An optimized method for intratracheal instillation in mice

Non-invasive intratracheal instillation is an important method for direct exposure of the respiratory tract which is commonly used in toxicology, environmental science, and other research fields. However, there is no standard operating process for non-invasive intratracheal instillation. To keep the reliability and accuracy of intratracheal instillation is vital, especially, for animal models of sub-chronic or chronic exposure which may need repeated operations performed on many animals. In this study, we improved the intratracheal instillation operation and verified the accuracy and reliability of this method. Adult female BALB/c mice were treated with ink solution, normal saline and PM2.5 suspension by the described intratracheal instillation method. After a short recovery, the mice were killed. The distribution of ink in the lungs and gastrointestinal tract of the mice was observed anatomically, and the dispersion of PM2.5 in the lungs and the status of lung injury were observed by pathological staining after 24 h. Scattered ink blots were observed in the lungs of the mice with instillation inks, but not in their gastrointestinal tract. Pathological staining of mouse lung showed that PM2.5 was distributed at the end of bronchiole and alveolar cavity, and caused diffuse acute lung injury in the mice. This study shows that the non-invasive intratracheal instillation method has good accuracy and reliability, which can reduce the use of mice, do less harm to the mice, and then improve 3R animal welfare. This method can be applied to establish a mouse model of short-term or long-term exposure through the respiratory tract.