Functional capacity of the rat olfactory bulb after neonatal naris occlusion

Adult rats which had unilateral naris closure when 1-6 days old were trained to detect different odor concentrations and discriminate between two odors, or used for anatomical study. After removal of the olfactory bulb ipsilateral to the open naris, animals could detect and discriminate odors but were initially less accurate on the lowest odor concentration and on the 2-odor discrimination task. In anatomical controls the size of the bulb ipsilateral to the closed naris was reduced. Horseradish peroxidase applied to the open naris on one rat was transported to olfactory sensory axons on the contralateral (closed naris) side. Thus, naris closure does not deprive the ipsilateral olfactory receptors of vapor stimulation; months after naris closure ipsilateral olfactory receptor neurons are functional and vapors entering one nasal fossa stimulate receptors in the contralateral fossa.