Functional magnetic resonance imaging (fMRI) is a valuable tool for studying neural activations in the central nervous system of animals due to its wide spatial coverage and non-invasive nature. However, the advantages of fMRI have not been fully realized in functional studies in mice, especially in the olfactory system, possibly due to the lack of suitable anesthesia protocols with spontaneous breathing. Since mice are widely used in biomedical research, it is desirable to evaluate different anesthesia protocols for olfactory fMRI studies in mice. Dexmedetomidine (DEX) as a sedative/anesthetic has been introduced to fMRI studies in mice, but it has a limited anesthesia duration. To extend the anesthesia duration, DEX has been combined with a low dose of isoflurane (ISO) or ketamine (KET) in previous functional studies in mice. In this report, olfactory fMRI studies were performed under three anesthesia protocols (DEX alone, DEX/ISO, and DEX/KET) in three different groups of mice. Isoamyl-acetate was used as an odorant, and the odorant-induced neural activations were measured by blood oxygenation-level dependent (BOLD) fMRI. BOLD fMRI responses were observed in the olfactory bulb (OB), anterior olfactory nuclei (AON), and piriform cortex (Pir). Interestingly, BOLD fMRI activations were also observed in the prefrontal cortical region (PFC), which are most likely caused by the draining vein effect. The response in the OB showed no adaptation to either repeated odor stimulations or continuous odor exposure, but the response in the Pir showed adaptation during the continuous odor exposure. The data also shows that ISO suppresses the olfactory response in the OB and AON, while KET enhances the olfactory response in the Pir. The DEX/KET should be an attractive anesthesia for olfactory fMRI in mice.

中文翻译：

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三种麻醉方案下小鼠嗅觉加工的 fMRI 研究：洞察氯胺酮对嗅觉加工的影响

由于其广泛的空间覆盖和非侵入性，功能磁共振成像 (fMRI) 是研究动物中枢神经系统神经激活的宝贵工具。然而，fMRI 的优势尚未在小鼠的功能研究中得到充分体现，尤其是在嗅觉系统中，这可能是由于缺乏合适的自主呼吸麻醉方案。由于小鼠广泛用于生物医学研究，因此需要评估小鼠嗅觉 fMRI 研究的不同麻醉方案。右美托咪定 (DEX) 作为镇静剂/麻醉剂已被引入小鼠的 fMRI 研究，但其麻醉持续时间有限。为了延长麻醉持续时间，在之前的小鼠功能研究中，DEX 与低剂量的异氟醚 (ISO) 或氯胺酮 (KET) 结合使用。在这份报告中，在三种不同的小鼠组中，在三种麻醉方案（单独的 DEX、DEX/ISO 和 DEX/KET）下进行嗅觉 fMRI 研究。乙酸异戊酯用作气味剂，气味剂引起的神经激活通过血氧水平依赖 (BOLD) fMRI 测量。在嗅球 (OB)、前嗅核 (AON) 和梨状皮层 (Pir) 中观察到 BOLD fMRI 反应。有趣的是，在前额叶皮质区域 (PFC) 中也观察到 BOLD fMRI 激活，这很可能是由引流静脉效应引起的。OB 中的反应表明对重复的气味刺激或持续的气味暴露均不适应，但 Pir 中的反应在持续的气味暴露期间表现出适应。数据还显示 ISO 抑制了 OB 和 AON 中的嗅觉反应，而 KET 增强了 Pir 的嗅觉反应。DEX/KET 应该是小鼠嗅觉功能磁共振成像的有吸引力的麻醉剂。