Tseng G F, Prince D A
Department of Neurology and Neurological Sciences, Stanford University School of Medicine, California 94305.
J Comp Neurol. 1993 Sep 1;335(1):92-108. doi: 10.1002/cne.903350107.
In order to examine the degree of diversity within a population of cortical projection neurons, rat corticospinal cells were retrogradely labeled in vivo by injecting rhodamine-tagged microspheres into the cervical spinal cord, and subsequently studied electrophysiologically and anatomically in neocortical slices maintained in vitro, by use of standard current clamp techniques and a double-labeling protocol (Tseng et al., J. Neurosci. Meth. 37:121-131, 1991). Three different subgroups were distinguished on the basis of their spiking behavior: (1) Adapting cells had a marked fast (50 ms) and slow phase (200 ms) of spike frequency adaptation; (2) regular spiking (RS) cells had only a period of fast adaptation; (3) some regular spiking neurons had prominent depolarizing afterpotentials (DAPs) and could generate bursts of spikes, often in repetitive fashion (RSDAP cells). Subgroups of RSDAP cells had different patterns of burst responses to depolarizing current pulses, suggesting differences in the types and/or sites of underlying ionic conductances. Adapting cells had a slightly higher membrane input resistance and more prominent slow hyperpolarizing afterpotentials than RS and RSDAP neurons; however, the activation of presumed anomalous rectifier current by intracellular hyperpolarizations was less prominent in adapting neurons. Orthodromic stimulation in layer I evoked presumed excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs)in all three types of cells, but prominent short-latency IPSPs were found in a higher percentage of adapting neurons. The morphology of electrophysiologically characterized corticospinal neurons was studied following intracellular injection of biocytin. All three spiking types were typical layer V pyramids with apical dendrites reaching layer 1, basal dendrites in infragranular layers, and deep-directed axons that had a moderate density of local collaterals in lower cortical layers. The profuseness of dendrites, examined by Sholl's analysis of two-dimensional, camera lucida-reconstructed neurons was comparable in the three neuronal subgroups, although a smaller somatic area and more slender apical dendritic trunk were found in adapting neurons. Our results suggest that corticospinal cells in rats are a heterogeneous population of projection neurons with respect to their spiking behavior, membrane properties, synaptic connections, and, to a lesser extent, their morphology. This diversity revealed in vitro adds new complexity to the classification of corticospinal neurons.
为了研究皮质投射神经元群体中的多样性程度，通过将罗丹明标记的微球注入颈脊髓，在体内对大鼠皮质脊髓细胞进行逆行标记，随后利用标准电流钳技术和双标记方案，在体外维持的新皮质切片中对其进行电生理和解剖学研究（曾等，《神经科学方法杂志》37:121 - 131, 1991）。根据它们的放电行为区分出三个不同的亚组：(1)适应型细胞具有明显的快速（50毫秒）和慢速（200毫秒）放电频率适应阶段；(2)规则放电（RS）细胞只有快速适应期；(3)一些规则放电神经元具有明显的去极化后电位（DAPs），并且能够产生一串动作电位，通常以重复方式（RSDAP细胞）。RSDAP细胞亚组对去极化电流脉冲的爆发反应模式不同，这表明潜在离子电导的类型和/或部位存在差异。与RS和RSDAP神经元相比，适应型细胞具有略高的膜输入电阻和更明显的慢速超极化后电位；然而，在适应型神经元中，细胞内超极化对假定的反常整流电流的激活不太明显。在I层进行的顺向刺激在所有三种类型的细胞中都诱发了假定的兴奋性和抑制性突触后电位（EPSPs和IPSPs），但在较高比例的适应型神经元中发现了明显的短潜伏期IPSPs。在细胞内注射生物胞素后，对电生理特征明确的皮质脊髓神经元的形态进行了研究。所有三种放电类型都是典型的V层锥体神经元，其顶端树突延伸至I层，基底树突位于颗粒下层，轴突向深部延伸，在较低皮质层具有中等密度的局部侧支。通过对二维、明视野重建神经元进行肖尔分析来检查树突的丰富程度，结果表明在这三个神经元亚组中是相当的，尽管在适应型神经元中发现了较小的胞体面积和更细长的顶端树突干。我们的结果表明，大鼠的皮质脊髓细胞在放电行为、膜特性、突触连接以及在较小程度上在形态方面是一群异质性的投射神经元。体外揭示的这种多样性为皮质脊髓神经元的分类增加了新的复杂性。
