Biella G, de Curtis M
Department of Experimental Neurophysiology, Istituto Nazionale Neurologico, 20133 Milan, Italy.
J Neurophysiol. 2000 Apr;83(4):1924-31. doi: 10.1152/jn.2000.83.4.1924.
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 microm 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 microm 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 CA1 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 microm 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.
内嗅皮质的外侧和内侧区域在连接性和激活模式方面存在显著差异。关于嗅觉输入，尽管解剖学研究表明嗅觉传入纤维局限于外侧和吻侧内嗅区域，但目前仍缺乏一份详细且广泛的嗅觉投射至内嗅皮质的生理图谱。我们通过分析体外分离的豚鼠脑不同内嗅亚区中外侧嗅束刺激所诱发的反应，研究了内侧和外侧内嗅区域对嗅觉处理的贡献。通过进行同步多部位记录或对用16通道硅探针获得的场电位层状分布应用电流源密度分析，重建了内侧和外侧内嗅区域的突触激活模式。电流源密度分析表明，仅在外侧内嗅皮质最吻侧部分的浅表300微米处存在直接的单突触嗅觉输入，而在整个皮质外侧100 - 350微米深度处观察到由梨状皮质产生的联合纤维介导的双突触汇聚。在内侧内嗅区域未记录到局部场反应，除非在海马体（齿状回和CA1区）中通过强度为在梨状皮质获得最大单突触反应所需强度3 - 5倍的刺激产生大量群体峰电位。在这些条件下，在CA1区同时记录到群体峰电位后10.6±0.9（标准差）毫秒，在内侧内嗅区域（III - V层）600 - 1000微米深度处记录到一个晚期汇聚。通过以2 - 8赫兹的频率重复低强度刺激外侧嗅束，也可获得内侧内嗅区域的弥漫性激活。更高或更低的刺激频率均未诱发海马体 - 内侧内嗅皮质激活。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显著不同的作用。
