Chapman A, Racine R J
Department of Psychology, McMaster University, Hamilton, Ontario, Canada.
Hippocampus. 1997;7(3):257-70. doi: 10.1002/(SICI)1098-1063(1997)7:3<257::AID-HIPO2>3.0.CO;2-I.
The entorhinal cortex receives input from many cortical areas and mediates the flow of information between these sites and the hippocampal formation. Long-term synaptic plasticity in cortical efferents to the entorhinal cortex may contribute to the transmission of neural activity to the hippocampus, as well as the storage of information, but little is known about plasticity in these pathways. We describe here the use of evoked field potential recordings from chronically implanted electrodes in the rat entorhinal cortex to investigate synaptic plasticity in the large piriform (olfactory) cortex projection to the superficial layers of the entorhinal cortex. Both kindling-induced potentiation and long-term potentiation (LTP) were tested. In addition, we attempted to modulate LTP induction by the co-induction of frequency potentiation and by the co-activation of the medial septum. Epileptogenic kindling stimulations of the piriform cortex (1-s, 60-Hz trains 3 times/day for 5 days) were found to result in a reliable potentiation of field responses evoked by piriform cortex test pulses. Non-epileptogenic tetanization of the piriform cortex with 400-Hz 16-pulse trains reliably resulted in LTP effects. These effects could be augmented by embedding brief LTP induction stimuli within 11-pulse, 15-Hz trains that alone produce only frequency potentiation. Co-activating the medial septum with 10-Hz trains, just prior to tetanization of the piriform cortex, augmented LTP of piriform cortex inputs to the entorhinal cortex in an input-specific manner. All potentiation effects were found to last for periods of weeks. These findings demonstrate that both epileptogenic and non-epileptogenic piriform cortex stimulation induces lasting potentiation of population field responses in the entorhinal cortex of the awake rat. The LTP effects were inducible in a graded manner and were sensitive to the temporal context of stimulation. The finding that low-frequency activation of the septum can enhance plasticity in the entorhinal cortex adds to a body of data indicating a role for the medial septum in contributing to theta activity and plasticity in both the entorhinal cortex and hippocampal formation.
内嗅皮质接收来自许多皮质区域的输入，并介导这些部位与海马结构之间的信息流。皮质传出纤维至内嗅皮质的长期突触可塑性可能有助于神经活动向海马体的传递以及信息的存储，但对这些通路中的可塑性了解甚少。我们在此描述了使用慢性植入大鼠内嗅皮质电极的诱发场电位记录，以研究梨状（嗅觉）大皮质投射至内嗅皮质浅层的突触可塑性。同时测试了点燃诱导的增强作用和长时程增强（LTP）。此外，我们试图通过频率增强的共诱导和内侧隔区的共同激活来调节LTP的诱导。发现对梨状皮质进行致痫性点燃刺激（每天3次，1秒，60赫兹串刺激，持续5天）可导致梨状皮质测试脉冲诱发的场反应可靠增强。用400赫兹16脉冲串对梨状皮质进行非致痫性强直刺激可可靠地产生LTP效应。将短暂的LTP诱导刺激嵌入仅产生频率增强的11脉冲、15赫兹串刺激中，可增强这些效应。在对梨状皮质进行强直刺激之前，用10赫兹串刺激共同激活内侧隔区，以输入特异性方式增强了梨状皮质输入至内嗅皮质的LTP。发现所有增强效应可持续数周。这些发现表明，致痫性和非致痫性梨状皮质刺激均可诱导清醒大鼠内嗅皮质群体场反应的持久增强。LTP效应呈分级诱导，且对刺激的时间背景敏感。低频激活隔区可增强内嗅皮质可塑性的这一发现，进一步充实了表明内侧隔区在促进内嗅皮质和海马结构的θ活动及可塑性方面发挥作用的数据。
