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Anatomical evidence for direct fiber projections from the cerebellar nucleus interpositus to rubrospinal neurons. A quantitative EM study in the rat combining anterograde and retrograde intra-axonal tracing methods
Authors:Jan J Dekker
Institution:Laboratory of Neurobiology, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, U.K.
Abstract:A quantitative electron microscopic (EM) study combining the anterograde intra-axonal transport of radioactive amino acids and the retrograde intra-axonal transport of the enzyme horseradish peroxidase (HRP) was performed in the magnocellular red nucleus of the rat to obtain anatomical evidence as to whether there is a direct projection from the cerebellar nucleus interpositus to the cells in the red nucleus that give rise to the rubrospinal tract. Large asymmetrical synaptic terminals were radioactively labeled in the magnocellular red nucleus following injections of 3H]leucine into the cerebellar nucleus interpositus. In these same animals, the postsynaptic target neurons were labeled with HRP granules after injection of this substance in the rubrospinal tract. A quantitative analysis showed that more than 85% of the large and giant neurons in the magnocellular red nucleus were labeled with HRP granules and also received synaptic contacts from radioactively-labeled terminals. Thus, it can be concluded that in the rat, afferents from the cerebellar nucleus interpositus establish asymmetrical synaptic contacts with large and giant rubrospinal neurons, thus confirming and extending the previous physiological evidence of such direct monosynaptic connections.
Keywords:interpositus terminals  rubrospinal neurons  electron microscopic autoradiography  retrograde HRP transport  tracing methods combined
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