A Golgi Study on the Nucleus Sphericus of the Striated Snake, Elaphe quadrivirgata

Abstract

Sununary: The intrinsic organization of the nucleus sphericus (NS) was studied in the striated snake using the rapid Golgi method. The NS is a large aggregation of cells located in the posterior portion of the telencephalon and is, as a whole, cupshaped with its hilus oriented in the rostral direction. From the periphery inward, the following three concentric layers were discernible: a marginal layer, mural layer and hilar layer. The marginal layer consists of scattered cells extending dendrites internally toward the hilar layer and externally into the anterior commissure (AC). The mural layer contains densely packed polygonal neurons with dendrites extending internally into the hilar layer and externally toward the marginal layer. The hilar layer consists of scattered cells whose dendrites extend in a transverse direction, distributing mainly in the hilar layer. The axons of the neurons in the marginal and mural layers travel rostromedially, and some axons can be traced into the AC, while those of the neurons in the hilar layer run rostrally, and some are lost among fibers of the accessory olfactory tract (AOT). The afferents to the NS are derived mainly from the AOT and AC. The AOT fibers travel caudally in a thick bundle through the hilus and are distributed totally within the hilar layer, forming a dense fiber plexus. The AC fibers enter the nucleus from the rostromedial aspect and run in an arched course, emitting numerous fine short collaterals.The nucleus sphericus (NS) is a prominent cellular aggregation located in the caudal portion of the telencephalon in certain families of reptiles, and is known to be one of the main terminal areas of the accessory olfactory tract (AOT) (Heimer, 1969;Halpern, 1976;1980;Ulinski and Peterson, 1981;Martinez-Garcia et al. 1991). From a hodological viewpoint, the NS is frequently compared to the posteromedial cortical nucleus of the amygdala in mammals. However, the structure of these two nuclei is very different: the NS displays concentric laminar organization and is considered to be an invagination of the pallium protruding into the ventricle (Ulinski and Peterson, 1981). The NS has been the subject of relatively few investigations. The efferent connections of the NS have been reported by several authors (Halpern and Silfen, 1974;Hoogland, 1977;Voneida and Sligar, 1979;Halpern, 1980;Stoll and Hoogland, 1984), while systematic analysis of its intrinsic organization has been more limited (Ulinski and Kanarek, 1973). Recently, the distribution of various chemicals in reptilian brains has been studied histochemically (Smeets et al. , 1986;Perez-Clausell, 1988;Smeets, 1988;Smeets and Steinbusch, 1988;. Further information on the structure of the NS is needed. The present study was undertaken to elucidate the intrinsic organization of the NS in the striated snake using the rapid Golgi method. The results revealed detailed features of neuronal morphology and terminal patterns of the afferent fibers, and these are discussed in the context of previous cytoarchitectural, hodologi...