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PubMed1985

Ontogeny of the visual system in the cuttlefish, Sepiella japonica. I. Morphological differentiation of the visual cell.

To provide morphological bases for functional studies, the differentiation of photoreceptors in the retina of a cuttlefish, Sepiella japonica, was examined by electron microscopy. Development of the retina occurs in four phases. In phase 1 (stages 21-23), the retinal epithelium consists of uniform columnar cells. In phase 2 (stages 24-29), the epithelial cells are classified into light and dark cells on the basis of the electron-density of their cytoplasm. The perikarya of the light cells are located in the distal half of the epithelium, each extending proximally (i.e., sclerad) a thin foot, which protruded out of the epithelium through a narrow break in the basal lamina. The nuclei of the dark cells are distributed in the proximal half of the epithelium. Both cell types have a short cilium in the distal end. In phase 3 (stages 30-35), the light and the dark cells morphologically differentiate into receptor and supporting cells, respectively. The distal end of the light (receptor) cell begins to form an apical process, which gives off short irregular microvilli from its lateral surface. Beneath the basal lamina the feet of the receptor cells swell and the nuclei migrate into them through narrow breaks in the basal lamina. Thus, at the end of phase 3, each receptor cell becomes divided into an outer and inner segment. In phase 4 (stages 36-40), the receptor cells complete the specific structure as photoreceptive cells. The microvilli arising from the apical processes increase in length, density, and regularity to be organized into rhabdomes. The lamellated membranes of the myeloid bodies appear first in the outer segment and later increase in number in the inner segment. Morphometric data on the rhabdomeric microvilli in the adult and embryonic retinas are presented.

Animals↗
PubMed1985

Visual-vestibular interaction studied with stroboscopically illuminated visual patterns.

Horizontal DC-electrooculograms were recorded in subjects rotating on a horizontal turntable sinusoidally at 0.1 Hz and 35 to 40 degrees amplitude. The subjects either fixated a stroboscopically illuminated vertically striped pattern (1.15 to 3.45 degrees period) rotating with the turntable or initiated Sigma-OKN before the rotation began and tried to maintain Sigma-OKN during rotation. In a third paradigm, interaction of vestibulo-ocular reflex (VOR) and Phi-OKN was studied. VOR-suppression by fixation was complete within the limits of EOG-recording precision (+/- 1 degree X s-1) for flash frequencies fs greater than 10 flashes X s-1. VOR-suppression decreased monotonically with fs between 10 and 1 flashes X s-1. A similar dependency on fs was found for VOR-suppression during Sigma- or Phi-OKN. Above 10 flashes X s-1 VOR-suppression remained incomplete; below 5 flashes X s-1 VOR-suppression was stronger with the Sigma-OKN paradigm than during fixation and depended on spatial frequency of the pattern. During sinewave rotation of the subject the perceived speed Vp of Sigma-movement correlated to the movement of gaze in space and not to the movement of the eye in head. In a control experiment with normal optokinetic stimulation, OKN-suppression by fixating a small flashing target was found to depend on fs in a similar way as VOR-suppression in the experiments described above.

Adult↗
PubMed1982

Posterior inferotemporal neuron activities during a visual fixation task and a visual tracking task.

Single neuron activities were recorded from the posterior inferotemporal cortex (PIT) while a monkey was fixating or tracking a target spot. Of 168 recorded neurons, 86 were activated by the extrafoveal slit stimuli; 48 were activated during eye fixation. Twenty were activated only during tracking, and not by fixation or a extrafoveal slit stimuli. It was suggested the PIT participates not only in the perception mechanisms but also in the foveation mechanisms such as fixation or tracking.

Animals↗

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