Transoral intratracheal inoculation method for use with neonatal rats

Background and Purpose: Studying the effects of toxic and infective compoun ds on the respiratory system requires a reliable method for delivering inoc ulum into the distal region of the lung. Although transoral intratracheal i noculation methods have been well documented for adult rats, to the authors ' knowledge, a reliable method has not been validated for neonatal rats. Th e purpose of the study reported here was to develop a simple method for tra nsoral inoculation in rat neonates, Methods: Seven-day-old Fischer 344 rats were anesthetized with halothane, a nd a spinal needle was inserted in the tracheal lumen, by use of illuminati on and a modified otoscope, Meconium was injected into the lungs as a marke r, and the neonates were kept under close observation After euthanasia at 2 4 h, lungs were removed and fixed in formalin, and the microscopic distribu tion of the inoculum was assessed in the left, right cranial, middle, media n, and caudal lung lobes. Results: Microscopic examination of lungs indicated that intratracheal inoc ulation was achieved in 100% of neonatal, lungs and the inoculum was consis tently distributed in the alveoli of all pulmonary lobes, Important complic ations or mortality were not observed in the neonates, Conclusions: Intratracheal inoculation of neonatal rats is possible by use of a modified otoscope for transoral illumination. This technique is simple and reproducible and ensures, without complications, widespread distributi on of inoculum in the lungs of neonatal rats.