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

Area of Science:

• Neuroscience
• Neuroanatomy
• Primate Brain Research

Background:

• The subthalamic nucleus is a key component of the basal ganglia motor circuit.
• Understanding its cellular architecture is crucial for deciphering basal ganglia function and dysfunction.
• Previous studies have provided limited detailed descriptions of subthalamic nucleus neuron morphology in primates.

Purpose of the Study:

• To characterize the morphological diversity of neurons within the adult monkey (Macaca mulatta) subthalamic nucleus.
• To differentiate between local interneurons and principal neuron subtypes (radiating and elongated fusiform).
• To describe dendritic morphology, somatic spines, and lipofuscin distribution in these neurons.

Main Methods:

• Golgi preparations of adult monkey (Macaca mulatta) brains.
• 1-micron thick plastic sections for light microscopy.
• Electron microscopy of squirrel monkey (Saimiri sciureus) for detailed ultrastructural analysis.
• Cresyl violet staining for identifying local interneuron cell bodies.

Main Results:

• Identified local interneurons and two principal neuron types: radiating and elongated fusiform, in the subthalamic nucleus.
• Radiating neurons exhibit few somatic spines and extensive, thin dendrites (up to 400 microns) with variable spine density.
• Elongated fusiform neurons possess smooth cell bodies, dendrites extending over 750 microns, and fewer dendritic spines.
• Lipofuscin granules were observed in principal neurons of Macaca mulatta, Macaca nemestrina, and Saimiri sciureus.
• Local interneurons feature small cell bodies, undulating dendrites with bulbous appendages, and beaded axon-like processes.

Conclusions:

• The subthalamic nucleus contains distinct principal neuron subtypes with unique dendritic arborizations and spine patterns.
• Local interneurons possess specialized dendritic structures, suggesting unique local circuit interactions.
• Variations in lipofuscin presence across primate species may reflect aging or metabolic differences.