Delineation of motoneuron subgroups supplying individual eye muscles in the human oculonnotor nucleus

The oculomotor nucleus (nIII) contains the motoneurons of medial, inferior, and superior recti (MR, IR, and SR),inferior oblique (IO),and levator palpebrae (LP) muscles. The delineation of motoneuron subgroups for each muscle is well-known in monkey, but not in human. We studied the transmitter inputs to human nIII and the trochlear nucleus (nIV),which innervates the superior oblique muscle (SO),to outline individual motoneuron subgroups. Parallel series of sections from human brainstems were immunostained for different markers: choline acetyltransferase combined with glutamate decarboxylase (GAD),calretinin (CR) or glycine receptor. The cytoarchitecture was visualized with cresyl violet, Gallyas staining and expression of non-phosphorylated neurofilaments. Apart from nIV, seven subgroups were delineated in nIII: the central caudal nucleus (CCN),a dorsolateral (DL),dorsomedial (DM),central (CEN),and ventral (VEN) group, the nucleus of Perlia (NP) and the non-preganglionic centrally projecting Edinger Westphal nucleus (EWcp). DL, VEN, NP and EWcp were characterized by a strong supply of GAD-positive terminals, in contrast to DM, CEN, and nIV. CR-positive terminals and fibers were confined to CCN, CEN, and NP. Based on location and histochemistry of the motoneuron subgroups in monkey, CEN is considered as the SR and 10 motoneurons, DL and VEN as the B- and A-group of MR motoneurons, respectively, and DM as IR motoneurons. A good correlation between monkey and man is seen for the CR input, which labels only motoneurons of eye muscles participating in upgaze (SR, 10, and LP). The CCN contained LP motoneurons, and nIV those of SO. This study provides a map of the individual subgroups of motoneurons in human nIII for the first time, and suggests that NP may contain upgaze motoneurons. Surprisingly, a strong GABAergic input to human MR motoneurons was discovered, which is not seen in monkey and may indicate a functional oculomotor specialization

Case Studies in Neuroscience: Instability of the visual near triad in traumatic brain injury-evidence for a putative convergence integrator.

Deficits of convergence and accommodation are common following traumatic brain injury, including mild traumatic brain injury, although the mechanism and localization of these deficits have been unclear and supranuclear control of the near-vision response has been incompletely understood. We describe a patient who developed profound instability of the near-vision response with inability to maintain convergence and accommodation following mild traumatic brain injury, who was identified to have a structural lesion on brain MRI in the pulvinar of the caudal thalamus, the pretectum, and the rostral superior colliculus. We discuss the potential relationship between posttraumatic clinical near-vision response deficits and the MRI lesion in this patient. We further propose that the MRI lesion location, specifically the rostral superior colliculus, participates in neural integration for convergence holding, given its proven anatomic connections with the central mesencephalic reticular formation and C-group medial rectus motoneurons in the oculomotor nucleus, which project to extraocular muscle nontwitch fibers specialized for fatigue-resistant, slow, tonic activity such as vergence holding. Supranuclear control of the near-vision response has been incompletely understood to date. We propose, based on clinical and anatomic evidence, functional pathways for vergence that participate in the generation of the near triad, "slow vergence," and vergence holding