Biological safety of nasal thallium-201 administration: a preclinical study for olfacto-scintigraphy.

Thallium-201/Nasal administration/Biological safety/Preclinical study. Nasal administration of thallium-201 (Tl) has previously been shown to be useful for the assessment of olfactory nerve connectivity in vivo. We assessed the biological effects of nasal Tl administration in mice to determine its safety before conducting clinical trials on humans. Tl uptake was evaluated in normal mice (n = 5) in vivo by using a high-resolution gamma camera and radiography 15 min, 1, 2 and 9 d after administration of TlCl to the right side of the nasal cavity (10 μl TlCl per nostril, 74 MBq/ml). Murine olfactory epithelial thickness (n = 5) was measured 9 d following nasal administration of TlCl. We assessed the odor detection ability of normal mice (n = 8) following nasal administration of TlCl to both sides of the nasal cavity, by observing cycloheximide solution avoidance behavior. We subsequently administrated TlCl (n = 4) or saline (n = 4) to both nostrils to assess the odor detection ability of mice following bilateral olfactory nerve transection. Tl uptake by the nasal cavity decreased immediately following nasal administration of Tl in normal mice. Nasal administration of Tl did not affect the olfactory epithelial thickness or the odor detection ability of normal mice. Recovery of odor detection ability following olfactory nerve transection was not significantly different between mice nasally administered with Tl, and mice administered with saline. Thus, nasal administration of Tl for the diagnosis of traumatic olfactory impairment did not produce harmful biological effects in vivo.