Thallium-201 Imaging in Intact Olfactory Sensory Neurons with Reduced Pre-Synaptic Inhibition In Vivo
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Thallium-201 Imaging in Intact Olfactory Sensory Neurons with Reduced Pre-Synaptic Inhibition In Vivo Hideaki Shiga 1 & Hiroshi Wakabayashi 2 & Kohshin Washiyama 3 & Tomohiro Noguchi 4 & Tomo Hiromasa 2 & Sadaharu Miyazono 4 & Masami Kumai 1 & Kazuma Ogawa 5 & Junichi Taki 2 & Seigo Kinuya 2 & Takaki Miwa 1 Received: 20 May 2020 / Accepted: 14 August 2020 # The Author(s) 2020
Abstract In this study, we determined whether the 201Tl (thallium-201)-based olfactory imaging is affected if olfactory sensory neurons received reduced pre-synaptic inhibition signals from dopaminergic interneurons in the olfactory bulb in vivo. The thallium-201 migration rate to the olfactory bulb and the number of action potentials of olfactory sensory neurons were assessed 3 h following left side nasal administration of rotenone, a mitochondrial respiratory chain complex I inhibitor that decreases the number of dopaminergic interneurons without damaging the olfactory sensory neurons in the olfactory bulb, in mice (6–7 animals per group). The migration rate of thallium-201 to the olfactory bulb was significantly increased following intranasal administration of thallium-201 and rotenone (10 μg rotenone, p = 0.0012; 20 μg rotenone, p = 0.0012), compared with that in control mice. The number of action potentials was significantly reduced in the olfactory sensory neurons in the rotenone treated side of 20 μg rotenone-treated mice, compared with that in control mice (p = 0.0029). The migration rate of thallium-201 to the olfactory bulb assessed with SPECT-CT was significantly increased in rats 24 h after the left intranasal administration of thallium-201 and 100 μg rotenone, compared with that in control rats (p = 0.008, 5 rats per group). Our results suggest that thallium-201 migration to the olfactory bulb is increased in intact olfactory sensory neurons with reduced pre-synaptic inhibition from dopaminergic interneurons in olfactory bulb glomeruli. Keywords Olfactory dysfunction . Dopaminergic interneuron . Tyrosine hydroxylase . Action potential . Olfactory transport . Rotenone
Hiroshi Wakabayashi, Kohshin Washiyama and Tomohiro Noguchi contributed equally to this work.
Introduction
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12035-020-02078-y) contains supplementary material, which is available to authorized users.
Detecting the mechanisms underpinning olfactory dysfunction is challenging, owing to the difficulty in directly viewing the connectivity of peripheral olfactory nerves using current magnetic resonance imaging (MRI). To date, we have visualized olfactory nerves in healthy volunteers and olfactory-impaired patients using a novel olfactory nerve tracer, radioisotope 201 Tl (thallium-201) [1, 2]. Thallium-201-based olfactory imaging is referred to as olfactory scintigraphy. The radioisotope thallium-201 is transported within olfactory neural tracts after nasal administration in rodents [3]. This transport is significantly decreased by transecting olfactory nerve fibers and corre
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