Immunology and Infection
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Effects of Exposure of Formaldehyde to a Rat Model of Atopic Dermatitis Induced by Neonatal Capsaicin Treatment
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Summary September 27th, 2017
We describe here methods for neonatal capsaicin treatment to induce atopic dermatitis in rats and exposure of vaporized formaldehyde to investigate the effects of formaldehyde inhalation on atopic dermatitis.
Transcript
The overall goal of this procedure is to induce atopic dermatitis-like symptoms by neonatal capsaicin treatment. And to measure the effect of formaldehyde on atopic dermatis-like symptoms. This method can help answer a key question related to the pathophysiological of atopic dermatitis in the dermatological field.
The major advantage of this technique are the induction of atopic dermatitis-like symptoms and the establishment of an important exposure system with the increments. To prepare five milligrams per milliliter capsaicin solution add one milliliter of Tween 80, one milliliter of 100%ethanol and 50 milligrams of capsaicin to a 15 milliliter conical tube. Then add eight milliliters of normal saline to the conical tube.
Cap and shake the tube vigorously until no separated layers are visible. It is critical to deliver the capsaicin between 12 to 48 hours after birth. Inject the capsaicin solution into the subcutaneous tissue on the midline and backside of the neck of a neonatal Sprague Dawley Rat.
To prevent respiratory arrest due to the capsaicin injection place the neonates in an oxygen chamber until respiration becomes normal. If necessary push the chest of neonates to encourage breathing. Begin by preparing plastic chambers equipped with a mirror to allow for full coverage for viewing and holes to allow the rats to breath.
Place the rats in the plastic chamber and cover the ceiling of the chamber with a heavy object to prevent the lid from opening. Then set up a digital video camera to simultaneously record both the mirror views and front views of the rats. Then record the spontaneous behaviors of the rats for one hour.
Play back the video clips and count the number of scratching behaviors such as those exhibited by the rat on the right. And the rat in the center. To score the lesions identify the extent and severity of dermatitis in the ears and other parts of an anesthetized rat.
Define the unit size for the extent of skin lesions as 0.25 centimeters squared. And the severity of skin lesions using this table. Prepare an acrylic glass box that has two connectors on opposite sides.
For circulation of formaldehyde gas the venting outlet should be placed higher than the gas intake outlet. Connect tubes to both connectors. Run the venting outlet tube to the circulation hood or outside of the building for emission of the gas.
And connect the other inlet tube to a medical oxygen regulator. Place a conventional rat cage inside the acrylic glass box. Put one week old rats in the cage and then seal the acrylic glass box as tightly as possible to prevent gas leakage.
Apply cling film to wrap the chamber and close the chamber with a rubberized lid for tight sealing. Add 0.5%formaldehyde solution to the humidifier bottle connected to the medical oxygen regulator. Don't forget that working in formaldehyde can be extremely hazardous.
And precaution such as masks and gloves should always be taken by performing this procedure. Next turn on the regulator and set the flow rate to five liters per minute. Expose the rats to formaldehyde gas for a two hour period.
Shown here are representative photographs of skin inflammation in the capsaicin-treated rat. The chronological development of dermatitis of the capsaicin-treated rats is shown here. This image shoes the chronological development of scratching behaviors in the capsaicin-treated rats.
This is a representative image of relapsing skin lesions of 16 week old capsaicin-treated rats. Serum IgE levels are significantly elevated in capsaicin-treated animals. Significant elevation of IL-4 mRNA expression is also observed in capsaicin-treated animals.
Significant elevation of IL-13 mRNA expression in capsaicin-treated animals is shown here. These representative photographs show atopic dermatitis after the fifth week of treatment using 1.2 parts per million. And 0.8 parts per million formaldehyde compared to controlled treatment with air.
Exposure to 1.2 parts per million formaldehyde but not 0.8 parts per million formaldehyde significantly exacerbated pruritis in the capsaicin-treated atopic dermatitis model. Similar results were observed when dermatitis was measured. Increased serum IgE levels were observed in the capsaicin-treated AD rat model treated with 1.2 parts per million formaldehyde exposure.
Following this procedure other materials like gylcol solution can be used to answer additional questions related to the effects of particular matter on atopic dermatitis. After these developments this technique paved the way for researchers in the field of dermatology to explore the role of environmental factors in the pathogenesis of atopic dermatitis.
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