Name: functional evaluation of olfactory pathways in living xenopus tadpoles
Uploaded: 2018-12-11T13:00:00
Description: Watch this Scientific Journal Video about Functional Evaluation of Olfactory Pathways in Living Xenopus Tadpoles at JoVE.com

This work was supported by grants from El Ministerio de Econom&#237;a y Competitividad (MINECO; SAF2015-63568-R) cofunded by the European Regional Development Fund (ERDF), by competitive research awards from the M. G. F. Fuortes Memorial Fellowship, the Stephen W. Kuffler Fellowship Fund, the Laura and Arthur Colwin Endowed Summer Research Fellowship Fund, the Fischbach Fellowship, and the Great Generation Fund of the Marine Biological Laboratory and the National Xenopus Resource RRID:SCR_013731 (Woods Hole, MA) where a portion of this work was conducted. We also thank CERCA Program/ Generalitat de Catalunya for institutional support. A.L. is a Serra H&#250;nter fellow.

All procedures were approved by the animal research ethics committee at University of Barcelona.
NOTE: X. tropicalis and X. laevis tadpoles are reared according to standard methods13,14. Tadpole water is prepared by adding commercial salts (see Table of Materials) to water obtained by reverse osmosis. Conductivity is adjusted to &#8764;700 &#181;S and &#8764;1,400 &#181;S for X. t...

<ol>
	<li>Hellsten, 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=The+genome+of+the+Western+clawed+frog+Xenopus+tropicalis.">The genome of the Western clawed frog Xenopus tropicalis.</a> Science. 328 (5978), 633-636 (2010).</li><li>Session, A. 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=Genome+evolution+in+the+allotetraploid+frog+Xenopus+laevis.">Genome evolution in the allotetraploid frog Xenopus laevis.</a> Nature. 538 (7625), 336-343 (2016).</li><li>Zhang, L. I., Tao, H. W., Holt, C. E., Harris, W. A., Poo, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+critical+window+for+cooperation+and+competition+among+developing+retinotectal+synapses.">A critical window for cooperation and competition among developing retinotectal synapses.</a> Nature. 395 (6697), 37-44 (1998).</li><li>Li, J., Erisir, A., Cline, H. <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+time-lapse+imaging+and+serial+section+electron+microscopy+reveal+developmental+synaptic+rearrangements.">In vivo time-lapse imaging and serial section electron microscopy reveal developmental synaptic rearrangements.</a> Neuron. 69 (2), 273-286 (2011).</li><li>Dietrich, H., Glasauer, S., Straka, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+Organization+of+Vestibulo-Ocular+Responses+in+Abducens+Motoneurons.">Functional Organization of Vestibulo-Ocular Responses in Abducens Motoneurons.</a> Journal of Neuroscience. 37 (15), 4032-4045 (2017).</li><li>Buhl, E., Roberts, A., Soffe, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+a+trigeminal+sensory+nucleus+in+the+initiation+of+locomotion.">The role of a trigeminal sensory nucleus in the initiation of locomotion.</a> Journal of Physiology. 590, 2453-2469 (2012).</li><li>Junek, S., Kludt, E., Wolf, F., Schild, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Olfactory+coding+with+patterns+of+response+latencies.">Olfactory coding with patterns of response latencies.</a> Neuron. 67 (5), 872-884 (2010).</li><li>Stout, R. P., Graziadei, P. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+the+olfactory+placode+on+the+development+of+the+brain+in+Xenopus+laevis+(Daudin).+I.+Axonal+growth+and+connections+of+the+transplanted+olfactory+placode.">Influence of the olfactory placode on the development of the brain in Xenopus laevis (Daudin). I. Axonal growth and connections of the transplanted olfactory placode.</a> Neuroscience. 5 (12), 2175-2186 (1980).</li><li>Yoshino, J., Tochinai, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+regeneration+of+the+olfactory+bulb+requires+reconnection+to+the+olfactory+nerve+in+Xenopus+larvae.">Functional regeneration of the olfactory bulb requires reconnection to the olfactory nerve in Xenopus larvae.</a> Development, Growth &amp; Differentiation. 48 (1), 15-24 (2006).</li><li>Terni, B., Pacciolla, P., Masanas, H., Gorostiza, P., Llobet, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tight+temporal+coupling+between+synaptic+rewiring+of+olfactory+glomeruli+and+the+emergence+of+odor-guided+behavior+in+Xenopus+tadpoles.">Tight temporal coupling between synaptic rewiring of olfactory glomeruli and the emergence of odor-guided behavior in Xenopus tadpoles.</a> Journal of Comparative Neurology. 525 (17), 3769-3783 (2017).</li><li>Goda, T., 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=Genetic+screens+for+mutations+affecting+development+of+Xenopus+tropicalis.">Genetic screens for mutations affecting development of Xenopus tropicalis.</a> PLOS Genetics. 2 (6), 91 (2006).</li><li>Nakayama, T., 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=Simple+and+efficient+CRISPR/Cas9-mediated+targeted+mutagenesis+in+Xenopus+tropicalis.">Simple and efficient CRISPR/Cas9-mediated targeted mutagenesis in Xenopus tropicalis.</a> Genesis. 51 (12), 835-843 (2013).</li><li>Jafkins, A., Abu-Daya, A., Noble, A., Zimmerman, L. B., Guille, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Husbandry+of+Xenopus+tropicalis.">Husbandry of Xenopus tropicalis.</a> Methods in Molecular Biology. 917, 17-31 (2012).</li><li>Sive, H. L., Grainger, R. M., Harland, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Early Development of Xenopus laevis. A Laboratory manual. , (2000).</li><li>Nieuwkoop, P. D., Faber, 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> Normal table of Xenopus laevis (Daudin). A systematical and chronological survey of the development from the fertilized egg till the end of metamorphosis. , (1956).</li><li>Xu, H., Dude, C. M., Baker, C. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fine-grained+fate+maps+for+the+ophthalmic+and+maxillomandibular+trigeminal+placodes+in+the+chick+embryo.">Fine-grained fate maps for the ophthalmic and maxillomandibular trigeminal placodes in the chick embryo.</a> Developmental Biology. 317 (1), 174-186 (2008).</li><li>Friedrich, R. W., Korsching, S. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combinatorial+and+chemotopic+odorant+coding+in+the+zebrafish+olfactory+bulb+visualized+by+optical+imaging.">Combinatorial and chemotopic odorant coding in the zebrafish olfactory bulb visualized by optical imaging.</a> Neuron. 18 (5), 737-752 (1997).</li><li>Ishibashi, S., Cliffe, R., Amaya, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+efficient+bi-allelic+mutation+rates+using+TALENs+in+Xenopus+tropicalis.">Highly efficient bi-allelic mutation rates using TALENs in Xenopus tropicalis.</a> Biology Open. 1 (12), 1273-1276 (2012).</li><li>Meijering, E., Dzyubachyk, O., Smal, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+for+cell+and+particle+tracking.">Methods for cell and particle tracking.</a> Methods in Enzymology. 504, 183-200 (2012).</li><li>Nussbaum-Krammer, C. I., Neto, M. F., Brielmann, R. M., Pedersen, J. S., Morimoto, R. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Investigating+the+spreading+and+toxicity+of+prion-like+proteins+using+the+metazoan+model+organism+C.+elegans.">Investigating the spreading and toxicity of prion-like proteins using the metazoan model organism C. elegans.</a> Journalof Visualized Experiments. (95), e52321 (2015).</li><li>Koide, T., 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=Olfactory+neural+circuitry+for+attraction+to+amino+acids+revealed+by+transposon-mediated+gene+trap+approach+in+zebrafish.">Olfactory neural circuitry for attraction to amino acids revealed by transposon-mediated gene trap approach in zebrafish.</a> Proceedings of the National Academy of Sciences of the United States of America. 106 (24), 9884-9889 (2009).</li><li>Love, N. 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=pTransgenesis:+a+cross-species,+modular+transgenesis+resource.">pTransgenesis: a cross-species, modular transgenesis resource.</a> Development. 138 (24), 5451-5458 (2011).</li><li>Tandon, P., Conlon, F., Furlow, J. D., Horb, M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expanding+the+genetic+toolkit+in+Xenopus:+Approaches+and+opportunities+for+human+disease+modeling.">Expanding the genetic toolkit in Xenopus: Approaches and opportunities for human disease modeling.</a> Developmental Biology. 426 (2), 325-335 (2017).</li><li>Pratt, K. G., Khakhalin, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+human+neurodevelopmental+disorders+in+the+Xenopus+tadpole:+from+mechanisms+to+therapeutic+targets.">Modeling human neurodevelopmental disorders in the Xenopus tadpole: from mechanisms to therapeutic targets.</a> Disease Models &amp; Mechanisms. 6 (5), 1057-1065 (2013).</li><li>Truszkowski, T. L., 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=Fragile+X+mental+retardation+protein+knockdown+in+the+developing+Xenopus+tadpole+optic+tectum+results+in+enhanced+feedforward+inhibition+and+behavioral+deficits.">Fragile X mental retardation protein knockdown in the developing Xenopus tadpole optic tectum results in enhanced feedforward inhibition and behavioral deficits.</a> Neural Development. 11 (1), 14 (2016).</li><li>Hassenkl&#246;ver, T., Manzini, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Olfactory+wiring+logic+in+amphibians+challenges+the+basic+assumptions+of+the+unbranched+axon+concept.">Olfactory wiring logic in amphibians challenges the basic assumptions of the unbranched axon concept.</a> Journal of Neuroscience. 33 (44), 17247-17252 (2013).</li><li>Haas, K., Sin, W. C., Javaherian, A., Li, Z., Cline, H. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-cell+electroporation+for+gene+transfer+in+vivo.">Single-cell electroporation for gene transfer in vivo.</a> Neuron. 29 (3), 583-591 (2001).</li><li>Sild, M., Van Horn, M. R., Schohl, A., Jia, D., Ruthazer, 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=Neural+Activity-Dependent+Regulation+of+Radial+Glial+Filopodial+Motility+Is+Mediated+by+Glial+cGMP-Dependent+Protein+Kinase+1+and+Contributes+to+Synapse+Maturation+in+the+Developing+Visual+System.">Neural Activity-Dependent Regulation of Radial Glial Filopodial Motility Is Mediated by Glial cGMP-Dependent Protein Kinase 1 and Contributes to Synapse Maturation in the Developing Visual System.</a> Journal of Neuroscience. 36 (19), 5279-5288 (2016).</li><li>McDiarmid, R., Altig, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Tadpoles: The biology of anuran larvae. , 149-169 (1999).</li><li>Heerema, J. L., 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=Behavioral+and+molecular+analyses+of+olfaction-mediated+avoidance+responses+of+Rana+(Lithobates)+catesbeiana+tadpoles:+Sensitivity+to+thyroid+hormones,+estrogen,+and+treated+municipal+wastewater+effluent.">Behavioral and molecular analyses of olfaction-mediated avoidance responses of Rana (Lithobates) catesbeiana tadpoles: Sensitivity to thyroid hormones, estrogen, and treated municipal wastewater effluent.</a> Hormones and Behavior. 101, 85-93 (2018).</li><li>Gaudin, A., Gascuel, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=3D+atlas+describing+the+ontogenic+evolution+of+the+primary+olfactory+projections+in+the+olfactory+bulb+of+Xenopus+laevis.">3D atlas describing the ontogenic evolution of the primary olfactory projections in the olfactory bulb of Xenopus laevis.</a> Journal of Comparative Neurology. 489 (4), 403-424 (2005).</li><li>Scheidweiler, U., Nezlin, L., Rabba, J., M&#252;ller, B., Schild, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Slice+culture+of+the+olfactory+bulb+of+Xenopus+laevis+tadpoles.">Slice culture of the olfactory bulb of Xenopus laevis tadpoles.</a> Chemical Senses. 26 (4), 399-407 (2001).</li><li>Manzini, I., Schild, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Classes+and+narrowing+selectivity+of+olfactory+receptor+neurons+of+Xenopus+laevis+tadpoles.">Classes and narrowing selectivity of olfactory receptor neurons of Xenopus laevis tadpoles.</a> Journal of General Physiology. 123 (2), 99-107 (2004).</li><li>Kludt, E., Okom, C., Brinkmann, A., Schild, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integrating+temperature+with+odor+processing+in+the+olfactory+bulb.">Integrating temperature with odor processing in the olfactory bulb.</a> Journal of Neuroscience. 35 (20), 7892-7902 (2015).</li></ol>

This paper describes techniques that are useful to investigate the functionality of olfactory pathways in living Xenopus tadpoles. The current protocol is particularly useful for those laboratories that work, or have access to Xenopus; however, it is also interesting for those researchers studying the cellular and molecular bases of neuronal regeneration and repair. Results obtained in Xenopus can be combined with data gathered in other vertebrate models to identify conserved mechanisms. The me...

Xenopus tadpoles constitute an excellent animal model to study the normal function of the nervous system. Transparency, a fully sequenced genome1,2, and accessibility to surgical, electrophysiological and imaging techniques are unique properties of Xenopus larvae that allow investigating neuronal functions in vivo3. Some of the multiple experimental possibilities of this animal model are illustrated by the thorough studies performed on tadpole sensory and motor systems4,5,6. A particularly well-suited neuronal circuit to study many aspects of information processing at the level of synapses is the Xenopus tadpole olfactory system7. Firstly, its synaptic connectivity is well defined: olfactory receptor neurons (ORNs) project to the olfactory bulb and establish synaptic contacts with dendrites of mitral/tufted cells within glomeruli to generate odor maps. Secondly, its ORNs are continuously generated by neurogenesis throughout life to maintain the functionality of olfactory pathways8. And thirdly, because the olfactory system shows a great regenerative capability, Xenopus tadpoles are able to entirely reform their olfactory bulb after ablation9.
In this paper, we describe approaches that combine imaging of olfactory glomeruli in living tadpoles with behavioral experiments to study the functionality of olfactory pathways. The methods detailed here were used to study the functional recovery of glomerular connectivity in the olfactory bulb after olfactory nerve transection10. Data obtained in Xenopus tadpoles are representative of vertebrates since olfactory processing is evolutionary conserved.
The methods described are exemplified using X. tropicalis but they can easily be implemented in X. laevis. Despite the larger size of adult X. laevis, both species are remarkably similar during tadpole stages. The main differences reside at the genomic level. X. laevis displays poor genetic tractability, mostly determined by its allotetraploid genome and long generation time (approximately 1 year). In contrast, X. tropicalis is more amenable to genetic modifications due to its shorter generation time (5&#8211;8 months) and diploid genome. The representative experiments are illustrated for wild-type animals and three different transgenic lines: Hb9:GFP (X. tropicalis), NBT:GFP (X. tropicalis) and tubb2:GFP (X. laevis).
The methodologies outlined in the current work should be considered alongside the genetic progresses in the Xenopus field. The simplicity and easy implementation of the techniques presented makes them particularly useful for evaluating already described mutants11, as well as Xenopus lines generated by CRISPR-Cas9 technology12. We also describe a surgical procedure used to transect olfactory nerves that can be implemented in any laboratory having access to Xenopus tadpoles. The approaches used for evaluating presynaptic calcium responses and olfactory-guided behavior require specific equipment, albeit available at a moderate cost. Methodologies are presented in a simple form to promote their use in research groups and could set the bases of more complex assays either by implementing improvements or by the association to other techniques, i.e., histological or genetic approaches.

<table border="0" cellpadding="0" cellspacing="0" style="width:1133px;" width="1132">
	<tbody>
		<tr height="40">
			<td height="40" style="height:40px;width:335px;">Salts for aquariums (Instant Ocean Salt)</td>
			<td style="width:359px;">Tecniplast</td>
			<td style="width:143px;">XPSIO25R</td>
			<td style="width:297px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Tricaine (Ethyl 3-aminobenzoate methanesulfonate)</td>
			<td>Sigma-Aldrich</td>
			<td>E10521</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Tweezers #5 (tip 0.025 x 0.005 mm)</td>
			<td>World Precision Instruments</td>
			<td>501985</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Vannas Scissors (tip 0.015 x 0.015)</td>
			<td>World Precision Instruments</td>
			<td>501778</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Whatman qualitative filter paper</td>
			<td>Fisher Scientific</td>
			<td>WH3030917</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">X. laevis tubb2-GFP</td>
			<td>National Xenopus Resource (NXR), RRID:SCR_013731</td>
			<td>NXR_0.0035</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">X.tropicalis NBT-GFP</td>
			<td>European Xenopus Resource Center (EXRC) RRID:SCR_007164</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">CellTracker CM-DiI</td>
			<td>ThermoFisher Scientific</td>
			<td>C-7001</td>
			<td style="width:297px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Calcium Green dextran, Potassium Salt, 10,000 MW, Anionic</td>
			<td>ThermoFisher Scientific</td>
			<td>C-3713</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Borosilicate capillaries for microinjection</td>
			<td>Sutter Instrument</td>
			<td>B100-75-10</td>
			<td>O.D.=1.0 mm., I.D.=0.75 mm.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Puller</td>
			<td>Sutter Instrument</td>
			<td>P-97</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Microinjector</td>
			<td>Parker Instruments</td>
			<td>Picospritzer III</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Sylgard-184</td>
			<td>Sigma-Aldrich</td>
			<td>761028-5EA</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Microfil micropipettes</td>
			<td style="width:359px;">World Precision Instruments</td>
			<td>MF28G-5</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Upright microscope</td>
			<td>Zeiss</td>
			<td>AxioImager-A1</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Master-8 stimulator</td>
			<td>A.M.P.I.</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">CCD Camera</td>
			<td>Hamamatsu</td>
			<td>Image EM</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Solenoid valves</td>
			<td>Warner Instruments</td>
			<td>VC-6 Six Channel system</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Dow Corning High Vacuum Grease</td>
			<td>VWR Scientific</td>
			<td>636082B</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Tubocurarine hydrochloride</td>
			<td>Sigma-Aldrich</td>
			<td>T2379</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CCD Camera</td>
			<td>Zeiss</td>
			<td>MRC-5 Camera</td>
			<td>Controlled by Zen software</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">camera lens</td>
			<td>Thorlabs</td>
			<td>MVL8ML3</td>
			<td>There are multiple possibilities that should be adapted to the camera model used</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Epoxy resin</td>
			<td>RS Components</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Manifold</td>
			<td>Warner Instruments</td>
			<td>MP-6 perfusion manifold</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Micromanipulator for local delivery of solutions</td>
			<td>Narishige</td>
			<td>MN-153</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mini magnetic clamps</td>
			<td>Warner Instruments</td>
			<td>MAG-7, MAG-6</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Polyethylene tubing</td>
			<td>Warner Instruments</td>
			<td>64-0755</td>
			<td>O.D.=1.57 mm., I.D.=1.14 mm.</td>
		</tr>
	</tbody>
</table>

functional evaluation of olfactory pathways in living xenopus tadpoles

Xenopus tadpoles offer a unique platform to investigate the function of the nervous system. They provide multiple experimental advantages, such as accessibility to numerous imaging approaches, electrophysiological techniques and behavioral assays. The Xenopus tadpole olfactory system is particularly well suited to investigate the function of synapses established during normal development or reformed after injury. Here, we describe methodologies to evaluate the processing of olfactory information in living Xenopus larvae. We outline a combination of in vivo measurements of presynaptic calcium responses in glomeruli of the olfactory bulb with olfactory-guided behavior assays. Methods can be combined with the transection of olfactory nerves to study the rewiring of synaptic connectivity. Experiments are presented using both wild-type and genetically modified animals expressing GFP reporters in central nervous system cells. Application of the approaches described to genetically modified tadpoles can be useful for unraveling the molecular bases that define vertebrate behavior.

In this paper, we present a combination of two complementary approaches to perform in vivo study of the functionality of the Xenopus tadpole olfactory system: i) a method for imaging presynaptic Ca2+ changes in the glomeruli of living tadpoles using a fluorescent calcium indicator, and ii) an odor guided behavioral assay that can be used to investigate the response to specific waterborne odorants. Since these approaches have been employed to evaluate the recov...

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Functional Evaluation of Olfactory Pathways in Living Xenopus Tadpoles

Xenopus tadpoles offer a unique platform to investigate the function of the nervous system in vivo. We describe methodologies to evaluate the processing of olfactory information in living Xenopus larvae in normal rearing conditions or after injury.

Functional Evaluation of Olfactory Pathways in Living Xenopus Tadpoles

Xenopus tadpoles offer a unique platform to investigate the function of the nervous system. They provide multiple experimental advantages, such as ...

This method can be useful to answer key questions in neurobiology fields such as how do presynaptic terminals function in vivo. The main advantage of this set of techniques is that we show complimentary approaches to asses the function of olfactory pathways using Xenopus tadpoles as animal model. Demonstrating this procedure will be myself, Beatrice Terni, and Paolo Pacciolla.Begin the transection procedure by wetting two pieces of cellulose qualitative filter paper in 0.02%MS2 22 anesthetic solution, and placing them under the dissecting scope. Then pick a tadpole from the tank and immerse it in a dish of anesthetic solution. The tadpole should stop swimming within two to four minutes.Check for proper anesthetization by the absence of a reaction to mechanical stimuli applied at the tail level using tweezers. Place the anesthetized tadpole on the filter paper under the scope. Position the animal with its dorsal side facing upward so brain structures can be visualized.For behavioral experiments, use veni scissors to transect both nerves to suppress all odorant information arriving to the olfactory bulb. Load a poled glass pipette with two microliters of calcium green one dextrine solution, and place it in the microinjector. Place an anesthetized tadpole under the dissecting microscope on filter paper, then move the tip of the pipette into the principal cavity of the nasal capsule, and deliver 0.15 to 0.3 microliters of the dye.Leave the tadpole in place for two to three minutes. Using a Pasteur pipette, drip 0.02%MS2 22 solution onto the more coddle parts of the animal to avoid drying. Transfer the animal to the recovery tank where the tadpole should recover normal swimming within 10 minutes or so.Observe florescence at the level of the glomerular layer of the olfactory bulb on the day after injection. Prepare an anesthetized tadpole for imaging by first removing the skin above the olfactory bulb. Use veni scissors to make a lateral incision on the tadpole's skin on the edge of the central nervous system at the level of the olfactory bulb.Avoid extending the cut to the tectum, which can be easily identified by the location of the optic nerve. Keep the animal moist by applying drops of 0.02%MS2 22 solution using a Pasteur pipette then pinch the cut skin using tweezers and pull it over the nervous system. Verify successful removal by the absence of melanocytes above the olfactory bulb.Place the tadpole into the well of the cell guard coated dish. Position a glass cover slip coated with high vacuum grease to cover the top of the tectum to the end of the tail. Ensure that the olfactory bulb and placodes remain exposed to the extracellular medium.Fill the pitri dish with Xenopus Ringer's solution containing 100 micromolar tubocurarine to prevent muscle contractions. Place the dish holding the tadpole under an upright microscope. Connect the reservoir containing Xenopus Ringer's solution with the dish using polyethylene tubing for continuous profusion of Xenopus Ringer's solution.Start perfusing Xenopus Ringer's solution. Maintain the level of the solution in the dish constant throughout the experiment. Continuously evaluate tadpole viability by observing blood circulation through the vessels.Begin live imaging by using a low magnification objective to visualize the tadpole. Move the micromanipulator axis to place the capillary delivering the odorant solution on the top of one nasal capsule, forming a 90 degree angle with the olfactory nerve. Find the olfactory bulb located ipsilaterally to the nasal capsule.Switch to a high-magnification water objective with a long working distance. Check the florescence emission by I.Glomerular structures should be obvious. Begin by pipetting 20 milliliters of fresh amino acid solution into an elevated reservoir.Then take six food deprived tadpoles from their housing tank, and place them in two liters of clean tadpole water to minimize the exposure to odorants. Place a modified six well dish on a white LED transilluminator. Fill each well with 10 milliliters of tadpole water.Place one tadpole per well, then leave to rest for at least three minutes. Start image acquisition and acquire movies that contain basal, stimulus, and recovery periods. An attractive response can be detected as a movement towards the nozzle delivering the solution of amino acids.Return animals to their tank after imaging. Tracking tadpole head positions within an area of 35 millimeters by 35 millimeters, or the equivalent size in pixels, allows a quantitative analysis of olfactory-guided behavior. The dotted line represents the proximal area to the odor solution inlet.Individual plots of tadpole movements are constructed using X Y coordinates obtained by image analysis. The extracted motility plots must faithfully reproduce video images. A region of interest of 8.75 millimeter radius centered on the solution inlet is used to classify the proximity of the animals to the odorant source.More time spent in the vicinity of the odorant's nozzle indicates positive tropism. Time spent by tadpoles near the nozzle during defined periods, for example, 15 second intervals, allows identification of the ability to detect amino acid solutions. The overall behavior of a population of tadpoles can be obtained by plotting the distribution of individual data.Positive tropism can be detected when the amino acid solution is prepared at one millimolar or 160 micromolar. Animals do not respond to water application. Following this procedure, other methods like histological techniques or electrophysiology, can be performed to answer additional questions like the alteration of synaptic properties after injury.After its development, this technique paved the way for researchers in the field of neurobiology to explore the processing of olfactory information in Xenopus tadpole.

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Neuroscience

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