Primate Subthalamic Nucleus Research Articles

Intracellular labelling of rat subthalamic neurones with horseradish peroxidase: Computer analysis of dendrites and characterization of axon arborization

Neurones of the rat subthalamic nucleus were identified by their response to cortical stimulation and then intracellularly labelled with horseradish peroxidase. After fixation, the brains were cut serially in sagittal plane and processed by the cobalt chloride-diaminobenzicline procedure. The morphology of nine of the twenty stained neurones strictly located inside the subthalamic nucleus is described by means of quantitative parameters following light-microscopic examination and three-dimensional computer reconstruction. They were all identified as Golgi type I neurones. The somata were ovoidal in shape. A mean of four dendritic stems arose from the soma and gave rise to a mean of 27 tips. The dendrites were thin with long and pedunculated spines. The dendritic fields were ellipsoidal in shape (1000 × 600 × 300 μm) and were parallel to the principal plane of the nucleus. The dimensions of the dendritic fields are very close to those of the nucleus, and some dendrites cross its limits. The axons gave off two branches, one going caudally and the other rostrally. The caudal-going branch of the axon of one neurone, followed into the substantia nigra, divided into several collaterals coursing dorsoventrally. The rostral-going branch was never followed up to its termination. An intranuclear axonal collateral was observed in only one case. The present data are compared with those obtained from the primate subthalamic neurones. In spite of slight differences in the pattern of dendritic branching, the neurones are similar in both species. However, major differences in the internal organization of the dendritic fields are observed. Dendrites mixing with other neuronal populations were never observed in the primate. Moreover, the relative sizes of the dendritic fields and of the nucleus are strikingly different. This gives to the primate subthalamic nucleus specific and more precisely organized afferent connections.

Subthalamic neurons in primates: A quantitative and comparative analysis

The anatomy of the subthalamic nucleus in primates was studied in the macaque and in man with relation to stereotaxic ventricular coordinates. Its cytoarchitecture was studied on cresyl violet stained sections and the subthalamic neurons were analysed on Golgi impregnated material from macaque, baboon and man. The distribution and morphology of the neurons were described by means of both algebraic (dendritic numbers) and geometric (lengths, surfaces and three-dimensional reconstructions) statistical parameters. The primates' subthalamic neurons were compared with those of cats. The unimodal distribution of all the statistically studied parameters strongly suggests that there is only one variety of subthalamic Golgi type I neuron which is identical in cat, monkey and man. The cell body is ovoidal in shape, giving it a fusiform appearance when it is observed parallel to its long axis, whereas it looks round or polygonal in other directions. On average, 7 dendritic stems originate from various points on the periphery of the so ma; they branch out in successive bifurcations giving rise to a mean of 27 dendritic tips. In the centrally located neurons, the dendritic domains are ellipsoidal. Their mean dimensions are 1200, 600 and 300 μm. The long axis of the dendritic domains is usually parallel to the main rostrocaudal axis of the nucleus. The marginal neurons that are close to the borders of the nucleus seem to lack the part of their dendritic arborization that could have crossed the borders. Their longest dendrites are parallel to the border of the nucleus. Cell bodies are somewhat smaller and dendrites shorter in the caudal part of the nucleus than in its oral part, but the dendritic domains are still ellipsoidal. In addition to the Golgi type I neurons, small neurons have been looked for in cat, baboon, macaque and human brains. None of the small cells found in baboon and in man had the characteristic morphology of a local circuit neuron. Thus the subthalamic nucleus appears to be a homogeneous closed nucleus whose Golgi type I neurons seem to belong to a single neuronal species that does not change from cat to man. As afferents and efferents to the nucleus also apparently remain the same, it is probably legitimate to extrapolate from studies on experimental species to man.

The neurons in the primate subthalamic nucleus: a Golgi and electron microscopic study.

In Golgi preparations of the adult monkey (Macaca mulatta) local interneurons and two varieties of principal neurons, radiating and elongated fusiform, are found in the subthalamic nucleus. The cell bodies of the radiating neurons have a few delicate, somatic spines some of which are occasionally bilobed and trilobed. Five to eight dendritic trunks give rise to branching, tapering dendrites, which may extend for over 400 microns. These dendrites are much thinner than the dendrites in the globus pallidus and the substantia nigra. Some neurons have many and some neurons have few dendritic spines. When numerous the dendritic spines are concentrated on the dendritic trunks and proximal dendrites. The relatively few elongated fusiform neurons are found not only in the capsule but also in the center of the nucleus. Most dendrites emerge from the opposite poles of their smooth surfaced cell bodies. They have a few dendritic spines. Some of these dendrites extend for more than 750 microsn. In 1-micron thick plastic sections lipofuscin granules are present in some but not all principal neuron cell bodies of the monkey (Macaca mulatta); but these granules are present in all principal neuron cell bodies of the pig-tail monkey (Macaca nemestrina) and of the squirrel monkey (Saimiri sciureus). The local interneurons have small cell bodies and a few relatively long undulating dendrites. The dendrites have bulbous dendritic appendages of varying complexity and beaded axon-like processes. The dendritic appendages and axon-like processes are more numerous distally and on the distal ends of the dendrites they form complex entanglements. Axons coming from the cell body have not been observed. The cell bodies of the local interneurons are identified in cresyl violet stained sections of the monkey (Macaca mulatta), in 1-micron thick plastic sections and electron micrographs of the squirrel monkey (Saimiri sciureus). They have relatively large nuclei surrounded by a thin rim of cytoplasm rich in polyribosomes.