We are grateful to all the members of the Dunnwald Lab who have contributed to the optimization of this protocol over the years, and to Gina Schatteman whose persistence in promoting the use of serial sectioning for wound analysis made its creation possible. This work was supported by funding from NIH/NIAMS to Martine Dunnwald (AR067739).

All experiments were completed in accordance and compliance with federal regulations and University of Iowa policy and procedures have been approved by the University of Iowa IACUC.
1. Animals and husbandry
<ol>
	<li>Use adult mice of the desired mouse line at 8-10 weeks of age when the hair follicle stage is in telogen.</li>
	<li>On the day of surgery, separate mice into clean cages and individually house to minimize wound disruption.</li>
</ol>
2. Surgery
<p class...

<ol>
	<li>Eming, S. A., Martin, P., Tomic-Canic, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wound+repair+and+regeneration:+mechanisms,+signaling,+and+translation.">Wound repair and regeneration: mechanisms, signaling, and translation.</a> Science Translational Medicine. 6 (265), (2014).</li><li>Park, 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=Tissue-scale+coordination+of+cellular+behaviour+promotes+epidermal+wound+repair+in+live+mice.">Tissue-scale coordination of cellular behaviour promotes epidermal wound repair in live mice.</a> Nature Cell Biology. 19 (2), 155-163 (2017).</li><li>Gurtner, G. C., Werner, S., Barrandon, Y., Longaker, M. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wound+repair+and+regeneration.">Wound repair and regeneration.</a> Nature. 453 (7193), 314-321 (2008).</li><li>Ansell, D. M., Campbell, L., Thomason, H. A., Brass, A., Hardman, M. 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+statistical+analysis+of+murine+incisional+and+excisional+acute+wound+models.">A statistical analysis of murine incisional and excisional acute wound models.</a> Wound Repair Regeneration. 22 (2), 281-287 (2014).</li><li>Elliot, S., Wikramanayake, T. C., Jozic, I., Tomic-Canic, 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+Modeling+Conundrum:+Murine+Models+for+Cutaneous+Wound+Healing.">A Modeling Conundrum: Murine Models for Cutaneous Wound Healing.</a> Journal of Investigative Dermatology. 138 (4), 736-740 (2018).</li><li>Crowe, M. J., Doetschman, T., Greenhalgh, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Delayed+wound+healing+in+immunodeficient+TGF-beta+1+knockout+mice.">Delayed wound healing in immunodeficient TGF-beta 1 knockout mice.</a> Journal of Investigative Dermatology. 115 (1), 3-11 (2000).</li><li>Pietramaggiori, 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=Improved+cutaneous+healing+in+diabetic+mice+exposed+to+healthy+peripheral+circulation.">Improved cutaneous healing in diabetic mice exposed to healthy peripheral circulation.</a> Journal of Investigative Dermatology. 129 (9), 2265-2274 (2009).</li><li>Cold Spring Harbor. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Paraformaldehyde+in+PBS.">Paraformaldehyde in PBS.</a> Cold Spring Harbor Protocols. 1 (1), (2006).</li><li>Gerharz, 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=Morphometric+analysis+of+murine+skin+wound+healing:+standardization+of+experimental+procedures+and+impact+of+an+advanced+multitissue+array+technique.">Morphometric analysis of murine skin wound healing: standardization of experimental procedures and impact of an advanced multitissue array technique.</a> Wound Repair Regeneration. 15 (1), 105-112 (2007).</li><li>Colwell, A. S., Krummel, T. M., Kong, W., Longaker, M. T., Lorenz, H. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skin+wounds+in+the+MRL/MPJ+mouse+heal+with+scar.">Skin wounds in the MRL/MPJ mouse heal with scar.</a> Wound Repair Regeneration. 14 (1), 81-90 (2006).</li><li>Le, 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=Transforming+growth+factor+beta+3+is+required+for+proper+excisional+wound+repair+in+vivo.">Transforming growth factor beta 3 is required for proper excisional wound repair in vivo.</a> PLoS One. 7 (10), 48040 (2012).</li><li>Sato, T., Yamamoto, M., Shimosato, T., Klinman, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Accelerated+wound+healing+mediated+by+activation+of+Toll-like+receptor+9.">Accelerated wound healing mediated by activation of Toll-like receptor 9.</a> Wound Repair Regeneration. 18 (6), 586-593 (2010).</li><li>Martin, P., Leibovich, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inflammatory+cells+during+wound+repair:+the+good,+the+bad+and+the+ugly.">Inflammatory cells during wound repair: the good, the bad and the ugly.</a> Trends in Cell Biology. 15 (11), 599-607 (2005).</li><li>Shaw, T. J., Martin, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wound+repair:+a+showcase+for+cell+plasticity+and+migration.">Wound repair: a showcase for cell plasticity and migration.</a> Current Opinion in Cell Biology. 42, 29-37 (2016).</li><li>Hoffman, M., Monroe, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low+intensity+laser+therapy+speeds+wound+healing+in+hemophilia+by+enhancing+platelet+procoagulant+activity.">Low intensity laser therapy speeds wound healing in hemophilia by enhancing platelet procoagulant activity.</a> Wound Repair Regeneration. 20 (5), 770-777 (2012).</li><li>Tomasek, J. J., Gabbiani, G., Hinz, B., Chaponnier, C., Brown, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Myofibroblasts+and+mechano-regulation+of+connective+tissue+remodelling.">Myofibroblasts and mechano-regulation of connective tissue remodelling.</a> Nature Reviews Molecular Cell Biology. 3 (5), 349-363 (2002).</li><li>Uchiyama, 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=SOX2+Epidermal+Overexpression+Promotes+Cutaneous+Wound+Healing+via+Activation+of+EGFR/MEK/ERK+Signaling+Mediated+by+EGFR+Ligands.">SOX2 Epidermal Overexpression Promotes Cutaneous Wound Healing via Activation of EGFR/MEK/ERK Signaling Mediated by EGFR Ligands.</a> Journal of Investigative Dermatology. 139 (8), 1809-1820 (2019).</li><li>Sen, C. 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=Human+skin+wounds:+a+major+and+snowballing+threat+to+public+health+and+the+economy.">Human skin wounds: a major and snowballing threat to public health and the economy.</a> Wound Repair Regeneration. 17 (6), 763-771 (2009).</li><li>Rhea, 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=Interferon+regulatory+factor+6+is+required+for+proper+wound+healing+in+vivo.">Interferon regulatory factor 6 is required for proper wound healing in vivo.</a> Developmental Dynamics. 249 (4), 509-522 (2020).</li></ol>

The authors declare that they have no competing financial interests.

The bilateral excisional wound model is a highly customizable procedure which can be used to study many different aspects of wound healing. Before beginning a wound healing project, investigators should perform a power analysis to determine the number of wounds needed to detect a defect of a particular effect size. Inconsistencies exist within the literature on whether individual mice or wounds should be used as biological replicates, however, a recent study showed that there is no significant correlation between two wou...

Cutaneous wound healing is a complex biological process with sequentially overlapping phases. It requires the coordination of cellular and molecular processes that are temporally and spatially regulated in order to restore the barrier function of the damaged epithelium. In the first phase, inflammation, neutrophils and macrophages migrate into the wound, mobilizing local and systemic defenses1. Following and overlapping the inflammatory phase is the proliferation stage. Fibroblasts begin rapidly proliferating and migrating into the granulation tissue. Keratinocytes away from the leading edge directionally proliferate towards the wound as differentiated keratinocytes in the leading edge migrate to re-epithelialize the wound2. Finally, the remodeling and maturation phase begins, during which fibroblasts in the granulation tissue start to synthesize and deposit collagen. The remodeling and organization of the new matrix can last up to 1 year following injury3. Due to the complexity of overlapping events involving cross-talk between multiple cell types, and despite years of research, many of the cellular and molecular mechanisms underlying wound healing remain poorly understood.
The mouse model is the predominant mammalian model for investigating mechanisms of wound healing due to their ease of use, relatively low cost and genetic manipulability1,4,5. Although different types of wounds have been described in the murine model, the most common is an excisional wound (either bilateral punch or direct punch biopsy), followed by incisional wound models4. The excisional wound model has a distinct advantage over the incisional model as it inherently generates control tissue that has not undergone the healing process. The punch biopsy tissue that is excised as part of the surgical protocol can be processed in the same manner as the wounded tissue and used to establish the homeostatic conditions for a desired criterion. Excised control tissue may also be useful if assessing the effects of a skin pretreatment or confirming successful gene alteration at the time of injury4.
Healing parameters can be assessed by many different techniques, including planimetry or histology. However, planimetry can only evaluate visible characteristics of the wound, and due to the presence of a scab, often does not correlate to measurements of healing that are visualized by histology, thereby making histology the &#8220;gold standard&#8221; of analysis4. Despite histological analysis being the gold standard, it is most often performed on an arbitrary subset of the wound6,7. For instance, cutting the wound in &#8220;half&#8221; prior to embedding and sectioning the wound is currently common practice to reduce the time and resources spent on sectioning materials and data analysis. The method of morphometric analysis described in this protocol was developed to encompass the entire wound tissue, to accurately reflect the morphological characteristics of the wound, and to increase the likelihood of detecting wound healing defects with a small effect size. In this protocol, we detail a surgical method for generating the most commonly studied murine wound, the bilateral full-thickness excisional wound, as well as a detailed and rigorous method for histological analysis such is rarely used in the field.

<table>
	<tbody>
		<tr>
			<td>100% ethanol</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>70% ethanol</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>80% ethanol</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>95% ethanol</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Alcohol Prep</td>
			<td>NOVAPLUS</td>
			<td>V9100</td>
			<td>70% Isopropyl alcohol, sterile</td>
		</tr>
		<tr>
			<td>Ammonium hydroxide</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Biopsy pads</td>
			<td>Cellpath</td>
			<td>22-222-012</td>
			<td></td>
		</tr>
		<tr>
			<td>Black plastic sheet</td>
			<td></td>
			<td></td>
			<td>Something firm yet manipulatable about the size of a sheet of paper</td>
		</tr>
		<tr>
			<td>Brightfield microscope</td>
			<td></td>
			<td></td>
			<td>With digital acquisition capabilities and a 4X objective</td>
		</tr>
		<tr>
			<td>Cotton tipped applicators</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Coverslips</td>
			<td></td>
			<td></td>
			<td>22 x 60 #1</td>
		</tr>
		<tr>
			<td>Dental wax sheets</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Digital camera</td>
			<td></td>
			<td></td>
			<td>Include a ruler for scale, if applicable</td>
		</tr>
		<tr>
			<td>Dissection teasing needle (straight)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Embedding molds</td>
			<td></td>
			<td></td>
			<td>22 x 22 x 12</td>
		</tr>
		<tr>
			<td>Embedding rings</td>
			<td>Simport Scientific Inc.</td>
			<td>M460</td>
			<td></td>
		</tr>
		<tr>
			<td>Eosin Y</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Glacial acetic acid</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Hair clipper</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Heating pad</td>
			<td>Conair</td>
			<td></td>
			<td>Moist dry Heating Pad</td>
		</tr>
		<tr>
			<td>Hematoxylin</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Microtome</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Microtome blades</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Paint brushes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Paraffin Type 6</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Permount</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate buffer solution (PBS)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Povidone-iodine</td>
			<td>Aplicare</td>
			<td>82-255</td>
			<td></td>
		</tr>
		<tr>
			<td>Processing cassette</td>
			<td>Simport Scientific Inc.</td>
			<td>M490-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Razor blades</td>
			<td>ASR</td>
			<td></td>
			<td>.009 Regular Duty</td>
		</tr>
		<tr>
			<td>Scalpel blades #10</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Scalpel handle</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sharp surgical scissors</td>
			<td></td>
			<td></td>
			<td>sterile for surgery</td>
		</tr>
		<tr>
			<td>Skin biopsy punches</td>
			<td></td>
			<td></td>
			<td>Size as determined by researcher</td>
		</tr>
		<tr>
			<td>Slide boxes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Slide warmers</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Superfrosted microscope slides</td>
			<td>Fisher Scientific</td>
			<td>22 037 246</td>
			<td></td>
		</tr>
		<tr>
			<td>Temperature control water bath</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue embedding station</td>
			<td></td>
			<td></td>
			<td>Minimum of a paraffin dispenser and a cold plate</td>
		</tr>
		<tr>
			<td>Tissue processor</td>
			<td></td>
			<td></td>
			<td>Minimum of a oven with a vacuum pump</td>
		</tr>
		<tr>
			<td>Triple antibiotic opthalmic ointment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>tweezers, curved tip</td>
			<td></td>
			<td></td>
			<td>sterile for surgery</td>
		</tr>
		<tr>
			<td>tweezers, tapered tip</td>
			<td></td>
			<td></td>
			<td>sterile for surgery</td>
		</tr>
		<tr>
			<td>WypAll X60</td>
			<td>Kimberly-Clark</td>
			<td>34865</td>
			<td></td>
		</tr>
	</tbody>
</table>

murine excisional wound healing model and histological morphometric wound analysis

The murine excisional wound model has been used extensively to study each of the sequentially overlapping phases of wound healing: inflammation, proliferation and remodeling. Murine wounds have a histologically well-defined and easily recognizable wound bed over which these different phases of the healing process are measurable. Within the field, it is common to use an arbitrarily defined &#8220;middle&#8221; of the wound for histological analyses. However, wounds are a three-dimensional entity and often not histologically symmetrical, supporting the need for a well-defined and robust method of quantification to detect morphometric defects with a small effect size. In this protocol, we describe the procedure for creating bilateral, full-thickness excisional wounds in mice as well as a detailed instruction on how to measure morphometric parameters using an image processing program on select serial sections. The two-dimension measurements of wound length, epidermal length, epidermal area, and wound area are used in combination with the known distance between sections to extrapolate the three-dimension epidermal area covering the wound, overall wound area, epidermal volume and wound volume. Although this detailed histological analysis is more time and resource consuming than conventional analyses, its rigor increases the likelihood of detecting novel phenotypes in an inherently complex wound healing process.

Figure 5 depicts the range in measured and calculated values obtained by performing morphometric analysis on wild-type wounds generated in different mouse strains by multiple surgeons and analyzed by different individuals. Wild-type mice from different strains can display statistical differences as described both in our studies and in the literature9,10. Based on these representative results, we recommend that, within one study, mice...

Watch this Scientific Journal Video about Murine Excisional Wound Healing Model and Histological Morphometric Wound Analysis at JoVE.com

Murine Excisional Wound Healing Model and Histological Morphometric Wound Analysis

This protocol describes how to generate bilateral, full-thickness excisional wounds in mice and how to subsequently monitor, harvest, and prepare the wounds for morphometric analysis. Included is an in-depth description of how to use serial histological sections to define, precisely quantify and detect morphometric defects.

The murine excisional wound model has been used extensively to study each of the sequentially overlapping phases of wound healing: inflammation, ...

This protocol uses histological analysis to obtain robust morphometric measurements of mouse excisional wounds. Using this technique, we can analyze the entire wound using a subset of serial sections, allowing us to more accurately detect defects that might otherwise be missed. Demonstrating the procedure will be Lindsey Rhea, a research associate from my laboratory.After confirming a lack of response to pedal reflex in an anesthetized adult mouse, apply ointment to the animal's eyes and use an electric razor clipper in a caudal-rostral motion to remove the fur on the back of the mouse at the shoulder level. Use a razor blade held at a 20 degree angle from the back in a rostral-caudal motion to remove any remaining hair from the exposed skin, then clean the skin with one povidone iodine and one 70%isopropyl alcohol prep pad wipe. For wound induction, drape a clean paper-based towel onto a flat surface covered with dental wax and position the mouse onto the towel in the prone position.Pinch the skin of the mouse between the shoulder blades along the dorsal midline and pull the sandwiched skin fold away from the body. Switching the mouse to a side-lying position, place a biopsy punch of the desired wound size as close to the body as possible and allow the skin to relax. Press down on the punch using a rocking motion to puncture all of the layers of the skin and remove the punch biopsies from the wound using sterile scissors and tweezers to free the punch from the surrounding skin as necessary.Then allow the mouse to recover with monitoring and analgesia. For morphometric analysis of the wound bed, open a digital stained wound image. To set the scale and measurement preferences, under Analyze, select Set Scale and enter the distance in pixels, the known distance, and the unit of length.Select Global and OK to keep the scale the same for each open image and select Analyze and Set Measurements to confirm that the area box is checked. To measure the wound length, select freehand, and use the tool to trace along the dermal-epidermal junction, starting from the last hair follicle of the uninjured tissue on one side of the wound to the first hair follicle of the uninjured tissue on the other side. If the epidermis does not cover the entire wound, follow the dermal-epidermal junction on one side of the wound where the migrating tongue ends and continue following the superior aspect of the granulation tissue or the junction between the granulation tissue and the scab until the migrating tongue and the first hair follicle of the uninjured tissue on the other side of the wound are reached.Then click Analyze and Measure. The length of the measurement will appear in the same units as set in the scale. If the epidermis does not cover the entire wound, measure the distance between each epidermal leading edge following the superior aspect of the granulation tissue or the junction between the granulation tissue and the scab to the first hair follicle.To measure the wound area, use the freehand tool to trace along the superior aspect of the epidermis or the superior aspect of the granulation tissue starting from the last hair follicle of the uninjured tissue on one side of the wound to the first hair follicle of the uninjured tissue on the other side. Continue to trace vertically along the hair follicle into the granulation tissue. Once the opposite hair follicle and adipose tissue or muscle are reached, follow the inferior border of the granulation tissue to the opposite side of the wound and join the starting point along the hair follicle to close the area.If the wound is not fully epithelialized, trace along the superior aspect of the epidermis until the leading edge and return to the starting point following the dermal-epidermal junction. As illustrated, when taking 2D measurements throughout the entire wound, we were able to calculate parameters not possible with 2D analysis on the middle of the wound only, which is a commonly used method in the field. In this experiment, 2D measurements of wound area were used and averaged over the whole wound or a middle subset of the wound and revealed no significant difference between experimental groups or the methods of analysis.The calculated wound volume, however, was significantly different between the experimental groups, demonstrating the importance of an in-depth histological analysis of wound healing parameters. Generating consistently sized wounds for histological analysis and performing rigorous serial sectioning are critical for an accurate morphometric analysis. Unstained sections can be used for immunofluorescence or Masson's trichrome staining to measure other aspects of wound healing while flash frozen wounds can be used alongside morphometry for quantitative protein analysis.

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Developmental Biology

11.2K Views.  University of Iowa. This protocol uses histological analysis to obtain robust morphometric measurements of mouse excisional wounds. Using this technique, we can analyze the entire wound using a subset of serial sections, allowing us to more accurately detect defects that might otherwise be missed. Demonstrating the procedure will be Lindsey Rhea, a research associate from my laboratory.After confirming a lack of response to pedal reflex in an anesthetized adult mouse, apply ointment to the animal's eyes a...