Direct Olfactory Transport of Inhaled Manganese (54MnCl2) to the Rat Brain: Toxicokinetic Investigations in a Unilateral Nasal Occlusion Model

• Published in: Toxicology and applied pharmacology Vol. 169; no. 3; pp. 238 - 248
• Main Authors: Brenneman, Karrie A., Wong, Brian A., Buccellato, Matthew A., Costa, Elisabeth R., Gross, Elizabeth A., Dorman, David C.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 15-12-2000; Elsevier
• Subjects: autoradiography; Biological and medical sciences; Chemical and industrial products toxicology. Toxic occupational diseases; gamma spectrometry; inhalation; manganese; Medical sciences; Metals and various inorganic compounds; nasal occlusion; neurotoxicity; olfactory transport; rat; toxicokinetics; Toxicology; inhalation; neurotoxicity; gamma spectrometry; rat; autoradiography; toxicokinetics; nasal occlusion; olfactory transport; manganese; Nervous system diseases; Rat; Toxicity; Rodentia; Route of administration; Inhalation; Heavy metal; Toxicokinetics; Vertebrata; Mammalia; Olfactory pathway; Animal; Distribution; Brain (vertebrata); Manganese
• ISSN: 0041-008X; 1096-0333
• DOI: 10.1006/taap.2000.9073

Inhalation exposure of humans to high concentrations of manganese (Mn) is associated with elevated Mn levels in the basal ganglia and an extrapyramidal movement disorder. In the rat, direct olfactory transport of Mn from the nose to the brain has been demonstrated following intranasal instillation of 54MnCl2. However, the contribution this route makes to brain Mn delivery following inhalation is unknown and was the subject of our study. Male 8-week old CD rats underwent a single 90-min nose-only exposure to a 54MnCl2 aerosol (0.54 mg Mn/m3; MMAD 2.51 μm). The left and right sides of the nose and brain, including the olfactory pathway and striatum, were sampled at 0, 1, 2, 4, and 8 days postexposure. Control rats were exposed to 54MnCl2 with both nostrils patent to evaluate the symmetry of Mn delivery. Another group of rats had the right nostril plugged to prevent nasal deposition of 54MnCl2 on the occluded side. Gamma spectrometry (n = 6 rats/group/time point) and autoradiography (n = 1 rat/group/time point) were used to compare the levels of 54Mn found on the left and right sides of the nose and brain to determine the contribution of olfactory uptake to brain 54Mn levels. Brain and nose samples from the side with the occluded nostril had negligible levels of 54Mn activity, validating the nasal occlusion procedure. High levels of 54Mn were observed in the olfactory bulb and tract/tubercle on the side or sides with an open nostril within 1–2 days following inhalation exposure. These results demonstrated, for the first time, that the olfactory route contributes the majority (up to >90%) of the 54Mn found in the olfactory pathway, but not in the striatum, of the rat brain up to 8 days following a single inhalation exposure. These findings suggest that the olfactory route may make a significant contribution to brain Mn levels following inhalation exposure in the rat.