Vestibular projections to the nuclei of the extraocular muscles Degeneration resulting from discrete partial lesions of the vestibular nuclei in the monkey

Abstract

In 35 monkeys attempts were made to produce localized unilateral lesions i n individual vestibular nuclei in order to study vestibular projections to nuclei of the extraocular muscles. Portions of the medial, superior and inferior vestibular nuclei were destroyed selectively; lesions in Deiters' nucleus involved small portions of either the superior or inferior vestibular nuclei. Fiber degeneration was studied by the Nauta-Gygax technic.Exclusively ascending fibers from the superior vestibular nucleus project to ipsilateral extraocular nuclei. Ascending fibers from the inferior vestibular arise only from rostra1 portions of the nucleus, are not numerous and pass to all extraocular nuclei. The medial vestibular nucleus projects ascending fibers via the MLF bilaterally, asymmetrically and differentially to all extraocular nuclei. Prominent projections pass to: ( a ) the contralateral trochlear nucleus, and (b) the contralateral intermediate cell column and the ipsilateral ventral nucleus of the oculomotor complex. Ascending fibers from Deiters' nucleus, arising only from ventral portions of the nucleus, project primarily to: (a) the contralateral abducens and trochlear nuclei, and ( b ) specific asymmetrical portions of the oculomotor complex.Ascending vestibular fibers from the medial and lateral vestibular nuclei appear capable of mediating all patterned eye movements resulting from stimulation of ampullary nerves from individual semicircular canals. Vestibular projections to nuclei of the extraocular muscles arc most abundant to those nuclei innervating muscles whose primary functions concern horizontal and rotatory eye movements.The labyrinths, the vestibular nuclei and secondary vestibular pathways projecting to the nuclei of the extraocular muscles appear to play a major role in the control of conjugate eye movements. Anatomical evidence that the vestibular nuclei are concerned with conjugate eye movements appears to have a secure foundation, since secondary vestibular fibers ascending in the medial longitudinal fasciculus projecl to all the nuclei of the extraocular muscles (Szenthgothai, '43; Brodal and Pompeiano, '57; Carpenter, '60; Carpenter and McMasters, '63). Physiological studies (Szentagothai, '52; Fluur, '59; Cohen, SUzuki and Bender, '64) provide clear evidence of a precise functional correlation between particular semicircular canals and eye movements in specific directions. The investigations of Szenthgothai ('50) leave little doubt that functionally the most important impulses mediating ocular AM. J. ANAT., 118: 163-194. movements in response to stimulation of the semicircular canals ascend in the medial longitudinal fasciculus (hereafter abbreviated MLF). These results suggest that impulses from individual semicircular canals must ultimately be transmitted differentially to all the nuclei of the extraocular muscles, including specific subdivisions of the oculomotor nuclear complex. SzentAgothai's ('43) studies of the distribution of degenerated fibers in the nuclei of the extraocul...

The site of brainstem lesions causing semicircular canal paresis: an MRI study.

“…13 14 In addition, Uemura and Cohen8 found that the horizontal component of caloric induced nystagmus was preserved after total SVN destruction. Our findings, showing a comparative lack of involvement of this nucleus in our patients with central canal paresis, are in agreement with this.…”

Mammalian Vestibular Physiology

“…The properties of the MVST, as revealed by impregnation of fibers degenerating as a result of lesions in the vestibular nuclei (Nyberg-Hansen, 1964;McMasters et al, 1966;Petras, 1967), differ from those of the LVST in several respects. (1) Unlike the LVST, the MVST is bilateral: since there is no evidence of crossing in the cord, fibers must cross in the brain stem.…”

Brain stem activation of the hippocampus: A role for the magnocellular reticular formation and the MLF

“…In studies comparable to the present one (Polc and Monnier 1970;Klemm 1972;Macadar et al 1974;Robinson and Vanderwolf 1978) the MLF has never been mentioned as an effective hippocampal synchronizing (or desynchronizing) site. Furthermore, the ascending MLF has generally been considered as an important pathway linking the vestibular nuclei with the oculomotor nuclei (Brodal and Pompeiano 1957;McMasters et al 1966;Carpenter 1971)and has not been thought to carry information that could affect forebrain structures such as the hippocampus. Recent evidence suggests that a significant number, and possibly a ma-jority, of the cells of the MMRF (at least those at the pontine level) send their axons via the MLF and these fibers may be responsible for the synchronizing effect elicited by MLF stimulation.…”