Biella Gerardo, Uva Laura, Hofmann Ulrich G, de Curtis Marco
Department Experimental Neurophysiology, Istituto Nazionale Neurologico, 20133 Milan, Italy.
J Neurophysiol. 2002 Sep;88(3):1159-65. doi: 10.1152/jn.2002.88.3.1159.
Associative fiber systems in the entorhinal cortex (EC) have been extensively studied in different mammals with tracing techniques. The largest contingent of intra-EC cortico-cortical fibers runs in the superficial layers and is distributed predominantly within longitudinal cortical bands. We studied the patterns of intrinsic EC connectivity in the in vitro isolated guinea pig brain preparation by performing current-source density analysis of field potential laminar profiles recorded with multi-channel silicon probes. The response pattern evoked by stimulation of the lateral olfactory tract was utilized to identify the lateral (l-EC) and medial (m-EC) entorhinal cortex. Stimulation of the deep layers did not evoke consistent responses. Local stimulation of the superficial layers in different portions of the EC induced an early, possibly direct response restricted to layer II-III in the close proximity to the stimulating electrode, followed by a late potential in the superficial layer I, that propagated at distance with a progressively increasing latency. The monosynaptic nature of the delayed response was verified by applying a pairing test. The results demonstrated that stimulation in the rostral-medial part of the EC generated activity restricted to the rostral pole of the l-EC, stimulation of the m-EC induced an associative activation that propagated rostrocaudally within the m-EC, stimulation of the caudal pole of the m-EC induced an additional response directed laterally, and stimulation of the lateral band of the EC determined a prominent longitudinal propagation of neuronal activity, but also induced associative potentials that propagated medially. The results are in partial agreement with the general picture derived from the anatomical studies performed in different species. Even though the largest associative interactions between superficial layers are restricted within either the m-EC or the l-EC, both rostral and caudal stimuli in the EC region close to the rhinal sulcus induced activity that propagated across the border between l- and m-EC.
内嗅皮质（EC）中的联合纤维系统已在不同哺乳动物中通过示踪技术进行了广泛研究。EC内最大的皮质-皮质纤维群位于浅层，主要分布在纵向皮质带内。我们通过对用多通道硅探针记录的场电位层状分布进行电流源密度分析，研究了体外分离的豚鼠脑标本中EC的内在连接模式。利用刺激外侧嗅束诱发的反应模式来识别外侧内嗅皮质（l-EC）和内侧内嗅皮质（m-EC）。刺激深层未诱发一致的反应。在EC不同部位的浅层进行局部刺激，会在靠近刺激电极处诱发一个早期的、可能是直接的反应，该反应局限于II-III层，随后在表层I出现一个晚期电位，该电位会在一定距离处传播，潜伏期逐渐增加。通过配对试验验证了延迟反应的单突触性质。结果表明，刺激EC的吻内侧部分产生的活动局限于l-EC的吻极，刺激m-EC诱发的联合激活在m-EC内沿前后方向传播，刺激m-EC的尾极诱发一个额外的侧向反应，刺激EC的外侧带则导致神经元活动显著的纵向传播，但也诱发了向内侧传播的联合电位。这些结果与在不同物种中进行的解剖学研究所得到的总体情况部分一致。尽管浅层之间最大的联合相互作用局限于m-EC或l-EC内，但靠近鼻沟的EC区域的吻侧和尾侧刺激均诱发了跨越l-EC和m-EC边界传播的活动。
