锥体束神经元在大鼠、树皮层的分布及其与GABA能神经元的关系

以大鼠和树作为研究材料，在脑桥下缘切断一侧锥体束，用HRP逆行标记和计算机三维重构观察锥体束神经元在皮层的分布，以及在光镜和电镜下观察锥体束神经元和GABA能神经元的关系。逆行标记的锥体来神经元主要分布于皮层的运动区和体感区，在枕区、扣带区、颞区和屏状皮层中都有少量分布。树锥体束神经元的总数是大鼠的1．5倍，用计算机重构显示HRP标记的锥体束神经元在脑内吻尾方向上的分布跨度比大鼠小，故其分布范围较大鼠集中，密度较高，且其中大细胞也较多．树的锥体来神经元长径在15μm以上者占74．0％；大鼠则占62．9％。在电镜下观察这些锥体束神经元的胞体上全分布着对称型的突触，其中既有GABA能，也有非GA-BA能者。不同胞体上接受GABA能和非GABA能突触的比例不同，一种较大的胞体上GABA与non－GABA阳性终末相比，前者数量大（13：3）而较小的胞体上则相反，两者的数量相比，为7：18。大鼠和树的锥体束神经元胞体的单位周长上接受的突触数目也不同，树锥体束神经元胞体的10μm单位周长上分布有4．4个突触。大鼠则为3．4个。随着动物进化锥体束神经元接受突触的数目有增加的趋势．

DISTRIBUTION OF PYRAMIDAL TRACT NEURONS IN THE CEREBRAL CORTEX OF RAT AND TREE SHREW AND THEIR RELATIONSHIP WITH GABAERGIC NEURONS

The distribution of pyramidal tract neurons (PTNs) in the cerebral cortex of rat and tree shrew was studied usingretrograde HRP labeling and computer-aided three-dimensional reconstruction. The relationship between PTNs and GABA-immunopositive neurons was also investigJrted with light and electron micro8copy.PTNs were found to be distributed mainly in the motor and somatosensory cortexl a srnall number of PTNs were also seenin the occipital l cingular, ternporal, and claustral cortex. The total number of PTNs in the tree shrew was about 1. 5 fold ofthose in the rat. However, in the cerebral cortex of the tree shrew, the PTNs were distributed more densely so that the cortical territory in which they were located was srnaller in size than that in the rat cortex in which PTNs of the rat were distributed. Furthermore, the percentage of large PTNs of which the longitudinal diameter of the cell body was>15μm wa862- 9% in the rat and 74. 0% in the tree shrew, respectively. Electronmicroscopic observation showed that on the soma ofPTNs all synapses were of symrnetrical type and some of thern were GABAergic and others were not. On the soma of onelarge PTN (soma section area 35 μm× 18 μm), in 16 synapses the ratio of GABAe rgic / non-GABAergic synapses was 13:3 and for another smaller PTN (soma section area 28 μm×14 μm)it was 7： 18 in 25 synapses. The relationship between thenumber of synapses and their perimeters was also analyzed. The density of synapses per unit perimeter of PTN was found tobe 3. 4/10μm in the rat and 4. 4/10μm in the tree shrew. It is therefore likely that the higher the animal species in evolutionthe more the synapses on its PTNs.