Mechawar N, Cozzari C, Descarries L
Département de pathologie et biologie cellulaire, Faculté de médecine, Université de Montréal, Montréal, Québec H3C 3J7, Canada.
J Comp Neurol. 2000 Dec 11;428(2):305-18. doi: 10.1002/1096-9861(20001211)428:2<305::aid-cne9>3.0.co;2-y.
A method for determining the length of acetylcholine (ACh) axons and number of ACh axon varicosities (terminals) in brain sections immunostained for choline acetyltransferase (ChAT) was used to estimate the areal and laminar densities of this innervation in the frontal (motor), parietal (somatosensory), and occipital (visual) cortex of adult rat. The number of ACh varicosities per length of axon (4 per 10 microm) appeared constant in the different layers and areas. The mean density of ACh axons was the highest in the frontal cortex (13.0 m/mm(3) vs. 9.9 and 11.0 m/mm(3) in the somatosensory and visual cortex, respectively), as was the mean density of ACh varicosities (5.4 x 10(6)/mm(3) vs. 3.8 and 4.6 x 10(6)/mm(3)). In all three areas, layer I displayed the highest laminar densities of ACh axons and varicosities (e.g., 13.5 m/mm(3) and 5.4 x 10(6)/mm(3) in frontal cortex). The lowest were those of layer IV in the parietal cortex (7.3 m/mm(3) and 2.9 x 10(6)/mm(3)). The lengths of ACh axons under a 1 mm(2) surface of cortex were 26.7, 19.7, and 15.3 m in the frontal, parietal, and occipital areas, respectively, for corresponding numbers of 11.1, 7.7, and 6.4 x 10(6) ACh varicosities. In the parietal cortex, this meant a total of 1.2 x 10(6) synaptic ACh varicosities under a 1 mm(2) surface, 48% of which in layer V alone, according to previous electron microscopic estimates of synaptic incidence. In keeping with the notion that the synaptic component of ACh transmission in cerebral cortex is preponderant in layer V, these quantitative data suggest a role for this innervation in the processing of cortical output as well as input. Extrapolation of particular features of this system in terms of total axon length and number of varicosities in whole cortex, length of axons and number of varicosities per cortically projecting neuron, and concentration of ACh per axon varicosity, should also help in arriving at a better definition of its roles and functional properties in cerebral cortex.
一种用于确定成年大鼠额叶（运动区）、顶叶（躯体感觉区）和枕叶（视觉区）皮质中，经胆碱乙酰转移酶（ChAT）免疫染色的脑切片中乙酰胆碱（ACh）轴突长度及ACh轴突膨体（终末）数量的方法，被用于估计该神经支配的面积密度和分层密度。每单位轴突长度的ACh膨体数量（每10微米4个）在不同层和区域中似乎恒定。ACh轴突的平均密度在额叶皮质中最高（13.0 m/mm³，而在躯体感觉皮质和视觉皮质中分别为9.9和11.0 m/mm³），ACh膨体的平均密度也是如此（5.4×10⁶/mm³，而在躯体感觉皮质和视觉皮质中分别为3.8和4.6×10⁶/mm³）。在所有这三个区域中，I层显示出ACh轴突和膨体的最高分层密度（例如，额叶皮质中为13.5 m/mm³和5.4×10⁶/mm³）。顶叶皮质IV层的密度最低（7.3 m/mm³和2.9×10⁶/mm³）。在额叶、顶叶和枕叶区域，皮质1平方毫米表面下的ACh轴突长度分别为26.7、19.7和15.3米，对应的ACh膨体数量分别为11.1、7.7和6.4×10⁶个。在顶叶皮质中，这意味着在1平方毫米表面下共有1.2×10⁶个突触性ACh膨体，根据先前电子显微镜对突触发生率的估计，其中仅V层就占48%。鉴于大脑皮质中ACh传递的突触成分在V层中占优势这一观点，这些定量数据表明该神经支配在皮质输出以及输入的处理中发挥作用。根据整个皮质中的总轴突长度和膨体数量、每个皮质投射神经元的轴突长度和膨体数量以及每个轴突膨体的ACh浓度，对该系统的特定特征进行外推，也应有助于更好地定义其在大脑皮质中的作用和功能特性。
