Biomedical subjects

D Troilo

Publications and source records attributed to D Troilo.

22 records · Page 2Linked to original sources

PubMed1987

Changes in corneal curvature during accommodation in chicks.

Evidence is presented for an active corneal component of accommodation in chicks. Using anesthetized chicks, consistent increases in corneal curvature were observed during accommodation produced either by electrical stimulation of the Edinger-Westphal nucleus or by topical application of 0.4% nicotine sulfate to the cornea. Electrical stimulation produced a mean accommodative amplitude of 9.2 diopters (D) and a change in corneal power of 3.9 D whereas nicotine treatment elicited 15.1 D of accommodation and 6.1 D of change in corneal power. The change in corneal power increased proportionately with accommodative amplitude up to about 10 D of total accommodation where the corneal power change appeared to level off at approximately 6 D. This limit to corneal curvature change implies that it plays a proportionately greater role in the lower range of accommodation.

Accommodation, Ocular↗

PubMed1987

Visual deprivation causes myopia in chicks with optic nerve section.

Deprivation of form vision restricted to a region of the retina produces myopia and axial elongation only in that region. We asked whether this control of eye growth by the presence or absence of visual stimuli might take place entirely within the eye. Chicks with neonatal optic nerve section, wearing an occluder that deprived one half of the retina of form vision, had vitreous chamber elongation and myopia both restricted to the deprived region. Chicks with optic nerve section but without occluders had eyes smaller than normal with severe hyperopia. These results suggest that two different mechanisms may control eye growth, one within the eye and the other in the brain.

Animals↗

PubMedDate not supplied

Functional architecture of area 17 in normal and monocularly deprived marmosets (Callithrix jacchus).

The organization of the primary visual cortex (VI) of the common marmoset (Callithrix jacchus) was studied both physiologically and by means of transneuronal labelling of geniculocortical afferents. We addressed the question whether monocular deprivation (MD) could stabilize segregation into ocular dominance (OD) columns, which are not seen in normal adult marmosets but are present in juvenile animals (Spatz, 1979, 1989). Properties of neurons in normal marmosets closely resembled those of other New-World and Old-World monkeys and orderly tangential progressions of preferred orientation were observed. However, in contrast to species that display well-defined OD columns, neurons of layer 4 in V1 of normal adult marmosets received balanced inputs from the two eyes. Early MD (even though followed by prolonged binocular experience into adulthood) resulted in a reduction of cell size in laminae of the lateral geniculate nucleus with input from the deprived eye and a dramatic overall shift in ocular dominance towards the nondeprived eye in the cortex. However, isolated clusters of cells dominated by the deprived eye were found in both layers 4 and 6. Injection of lectin-conjugated horseradish peroxidase (WGA-HRP) into the deprived eye revealed elongated patches of terminal label, about 350 microns wide, in flat-mounted sections through layer 4. Afferent segregation was sharper and more regular in the region of V1 representing parafoveal visual space than in that representing the fovea. Our findings support the notion that all Old-World and New-World monkeys possess the capacity for segregation of geniculocortical afferents into OD columns.

Afferent Pathways↗

PubMedDate not supplied

Factors controlling the dendritic arborization of retinal ganglion cells.

The effects of changing retinal ganglion cell (RGC) density and availability of presynaptic sites on the development of RGC dendritic arbor in the developing chick retina were contrasted. Visual form deprivation was used to induce ocular enlargement and expanded retinal area resulting in a 20-30% decrease in RGC density. In these retinas, RGC dendritic arbors increased in a compensatory manner to maintain the inner nuclear layer to RGC convergence ratio in a way that is consistent with simple stretching; RGC dendritic arbors become larger with increased branch lengths, but without change in the total number of branches. In the second manipulation, partial optic nerve section was used to produce areas of RGC depletion of approximately 60% in the central retina. This reduction in density is comparable to the density of locations in the normal peripheral retina. In RGC depleted retinas, dendritic arbor areas of RGCs in the central retina grow to match the size of normal peripheral arbors. In contrast to the expanded case, two measures of intrinsic arbor structure are changed in RGC-depleted retinas; the branch density of RGC dendrites is greater, and the relative areas of the two arbors of bistratified cells are altered. We discuss the potential roles of retinal growth, local RGC density, and availability of presynaptic terminals in the developmental control of RGC dendritic arbor.

Animals↗