Avendaño C, Isla A J, Rausell E
Department of Morphology, School of Medicine, Autónoma University, Madrid, Spain.
J Comp Neurol. 1992 Jul 15;321(3):373-86. doi: 10.1002/cne.903210306.
It is well known that area 3a in the cat may monosynaptically influence the activity of neurons in the motor cortex. Much less information is available, however, on the anatomy of these connections. By using single or combined injections of different retrograde axonal tracers, we investigated the topography (horizontal and laminar) of area 3a neurons projecting to the motor cortex, and the anatomical relationships between these neurons and those projecting to other areas (2, 5, and SII) which, in turn, project to the motor cortex. Area 3a projects to all parts of area 4 gamma, to area 4 delta, and to the agranular area 6 in the lateral bank of the presylvian sulcus (area 6 alpha gamma), but not to other parts of areas 4 and 6. This projection exhibits a loose topographic organization along the mediolateral dimension of area 3a, and, in many cases, arises predominantly from the rostral half of this area. Although single small injections in the motor cortex produced two or more separate patches of retrograde labeling in 3a, after simultaneous injections of fluorochromes in two separate loci there often appeared in area 3a overlapping populations of neurons which were labeled retrogradely by each of the dyes, but with very few double-labeled neurons. In horseradish peroxidase (HRP) cases, 72% of area 3a neurons projecting to area 4 gamma were distributed in supragranular layers (mainly layer III), although the proportion of labeling in infragranular layers was larger when using fluorescent dyes. Double-labeled cells predominated in infragranular layers. These results have a bearing upon the functional roles that have been attributed to area 3a, as a cortical locus involved in muscle sensation, and a cortical relay to the motor cortex of rapid feedback information from muscle activity during movement.
众所周知，猫的3a区可能通过单突触影响运动皮层中神经元的活动。然而，关于这些连接的解剖结构的信息却少得多。通过使用不同逆行轴突示踪剂的单次或联合注射，我们研究了投射到运动皮层的3a区神经元的拓扑结构（水平和分层），以及这些神经元与投射到其他区域（2区、5区和第二躯体感觉区）的神经元之间的解剖关系，而这些区域又反过来投射到运动皮层。3a区投射到4γ区的所有部分、4δ区以及前薛氏沟外侧壁的无颗粒6区（6αγ区），但不投射到4区和6区的其他部分。这种投射在3a区的内外侧维度上呈现出松散的拓扑组织，并且在许多情况下，主要起源于该区域的前半部分。虽然在运动皮层进行单次小剂量注射会在3a区产生两个或更多个单独的逆行标记斑块，但在两个不同位点同时注射荧光染料后，3a区经常会出现重叠的神经元群体，每个染料都能使这些神经元逆行标记，但双标记神经元很少。在辣根过氧化物酶（HRP）标记的情况下，投射到4γ区的3a区神经元中有72%分布在颗粒上层（主要是III层），尽管使用荧光染料时颗粒下层的标记比例更大。双标记细胞在颗粒下层占主导地位。这些结果与归因于3a区的功能作用有关，3a区是一个参与肌肉感觉的皮层位点，也是运动过程中肌肉活动快速反馈信息到运动皮层的皮层中继站。
