The Afferent and Efferent Vestibular Pathways: Morphologic Aspects
Our knowledge of the course and connections of the neurons serving vestibular reflexes has been greatly expanded over the last ten years by the use of modern neuroanatomic techniques. Anterograde methods utilizing the phenomenon of wallerian degeneration have been employed to demonstrate the termination of first order vestibular neurons in the vestibular nuclei and the projection of second order neurons in the vestibular nuclei serving vestibuloocular and vestibulospinal reflexes (3,18). These anterograde techniques employed selective silver impregnation methods (the Nauta method) to trace fine axon terminals in the central nervous system and a myelin stain (Sudan black) to overcome technical difficulties involved in the study of neurons surrounded by the temporal bone. Although these methods successfully demonstrated the course and termination of first and second order vestibular neurons, the development of a reliable retrograde technique was necessary to identify the precise location of cells within the vestibular nuclei that project to the effector organs. The retrograde axoplasmic tracer method utilizing horseradish peroxidase has fulfilled this need and has been utilized widely as a standard neuroanatomic technique (14). It has been a great aid in the elucidation of the precise location of central nervous system neurons. This discussion will review the neuroanatomic features of the vestibular system in the cat that have been revealed by these techniques.
KeywordsNeurol Tral Dial Acetylcholinesterase Sudan
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