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Passive narcosis for anesthesia induction in cotton rats (Sigmodon hispidus)


Cotton rats (Sigmodon hispidus) are widely used as animal models for infectious disease and immunological research. They emulate many aspects of human disease pathogenesis, and the introduction of cotton rat-specific immunological reagents, cell lines and sequencing of relevant genes have all helped to increase the popularity of this disease model. However, the use of cotton rats is problematic owing to their propensity for aggressive responses when handled, which can lead to escape, increased stress to the animals, and bites to staff. When cotton rats are co-housed, which is recommended under current social housing guidelines, these risks are increased. Here, we describe a method of isoflurane anesthesia induction in the home cage that reduces the risk of animal escape, minimizes stress during induction, and provides additional safety for staff. The method uses inexpensive materials that are widely available and can be easily disinfected. Our method also eliminates the need for expensive and cumbersome machines traditionally used with anesthetic chambers, and uses a minimal amount of inhalant anesthetic, saving resources and protecting staff from inhalation of leaked gas.

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Figure 1: Image of typical filter-top isolation cages, each containing a single housing structure and a pair of cotton rats, were used for the experiment.
Figure 2
Figure 3: Image of 2-3 cotton balls inserted into the bottom of each tube just below the level of the holes shown in Figure 2.
Figure 4: Image of 2-3 mL of isoflurane slowly added via syringe or disposable pipette to each tube to prevent spillage and allow absorption into the cotton balls.
Figure 5: The cover from the isolation cage is quickly removed and the housing structure then covered with the anesthesia box being careful to ensure that both cotton rats (if co-housed) are captured inside the structure.
Figure 6: Once both animals are sternally recumbent, the anesthesia box is removed and set onto its lid to prevent anesthetic gas leakage.


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The project described was supported by Artificial Cell Technologies, New Haven, CT.

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Correspondence to Ralph A. Tripp.

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The authors declare no competing financial interests.

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Supplementary Video 1

Video depicting passive narcosis procedure for cotton rats (MP4 26319 kb)

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Hanson, J., Anderson, L., Williams, C. et al. Passive narcosis for anesthesia induction in cotton rats (Sigmodon hispidus). Lab Anim 45, 333–337 (2016).

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