Ulinski Philip S, Rainey W Todd
Department of Anatomy and the Committee on Neurobiology, University of Chicago, Chicago, Illinois 60637.
J Morphol. 1980 Jul;165(1):85-116. doi: 10.1002/jmor.1051650108.
Lateral cortex is the most laterally placed of the four cortical areas in snakes. Earlier studies suggest that it is composed of several subdivisions but provide no information on their organization. This paper first investigates the structure of lateral cortex in boa constrictors (Constrictor constrictor), garter snakes (Thamnophis sirtalis), and banded water snakes (Natrix sipedon) using Nissl and Golgi preparations; and secondly examines the relation of main olfactory bulb projections to the subdivisions of lateral cortex using Fink-Heimer and electron microscopic preparations. Lateral cortex is divided on cytoarchitectonic grounds into two major parts called rostral and caudal lateral cortex. Each part is further divided into dorsal and ventral subdivisions so that lateral cortex has a total of four subdivisions: dorsal rostral lateral cortex (drL), ventral rostral lateral cortex (vrL), dorsal caudal lateral cortex (dcL) and ventral caudal lateral cortex (vcL). Systematic analyses of Golgi preparations indicate that the rostral and caudal parts each contain distinct populations of neurons. Rostral lateral cortex contains bowl cells whose dendrites arborize widely in the outer cortical layer (layer 1). The axons of some bowl cells can be traced medially into dorsal cortex, dorsomedial cortex and medial cortex. Caudal lateral cortex contains pyramidal cells whose somata occur in layers 2 and 3 and whose dendrites extend radially up to the pial surface. In addition, three populations of neurons occur in both rostral and caudal lateral cortex. Stellate cells occur in all three layers and have dendrites which arborize in all directions. Double pyramidal cells occur primarily in layer 2 and have dendrites which form two conical fields whose long axes are oriented radially. Horizontal cells occur in layer 3 and have dendrites oriented concentric with the ependyma. Fink-Heimer preparations of snakes which underwent lesions of the main olfactory bulb show that the primary olfactory projections to cortex are bilateral and restricted precisely to rostral lateral cortex. Electron microscopic degeneration experiments indicate that the olfactory bulb fibers end as terminals which have clear, spherical vesicles and asymmetric active zones. The majority are presynaptic to dendritic spines in outer layer 1. These studies establish that lateral cortex in snakes is heterogeneous and contains two major parts, each containing two subdivisions. The rostral and caudal parts have characteristic neuronal populations. Primary olfactory input is restricted to rostral lateral cortex and seems to terminate heavily on the distal dendrites of bowl cells. Axons of some of these cells leave lateral cortex, so that the rostral lateral cortex forms a direct route by which olfactory information reaches other cortical areas. The functional role of caudal lateral cortex is not clear.
外侧皮质是蛇类四个皮质区域中位置最靠外侧的。早期研究表明它由几个亚区组成，但未提供关于其组织结构的信息。本文首先使用尼氏染色和高尔基染色制剂研究了红尾蚺（蚺科蚺属）、束带蛇（美洲束带蛇属）和带纹水蛇（锦蛇属）的外侧皮质结构；其次使用芬克 - 海默染色和电子显微镜制剂研究了主嗅球投射与外侧皮质亚区的关系。外侧皮质根据细胞构筑学分为两个主要部分，称为吻侧和尾侧外侧皮质。每个部分又进一步分为背侧和腹侧亚区，因此外侧皮质共有四个亚区：背侧吻侧外侧皮质（drL）、腹侧吻侧外侧皮质（vrL）、背侧尾侧外侧皮质（dcL）和腹侧尾侧外侧皮质（vcL）。对高尔基染色制剂的系统分析表明，吻侧和尾侧部分各自包含不同的神经元群体。吻侧外侧皮质包含碗状细胞，其树突在外皮质层（第1层）广泛分支。一些碗状细胞的轴突可向内侧追踪至背侧皮质、背内侧皮质和内侧皮质。尾侧外侧皮质包含锥体细胞，其胞体出现在第2层和第3层，树突径向延伸至软膜表面。此外，在吻侧和尾侧外侧皮质中都存在三种神经元群体。星状细胞出现在所有三层，其树突向各个方向分支。双锥体细胞主要出现在第2层，其树突形成两个圆锥场，其长轴径向排列。水平细胞出现在第3层，其树突与室管膜同心排列。对主嗅球损伤的蛇进行芬克 - 海默染色显示，向皮质的初级嗅觉投射是双侧的，并且精确地局限于吻侧外侧皮质。电子显微镜变性实验表明，嗅球纤维以具有清晰球形囊泡和不对称活性区的终末结束。大多数终末与外层1中的树突棘形成突触前联系。这些研究表明，蛇的外侧皮质是异质的，包含两个主要部分，每个部分包含两个亚区。吻侧和尾侧部分具有特征性的神经元群体。初级嗅觉输入局限于吻侧外侧皮质，并且似乎大量终止于碗状细胞的远端树突上。其中一些细胞的轴突离开外侧皮质，因此吻侧外侧皮质形成了嗅觉信息到达其他皮质区域的直接途径。尾侧外侧皮质的功能作用尚不清楚。
