Olfactory inputs activate the medial entorhinal cortex via the hippocampus
Olfactory inputs activate the medial entorhinal cortex via the hippocampus
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DOI：
10.1152/jn.2000.83.4.1924
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发表时间：
2000-04-01
影响因子：
2.5
通讯作者：
De Curtis, M
中科院分区：
文献类型：
--
作者：
Biella, G;De Curtis, M
内嗅皮层的外侧和内侧区域在连通性和激活模式方面有很大的不同。关于嗅觉输入，尽管解剖学研究表明嗅觉传入仅限于侧嗅区和鼻侧嗅区，但嗅觉投射到内嗅皮层的详细而广泛的生理图谱仍然缺失。通过分析体外离体豚鼠不同脑内嗅亚区在侧嗅道刺激下的反应，探讨了内嗅区和外侧嗅区对嗅觉加工的贡献。通过同时进行多位点记录或对16通道硅探针获得的场电位层流剖面进行电流源密度分析，重建了内嗅内侧和外侧区域的突触激活模式。电流源密度分析表明，存在直接的单突触嗅觉输入，仅在外侧内嗅皮层最吻侧部分的表层300 μ m处，而在整个外侧皮层的100-350 μ m处，观察到由梨状皮质产生的联合纤维介导的突触汇。在内侧内嗅区没有记录到局部场反应，除非在梨状皮质获得最大单突触反应所需强度的3-5倍的刺激下，海马（齿状回和CAl区）产生大量的群体尖峰。在这些条件下，在CA1同时记录到种群峰值后10.6 +/- 0.9 (SD) msec，内侧内嗅区（III-V层）深度600-1000 μ m处记录到一个后期沉降。通过重复低强度刺激2-8 Hz的外侧嗅道，也可以获得内嗅区的弥漫性激活。较高或较低的刺激频率均未引起海马-内侧内嗅皮层的激活。这些结果表明，内侧和外侧内嗅区域在处理嗅觉感觉输入方面具有本质上不同的作用。
The lateral and medial regions of the entorhinal cortex differ substantially in terms of connectivity and pattern of activation. With regard to olfactory input, a detailed and extensive physiological map of the olfactory projection to the entorhinal cortex is missing, even if anatomic studies suggest that the olfactory afferents are confined to the lateral and rostral entorhinal region. We studied the contribution of the medial and lateral entorhinal areas to olfactory processing by analyzing the responses induced by lateral olfactory tract stimulation in different entorhinal subfields of the in vitro isolated guinea pig brain. The pattern of synaptic activation of the medial and lateral entorhinal regions was reconstructed either by performing simultaneous multisite recordings or by applying current source density analysis on field potential laminar profiles obtained with 16-channel silicon probes. Current source density analysis demonstrated the existence of a direct monosynaptic olfactory input into the superficial 300 mu m of the most rostral part of the lateral entorhinal cortex exclusively, whereas disynaptic sinks mediated by associative fibers arising from the piriform cortex were observed at 100-350 mu m depth in the entire lateral aspect of the cortex. No local field responses were recorded in the medial entorhinal region unless a large population spike was generated in the hippocampus (dentate gyrus and CAl region) by a stimulus 3-5x the intensity necessary to obtain a maximal monosynaptic response in the piriform cortex. In these conditions, a late sink was recorded at a depth of 600-1000 mu m in the medial entorhinal area (layers III-V) 10.6 +/- 0.9 (SD) msec after a population spike was simultaneously recorded in CA1. Diffuse activation of the medial entorhinal region was also obtained by repetitive low-intensity stimulation of the lateral olfactory tract at 2-8 Hz. Higher or lower stimulation frequencies did not induce hippocampal-medial entorhinal cortex activation. These results suggest that the medial and the lateral entorhinal regions have substantially different roles in processing olfactory sensory inputs.