Biology Reference
In-Depth Information
11. Cotton rats can generally tolerate anesthesia and treatment once or twice a day
for up to 5 days. The more often an animal is anesthetized, the less sensitive it
becomes to the anesthesia.
12. Use no more than 20 μL for intranasal administration of liquid formulations as
instillation volumes of >20 μL will result in some of the liquid entering the
trachea and possibly the lungs.
13. If the semi-solid formulation is heat tolerant, then the formulation can be warmed
in a water bath above its melting point to allow the melted semi-solid to be
drawn into the syringe without the attached catheter. For non-heat tolerant
formulations, the semi-solid can be loaded into a syringe using a spatula and
the syringe plunger to load the formulation in the syringe barrel from the top.
Before affixing the catheter to the syringe, ensure that the syringe tip is wiped
free of formulation or the catheter can “pop-off” the syringe during instillation.
Using a lure lock syringe or parafilm to secure the catheter can also help prevent
this.
14. For semi-solid formulations, lighter anesthesia than is used for liquid formula-
tions is generally better than deep anesthesia. This will better allow the cotton
rats to clear their nares of the semi-solid formulation and help prevent respiratory
distress.
15. Care should be taken when inserting the catheter in the nostril as the tip of the
catheter is sharp and can cut the inside of the nostrils. To help prevent this,
smear some of the formulation on the tip of the catheter to act as a lubricant.
16. The more viscous the formulation, the more difficult it is to control the exact
dosing of the semi-solid. More viscous formulations will continue to ooze from
the syringe after pressure is released from the plunger making exact dosing
difficult.
17. Instillation of semi-solid formulations into both nostrils will occasionally lead
to respiratory distress as cotton rats are obligate nose breathers. Some distress
is normal as the animals gasp to clear their nasal passages, but very labored
breathing may require additional massage of the nose and possible breathing
assistance in the form of gentle compressions of the rib cage to deflate and inflate
the lungs. Respiratory distress mostly occurs with smaller, over-anesthetized,
or sick animals. Cotton rats should be monitored until they display normal
breathing following nasal instillation of semi-solids.
18. Depending on the strain of S. aureus instilled, cotton rats can remain nasally
colonized with S. aureus for up to and possibly greater than 2 months (18) .
Shedding of excess or non-adherent S. aureus appears to occur primarily within
the first 2 or 3 days, after which point the nasal colonization appears to reach a
relatively steady state (19) . We generally allow 4-6 days post-instillation prior
to any treatments and harvest the noses between 7 and 10 days post-bacterial
instillation or 24 h after the final treatment. For some defined genetic S. aureus
mutants, a longer colonization time (2-3 weeks) is required to see a significant
difference between colonization by the mutant and wild-type bacteria (20) .
 
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