Light microscopic analysis of Golgi-impregnated rat subthalamic neurons.

The neuronal morphology of the rat subthalamic nucleus (STH) was studied using Golgi techniques and Nissl stain. The results show that the somatic shapes of STH neurons vary from fusiform to oval or polygonal. Somatic cross-sectional areas vary between 140 microns2 and 440 microns2. Some of the cells have a few somatic spines. Two to six primary dendrites gave rise to tapering daughter dendrites which extend up to 500 microns. These dendrites are sparsely covered with spines. Some distal dendrites and primary dendrites of the STH also bear filiform appendages. Neurons located in the deep portion of the STH have oval dendritic fields whose long axis is parallel to the long axis of the nucleus in frontal or sagittal planes. Some of these neurons have one or two dendrites which cross the borders of the STH into the zona incerta, the lateral hypothalamus, or the cerebral peduncle. Generally, neurons located at the borders of the STH have their dendritic fields extending parallel to the borders and are confined to the nucleus. However, some neurons adjacent to the ventrolateral border of the nucleus have some dendrites extending into the cerebral peduncle. Quantitative analysis of the STH neurons showed a unimodal distribution of somatic sizes as well as the number of primary dendrites. No neurons with obvious Golgi type II characteristics were found. Two types of afferent fibers were observed entering the STH. One type consists of axon collaterals arising from the cerebral peduncle ventrolaterally, or the internal capsule rostrally, while the other enters the nucleus after crossing the internal capsule rostrally. These results suggest that the rat STH is an open nucleus in contrast to other species such as man, monkey, and cat, where it is closed, and that the rat STH may contain only one type of neuron.

A golgi study of the optic tectum of the tegu lizard, Tupinambis nigropunctatus.

The dendritic patterns of cells in the optic tectum of the tegu lizard, Tupinambis nigropunctatus, were analyzed with the Ramon-Moliner modification of the Golgi-Cox technique. Cell types were compared with those described by other authors in the tectum of other reptiles; particular comparisons of our results were made with the description of cell types in the chameleon (Ramn, 1896), as the latter is the most complete analysis in the literature. The periventricular gray layers 3 and 5 consist primarily of two cell types--piriform or pyramidal shaped cells and horizontal cells. Cells in the medial portion of the tectum, in an area coextensive with the bilateral spinal projection zone, possess dendrites that extend across the midline. The latter cells have either fusiform or pyramidal shaped somas. The central white zone, layer 6, contains fibers, large fusiform or pyramidal shaped cells, fusiform cells, and small horizontal cells. The central gray zone, layer 7, is composed predominately of fusiform cells which have dendrites extending to the superficial optic layers, large polygonal cells, and horizontal cells. The superficial gray and white layers, layers 8-13, contain polygonal, fusiform, stellate, and horizontal elements. Layer 14 is composed solely of afferent optic tract fibers. Several differences in the occurrence and distribution of cell types between the tegu and the other reptiles studied are noted. Additionally, the laminar distribution of retinal, tectotectal, telencephalic, and spinal projections in the tegutectum can be related to the distribution of cell types, and those cells which may be postsynaptic to specific inputs can be identified. The highly differentiated laminar structure of the reptilian optic tectum, both in regard to cell type and to afferent and efferent connections, may serve as a model for studying some functional properties of lamination common to cortical structures.