Axonal transport of rubidium and thallium in the olfactory nerve of mice

Following intranasal administration of radioactive ⁸⁶Rb ⁺ and ²⁰¹Tl⁺ in mice, we observed this direct transport via the olfactory nerve pathway. The ⁸⁶RbCl and ²⁰¹TlCl solutions were administered to two groups of mice, the unilateral intranasal and intravenous administration groups. After sacrifice, their heads were divided into the right and left side, which were then subdivided into seven parts; the nasal mucosa and brain regions were separated. Following the unilateral intranasal administration, uptake after 6 h by the olfactory bulb was significantly higher on the ipsilateral side ( ⁸⁶Rb, 0.7 %dose; ²⁰¹Tl, 0.5 %dose) than on the contralateral side (⁸⁶Rb, 0.08 %dose; ²⁰¹Tl, 0.15 %dose). Moreover, the ⁸⁶Rb and ²⁰¹Tl that accumulated in the olfactory bulb were gradually transported to other brain regions of the olfactory tract, the telencephalon and the diencephalon on the side corresponding to the nostril used for administration. Significant differences were observed between the right and left side of the brain regions 6 and 12 h after administration. Further, ²⁰¹Tl autoradiography clearly showed striped patterns of dense accumulation, localized in the region around the glomerular layer and granule cell layer of the olfactory bulb and around the olfactory cortex. These results provide clear evidence of axonal transport via the olfactory nerve pathway, from nasal cavity to the olfactory bulb, as well as to the olfactory cortex through the synaptic junctions. The olfactory transport of the ⁸⁶Rb⁺ and ²⁰¹Tl⁺ is thought to represent the behavior of K⁺ in the olfactory system.