Feldman D E, Nicoll R A, Malenka R C
Department of Psychiatry, University of California, San Francisco, California 94143, USA.
J Neurobiol. 1999 Oct;41(1):92-101.
Thalamocortical synaptic transmission in the rat's primary somatosensory (S1) cortex is modified by sensory experience during a critical period early in life. Despite the importance of such plasticity for the maturation of thalamocortical circuits, the synaptic basis of this plasticity is unknown. Here, we review evidence suggesting that long-term potentiation and depression (LTP and LTD) of thalamocortical synaptic transmission may be involved in this plasticity. In an in vitro slice preparation, thalamocortical synaptic responses exhibit N-methyl-D-aspartate (NMDA) receptor-dependent LTP and LTD during a developmental period similar to the critical period in vivo. The inability to induce LTP and LTD after the critical period may result in part from a developmental reduction in the duration of NMDA receptor currents. In addition, during the critical period many thalamocortical synapses exhibit NMDA receptor currents but no detectable AMPA receptor currents, and thus may be functionally silent at resting membrane potentials. LTP converts silent synapses to functional ones by causing the rapid appearance of AMPA currents. These observations suggest that thalamocortical synapses may be formed as silent synapses which are subsequently made functional by LTP. LTP and LTD may then regulate the efficacy of these functional synapses and thereby contribute to experience-dependent changes in S1 thalamocortical circuits.
大鼠初级体感（S1）皮层中的丘脑皮质突触传递在生命早期的关键时期会受到感觉经验的影响。尽管这种可塑性对丘脑皮质回路的成熟至关重要，但其可塑性的突触基础尚不清楚。在这里，我们回顾了一些证据，这些证据表明丘脑皮质突触传递的长时程增强和抑制（LTP和LTD）可能与这种可塑性有关。在体外脑片制备中，丘脑皮质突触反应在与体内关键时期相似的发育阶段表现出N-甲基-D-天冬氨酸（NMDA）受体依赖性LTP和LTD。关键时期后无法诱导LTP和LTD可能部分是由于NMDA受体电流持续时间的发育性缩短。此外，在关键时期，许多丘脑皮质突触表现出NMDA受体电流，但没有可检测到的AMPA受体电流，因此在静息膜电位下可能在功能上处于沉默状态。LTP通过使AMPA电流迅速出现将沉默突触转变为功能性突触。这些观察结果表明，丘脑皮质突触可能以沉默突触的形式形成，随后通过LTP使其具有功能。然后，LTP和LTD可能调节这些功能性突触的效能，从而有助于S1丘脑皮质回路中依赖经验的变化。
