Yun S H, Huh K, Jung M W
Neuroscience Laboratory, Institute for Medical Sciences, Ajou University School of Medicine, Suwon 442-721, Korea.
Synapse. 2000 Jan;35(1):1-7. doi: 10.1002/(SICI)1098-2396(200001)35:1<1::AID-SYN1>3.0.CO;2-L.
The contribution of NMDA receptors to the expression of long-term potentiation (LTP) is controversial. In entorhinal cortex (EC) previous studies reported either that LTP was exclusively expressed through NMDA receptors or that both NMDA and non-NMDA receptors were involved in LTP expression. To reexamine this issue, horizontal entorhinal cortical slices were prepared from adult rats and electrical stimulation was delivered in layer II/III, while field potential recordings were made in layer III. In the standard condition (2.5 mM Mg(++)), LTP was reliably induced by theta burst stimulation, but was blocked by 100 microM D-AP5, an NMDA receptor antagonist. This corroborates previous reports that NMDA receptor activation is required for induction of EC LTP. The field potential response was not affected by D-AP5, but completely blocked by 10 microM CNQX, a non-NMDA receptor antagonist. This indicates that the expression of LTP is mediated by non-NMDA receptors in the standard condition. LTP of NMDA receptor-mediated responses was tested by comparing NMDA responses before and after applying theta burst stimulation in medium containing low magnesium (0.4-1 mM). Theta burst stimulation induced 43.2+/-9.7% increase of non-NMDA responses (i.e., AP5-insensitive fast component) but 5.6+/-9.0% decrease of the NMDA receptor component (AP5-sensitive slow component). These results indicate that activation of NMDA receptors is critical for induction of LTP, but LTP expression is mediated by non-NMDA receptors in EC under these experimental conditions.
N-甲基-D-天冬氨酸（NMDA）受体对长时程增强（LTP）表达的作用存在争议。在内嗅皮质（EC），以往的研究报告称，LTP要么仅通过NMDA受体表达，要么NMDA和非NMDA受体都参与LTP的表达。为了重新审视这个问题，从成年大鼠制备了水平内嗅皮质切片，并在II/III层进行电刺激，同时在III层记录场电位。在标准条件下（2.5 mM Mg++），θ波爆发刺激可可靠地诱导LTP，但被100 μM D-AP5（一种NMDA受体拮抗剂）阻断。这证实了先前的报道，即EC LTP的诱导需要NMDA受体激活。场电位反应不受D-AP5影响，但被10 μM CNQX（一种非NMDA受体拮抗剂）完全阻断。这表明在标准条件下，LTP的表达由非NMDA受体介导。通过比较在含低镁（0.4 - 1 mM）的培养基中施加θ波爆发刺激前后的NMDA反应，测试了NMDA受体介导反应的LTP。θ波爆发刺激诱导非NMDA反应（即对AP5不敏感的快速成分）增加43.2±9.7%，但NMDA受体成分（对AP5敏感的慢速成分）减少5.6±9.0%。这些结果表明，NMDA受体的激活对LTP的诱导至关重要，但在这些实验条件下，EC中LTP的表达由非NMDA受体介导。
