We thank Hanns Ulrich Zeilhofer for generously supporting this work. Hendrik Wildner was supported by the Olga Mayenfisch foundation. We thank Carmen Birchmeier for the Lmx1b antibody.

All animal experiments were approved by the Swiss cantonal veterinary office (Zurich) and are in accordance and compliance with all relevant regulatory and institutional guidelines.
NOTE: All materials along with respective manufacturers and/or vendors are listed in the Table of Materials.
1. Generation of Cre-dependent AAV Vectors
NOTE: A variety of Cre-dependent vectors with different promoters can be purchased (see <stro...

<ol>
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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuronal+circuitry+for+pain+processing+in+the+dorsal+horn.">Neuronal circuitry for pain processing in the dorsal horn.</a> Nat Rev Neurosci. 11 (12), 823-836 (2010).</li><li>Sandkuhler, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Models+and+mechanisms+of+hyperalgesia+and+allodynia.">Models and mechanisms of hyperalgesia and allodynia.</a> Physiol Rev. 89 (2), 707-758 (2009).</li><li>Zeilhofer, H. U., Wildner, H., Yevenes, G. 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(73), e50313 (2013).</li><li>Kohro, 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=A+new+minimally-invasive+method+for+microinjection+into+the+mouse+spinal+dorsal+horn.">A new minimally-invasive method for microinjection into the mouse spinal dorsal horn.</a> Sci Rep. 5, 14306 (2015).</li><li>Bourane, 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=Gate+control+of+mechanical+itch+by+a+subpopulation+of+spinal+cord+interneurons.">Gate control of mechanical itch by a subpopulation of spinal cord interneurons.</a> Science. 350 (6260), 550-554 (2015).</li><li>Bourane, 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=Identification+of+a+spinal+circuit+for+light+touch+and+fine+motor+control.">Identification of a spinal circuit for light touch and fine motor control.</a> Cell. 160 (3), 503-515 (2015).</li><li>Duan, B., 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=Identification+of+spinal+circuits+transmitting+and+gating+mechanical+pain.">Identification of spinal circuits transmitting and gating mechanical pain.</a> Cell. 159 (6), 1417-1432 (2014).</li><li>Gutierrez-Mecinas, 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=Preprotachykinin+A+is+expressed+by+a+distinct+population+of+excitatory+neurons+in+the+mouse+superficial+spinal+dorsal+horn+including+cells+that+respond+to+noxious+and+pruritic+stimuli.">Preprotachykinin A is expressed by a distinct population of excitatory neurons in the mouse superficial spinal dorsal horn including cells that respond to noxious and pruritic stimuli.</a> Pain. 158 (3), 440-456 (2017).</li><li>Awatramani, R., Soriano, P., Rodriguez, C., Mai, J. J., Dymecki, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cryptic+boundaries+in+roof+plate+and+choroid+plexus+identified+by+intersectional+gene+activation.">Cryptic boundaries in roof plate and choroid plexus identified by intersectional gene activation.</a> Nat Genet. 35 (1), 70-75 (2003).</li><li>Kim, J. C., 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=Linking+genetically+defined+neurons+to+behavior+through+a+broadly+applicable+silencing+allele.">Linking genetically defined neurons to behavior through a broadly applicable silencing allele.</a> Neuron. 63 (3), 305-315 (2009).</li><li>Kim, J. C., Dymecki, S. 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The authors have nothing to disclose.

Intraspinal injection of AAVs may become a powerful technique in a research laboratory, enabling the analysis of spinal cells with a high temporal and spatial solution. This protocol enables the transduction of the three main spinal segments innervated by sensory neurons extending their peripheral axons to the hindlimb. Transducing three segments produces robust and reproducible behavioral data. It also enables testing of a larger sensory area than possible after a single intraspinal injection. For example, the same inje...

The dorsal spinal cord is essential for information exchange between the periphery of the body and the brain. Sensory stimuli such as heat, cold, touch, or noxious stimuli are detected by specialized peripheral neurons, which convey this information to neurons of the spinal cord dorsal horn. Here, a complex network of inhibitory and excitatory interneurons modulates and eventually relays sensory information via spinal projection neurons to supraspinal sites1,2. The computations carried out by spinal inter- and projection neurons gate sensory information, thus determining which information is suppressed or relayed at which intensity. Changes in the integration of sensory stimuli, such as an altered balance between inhibition and excitation, can cause sensory dysfunctions such as hypersensitivity or allodynia (painful sensations after normally non-painful stimulation). These changes are thought to be the underlying cause of various chronic pain states3,4. Thus, spinal circuits are of high importance in sensory processing and consequently in the perception of an organism&#39;s environment and self. With the recent advent and combination of molecular, genetic, and surgical techniques that allow the precise manipulation of genetically identified spinal neuron subpopulations, scientists are now beginning to understand the underlying spinal circuits responsible for the processing of distinct sensory modalities.
Intraspinal injection of rAAV into wild-type or transgenic mice has greatly contributed to the manipulation, analysis, and understanding of the function of specific subsets of spinal neurons5,6,7,8,9,10,11. This technique allows the delivery of marker proteins (such as GFP/ GFP fusion proteins), reporter proteins (such as GCaMP), or effector proteins (such as bacterial toxins, channelrhodopsin, or pharmacogenetic receptors) in a spatially restricted manner to spinal neurons. Local injection of Cre-dependent rAAVs into transgenic mice expressing Cre recombinase in a specific subset of spinal neurons allows the specific analysis of the respective neuronal population. We have employed this technique to label, ablate, inhibit or activate spinal glycinergic neurons demonstrating that they are an essential part of the spinal gate controlling pain and itch transmission7. In these experiments, intraspinal injection of Cre-dependent rAAV into GlyT2::Cre mice enabled the selective manipulation of glycinergic neurons in the lumbar spinal cord. Thereby, simultaneous manipulation of supraspinal circuits that contain glycinergic neurons critical for the survival of the animal can be avoided.
While an intraspinal injection of rAAVs limits infection to the site of injection, viral transduction can occur not only in local neurons but also in neurons that connect to the injection site via axonal projections. The latter is often used to trace CNS areas providing neuronal input to a particular nucleus in the brain. The infection of axonal projections can, however, also be a confounding factor when a defined population of neurons shall be studied at a particular site. To address these issues, we have recently conducted a comprehensive analysis of AAV serotypes and expression cassettes to identify serotypes and promoters that can be used to either minimize or maximize retrograde transduction. In the context of this specific research in spinal circuits, we analyzed the ability of different serotypes and promoters to retrogradely transduce neurons in the dorsal root ganglia (DRG), the rostral ventromedial medulla (RVM), and the somatosensory cortex12. The technique outlined in this protocol can therefore be used either to analyze spinal neurons at the injection site or to analyze projection neurons that provide input to the injected site of the spinal cord. In the protocol described here, three injections of rAAV into the left side of the lumbar spinal cord are performed to enable transduction of neurons in the three lumbar segments (L3-L5). The L3-L5 segments receive the majority of the sensory input from the hindlimb ipsilateral to the injection site. We demonstrate that functional manipulation of genetically labeled neurons in L3-L5 is sufficient to evoke robust behavioral changes, thus providing functional evidence for the circuit function of such a genetically labeled neuron subtype.

<table>
	<tbody>
		<tr>
			<td>Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>micropipette puller: DMZ-Universal-Electrode-Puller</td>
			<td>Zeitz</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>anesthesia unit: Oxymat3 oxygen concentrator</td>
			<td>Weinmann</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>anesthesia unit: VIP 3000 Veterinary Vaporizer</td>
			<td>Midmark</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Heat mat: Mio Star Thermocare 100</td>
			<td>Migros</td>
			<td>717614700000</td>
			<td></td>
		</tr>
		<tr>
			<td>Electric shaver</td>
			<td>Philips</td>
			<td>BT9290</td>
			<td></td>
		</tr>
		<tr>
			<td>surgical microscope (OPMI pico)</td>
			<td>Zeiss</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Small animal stereotaxic apparatus</td>
			<td>Kopf</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Neurostar StereoDrive (optional)</td>
			<td>Neurostar</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Model 51690 Cunningham mouse spinal adaptor</td>
			<td>Harvard Apparatus</td>
			<td>72-4811</td>
			<td></td>
		</tr>
		<tr>
			<td>PHD Ultra syringe pump with nanomite</td>
			<td>Harvard Apparatus</td>
			<td>70-3601</td>
			<td></td>
		</tr>
		<tr>
			<td>Hamilton 701 RN 10 &#956;l glass microliter syringe</td>
			<td>Hamilton</td>
			<td>7635-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Hamilton Removable needle (RN) compression fitting 1 mm</td>
			<td>Hamilton</td>
			<td>55750-01</td>
			<td></td>
		</tr>
		<tr>
			<td>fine dentistry drilling apparatus: Osada success 40</td>
			<td>Osada</td>
			<td>OS-40</td>
			<td></td>
		</tr>
		<tr>
			<td>spherical cutter, 0.5mm</td>
			<td>Busch</td>
			<td>12001005B</td>
			<td></td>
		</tr>
		<tr>
			<td>electronic von Frey anesthesiometer</td>
			<td>IITC</td>
			<td>23905</td>
			<td></td>
		</tr>
		<tr>
			<td>flexible von Frey hairs</td>
			<td>IITC</td>
			<td>#7</td>
			<td></td>
		</tr>
		<tr>
			<td>LSM710 Pascal confocal microscope</td>
			<td>Zeiss</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>0.8 NA &#215; 20 Plan-apochromat objective</td>
			<td>Zeiss</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>1.3 NA &#215; 40 EC Plan-Neofluar oil-immersion objective</td>
			<td>Zeiss</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Surgical Tools</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Scalpel Handle #4, 13cm</td>
			<td>Fine Science Tools</td>
			<td>10004-13</td>
			<td></td>
		</tr>
		<tr>
			<td>Extra Fine Bonn Scissors</td>
			<td>Fine Science Tools</td>
			<td>14084-08</td>
			<td></td>
		</tr>
		<tr>
			<td>Adson forceps, 1 x 2 teeth, 12 cm</td>
			<td>Fine Science Tools</td>
			<td>11027-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Friedman-Pearson rongeurs, curved, 0.7 mm cup</td>
			<td>Fine Science Tools</td>
			<td>16121-14</td>
			<td></td>
		</tr>
		<tr>
			<td>Dumont #2 laminectomy forceps</td>
			<td>Fine Science Tools</td>
			<td>11223-20</td>
			<td></td>
		</tr>
		<tr>
			<td>Olsen-Hegar needle holders, serrated, 8.5 mm clamp length</td>
			<td>Fine Science Tools</td>
			<td>12002-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Fine forceps #5</td>
			<td>Fine Science Tools</td>
			<td>11254-20</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Consumables and Chemicals</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Thin-wall glass capillary, 1mm outside diameter</td>
			<td>World Precision Instruments</td>
			<td>TW 100-3</td>
			<td></td>
		</tr>
		<tr>
			<td>Syringes (1, 5 and 20 ml)</td>
			<td>B. Braun</td>
			<td>(9166917V, 4606051V, 4606205V)</td>
			<td></td>
		</tr>
		<tr>
			<td>26G beveled needle</td>
			<td>B. Braun</td>
			<td>4665457</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterile scalpel blades</td>
			<td>B. Braun</td>
			<td>BB523</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical sutures Safil Quick+ 4/0, absorbable</td>
			<td>B. Braun</td>
			<td>C1046220</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical sutures Premilene 5/0, non-absorbable</td>
			<td>B. Braun</td>
			<td>C0932191</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterile PBS or saline (0.9%)</td>
			<td></td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol, 70% (disinfectant)</td>
			<td></td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Iodine solution (e.g. Braunol)</td>
			<td>B. Braun</td>
			<td>18380</td>
			<td></td>
		</tr>
		<tr>
			<td>Anaesthetics&#160; (e.g. Attane isoflurane)</td>
			<td>Provet</td>
			<td>2222</td>
			<td></td>
		</tr>
		<tr>
			<td>Aldasorber</td>
			<td>Provet</td>
			<td>333526</td>
			<td></td>
		</tr>
		<tr>
			<td>analgesics (e.g. buprenorphine: temgesic)</td>
			<td>Indivior</td>
			<td>GTIN: 7680419310018</td>
			<td></td>
		</tr>
		<tr>
			<td>Ophthalmic ointment (e.g. vita-pos)</td>
			<td>Pharma medica</td>
			<td>GTIN: 4031626710635</td>
			<td></td>
		</tr>
		<tr>
			<td>Cotton swabs (e.g. from)</td>
			<td>IVF Hartmann</td>
			<td>1628100</td>
			<td></td>
		</tr>
		<tr>
			<td>Facial tissues (e.g. from)</td>
			<td>Uehlinger AG</td>
			<td>2015.10018</td>
			<td></td>
		</tr>
		<tr>
			<td>Superfrost plus microscope slides</td>
			<td>ThermoScientific</td>
			<td>J1800AMNZ</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Mice</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>C57BL/6J mice&#160; (wildtype)</td>
			<td>The Jackson Laboratory</td>
			<td>RRID:IMSR_JAX:000664</td>
			<td></td>
		</tr>
		<tr>
			<td>Rorbtm1.1(cre)Hze/J mice (ROR&#946;Cre)</td>
			<td>The Jackson Laboratory</td>
			<td>RRID:IMSR_JAX:023526</td>
			<td></td>
		</tr>
		<tr>
			<td>&#160;Gt(ROSA)26Sortm14(CAG-tdTomato)Hze/J mice (R26Tom)</td>
			<td>The Jackson Laboratory</td>
			<td>RRID: IMSR_JAX:007914</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Viral vectors</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>AAV1.CB7.CI.eGFP.WPRE.rBG (AAV1.CAG.eGFP)</td>
			<td>Penn Vector Core</td>
			<td>AV-1-PV1963</td>
			<td></td>
		</tr>
		<tr>
			<td>AAV1.CAG.flex.eGFP.WPRE.bGH (AAV1.CAG.flex.eGFP)</td>
			<td>Penn Vector Core</td>
			<td>AV-1-ALL854</td>
			<td></td>
		</tr>
		<tr>
			<td>AAV1.CAG.flex.tdTomato.WPRE.bGH (AAV1.CAG.flex.tdTomato)</td>
			<td>Penn Vector Core</td>
			<td>AV-1-ALL864</td>
			<td></td>
		</tr>
		<tr>
			<td>AAV1.EF1a.flex.DTA.hGH (AAV1.EF1a.flex.DTA)</td>
			<td>Penn Vector Core</td>
			<td>Custom production</td>
			<td></td>
		</tr>
		<tr>
			<td>AAV1.hSyn.DIO.hM3D(Gq)-mCherry.hGH (AAV.flex.hM3D(Gi))</td>
			<td>Penn Vector Core</td>
			<td>Custom production</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Plasmids</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>pAAV.hSyn.flex.hM3D(Gq)-mCherry</td>
			<td>Addgene</td>
			<td>44361</td>
			<td></td>
		</tr>
		<tr>
			<td>pAAV.EF1&#945;.flex.hChR2(H134R)-eYFP</td>
			<td>Addgene</td>
			<td>20298</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Bacteria</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>MDS42</td>
			<td>ScarabGenomics</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Stbl3</td>
			<td>ThermoScientific</td>
			<td>C737303</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Reagents</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>EndoFree Plasmid Maxi Kit</td>
			<td>Quiagen</td>
			<td>12362</td>
			<td></td>
		</tr>
		<tr>
			<td>NucleoBond PC 500</td>
			<td>Machery &#38; Nagel</td>
			<td>740574</td>
			<td></td>
		</tr>
		<tr>
			<td>clozapine-N-oxide (CNO)</td>
			<td>Enzo Life Sciences</td>
			<td>BBL-NS105-0025</td>
			<td></td>
		</tr>
		<tr>
			<td>chloroquine diphosphate salt</td>
			<td>Sigma</td>
			<td>C6628</td>
			<td></td>
		</tr>
		<tr>
			<td>histamine</td>
			<td>Sigma</td>
			<td>H7125</td>
			<td></td>
		</tr>
		<tr>
			<td>Dapi</td>
			<td>Invitrogen</td>
			<td>D3571</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Antibodies (dilution)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Rabbit anti-GFP (1:1000)</td>
			<td>Molecular Probes</td>
			<td>RRID:AB_221570</td>
			<td></td>
		</tr>
		<tr>
			<td>Rabbit anti-NeuN (1:3000)</td>
			<td>Abcam</td>
			<td>RRID:AB_10711153</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat anti-Pax2 (1 : 200)</td>
			<td>R &#38; D Systems</td>
			<td>RRID:AB_10889828</td>
			<td></td>
		</tr>
		<tr>
			<td>Guinea pig anti-Lmx1b (1 : 10 000)</td>
			<td>Dr Carmen Birchmeier</td>
			<td>Muller et al. 2002</td>
			<td></td>
		</tr>
		<tr>
			<td>Rabbit anti-GFAP (1 : 1000)</td>
			<td>DakoCytomation</td>
			<td>RRID:AB_10013382</td>
			<td></td>
		</tr>
		<tr>
			<td>Secondary antibodies raised in donkey (1:800)</td>
			<td>Jackson ImmunoResearch Laboratories</td>
			<td>NA</td>
			<td></td>
		</tr>
	</tbody>
</table>

adeno-associated virus-mediated transgene expression in genetically defined neurons of the spinal cord

Selective manipulation of spinal neuronal subpopulations has mainly been achieved by two different methods: 1) Intersectional genetics, whereby double or triple transgenic mice are generated in order to achieve selective expression of a reporter or effector gene (e.g., from the Rosa26 locus) in the desired spinal population. 2) Intraspinal injection of Cre-dependent recombinant adeno-associated virus (rAAV); here Cre-dependent AAV vectors coding for the reporter or effector gene of choice are injected into the spinal cord of mice expressing Cre recombinase in the desired neuronal subpopulation. This protocol describes how to generate Cre-dependent rAAV vectors and how to transduce neurons in the dorsal horn of the lumbar spinal cord segments L3-L5 with rAAVs. As the lumbar spinal segments L3-L5 are innervated by those peripheral sensory neurons that transmit sensory information from the hindlimbs, spontaneous behavior and responses to sensory tests applied to the hindlimb ipsilateral to the injection side can be analyzed in order to interrogate the function of the manipulated neurons in sensory processing. We provide examples of how this technique can be used to analyze genetically defined subsets of spinal neurons. The main advantages of virus-mediated transgene expression in Cre transgenic mice compared to classical reporter mouse-induced transgene expression are the following: 1) Different Cre-dependent rAAVs encoding various reporter or effector proteins can be injected into a single Cre transgenic line, thus overcoming the need to create several multiple transgenic mouse lines. 2) Intraspinal injection limits manipulation of Cre-expressing cells to the injection site and to the time after injection. The main disadvantages are: 1) Reporter gene expression from rAAVs is more variable. 2) Surgery is required to transduce the spinal neurons of interest. Which of the two methods is more appropriate depends on the neuron population and research question to be addressed.

In order to illustrate the expression levels that can be obtained by the intraspinal injection of rAAV encoding a marker protein, we first injected AAV1.CAG.eGFP into the lumbar spinal cord of wild-type mice. Three injections spaced approximately 1 mm apart produced a nearly continuous infection of lumbar spinal segments L3 to L5 (Figure 1A-C). Virus injection at a depth of 300 &#181;m from the spinal surface leads to predominant infection of...

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Adeno-associated Virus-mediated Transgene Expression in Genetically Defined Neurons of the Spinal Cord

Intraspinal injection of recombinase dependent recombinant adeno-associated virus (rAAV) can be used to manipulate any genetically labelled cell type in the spinal cord. Here we describe how to transduce neurons in the dorsal horn of the lumbar spinal cord. This technique enables functional interrogation of the manipulated neuron subtype.

Selective manipulation of spinal neuronal subpopulations has mainly been achieved by two different methods: 1) Intersectional genetics, whereby double or ...

The overall goal of intraspinal delivery of recombinant adeno-associated viruses is to enable the histological labeling and functional manipulation of genetically defined neurons in the dorsal spinal cord. This method can help answer key questions in the pain field, such as which neuronal circuits are required for the perception of different pain modalities. The main advantage of this technique is that genetically labeled neurons can be manipulated in a specially restricted and temporally controlled fashion.Locate the most caudal rib pair by palpating along the vertebral column of the anesthetized mouse. Then, make a 1.5 to 2.5 centimeter longitudinal cut into the skin, starting from just rostral to the most caudal rib pair. Lift the skin with forceps and detach it from the underlying muscle with scissors.Throughout the surgery, keep the exposed tissues moist with sterile 0.9%sodium chloride. Using fine forceps and small scissors, make an incision into the next to thin membranous layer, right next to the midline, and cut it away from the spinous processes. Several anatomical landmark can aid in identifying the correct vertebrae to target.Here, we describe three alternatives. Palpate along the vertebral column. The most caudal rib pair is located just rostral to the T13 vertebrae and the pelvic bone at hip level is at the level of the L6 vertebrae.Alternatively, pull back the skin towards the tail to expose the iliac crest. At the same level, the most caudal pair of visible intetransverse ligaments joins the L6 spinal process. Count backwards in a caudal to rostral direction to identify the vertebrae of interest.Otherwise, locate the spot where the tendon along the side of the vertebral column is whitest and most medial. The T13 vertebrae is located just rostral. The lumbar spinal cord segment L4 is located within this vertebrae.Next, place the animal onto a cushion of rolled up tissues to elevate it to the spinal clamps of the stereotaxic frame. Align the clamps adjacent to the target vertebrae. Fix one clamp in position, then hold the vertebral column with Adson forceps while fixing the second clamp.Confirm proper clamping by carefully pressing on the targeted vertebrae. Then, remove the paraspinous muscle above the vertebrae of interest. First, make an incision just medial to the tendons parallel to the vertebral column.Then, make perpendicular incisions rostral and caudal to the target vertebrae. Next, use rongeurs to tear or cut away the paraspinous muscle above the vertebrae of interest. Use forceps as needed to remove tissue remaining on the vertebrae or above the dura in the intravertebral space.The dorsal blood vessel should now be visible, marking the midline of the spinal cord. For unilateral injections, perform a partial laminectomy using a fine dentist drill equipped with a 0.5 millimeter spherical cutter to very carefully drill a hole into the middle of the target side of the vertebrae. Remove any remaining bone fragments with a 26 gauge beveled needle to expose the spinal cord.Use the needle to perforate the dura in the intravertebral spaces rostral and caudal to the target vertebrae, approximately 300 microns lateral to the dorsal blood vessel. Then, perforate the dura underneath the drilled hole. At this point, cerebrospinal fluid should escape from the holes and the spinal cord should be slightly bulging out.Prepare the injection syringe by first mounting the glass capillary onto a microliter syringe. Fasten the nut tightly to ensure a tight and secure fit. Fill the microliter syringe with sterile distilled water, then depress the plunger.If the water is not easily expelled from the tip, the micropipette is likely blocked and should be exchanged. Mount the syringe onto a micromanipulator connected to an electronically controlled microinjector. Then, use the microinjector to draw up about one microliter of air to separate the water and virus.Next, pipette a 2.5 microliter droplet of diluted virus solution onto a piece of paraffin film. Carefully move the tip of the micropipette into the droplet using the sterotaxic frame and draw it up into the micropipette. Then, press dispense until a drop of virus solution emerges at the tip.Retract the syringe and use a pen to mark the micropipette with a scale to monitor the dispensed volume. Use the stereotaxic arm to move the tip of the micropipette over one of the holes in the dura and then down until a slight depression appears on the surface of the exposed spinal cord. To target the injection to the spinal dorsal horn, move the tip down to a depth of 500 microns in 100 micron increments and then up 200 microns to allow for mechanical stabilization of the tissue.The final depth of the tip is 300 microns. After programming the pump to inject 300 nanoliters at an injection speed of 50 nanoliters per minute, press the start button to begin the infusion. After the injection is complete, check the scale on the micropipette to see whether the virus level has dropped.Leave the micropipette in place for an additional three minutes to allow the pressure to equilibrate. After three minutes, slowly retract the micropipette and then repeat the procedure for the other two injection sites. After the final injection, remove the spinal clamps and the cushion below the mouse.Close the incision layers with interrupted stitches, suturing the superficial tissue layers with absorbable sutures and the skin with non-absorbable sutures. Apply iodine disinfectant on the sutured wound. Terminate the anesthesia and leave the animal on the heat mat until it recovers before returning it to its home cage.Spinal tissue at the injection site is to be examined at the end of the experiment. This is necessary to verify successful injection and transduction and to exclude excessive tissue damage as a result of the surgery. To illustrate the expression levels that can be obtained by intraspinal injection of recombinant AAV, a virus encoding the eGFP fluorescent protein was injected into the lumbar spinal cord of wild-type mice.Three injections spaced approximately one millimeter apart produced a nearly continuous infection of lumbar spinal segments L3 to L5.Virus injection at a depth of 300 microns from the spinal surface leads to predominant infection of cells in the spinal cord dorsal horn. However, infected cells could also be found in the ventral horn. A cre dependent flex vector expressing eGFP was injected into the spinal cord of GlyT2:Cre transgenic mice.This resulted in more restricted eGFP expression reflecting the distribution of GLYT2 positive neurons. Following this protocol will allow targeting of three consecutive spine segments. We found that this is sufficient to obtain robust behavior results.This technique will allow studying the function of specific neuron and cell populations and sensory pathways.

adeno-associated-virus-mediated-transgene-expression-genetically

Research

JoVE Journal

Neuroscience

17.7K vues.  University of Zurich. The overall goal of intraspinal delivery of recombinant adeno-associated viruses is to enable the histological labeling and functional manipulation of genetically defined neurons in the dorsal spinal cord. This method can help answer key questions in the pain field, such as which neuronal circuits are required for the perception of different pain modalities. The main advantage of this technique is that genetically labeled neurons can be manipulated in a specially restricted and temporally con...