The effect of odor enrichment on olfactory acuity: Olfactometric testing in mice using two mirror-molecular pairs
The effect of odor enrichment on olfactory acuity: Olfactometric testing in mice using two mirror-molecular pairs
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DOI：
10.1371/journal.pone.0233250
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发表时间：
2020-07-30
期刊：
影响因子：
3.7
通讯作者：
Coppola, David M.
中科院分区：
文献类型：
--
作者：
Blount, Alyson;Coppola, David M.
自然界中的智能系统，如哺乳动物的神经系统，受益于适应性强的输入，可以根据时间和空间的变化来调整响应曲线。对这种可塑性的研究，在其所有表现形式中，形成了古典和现代神经科学的支柱。本研究关注嗅觉系统中一种新的可塑性形式，称为诱导。在这个过程中，无法闻到特定气味或无法区分相似气味的受试者，通过长时间暴露于气味而无需注意或反馈（奖励或惩罚）来获得这些能力。然而，很少有诱导的研究严格记录了用于“富集”的气味的嗅觉阈值的变化。“我们在操作嗅觉仪（go/no go任务）中训练了36只CD-1小鼠，以使用两种对映体对：柠檬烯和香芹酮来区分立体异构体的混合物和单独的立体异构体。我们还测量了每个受试者检测每种气味的立体异构体之一的能力。为了评估气味富集对对映体辨别和检测的影响，将小鼠暴露于柠檬烯或香芹酮的两种立体异构体2至12周。通过在受试者的食物中掺入一对对映体（被动富集）或通过在日常操作性辨别测试中将受试者暴露于对映体（主动富集）来实现富集。我们发现，无论是形式的富集改变歧视或检测。这一结果与受试者内或受试者间的实验设计有关。出乎意料的是，我们的阈值测量值是有史以来任何物种中最低的，我们将其归因于与其他报告相比，我们允许我们的小鼠进行相对较多的练习（任务复制）。有趣的是，歧视阈值没有更大（柠檬烯）或只是适度更大（香芹酮）从检测阈值表明手性特异性嗅觉受体确定这些化合物的阈值。在这项研究中显示，小鼠对柠檬烯和香芹酮对映体的超敏感性，与其他地方报道的人类对这些化合物的敏锐度低得多相比，可能会解决为什么前一组嗅觉受体比前一组多四倍的谜团，在以前的研究中，与后一组有相似的阈值。最后，我们的研究结果是一致的结论，监督知觉学习，即涉及重复反馈的正确和不正确的决定，而不是诱导，是可塑性的形式，使动物充分认识到他们的嗅觉系统的能力。
Intelligent systems in nature like the mammalian nervous system benefit from adaptable inputs that can tailor response profiles to their environment that varies in time and space. Study of such plasticity, in all its manifestations, forms a pillar of classical and modern neuroscience. This study is concerned with a novel form of plasticity in the olfactory system referred to as induction. In this process, subjects unable to smell a particular odor, or unable to differentiate similar odors, gain these abilities through mere exposure to the odor(s) over time without the need for attention or feedback (reward or punishment). However, few studies of induction have rigorously documented changes in olfactory threshold for the odor(s) used for "enrichment." We trained 36 CD-1 mice in an operant-olfactometer (go/no go task) to discriminate a mixture of stereoisomers from a lone stereoisomer using two enantiomeric pairs: limonene and carvone. We also measured each subject's ability to detect one of the stereoisomers of each odor. In order to assess the effect of odor enrichment on enantiomer discrimination and detection, mice were exposed to both stereoisomers of limonene or carvone for 2 to 12 weeks. Enrichment was effected by adulterating a subject's food (passive enrichment) with one pair of enantiomers or by exposing a subject to the enantiomers in daily operant discrimination testing (active enrichment). We found that neither form of enrichment altered discrimination nor detection. And this result pertained using either within-subject or between-subject experimental designs. Unexpectedly, our threshold measurements were among the lowest ever recorded for any species, which we attributed to the relatively greater amount of practice (task replication) we allowed our mice compared to other reports. Interestingly, discrimination thresholds were no greater (limonene) or only modestly greater (carvone) from detection thresholds suggesting chiral-specific olfactory receptors determine thresholds for these compounds. The super-sensitivity of mice, shown in this study, to the limonene and carvone enantiomers, compared to the much lesser acuity of humans for these compounds, reported elsewhere, may resolve the mystery of why the former group with four-fold more olfactory receptors have tended, in previous studies, to have similar thresholds to the latter group. Finally, our results are consistent with the conclusion that supervised-perceptual learning i.e. that involving repeated feedback for correct and incorrect decisions, rather than induction, is the form of plasticity that allows animals to fully realize the capabilities of their olfactory system.