The Journal of comparative neurology
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Comparative Study
Premotor neurons for vertical eye movements in the rostral mesencephalon of monkey and human: histologic identification by parvalbumin immunostaining.
In the monkey, premotor neurons for vertical gaze are located in the mesencephalic reticular formation: the rostral interstitial nucleus of the medial longitudinal fascicle (riMLF) contains medium-lead burst neurons, and the interstitial nucleus of Cajal (iC) acts as integrator for the eye-velocity signals to eye-position signals. Both nuclei lie adjacent to each other and are similar in appearance at the transition zone in Nissl-stained sections, which makes a delineation of the functionally different nuclei difficult in human. For a neuropathologic analysis of degenerative changes in saccadic disorders of patients, the histologic identification of the riMLF and the iC is important. ⋯ The immunocytochemical staining of human brainstem sections revealed the riMLF as a cluster of medium-sized, elongated parvalbumin-positive cells, with a similar appearance and at a similar location as that in monkey: a wing-shaped nucleus dorsomedial to the red nucleus, rostral to the traversing tractus retroflexus, dorsally bordered by the thalamo-subthalamic paramedian artery. The adjacent iC could be distinguished easily by its more densely packed, round parvalbumin-immunoreactive neurons. The exact identification of premotor neurons of the vertical system in the normal human brain provides a reference basis for the neuropathologic analysis of vertical gaze disorders at a cellular level.
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Two different populations of projection neurons are intermingled in the cerebellar nuclei. One group consists of small, gamma-aminobutyric acid-containing (GABAergic) neurons that project to the inferior olive, and the other group consists of larger, non-GABAergic neurons that provide an input to one or more, usually premotor, centers in the brainstem, such as the red nucleus, the thalamus, and the superior colliculus. All cerebellar nuclear neurons are innervated by GABAergic Purkinje cells. ⋯ Nine out of 367 investigated BDA-labeled terminals were observed to be presynaptic to a WGA-HRP-labeled profile as well as to a gold lectin-labeled profile. This indicates that nuclear cells that project to the inferior olive as well as those that project to premotor centers are under the influence of the same Purkinje cells. Such an arrangement would suggest an in-phase cortical modulation of the activation patterns of the inhibitory cells that project to the inferior olive and excitatory cells that project to premotor nuclei, which could explain why olivary neurons, especially those of the rostral part of the dorsal accessory olive, appear to be unresponsive to stimuli generated during active movement.