Tonic vestibular control of eye position in postnatal developing rabbits

Orienting otolith-ocular reflexes in the rabbit during static and dynamic tilts and off-vertical axis rotation

Orienting otolith-ocular reflexes were assessed in rabbits using static tilt, off-vertical axis rotation (OVAR) and sinusoidal oscillation about earth-horizontal axes. In all paradigms, head pitch produced ocular counter-pitch and vergence, and head roll produced ocular counter-roll and conjugate yaw version. Thus, vergence and version are essential components of orienting reflexes along the naso-occipital and bitemporal axes. Vergence and version caused misalignment between the axes of eye and head movement during pitch and roll head movements. Semicircular canal input broadened the band-pass of these orienting reflexes, which would make them more appropriate when compensating for head movement during active motion.

Orientation of the eyes to gravitoinertial acceleration

Orientation of the eyes to gravitoinertial acceleration, i.e., to the sum of gravity and the linear accelerations acting on the head and body, is a basic property of the linear vestibulo-ocular reflex to support vision. Present in a wide range of species from the lateral-eyed rabbit to frontal-eyed monkeys and humans, the eyes deviate in pitch, roll and yaw in response to pitch, roll and yaw head movements. The eyes also converge in response to naso-occipital linear acceleration. This paper provides examples of ocular orientation generated by static tilt and off-vertical axis rotation in three dimensions and demonstrates specifically how vergence would support vision in the rabbit.

The development of the static vestibulo-ocular reflex in the southern clawed toad, Xenopus laevis. I. Intact animals

In the clawed toad, Xenopus laevis, the static vestibulo-ocular reflex appears in 3 days old tadpoles (developmental stage 42) (Fig. 2). The amplitude and gain of this reflex increase up to stage 52, and then decrease to an almost constant value at stage 60 and older tadpoles (Fig. 3). The most effective roll angle gradually increases during development (Fig. 4). The size of the sensory epithelia reaches the final value at the end of the premetamorphic period (stage 56) (Fig. 5). The small-cellular medial ventral vestibular nucleus (VVN) reaches its maximal number of neurons before the large-cellular lateral VVN. Cell death is more pronounced in the medial than in the lateral part of the VVN. In the dorsal vestibular nucleus (DVN), the numerical development of the small and large neurons is similar to that in the small-cellular medial and large-cellular lateral portion of the VVN (Fig. 7). The results demonstrate that labyrinth and oculomotor centres are anatomically connected before the labyrinth and the vestibular nuclei are fully developed. We discuss the possibility that the ciliary polarity pattern of the sensory epithelium is radial during the first period of life, and changes to the vertebrate fan-type pattern during the second week of life. According to the increase of gain during the first three weeks of life, an increase of the spontaneous activity of vestibular neurons may occur during this period.

Effect of roll and pitch on flash-induced nystagmus: support for involvement of retinal direction-selective elements?

The direction of eye movement (i.e., the angle of the resultant velocity vector calculated from the horizontal and vertical components) during flash-induced nystagmus was evaluated in static roll and pitch positions. It appeared that this direction coincided with the orientation of the visual streak, as influenced by the ocular countertorsion which is known to occur in the various body positions. This supports the hypothesis that flash-induced nystagmus results from stimulation of direction-selective retinal elements. The intensity of flash-induced nystagmus, evaluated either by measuring slow-phase velocity (i.e., magnitude of resultant vector) or by beat frequency, was minimal in approximately 90 and 270 degrees roll or pitch positions, presumably because the total combined (utricular and saccular, left and right) excitatory otolith stimulation was maximal in these positions, the effect of this stimulation being inhibitory to the flash-induced nystagmus.