after+stroke.">Intranasal delivery of caspase-9 inhibitor reduces caspase-6-dependent axon/neuron loss and improves neurological function after stroke.</a> The Journal of neuroscience : the official journal of the Society for Neuroscience. 31 (24), 8894-8904 (2011).</li><li>Fulmer, C. 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=Astrocyte-derived+BDNF+supports+myelin+protein+synthesis+after+cuprizone-induced+demyelination.">Astrocyte-derived BDNF supports myelin protein synthesis after cuprizone-induced demyelination.</a> The Journal of neuroscience : the official journal of the Society for Neuroscience. 34 (24), 8186-8196 (2014).</li><li>Thakker-Varia, 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=The+neuropeptide+VGF+is+reduced+in+human+bipolar+postmortem+brain+and+contributes+to+some+of+the+behavioral+and+molecular+effects+of+lithium.">The neuropeptide VGF is reduced in human bipolar postmortem brain and contributes to some of the behavioral and molecular effects of lithium.</a> The Journal of neuroscience : the official journal of the Society for Neuroscience. 30 (28), 9368-9380 (2010).</li><li>Greferath, U., 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=Enlarged+cholinergic+forebrain+neurons+and+improved+spatial+learning+in+p75+knockout+mice.">Enlarged cholinergic forebrain neurons and improved spatial learning in p75 knockout mice.</a> The European journal of neuroscience. 12 (3), 885-893 (2000).</li><li>Brashear, H. R., Zaborszky, L., Heimer, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Distribution+of+GABAergic+and+cholinergic+neurons+in+the+rat+diagonal+band.">Distribution of GABAergic and cholinergic neurons in the rat diagonal band.</a> Neuroscience. 17 (2), 439-451 (1986).</li><li>Clarke, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cholinergic+innervation+of+the+rat+dentate+gyrus:+an+immunocytochemical+and+electron+microscopical+study.">Cholinergic innervation of the rat dentate gyrus: an immunocytochemical and electron microscopical study.</a> Brain research. 360 (1-2), 349-354 (1985).</li><li>Garcia-Osta, A., Alberini, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amyloid+beta+mediates+memory+formation.">Amyloid beta mediates memory formation.</a> Learning &amp; memory. 16 (4), 267-272 (2009).</li></ol>

To achieve a successful A&#946;1-42 injection the experimenter or surgeon must: 1) use aseptic technique; 2) correctly identify the brain region of interest with accurate coordinates; 3) be able to properly secure the mouse in the stereotaxic frame with the brain leveled in the AP and ML axis; 4) have the ability to operate the micromanipulator with precision; 5) ensure proper post-operative care. If these key steps are followed the mouse should survive the surgery with no observable infection.
<p class="j...

Amyloid plaque deposits, which are composed of amyloid-beta (A&#946;1-42), are a key feature of the pathology of Alzheimer&#8217;s disease (AD). Numerous studies have shown that high or toxic levels of recombinant oligomeric A&#946;1-42 elicit neuronal death, synaptic dystrophy, loss and dysfunction; as well as learning and memory deficits1-4. Brain regions affected include the hippocampus, the cortex, and subcortical structures such as the basal forebrain and the amygdala5,6. To date, there are multiple transgenic mouse models that attempt to simulate the A&#946;1-42 pathology of AD. Depending on the strain these animals prove to be useful in examining select pathological features of AD. Unfortunately, with the exception of 2 transgenic lines, APP23 and 5XFAD, these mice never fully replicate neuronal loss, a key aspect of AD. Even with the neuronal loss observed in APP23 and 5XFAD, the neuronal death observed was subtle, age dependent, and isolated to a few select regions7,8.
The direct infusion of oligomeric A&#946;1-42 into the wild-type mouse brain provides an excellent in vivo model which replicates the neuronal death aspect of amyloidopathy1,9,10. Unlike the commonly utilized transgenic mouse models the oligomeric A&#946;1-42 infusion model is ideal for acutely elevating A&#946;1-42 levels in a spatial and temporal manner. The advantage of using wild-type mice for this model obviates potential compensation or side effects from the mutations introduced in transgenic mouse lines. Past studies have shown that infusing toxic levels of A&#946;1-42 into the hippocampus elicits neuron death in the vicinity of the injection site within 1 week1. Moreover, consistent with the observation that A&#946;1-42 is toxic for cholinergic neurons11 the basal forebrain cholinergic neuron (BFCN) population which projects to the hippocampus is decreased 20-50% within 7-14 days following beta-amyloid infusion1,10 in mice, effectively allowing for the examinations of isolated neuronal circuitry in the brain. Since BFCN project ipsilaterally to the dentate gyrus of the hippocampus12, for the most part control/vehicle and oligomeric A&#946;1-42 solutions can be injected on either side of the brain allowing comparisons to be made between the left and right hemispheres1.
In this report we will provide a detailed surgical and injection methodology for adult wild-type C57BL/6J mice. This mouse strain is chosen because of its wide use in research. Technically, any brain region can be targeted for infusion, however here we will use the dentate gyrus of the hippocampus as the target to illustrate the technique.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Ketamine HCl (100mg/ml)</td>
			<td>Henry Schein Medical</td>
			<td>1049007</td>
			<td>100 mg ketamine per 1 kg animal</td>
		</tr>
		<tr>
			<td>Xylazine (20mg/ml)</td>
			<td>Henry Schein Medical</td>
			<td>not available</td>
			<td>10 mg xylazine per 1 kg animal</td>
		</tr>
		<tr>
			<td>Buprenex (0.3mg/ml)</td>
			<td>Henry Schein Medical</td>
			<td>1217793</td>
			<td>0.1 mg buprenex per 1 kg animal</td>
		</tr>
		<tr>
			<td>A&#946;1-42</td>
			<td>David Teplow/UCLA</td>
			<td>not available</td>
			<td>100 &#956;M; This amyloid was used in the paper</td>
		</tr>
		<tr>
			<td>A&#946;1-42</td>
			<td>Bachem</td>
			<td>H-1368</td>
			<td>Can be used in place of amyloid from the Teplow lab</td>
		</tr>
		<tr>
			<td>A&#946;1-42</td>
			<td>American Peptide</td>
			<td>62-0-80B</td>
			<td>Can be used in place of amyloid from the Teplow lab</td>
		</tr>
		<tr>
			<td>Scrambled A&#946;1-42</td>
			<td>American Peptide</td>
			<td>62-0-46B</td>
			<td>Can be used as control peptide for comparing A&#946;1-42</td>
		</tr>
		<tr>
			<td>NU4 Antibody (Oligomeric Amyloid Antibody)</td>
			<td>Gift from William Klein/Northwestern U.</td>
			<td>not available</td>
			<td>1:2000 dilution</td>
		</tr>
		<tr>
			<td>Anti-Amyloid Oligomeric Antibody&#160; (Polyclonal Rabbit)</td>
			<td>EMD Millipore</td>
			<td>AB9234</td>
			<td>May be used in place of Nu4; needs to&#160; be tested by the end user</td>
		</tr>
		<tr>
			<td>6E10 Antibody (Monoclonal Mouse) (Amyloid Antibody)</td>
			<td>Biolegend</td>
			<td>sig-39320</td>
			<td>1:1000 dilution</td>
		</tr>
		<tr>
			<td>ChAT Antibody (Polyclonal Goat)</td>
			<td>Millipore</td>
			<td>AB144P</td>
			<td>1:100 dilution</td>
		</tr>
		<tr>
			<td>DeadEnd Fluorometric TUNEL system</td>
			<td>Promega</td>
			<td>G3250</td>
			<td>Follow manufacturer&#39;s directions for use</td>
		</tr>
		<tr>
			<td>Prolong Gold Antifade Reagent with DAPI</td>
			<td>Invitrogen</td>
			<td>P36935</td>
			<td>Use when coverslipping slides</td>
		</tr>
		<tr>
			<td>Fluorogold</td>
			<td>Fluorochrome, LLC</td>
			<td>not available</td>
			<td>2% solution</td>
		</tr>
		<tr>
			<td>Absolute Ethanol (200 proof)</td>
			<td>Fisher Scientific</td>
			<td>BP2818-4</td>
			<td>For making 70% ethanol for sanitizing and disinfecting</td>
		</tr>
		<tr>
			<td>Novex 10-20% Tricine gel</td>
			<td>Life Technologies</td>
			<td>EC6625BOX</td>
			<td>For separating A&#946;1-42</td>
		</tr>
		<tr>
			<td>Novex Tricine SDS Running Buffer (10X)</td>
			<td>Life Technologies</td>
			<td>LC1675</td>
			<td>For running 10-20% Tricine gels</td>
		</tr>
		<tr>
			<td>Novex Tris-Glycine Transfer Buffer (25X)</td>
			<td>Life Technologies</td>
			<td>LC3675</td>
			<td>For transferring 10-20% Tricine gels</td>
		</tr>
		<tr>
			<td>SuperSignal Western Blot Enhancer</td>
			<td>Thermo Scientific</td>
			<td>46640</td>
			<td>For enhancing A&#946;1-42 signal; follow manufacturer&#39;s protocol</td>
		</tr>
		<tr>
			<td>Protran BA79 Nitrocellulose Blotting Membrane, 0.1 &#956;m</td>
			<td>GE Healthcare Life Sciences</td>
			<td>10402088</td>
			<td>For transferring 10-20% Tricine gels</td>
		</tr>
		<tr>
			<td>Xcell SureLock Mini-Cell</td>
			<td>Life Technologies</td>
			<td>EI0001</td>
			<td>Electrophoresis aparatus for running 10-20% Tricine gels</td>
		</tr>
		<tr>
			<td>GenTeal Lubricant Eye Gel</td>
			<td>Novartis</td>
			<td>not available</td>
			<td>For keeping the mouse eyes moist during surgery; can be found in local pharmacy stores</td>
		</tr>
		<tr>
			<td>Refresh Optive Lubricant Eye Drops</td>
			<td>Allergan</td>
			<td>not available</td>
			<td>For keeping the mouse eyes moist during surgery; can be found in local pharmacy stores; Can be used in place of GenTeal</td>
		</tr>
		<tr>
			<td>Betadine</td>
			<td>Stoelting</td>
			<td>50998</td>
			<td>For sanitizing and disinfecting</td>
		</tr>
		<tr>
			<td>Round/Tapered Spatula&#160;</td>
			<td>VWR</td>
			<td>82027-490</td>
			<td>For opening animal mouth</td>
		</tr>
		<tr>
			<td>Bulldog Serrefines Clamps (Jaw Dims. 9X1.6mm; Length 28mm)</td>
			<td>Fine Science Tools</td>
			<td>18050-28</td>
			<td>Optional; For keeping scalp skin apart during injection</td>
		</tr>
		<tr>
			<td>Straight Fine Scissors (Cutting edge 25mm; Length 11.5cm)</td>
			<td>Fine Science Tools</td>
			<td>14060-11</td>
			<td>For cutting scalp</td>
		</tr>
		<tr>
			<td>#3 Scalpel Handle</td>
			<td>Fine Science Tools</td>
			<td>10003-12</td>
			<td></td>
		</tr>
		<tr>
			<td>#11 Surgical Blade</td>
			<td>Fine Science Tools</td>
			<td>10011-00</td>
			<td>For making scalp incision</td>
		</tr>
		<tr>
			<td>Student Standard Pattern Forcep (Tip Dims. 2.5x1.5mm; Length 11.5cm)</td>
			<td>Fine Science Tools</td>
			<td>91100-12</td>
			<td>For holding scalp closed during suturing</td>
		</tr>
		<tr>
			<td>Trimmer Combo Kit</td>
			<td>Kent Scientific</td>
			<td>CL9990-1201</td>
			<td>For shaving hair</td>
		</tr>
		<tr>
			<td>T/Pump Warm Water Recirculator&#160;</td>
			<td>Kent Scientific&#160;</td>
			<td>TP-700</td>
			<td>For warming animal during surgery</td>
		</tr>
		<tr>
			<td>Resusable Warmining Pad (5&#34; x 10&#34;)</td>
			<td>Kent Scientific&#160;</td>
			<td>TPZ-0510FEA</td>
			<td>For attaching it to the T/Pump warm water recirculator to warm the animal during surgery</td>
		</tr>
		<tr>
			<td>Cordless Micro Drill</td>
			<td>Stoelting</td>
			<td>58610</td>
			<td>Use 0.8mm steel burrs to drill holes in the skull</td>
		</tr>
		<tr>
			<td>Lab Standard Stereotaxic Instrument with Mouse &#38; Neonatal Rat Adaptor</td>
			<td>Stoelting</td>
			<td>51615</td>
			<td></td>
		</tr>
		<tr>
			<td>Just for Mouse Stereotaxic Instrument</td>
			<td>Stoelting</td>
			<td>51730</td>
			<td>Can use this in place of Stoelting Cat. #51615</td>
		</tr>
		<tr>
			<td>Quintessential Stereotaxic Injector</td>
			<td>Stoelting</td>
			<td>53311</td>
			<td></td>
		</tr>
		<tr>
			<td>Dry Glass Bead Sterilizer</td>
			<td>Stoelting</td>
			<td>50287</td>
			<td>For sterilizing stainless steel instruments</td>
		</tr>
		<tr>
			<td>Sterile Surgical Drape (18&#34; x 26&#34;)</td>
			<td>Stoelting</td>
			<td>50981</td>
			<td></td>
		</tr>
		<tr>
			<td>Hamilton Syringe 50 ml, Model 705 RN SYR, NDL</td>
			<td>Hamilton Company</td>
			<td>7637-01</td>
			<td>For brain injection; use different syringes for different solutions</td>
		</tr>
		<tr>
			<td>29 Gauge Needle, Small Hub RN NDL</td>
			<td>Hamilton Company</td>
			<td>7803-06</td>
			<td>For attaching to the Hamilton syringe for brain injection</td>
		</tr>
		<tr>
			<td>1 ml BD Tuberculin Syringes</td>
			<td>VWR</td>
			<td>BD309659</td>
			<td>For administering anesthesia and saline</td>
		</tr>
		<tr>
			<td>30 Gauge Needle (0.5&#34;)</td>
			<td>VWR</td>
			<td>BD305106</td>
			<td>For administering anesthesia and saline</td>
		</tr>
		<tr>
			<td>Portable Electronic CS Series Scale (Ohaus)</td>
			<td>VWR</td>
			<td>65500-202</td>
			<td>For weighing animals to determine anesthesia dose</td>
		</tr>
		<tr>
			<td>Hot plate (Top Plate Dims. 7.25x7.25in)</td>
			<td>VWR</td>
			<td>47751-148</td>
			<td>For warming animals post-surgery</td>
		</tr>
		<tr>
			<td>Sofsilk Silk Suture C-1 Cutting 3/8, 12 mm</td>
			<td>Covidien</td>
			<td>S1173</td>
			<td>For closing wound</td>
		</tr>
		<tr>
			<td>Vetbond Tissue Adhesive (3M)</td>
			<td>Santa Cruz Biotechnology</td>
			<td>sc-361931</td>
			<td>Optional: for aiding in wound closure; Use with suture.</td>
		</tr>
		<tr>
			<td>Cotton-Tipped Wooden-Shaft Sterile Applicators</td>
			<td>Fisher scientific</td>
			<td>22-029-488</td>
			<td>For cleaning and drying surgical wound</td>
		</tr>
		<tr>
			<td>Fisherbrand Superfrost Plus Microscope Slides</td>
			<td>Fisher Scientific&#160;</td>
			<td>12-550-15</td>
			<td>For collecting brain sections</td>
		</tr>
		<tr>
			<td>VWR Micro Cover Glass 24 X 50 mm</td>
			<td>VWR</td>
			<td>48393241</td>
			<td>For mounting microscope slides</td>
		</tr>
		<tr>
			<td>Thermo Scientific Nalgene Syringe Filter 0.2 &#956;m</td>
			<td>Fisher Scientific</td>
			<td>194-2520</td>
			<td>For sterilizing saline solution</td>
		</tr>
		<tr>
			<td>Sterile dual tip skin markers by Viscot Medical</td>
			<td>Medline</td>
			<td>VIS1422SRL91</td>
			<td>For marking coordinates on the skull</td>
		</tr>
	</tbody>
</table>

stereotaxic infusion of oligomeric amyloid-beta into the mouse hippocampus

Alzheimer&#8217;s disease is a neurodegenerative disease affecting the aging population. A key neuropathological feature of the disease is the over-production of amyloid-beta and the deposition of amyloid-beta plaques in brain regions of the afflicted individuals. Throughout the years scientists have generated numerous Alzheimer&#8217;s disease mouse models that attempt to replicate the amyloid-beta pathology. Unfortunately, the mouse models only selectively mimic the disease features. Neuronal death, a prominent effect in the brains of Alzheimer&#8217;s disease patients, is noticeably lacking in these mice. Hence, we and others have employed a method of directly infusing soluble oligomeric species of amyloid-beta - forms of amyloid-beta that have been proven to be most toxic to neurons - stereotaxically into the brain. In this report we utilize male C57BL/6J mice to document this surgical technique of increasing amyloid-beta levels in a select brain region. The infusion target is the dentate gyrus of the hippocampus because this brain structure, along with the basal forebrain that is connected by the cholinergic circuit, represents one of the areas of degeneration in the disease. The results of elevating amyloid-beta in the dentate gyrus via stereotaxic infusion reveal increases in neuron loss in the dentate gyrus within 1 week, while there is a concomitant increase in cell death and cholinergic neuron loss in the vertical limb of the diagonal band of Broca of the basal forebrain. These effects are observed up to 2 weeks. Our data suggests that the current amyloid-beta infusion model provides an alternative mouse model to address region specific neuron death in a short-term basis. The advantage of this model is that amyloid-beta can be elevated in a spatial and temporal manner.

The present method of preparing human recombinant oligomeric A&#946;1-42 yields soluble oligomeric species consisting of monomers, dimers, trimers, and tetramers (Figure 1A). These low molecular weight A&#946;1-42 species, but not the fibrils and plaques, have been shown in numerous settings to be most toxic to neurons1,4,9,17-19. To determine whether or not oligomeric A&#946;1-42 induces neuron death in the mouse brain A&#946;1-42 (4 &#181;l of 100 ...

Watch this Scientific Journal Video about Stereotaxic Infusion of Oligomeric Amyloid-beta into the Mouse Hippocampus at JoVE.com

Stereotaxic Infusion of Oligomeric Amyloid-beta into the Mouse Hippocampus

Here, we present a protocol for direct stereotaxic brain infusion of amyloid-beta. This methodology provides an alternative in vivo mouse model to address the short-term effects of amyloid-beta on brain neurons.

Alzheimer&#8217;s disease is a neurodegenerative disease affecting the aging population. A key neuropathological feature of the disease is the ...

stereotaxic-infusion-oligomeric-amyloid-beta-into-mouse

Research

JoVE Journal

Neuroscience

Visualization and Genetic Manipulation of Dendrites and Spines in the Mouse Cerebral Cortex and Hippocampus using In utero Electroporation

In utero electroporation (IUE) has become a powerful technique to study the development of different regions of the embryonic nervous system 1-5. To date this tool has been widely used to study the regulation of cellular proliferation, differentiation and neuronal migration especially in the developing cerebral cortex 6-8. Here we detail our protocol to electroporate in utero the cerebral cortex and the hippocampus and provide evidence that this approach can be used to study dendrites and spines in these two cerebral regions.
Visualization and manipulation of neurons in primary cultures have contributed to a better understanding of the processes involved in dendrite, spine and synapse development. However neurons growing in vitro are not exposed to all the physiological cues that can affect dendrite and/or spine formation and maintenance during normal development. Our knowledge of dendrite and spine structures in vivo in wild-type or mutant mice comes mostly from observations using the Golgi-Cox method 9. However, Golgi staining is considered to be unpredictable. Indeed, groups of nerve cells and fiber tracts are labeled randomly, with particular areas often appearing completely stained while adjacent areas are devoid of staining. Recent studies have shown that IUE of fluorescent constructs represents an attractive alternative method to study dendrites, spines as well as synapses in mutant / wild-type mice 10-11 (Figure 1A). Moreover in comparison to the generation of mouse knockouts, IUE represents a rapid approach to perform gain and loss of function studies in specific population of cells during a specific time window. In addition, IUE has been successfully used with inducible gene expression or inducible RNAi approaches to refine the temporal control over the expression of a gene or shRNA 12. These advantages of IUE have thus opened new dimensions to study the effect of gene expression/suppression on dendrites and spines not only in specific cerebral structures (Figure 1B) but also at a specific time point of development (Figure 1C).
Finally, IUE provides a useful tool to identify functional interactions between genes involved in dendrite, spine and/or synapse development. Indeed, in contrast to other gene transfer methods such as virus, it is straightforward to combine multiple RNAi or transgenes in the same population of cells. 
In summary, IUE is a powerful method that has already contributed to the characterization of molecular mechanisms underlying brain function and disease and it should also be useful in the study of dendrites and spines.

Visualization and Genetic Manipulation of Dendrites and Spines in the Mouse Cerebral Cortex and Hippocampus using In utero Electroporation

This article describes in detail a protocol to electroporate in utero the cerebral cortex and the hippocampus at E14.5 in mice. We also show that this is a valuable method to study dendrites and spines in these two cerebral regions.

In utero electroporation (IUE) has become a powerful technique to study the development of different regions of the embryonic nervous system 1-5. To date ...

Stereotaxic Injection of a Viral Vector for Conditional Gene Manipulation in the Mouse Spinal Cord

Intraparenchymal injection of a viral vector enables conditional gene manipulation in distinct populations of neurons or particular regions of the central nervous system. We demonstrate a stereotaxic injection technique that allows targeted gene expression or silencing in the dorsal horn of the mouse spinal cord. The surgical procedure is brief. It requires laminectomy of a single vertebra, providing for quick recovery of the animal and unimpaired motility of the spine. Controlled injection of a small vector suspension volume at low speed and use of a microsyringe with beveled glass cannula minimize the tissue lesion. The local immune response to the vector depends on the intrinsic properties of the virus employed; in our experience, it is minor and short-lived when a recombinant adeno-associated virus is used. A reporter gene such as enhanced green fluorescent protein facilitates monitoring spatial distribution of the vector, and the efficacy and cellular specificity of the transfection.

Viral vectors allow for targeted gene manipulation. We demonstrate a method for conditional gene expression or ablation in the mouse spinal cord, using stereotaxic injection of a viral vector into the dorsal horn, a prominent site of synaptic contact between primary somatosensory afferents and neurons of the central nervous system.

Intraparenchymal injection of a viral vector enables conditional gene manipulation in distinct populations of neurons or particular regions of the central ...

Building An Open-source Robotic Stereotaxic Instrument

This protocol includes the designs and software necessary to upgrade an existing stereotaxic instrument to a robotic (CNC) stereotaxic instrument for around $1,000 (excluding a drill), using industry standard stepper motors and CNC controlling software. Each axis has variable speed control and may be operated simultaneously or independently. The robot&#39;s flexibility and open coding system (g-code) make it capable of performing custom tasks that are not supported by commercial systems. Its applications include, but are not limited to, drilling holes, sharp edge craniotomies, skull thinning, and lowering electrodes or cannula. In order to expedite the writing of g-coding for simple surgeries, we have developed custom scripts that allow individuals to design a surgery with no knowledge of programming. However, for users to get the most out of the motorized stereotax, it would be beneficial to be knowledgeable in mathematical programming and G-Coding (simple programming for CNC machining).
The recommended drill speed is greater than 40,000 rpm. The stepper motor resolution is 1.8&#176;/Step, geared to 0.346&#176;/Step. A standard stereotax has a resolution of 2.88 &#956;m/step. The maximum recommended cutting speed is 500 &#956;m/sec. The maximum recommended jogging speed is 3,500 &#956;m/sec. The maximum recommended drill bit size is HP 2.

This protocol includes the designs and software necessary to upgrade an existing stereotaxic instrument to a robotic (computer numeric controlled; CNC) stereotaxic instrument for around $1,000 (excluding a drill).

This protocol includes the designs and software necessary to upgrade an existing stereotaxic instrument to a robotic (CNC) stereotaxic instrument for ...

Mouse Microsurgery Infusion Technique for Targeted Substance Delivery into the CNS via the Internal Carotid Artery

Animal models of central nervous system (CNS) diseases and, consequently, blood-brain barrier disruption diseases, require the delivery of exogenous substances into the brain. These exogenous substances may induce injurious impact or constitute therapeutic strategy. The most common delivery methods of exogenous substances into the brain are based on systemic deliveries, such as subcutaneous or intravenous routes. Although commonly used, these approaches have several limitations, including low delivery efficacy into the brain. In contrast, surgical methods that locally deliver substances into the CNS are more specific and prevent the uptake of the exogenous substances by other organs. Several surgical methods for CNS delivery are available; however, they tend to be very traumatic. Here, we describe a mouse infusion microsurgery technique, which effectively delivers substances into the brain via the internal carotid artery, with minimal trauma and no interference with normal CNS functionality.

Mouse Microsurgery Infusion Technique for Targeted Substance Delivery into the CNS via the Internal Carotid Artery

The present protocol describes a mouse microsurgery infusion technique, which effectively delivers substances directly into the brain via the internal carotid artery.

Animal models of central nervous system (CNS) diseases and, consequently, blood-brain barrier disruption diseases, require the delivery of exogenous ...

Stereotaxic Surgery for Genetic Manipulation in Striatal Cells of Neonatal Mouse Brains

Many genes are expressed in embryonic brains, and some of them are continuously expressed in the brain after birth. For such persistently expressed genes, they may function to regulate the developmental process and/or physiological function in neonatal brains. To investigate neurobiological functions of specific genes in the brain, it is essential to inactivate genes in the brain. Here, we describe a simple stereotaxic method to inactivate gene expression in the striatum of transgenic mice at neonatal time windows. AAV-eGFP-Cre viruses were microinjected into the striatum of Ai14 reporter gene mice at postnatal day (P) 2 by stereotaxic brain surgery. The tdTomato reporter gene expression was detected in P14 striatum, suggesting a successful Cre-loxP mediated DNA recombination in AAV-transduced striatal cells. We further validated this technique by microinjecting AAV-eGFP-Cre viruses into P2Foxp2fl/fl mice. Double labeling of GFP and Foxp2 showed that GFP-positive cells lacked Foxp2 immunoreactivity in P9 striatum, suggesting the loss of Foxp2 protein in AAV-eGFP-Cre transduced striatal cells. Taken together, these results demonstrate an effective genetic deletion by stereotaxically microinjected AAV-eGFP-Cre viruses in specific neuronal populations in the neonatal brains of floxed transgenic mice. In conclusion, our stereotaxic technique provides an easy and simple platform for genetic manipulation in neonatal mouse brains. The technique can not only be used to delete genes in specific regions of neonatal brains, but it also can be used to inject pharmacological drugs, neuronal tracers, genetically modified optogenetics and chemogenetics proteins, neuronal activity indicators and other reagents into the striatum of neonatal mouse brains.

We describe a protocol of stereotaxic surgery with a homemade head-fixed device for microinjecting reagents into the striatum of neonatal mouse brains. This technique allows genetic manipulation in neuronal cells of specific regions of neonatal mouse brains.

Many genes are expressed in embryonic brains, and some of them are continuously expressed in the brain after birth. For such persistently expressed genes, ...

Recording Spatially Restricted Oscillations in the Hippocampus of Behaving Mice

The local field potential (LFP) emerges from ion movements across neural membranes. Since the voltage recorded by LFP electrodes reflects the summed electrical field of a large volume of brain tissue, extracting information about local activity is challenging. Studying neuronal microcircuits, however, requires a reliable distinction between truly local events and volume-conducted signals originating in distant brain areas. Current source density (CSD) analysis offers a solution for this problem by providing information about current sinks and sources in the vicinity of the electrodes. In brain areas with laminar cytoarchitecture such as the hippocampus, one-dimensional CSD can be obtained by estimating the second spatial derivative of the LFP. Here, we describe a method to record multilaminar LFPs using linear silicon probes implanted into the dorsal hippocampus. CSD traces are computed along individual shanks of the probe. This protocol thus describes a procedure to resolve spatially restricted neuronal network oscillations in the hippocampus of freely moving mice.

This protocol describes the recording of local field potentials with multi-shank linear silicon probes. Conversion of the signals using current source density analysis allows the reconstruction of local electrical activity in the mouse hippocampus. With this technique, spatially restricted brain oscillations can be studied in freely moving mice.

The local field potential (LFP) emerges from ion movements across neural membranes. Since the voltage recorded by LFP electrodes reflects the summed ...

Transplantation of Chemogenetically Engineered Cortical Interneuron Progenitors into Early Postnatal Mouse Brains

Neuronal development is regulated by a complex combination of environmental and genetic factors. Assessing the relative contribution of each component is a complicated task, which is particularly difficult in regards to the development of &#947;-aminobutyric acid (GABA)ergic cortical interneurons (CIs). CIs are the main inhibitory neurons in the cerebral cortex, and they play key roles in neuronal networks, by regulating both the activity of individual pyramidal neurons, as well as the oscillatory behavior of neuronal ensembles. They are generated in transient embryonic structures (medial and caudal ganglionic eminences -&#160;MGE and CGE) that are very difficult to efficiently target using in utero electroporation approaches. Interneuron progenitors migrate long distances during normal embryonic development, before they integrate in the cortical circuit. This remarkable ability to disperse and integrate into a developing network can be hijacked by transplanting embryonic interneuron precursors into early post-natal host cortices. Here, we present a protocol that allows genetic modification of embryonic interneuron progenitors using focal ex vivo electroporation. These engineered interneuron precursors are then transplanted into early post-natal host cortices, where they will mature into easily identifiable CIs. This protocol allows the use of multiple genetically encoded tools, or the ability to regulate the expression of specific genes in interneuron progenitors, in order to investigate the impact of either genetic or environmental variables on the maturation and integration of CIs.

Here we present a protocol, designed to use chemogenetic tools to manipulate the activity of cortical interneuron progenitors transplanted into the cortex of early postnatal mice.

Neuronal development is regulated by a complex combination of environmental and genetic factors. Assessing the relative contribution of each component is ...

Microdissection of Mouse Brain into Functionally and Anatomically Different Regions

The brain is the command center for the mammalian nervous system and an organ with enormous structural complexity. Protected within the skull, the brain consists of an outer covering of grey matter over the hemispheres known as the cerebral cortex. Underneath this layer reside many other specialized structures that are essential for multiple phenomenon important for existence. Acquiring samples of specific gross brain regions requires quick and precise dissection steps.&#160;It is understood that at the microscopic level, many sub-regions exist and likely cross the arbitrary regional boundaries that we impose for the purpose of this dissection.
Mouse models are routinely used to study human brain functions and diseases. Changes in gene expression patterns may be confined to specific brain areas targeting a particular phenotype depending on the diseased state. Thus, it is of great importance to study regulation of transcription with respect to its well-defined structural organization. A complete understanding of the brain requires studying distinct brain regions, defining connections, and identifying key differences in the activities of each of these brain regions. A more comprehensive understanding of each of these distinct regions may pave the way for new and improved treatments in the field of neuroscience. Herein, we discuss a step-by-step methodology for dissecting the mouse brain into sixteen distinct regions. In this procedure, we have focused on male mouse C57Bl/6J (6-8 week old) brain removal and dissection into multiple regions using neuroanatomical landmarks to identify and sample discrete functionally-relevant and behaviorally-relevant&#160;brain regions. This work will help lay a strong foundation in the field of neuroscience, leading to more focused approaches in the deeper understanding of brain function.

We present a hands-on, step-by-step, rapid protocol for mouse brain removal and dissection of discrete regions from fresh brain tissue. Obtaining brain regions for molecular analysis has become routine in many neuroscience labs. These brain regions are immediately frozen to obtain high quality transcriptomic data for system level analysis.

The brain is the command center for the mammalian nervous system and an organ with enormous structural complexity. Protected within the skull, the brain ...

Full- versus Sub-Regional Quantification of Amyloid-Beta Load on Mouse Brain Sections

Extracellular accumulation of amyloid-beta (A&#946;) plaques is one of the major pathological hallmarks of Alzheimer's disease (AD), and is the target of the only FDA-approved disease-modifying treatment for AD. Accordingly, the use of transgenic mouse models that overexpress the amyloid precursor protein and thereby accumulate cerebral A&#946; plaques are widely used to model human AD in mice. Therefore, immunoassays, including enzyme-linked immunosorbent assay (ELISA) and immunostaining, commonly measure the A&#946; load in brain tissues derived from AD transgenic mice. Though the methods for A&#946; detection and quantification have been well established and documented, the impact of the size of the region of interest selected in the brain tissue on A&#946; load measurements following immunostaining has not been reported. Therefore, the current protocol aimed to compare the A&#946; load measurements across the full- and sub-regions of interest using an image analysis software. The steps involved in brain tissue preparation, free-floating brain section immunostaining, imaging, and quantification of A&#946; load in full- versus sub-regions of interest are described using brain sections derived from 13-month-old APP/PS1 double transgenic male mice. The current protocol and the results provide valuable information about the impact of the size of the region of interest on A&#946;-positive area quantification, and show a strong correlation between the A&#946;-positive area obtained using the full- and sub-regions of interest analyses for brain sections derived from 13-month-old male APP/PS1 mice that show widespread A&#946; deposition.

The present protocol describes and compares the procedure to perform a full-region or sub-region of interest analysis of sagittal mouse brain sections to quantify amyloid-beta load in the APP/PS1 transgenic mouse model of Alzheimer's disease.

Extracellular accumulation of amyloid-beta (A&#946;) plaques is one of the major pathological hallmarks of Alzheimer's disease (AD), and is the target of ...

In Vivo Chronic Two-Photon Imaging of Microglia in the Mouse Hippocampus

Microglia, the only immune cells resident in the brain, actively participate in neural circuit maintenance by modifying synapses and neuronal excitability. Recent studies have revealed the differential gene expression and functional heterogeneity of microglia in different brain regions. The unique functions of the hippocampal neural network in learning and memory may be associated with the active roles of microglia in synapse remodeling. However, inflammatory responses induced by surgical procedures have been problematic in the two-photon microscopic analysis of hippocampal microglia. Here, a method is presented that enables the chronic observation of microglia in all layers of the hippocampal CA1 through an imaging window. This method allows the analysis of morphological changes in microglial processes for more than 1 month. Long-term and high-resolution imaging of the resting microglia requires minimally invasive surgical procedures, appropriate objective lens selection, and optimized imaging techniques. The transient inflammatory response of hippocampal microglia may prevent imaging immediately after surgery, but the microglia restore their quiescent morphology within a few weeks. Furthermore, imaging neurons simultaneously with microglia allows us to analyze the interactions of multiple cell types in the hippocampus. This technique may provide essential information about microglial function in the hippocampus.

In Vivo Chronic Two-Photon Imaging of Microglia in the Mouse Hippocampus

This paper describes a method for chronic in vivo observation of the resting microglia in the mouse hippocampal CA1 using precisely controlled surgery and two-photon microscopy.