Uva L, de Curtis M
Department of Experimental Neurophysiology, Istituto Nazionale Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Neuroscience. 2005;130(1):249-58. doi: 10.1016/j.neuroscience.2004.08.042.
Interactions between olfactory cortices and the hippocampus support sensory discrimination and spatial learning functions. The olfactory input accesses the hippocampal formation via a polysynaptic pathway mediated by the lateral and rostral entorhinal cortex (EC). We recently demonstrated that following repetitive stimulation of the lateral olfactory tract (LOT) at 2-8 Hz, a delayed response (onset at circa 60 ms) was evoked in the caudal portion of the EC, identified as medial EC, that does not receive a direct olfactory input. By performing simultaneous laminar profile analysis in the EC and in different hippocampal subfields, we conclusively demonstrate that the delayed EC response evoked by repetitive ipsilateral LOT stimulation is headed by the sequential activation of the dentate gyrus and the CA3/CA1 subfields in the septal and temporal hippocampus. Repetitive stimulation of the contralateral LOT also induced an EC response that peaked at 76.28+/-2.42 ms (n=15). Current source density analysis and time-delay analysis of simultaneous field potential laminar profiles performed from the EC and from DG, CA3 and CA1 hippocampal subfields suggested that the contralateral EC response is mainly carried by an intrahippocampal CA3-CA3 commissural pathway. Contralateral LOT stimulation also induced a later EC component (delay >100 ms) generated in the superficial layers, mediated either by local associative interactions or by extrahippocampal circuits. The opportunity to activate the ipsi- and contralateral olfactory pathways in the same experiment and to record field potentials profiles simultaneously in different structures of both hemispheres in the isolated guinea-pig brain confirms that this preparation is unique and is particularly suitable for investigating the system physiology of the limbic region. The present study demonstrates that patterned stimulation of the olfactory input that mimics sniffing patterns during odor discrimination induces a diffuse activation of both ipsi- and contralateral hippocampi and ECs. The findings contribute to the understanding the physiological mechanisms that underlie associative interactions between olfactory and non-olfactory cortical inputs converging into the mesial temporal region.
嗅觉皮层与海马体之间的相互作用支持感觉辨别和空间学习功能。嗅觉输入通过由外侧和嘴侧内嗅皮层(EC)介导的多突触通路进入海马结构。我们最近证明,在以2-8Hz重复刺激外侧嗅束(LOT)后,在EC的尾部(被确定为内侧EC)诱发了延迟反应(约60ms开始),该区域不接受直接的嗅觉输入。通过在EC和不同海马亚区进行同步层状分析,我们确凿地证明,重复同侧LOT刺激诱发的延迟EC反应是由齿状回以及隔区和颞叶海马体中的CA3/CA1亚区的顺序激活所引导的。对侧LOT的重复刺激也诱导了EC反应,其在76.28±2.42ms达到峰值(n = 15)。对来自EC以及DG、CA3和CA1海马亚区的同步场电位层状分布进行电流源密度分析和时间延迟分析表明,对侧EC反应主要由海马内CA3-CA3连合通路传导。对侧LOT刺激还诱导了在浅层产生的较晚的EC成分(延迟>100ms),其由局部联合相互作用或海马外回路介导。在同一实验中激活同侧和对侧嗅觉通路,并在离体豚鼠脑的两个半球的不同结构中同时记录场电位分布的机会,证实了这种制备方法是独特的,特别适合于研究边缘区域的系统生理学。本研究表明,模仿气味辨别期间嗅吸模式的嗅觉输入的模式化刺激会诱导同侧和对侧海马体及EC的弥漫性激活。这些发现有助于理解汇聚到内侧颞叶区域的嗅觉和非嗅觉皮层输入之间联合相互作用的生理机制。