Flint A C, Maisch U S, Kriegstein A R
Center for Neurobiology and Behavior, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
J Neurophysiol. 1997 Oct;78(4):1990-6. doi: 10.1152/jn.1997.78.4.1990.
One form of rhythmic activity intrinsic to neocortex can be induced in slices of adult somatosensory cortex by lowering [Mg2+]o to unblock N-methyl--aspartate (NMDA) receptors. It has been suggested that a population of intrinsically burst-firing (IB) neurons that are unique to cortical layer 5 may play a role in the rhythmic activity seen under these conditions. Whole cell patch-clamp and field-potential recordings in slices of somatosensory cortex from neonatal rats were used to study the development of IB cells and the development of 0 [Mg2+] oscillations. IB cells were not encountered before postnatal day 12 (P12) in layer 5, but from P13 to P19 an increasing proportion of cells had IB properties. Recordings from cells at P7, P17, and P19 in 0 [Mg2+] indicate that dramatic changes occur postnatally in 0 [Mg2+]-induced activity. At P7, cells largely showed trains of single action potentials. In contrast, at P19, cells showed organized bursts of rhythmic activity lasting 0.5-5 s separated by periods of relative quiescence. Cells recorded at P17 were found to have less organized rhythmic activity than cells from P19 cortex. Field-potential recordings in 0 [Mg2+] made at P7 showed infrequent and slowly occurring field depolarizations, whereas field-potential recordings at P19 consisted of spontaneous bursts of 4-12 Hz oscillations identical to those observed in the adult. Application of NE, which inhibits burst-firing of layer 5 IB cells, significantly altered the discharge pattern of 0 [Mg2+] oscillations at P19. These data suggest that the maturation of one type of rhythmic network activity intrinsic to neocortex is influenced by the development of the membrane properties of a single cell type.
通过降低细胞外镁离子浓度（[Mg2+]o）以解除N-甲基-D-天冬氨酸（NMDA）受体的阻断，可在成年躯体感觉皮层切片中诱导出一种新皮层固有的节律性活动形式。有人提出，皮层第5层特有的一群固有爆发式放电（IB）神经元可能在这些条件下所见的节律性活动中发挥作用。利用新生大鼠躯体感觉皮层切片中的全细胞膜片钳和场电位记录来研究IB细胞的发育以及零镁离子振荡的发育。在出生后第12天（P12）之前，第5层中未发现IB细胞，但从P13到P19，具有IB特性的细胞比例不断增加。在零镁离子条件下对P7、P17和P19细胞的记录表明，出生后零镁离子诱导的活动发生了显著变化。在P7时，细胞主要表现为一连串的单动作电位。相比之下，在P19时，细胞表现出有组织的节律性活动爆发，持续0.5 - 5秒，中间间隔相对静止期。发现P17记录的细胞的节律性活动不如P19皮层的细胞有组织。P7时在零镁离子条件下的场电位记录显示场去极化不频繁且发生缓慢，而P19时的场电位记录由4 - 12赫兹振荡的自发爆发组成，与成年时观察到的相同。应用去甲肾上腺素（NE）可抑制第5层IB细胞的爆发式放电，显著改变了P19时零镁离子振荡的放电模式。这些数据表明，新皮层固有的一种节律性网络活动的成熟受到单一细胞类型膜特性发育的影响。
