POSTNATAL MATURATION OF THE DIRECT CORTICOSPINAL PROJECTIONS IN THE MACAQUE MONKEY
POSTNATAL MATURATION OF THE DIRECT CORTICOSPINAL PROJECTIONS IN THE MACAQUE MONKEY
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DOI：
10.1093/cercor/5.6.518
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发表时间：
1995-11-01
期刊：
影响因子：
3.7
通讯作者：
DARIANSMITH, I
中科院分区：
文献类型：
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作者：
GALEA, MP;DARIANSMITH, I
用逆行荧光示踪法观察了猕猴皮质脊髓多个投射的形态学变化，发现其与猴获得手灵巧性有关，出生后8个月左右，猴的行为和解剖学均已成熟。在出生时，主要运动皮层（4区）、近中辅助运动区和扣带回23和24区、12区、背外侧区6a β、背外侧区和腹侧区6a α（F4区）、顶叶区2/5、7 b和岛周皮层的皮质脊髓投射是精细的体视组织（包括SII区），定义明确，轴突延伸至所有脊髓节段。虽然这种区域投射模式与成熟猕猴的大致相似，但在出生后8个月内，存在实质性的成熟变化，这些变化包括：（1）对侧皮质脊髓投射起源的大脑皮质面积减半;（2）投射到脊髓所有节段的标记皮质脊髓神经元数量减少三倍。侧支清除而不是神经元细胞死亡可能是成年猕猴皮质脊髓神经元数量和面积减少的机制，存活的皮质脊髓轴突终末也在出生后大量发育，出生时一些终末已侵入各脊髓节段的中间区，但很少有终末穿过背角和腹角。出生后6个月，然而，许多皮质脊髓神经元逆行标记后，这些脊髓区注射荧光标记在颈椎和腰椎spinalsegment.These数据表明，相当大的出生后减少皮质脊髓神经元投射到对侧脊髓，并暗示，许多轴突被淘汰从来没有突触的脊髓神经元。这表明，在胎儿中期，成熟猴的第五层皮层神经元的轴突将终止于丘脑、脑干或脊髓中的特定神经元群体，穿过一条共同的通路向下穿过内囊进入脊髓，靠近这些连续的靶点，并可能在这些水平形成侧枝。在出生后的时期，每个这样的神经元建立一个稳定的，有效的突触输入，只有一个或几个这些皮层下的目标群体，其余的侧支退化，出生后成熟的皮质脊髓神经元，在这项研究中，是兼容的这样一个模型。
Postnatal changes in the topography of the multiple corticospinal projections in the macaque monkey were followed using retrogradely transported fluorescent tracers, and related to the monkey's acquisition of manual dexterity; both behavioral and anatomical maturation were completed by about 8 postnatal months.Cortical origins of the corticospinal projections were examined by constructing planar projection maps of the distributions of labeled corticospinal neuron somas; these somas were found only in lamina V. At birth elaborate somatotopically organized corticospinal projections from primary motor cortex (area 4), the mesial supplementary motor area and cingulate areas 23 and 24, area 12, dorsolateral area 6a beta, the dorsolateral and ventral area 6a alpha (area F4), parietal areas 2/5, 7b and the peri-insular cortex (including area SII), were clearly defined, with axons extending to all spinal cord segments. While this pattern of regional projections broadly resembled that of the mature macaque, there were, however, substantial maturational changes during the 8 months after birth, These included (1) a halving of the area of cerebral cortex from which the contralateral corticospinal projection originated and (2) a threefold reduction in the number of labeled corticospinal neurons projecting to all segments of the cord. Collateral elimination rather than neuronal cell death was the likely mechanism for this reduction in the population and areal extent of corticospinal neurons in the maturing macaque.The surviving corticospinal axon terminals also developed substantially during the postnatal period, At birth some terminals had invaded the intermediate zone in each spinal segment, hut few had penetrated the dorsal and ventral horns. By 6 postnatal months, however, many corticospinal neurons were retrogradely labeled following the injection of fluorescent labels into each of these spinal zones in cervical and lumbar spinal segments.These data demonstrate a considerable postnatal reduction in corticospinal neurons projecting to the contralateral spinal cord, and imply that many of the axons that are eliminated never synapse on spinal neurons. It is suggested that during the middle fetal period the axons of many of the cortical neurons in lamina V that in the mature monkey will terminate on particular neuron populations in the thalamus, brainstem, or spinal cord, traverse a common pathway down through the internal capsule into the spinal cord, passing close to these successive targets, and possibly forming collaterals at these levels. In the postnatal period each such neuron establishes a stable, effective synaptic input to only one or a few of these subcortical target populations, and the remaining collateral branches regress, The postnatal maturation of corticospinal neurons, examined in this study, is compatible with such a model.