Nicol Alister U, Sanchez-Andrade Gabriela, Collado Paloma, Segonds-Pichon Anne, Kendrick Keith M
Sub-department of Animal Behaviour, University of Cambridge Cambridge, UK.
Wellcome Trust Sanger Institute Hinxton, Cambridge, UK.
Front Behav Neurosci. 2014 Jun 5;8:193. doi: 10.3389/fnbeh.2014.00193. eCollection 2014.
Neural plasticity changes within the olfactory bulb are important for olfactory learning, although how neural encoding changes support new associations with specific odors and whether they can be investigated under anesthesia, remain unclear. Using the social transmission of food preference olfactory learning paradigm in mice in conjunction with in vivo microdialysis sampling we have shown firstly that a learned preference for a scented food odor smelled on the breath of a demonstrator animal occurs under isofluorane anesthesia. Furthermore, subsequent exposure to this cued odor under anesthesia promotes the same pattern of increased release of glutamate and gamma-aminobutyric acid (GABA) in the olfactory bulb as previously found in conscious animals following olfactory learning, and evoked GABA release was positively correlated with the amount of scented food eaten. In a second experiment, multiarray (24 electrodes) electrophysiological recordings were made from olfactory bulb mitral cells under isofluorane anesthesia before, during and after a novel scented food odor was paired with carbon disulfide. Results showed significant increases in overall firing frequency to the cued-odor during and after learning and decreases in response to an uncued odor. Analysis of patterns of changes in individual neurons revealed that a substantial proportion (>50%) of them significantly changed their response profiles during and after learning with most of those previously inhibited becoming excited. A large number of cells exhibiting no response to the odors prior to learning were either excited or inhibited afterwards. With the uncued odor many previously responsive cells became unresponsive or inhibited. Learning associated changes only occurred in the posterior part of the olfactory bulb. Thus olfactory learning under anesthesia promotes extensive, but spatially distinct, changes in mitral cell networks to both cued and uncued odors as well as in evoked glutamate and GABA release.
嗅球内的神经可塑性变化对嗅觉学习很重要，尽管神经编码变化如何支持与特定气味的新关联以及它们是否能在麻醉状态下进行研究仍不清楚。我们结合体内微透析采样，在小鼠中使用食物偏好嗅觉学习范式的社会传递，首先表明在异氟烷麻醉下，对示范动物呼出气味中闻到的有香味食物气味会产生习得性偏好。此外，随后在麻醉状态下接触这种提示气味，会促进嗅球中谷氨酸和γ-氨基丁酸（GABA）释放增加，其模式与之前在嗅觉学习后的清醒动物中发现的相同，并且诱发的GABA释放与食用的有香味食物量呈正相关。在第二个实验中，在异氟烷麻醉下，对一种新的有香味食物气味与二硫化碳配对之前、期间和之后，从嗅球的二尖瓣细胞进行多阵列（24个电极）电生理记录。结果显示，在学习期间和之后，对提示气味的总体放电频率显著增加，而对未提示气味的反应减少。对单个神经元变化模式的分析表明，其中很大一部分（>50%）在学习期间和之后显著改变了它们的反应特征，大多数之前被抑制的神经元变得兴奋。大量在学习前对气味无反应的细胞在之后要么被兴奋要么被抑制。对于未提示气味，许多之前有反应的细胞变得无反应或被抑制。学习相关的变化只发生在嗅球的后部。因此，麻醉状态下的嗅觉学习促进了二尖瓣细胞网络对提示和未提示气味以及诱发的谷氨酸和GABA释放的广泛但空间上不同的变化。
