The torus semicircularis in a gekkonid lizard

Abstract

The cytoarchitecture and neuromorphology of the torus semicircularis in the tokay gecko, Gekko gecko, were examined in Nissl-stained, fiber-stained, and Golgi-impregnated tissues. From a superficial position, the torus semicircularis extends rostrally under the caudal half of the optic tectum. Caudally, the two tori abut upon one another; rostrally, they diverge. The torus semicircularis consists of central, laminar, and superficial nuclei. The central nucleus consists of fusiform, spherical and triangular neurons. Their dendrites are highly branched, with numerous dendritic spines, and are oriented mediolaterally, dorsoventrally, and rostrocaudally. Fusiform and spherical neurons display two dendritic patterns: "single axis," ramifying in one axis, and "dual axis," exhibiting higher-order branches perpendicular to the primary dendrites. Triangular neurons exhibit a "radiate" dendritic pattern. In the rostral half of the torus semicircularis, the laminar nucleus caps the central nucleus. The laminar nucleus encircles the central nucleus in the caudal torus semicircularis. The neurons of the laminar nucleus have dendritic arrays oriented parallel to the border of the central nucleus. These dendrites exhibit a paucity of dendritic spines and higher-order branches. Fusiform and spherical neurons exhibit "single axis" and "dual axis" dendritic patterns. Triangular neurons display "radiate" patterns. The caudal superficial nucleus lies dorsal and dorsolateral to the central nucleus. The superficial nucleus is sparsely populated by small fusiform and spherical neurons with moderately branched dendrites and moderate numbers of dendritic spines. These neurons display "single axis" (fusiform neurons) as well as "dual axis" and "radiate" (spherical neurons) dendritic patterns. They are oriented either parallel to or perpendicular to the boundary of the laminar nucleus.

Calcium‐binding protein immunoreactivity characterizes the auditory system of Gekko gecko

“…The caudal portion bulges outward, behind the caudal pole of the tectum, and is fused at the midline ( Fig. 8; Kennedy and Browner, 1981). The TSc then extends lateroventrally under the tectum, where it is divided into left and right by the medial portions of the tectum and commissure of optic tectum.…”

“…We focus only on the auditory central nucleus of the torus or toral nucleus, separate from the surrounding areas, which are sometimes referred to as the shell (Zeng et al, 2007;Browner and Baruch, 1984;Browner and Rubinson, 1977). The central nucleus is the recipient of the lateral lemniscal fibers (Foster and Hall, 1978) and projects to the auditory nucleus of the thalamus (Foster and Hall, 1978;Kennedy and Browner, 1981;Pritz, 1974;ten Donkelaar et al, 1987). The reported auditory responses in previous studies were probably recorded in the TSc in Gekko gecko (Kennedy, 1974;Kennedy and Browner, 1981;Manley, 1981).…”

“…In lizards, the torus is divided into an auditory central nucleus, surrounded by intercollicular and preisthmic superficial areas (Browner and Rubinson, 1977;Díaz et al, 2000;Kennedy and Browner, 1981;Puelles et al, 1995;Smeets et al, 2006;ten Donkelaar et al, 1987). In this study, we will focus only on the central nucleus (TSc).…”

“…In lizards, the torus was previously divided into a central nucleus, surrounded by laminar and superficial nuclei (Browner and Rubinson, 1977;Díaz et al, 2000;Kennedy and Browner, 1981;Smeets et al, 2006;ten Donkelaar et al, 1987). Only portions of the laminar nucleus correspond to the avian intercollicular nucleus, however, and Diaz et al (2000) have proposed that use of this term be discontinued, because the area incorporates cytoarchitectonically distinct regions.…”

“…The central nucleus is the recipient of the lateral lemniscal fibers (Foster and Hall, 1978) and projects to the auditory nucleus of the thalamus (Foster and Hall, 1978;Kennedy and Browner, 1981;Pritz, 1974;ten Donkelaar et al, 1987). The reported auditory responses in previous studies were probably recorded in the TSc in Gekko gecko (Kennedy, 1974;Kennedy and Browner, 1981;Manley, 1981).Immunoreactivity for CR, PV, and CB display distinct distribution patterns in the TSc. These distribution patterns suggest the presence of subdivisions within the central nucleus and different recipient zones for first-order, olivary, and lemniscal input.…”