Gigg J, Finch D M, O'Mara S M
Department of Psychology, University of Dublin, Trinity College, 2, Dublin, Ireland.
Brain Res. 2000 Nov 24;884(1--2):35-50. doi: 10.1016/s0006-8993(00)02878-x.
There has been little electrophysiological examination of the afferent projection from lateral entorhinal cortex to dorsal subiculum. Here we provide evidence that synaptic inputs from lateral entorhinal cortex and CA1 converge onto single dorsal subicular neurons in vivo. Subicular responses to CA1 stimulation consisted of excitation and/or long-duration inhibition. Neurons excited by CA1 activation usually showed inhibition to entorhinal stimulation. The latter inhibition was usually of short duration, however, long duration inhibition was seen in a significant proportion of responses. Entorhinal stimulation produced excitatory responses in four bursting cells and it was these cells that also tended to show the longest inhibition. Only bursting cells could be driven antidromically by entorhinal stimulation. Biocytin-filled multipolar and pyramidal cells displayed excitation-inhibition sequences to CA1 and inhibition to entorhinal stimulation. These data strongly suggest that subicular inhibitory neurons receive excitatory input from CA1 and display mutual inhibition. The source of entorhinal-evoked inhibition is less clear. The relative sparseness of observed entorhinal-evoked responses suggests that the input to dorsal subiculum from any one part of lateral entorhinal cortex is spatially restricted. These data show that excitation-inhibition sequences can be seen in subicular pyramidal and multipolar cells and that single subicular neurons receive convergent inputs from CA1 and entorhinal cortex. We show for the first time that bursting cells can be driven both orthodromically and antidromically by direct entorhinal stimulation. These data support the existence of a reciprocal excitatory connection between lateral entorhinal cortex and dorsal subiculum and suggest further that this connection may involve only bursting subicular neurons.
对于从外侧内嗅皮层到背侧海马下脚的传入投射，几乎没有进行过电生理检查。在此，我们提供证据表明，在体内，来自外侧内嗅皮层和CA1区的突触输入汇聚到单个背侧海马下脚神经元上。海马下脚对CA1区刺激的反应包括兴奋和/或长时抑制。被CA1区激活兴奋的神经元通常对内嗅皮层刺激表现出抑制。然而，后者的抑制通常持续时间较短，不过在相当一部分反应中也观察到了长时抑制。内嗅皮层刺激在四个爆发性细胞中产生了兴奋反应，而正是这些细胞往往也表现出最长时间的抑制。只有爆发性细胞能被内嗅皮层刺激逆向驱动。用生物胞素填充的多极细胞和锥体细胞对CA1区刺激呈现兴奋-抑制序列，对内嗅皮层刺激表现出抑制。这些数据强烈表明，海马下脚抑制性神经元接受来自CA1区的兴奋性输入并表现出相互抑制。内嗅皮层诱发抑制的来源尚不清楚。观察到的内嗅皮层诱发反应相对稀少，这表明外侧内嗅皮层任何一个部位对背侧海马下脚的输入在空间上是受限的。这些数据表明，在海马下脚锥体细胞和多极细胞中可以看到兴奋-抑制序列，并且单个海马下脚神经元接受来自CA1区和内嗅皮层的汇聚输入。我们首次表明，爆发性细胞可被直接的内嗅皮层刺激顺向和逆向驱动。这些数据支持外侧内嗅皮层和背侧海马下脚之间存在相互兴奋性连接，并进一步表明这种连接可能仅涉及爆发性海马下脚神经元。
