Electron Microscopic Examination of the Cat Oculomotor Nucleus Innervating the Medial Rectus Muscle

Oculoinotor nerve is a very important nerve in the ophthalornology, innervating the medial rectus, inferior rectus, inferior oblique, superior rectus, levator palpebrae superioris, and the presynaptic parasyrnpathetic outflow to the internal muscles of eye (the ciliary muscle and the sphincter muscle of the iris) . To examine the fine structure of neurons and synapses in the oculomotor nucleus projecting the rnedial rectus Hiuscle, 50% horseradish peroxidase (HRP) solution was injected into the rnedial rectus rnuscle of the cat, and serial sections of midbrain were studied with electron microscopes. Large motor neuron, small motor neuron and spindleshape motor neuron were examined. Cell body contained rich organells that. were nucleus, rough endoplasmic reticulum, HRP containing lysosorne, mitochondria and ribosome etc. Three kinds of synapses that are axosomatic synapse, axo-dendritic synapse and axo-axonic synapse were examed. Moreover, the nerve terminals had spherical-shaped synaptic vesicles. These results suggest that the function of inotorneurons related to the medial rectus muscle is not. defined by the shape and distribution of nerve terrninals but. depends on the shape of synaptic vesicles.

LOCALIZATION OF MOTOR NEURONS IN THE OCULOMOTOR NUCLEUS INNERVATING THE INFERIOR OBLIQUE MUSCLE AND THEIR DENDRITIC ARCHITECTURE IN THE RABBIT——A STUDY USING CT-HRP / 解剖学报

The localization of the neurons which control the inferior oblique muscle in the oculomotor nucleus and their dendritic architecture were studied by injecting the conjugated cholera toxin-horseradish peroxidase (CT-HRP) into the inferior oblique muscle of 7 rabbits.The oculomotor nucleus could be divided into oral, middle and caudal parts. The middle part was further divided into dorsomedial and ventrolateral parts, and the caudal part divided into dorsal and ventral parts. The labeled neurons innervating the inferior oblique muscle were mainly distributed ipsilaterally and occupying two thirds. of the rostrocaudal extent of the oculomotor nucleus, a few were scattered contralaterally.The labeled cells were found in the dorsomedial part of the nucleus orally, and shifted in successive caudal sections to the medial and then to the ventral part. No labeled cells in the oral and caudal ends of the nucleus could be identified.The dendritic branches of the labeled neurons covered the whole nucleus, but densest in its dorsomedial part. Many of them extended beyond the boundary of the nucleus into the central gray matter dorsally, some even approacheding the aqueduct, or through the medial longitudinal fasciculus into the reticular formation laterally and ventrally. A few dendrites crossed the midline into the contralateral nucleus. Therefore the receptive field of the oculomotor nucleus is presumably much larger than the area of the nucleus itself.