Filling in at partially deafferented visual cortex.

METHODS: Perceptual visual filling in at the corresponding area of toxoplasmic retinochoroiditis scotomas in the fellow eye was studied in 14 patients. Targets were programmed to appear inside the scotoma corresponding area in the fellow eye, and at two control points. RESULTS: The results showed faster perceptual filling-in latencies (p<0.0001) in the scotoma corresponding area than at the control points. CONCLUSIONS: Perceptual filling in is facilitated at the corresponding area of retinal scotomas. The neural mechanisms of this visual facilitation might be similar to those found following somatosensory cortex partial deafferentation.

Color vision discrimination in the capuchin monkey Cebus apella: evidence for trichromaticity.

Primates display significant differences in color vision. The purpose of this study was to assess the ability of capuchin monkeys in discriminating chromatic and achromatic Munsell color chips through behavioral tests. The subjects were trained in a simple and reverse discrimination learning procedure. All subjects were capable of discriminations along five color categories investigated. The results are discussed in terms of the hypothesis of male dichromatism in New World monkeys, the role of color vision in adaptation to feeding ecology, as well as to aspects regarding primate evolution.

Relative sizes of cortical visual areas in marmosets: functional and phylogenetic implications.

Visual areas V1, V2 and MT (V5) were identified through myeloarchitectonic criteria and their sizes estimated in a flattened map of caudal cerebral cortex in the marmoset Callithrix penicillata. The ratio MT/V1 in this species is similar to values reported for other species of primates, but the ratio V2/V1 in Callithrix penicillata is smaller than that in macaques and larger than that in Aotus. The possible implications of these results are discussed.

Ganglion cell size and distribution in the retina of the two-toed sloth (Choloepus didactylus L.).

The distribution of ganglion cell densities and sizes was studied in Nissl-stained flat-mount retinae of the two-toed sloth. The area centralis, a weak specialization with low ganglion cell density, is located in the temporal retina close to the center of the eye. The presence of a visual streak was noted. The distribution of different ganglion cell sizes was approximately equal throughout the retina. Although the retinal organization differs from that of the closely related three-toed sloth, the presumed function of retinal specializations in both species is to guide limb movements by permitting visualization of the branch along which the animal is climbing.

Ganglion cell size and distribution in the retina of the two-toed sloth (Choloepus didactylus L.)

The distribution of ganglion cell densities and sizes was studied in Nissl-stained flat-mount retinae fo the two-toed sloth. The area centrailis, a weak specializtion with low ganglion cell density, is located in the temporal retina close to the center of the eye. The presence of a visual treak was nsoted. The distribution of different ganglion cell sizes was approximately equal throughout the retina. Although the retinal organization differs from that of the closely related three-toed sloth, presumed function of retinl specializations in both species is to guide limb movements by permiting visualization of the branch along which the animal is climbing

Distribution of motoneurones innervating extraocular muscles in the brain of the marmoset (Callithrix jacchus).

Extraocular muscle motoneurones were localised in the oculomotor nucleus (ON), trochlear nucleus (TN) and abducens nucleus (AN) in the marmoset brain using the horseradish peroxidase (HRP) retrograde labelling technique. HRP pellets injected into individual extraocular muscles revealed one or more groups of labelled neurones occupying discrete loci within these nuclei. Relatively little overlap of motoneurone pools was observed, except in the case of the inferior oblique and superior rectus muscles. Injections of HRP into the medial rectus muscle revealed three separate populations of labelled cells in the ipsilateral ON. Motoneurones innervating the inferior rectus muscle were mainly localised in the lateral somatic cell column of the ipsilateral ON. A second smaller grouping was observed in the medial longitudinal fasciculus. The inferior oblique muscle motoneurones were localised in the ipsilateral medial somatic cell column intermingled with motoneurones supplying the superior rectus muscle of the opposite eye. The superior oblique muscle motoneurones occupied the entire TN and the lateral rectus muscle motoneurones the AN. It was concluded that the organisation of nuclei and subnuclei responsible for controlling the extraocular muscles in the marmoset is broadly similar to that of other primates.

Unusual distribution of ganglion cells in the retina of the three-toed sloth (Bradypus variegatus).

1. The distribution and size of retinal ganglion cells labelled with horseradish peroxidase (HRP) were studied in flat-mounted retinas of three-toed sloths. 2. Massive injections of HRP solution were made throughout the thalamus and midbrain in anesthetized sloths in order to retrogradely label the retinal ganglion cell population. Twenty to thirty h later the eyes were excised and the retinas flat-mounted and reacted with phenylenediamine-HCl and H2O2 to label ganglion cells, thus distinguishing them from other cells in the same retinal layer. 3. Ganglion cell density gradually increased from about 500 cells/mm2 at the far periphery to a peak of about 1,500 cells/mm2 in an area, termed the area centralis, deep in the inferior temporal retina. The presence of a vertical visual streak was also noted. 4. The area centralis contained a higher frequency of small ganglion cells than the peripheral retina where large cells predominated. 5. The unusual position of the area centralis and visual streak in the retina can be explained by the sloth's unique ability to rotate its head 180 degrees while climbing upside-down along horizontal branches so that the head is right-side-up. If it is assumed that the branch directly above the sloth's head needs to be visualized for accurate claw placement then the branch would be imaged on the inferior temporal retina in an area corresponding to the maximum density region.

Unusual distribution of ganglion cells in the retina of the three-toed sloth (Bradypus variegatus)

1. The distribution ans size of retinal ganglion cells labelled with horseradish preoxidase (HRP) were studied in flat-mounted retinas of three-toed sloths. 2. Massive injections of HRP solution were made throughout the thalamus and midbrain in anesthetized sloths in order to retrogradely label the retinal ganglion cell population. Twenty to thirty h later the eyes were and the retinas flat-mounted and reacted with phenylenediamine-HCL and H2O2 to label ganglion cells,thus distinguishing then from other cells int he same retinal layer. 3. Ganglion cell density graually increased from about 500 cell/mm2 at the far periphery to a peak of about 1,500 cells/mm2 in an area, termed the area centralis, deep in the inferior temporal retina. The presence of a vertical visual steak was also noted. 4. The area centralis contained a higher frequency of small ganglion cells than the peripheral retina where large cells preominated. 5. /the unusual postion of the area centralis and cisual streak in the retina can be explained by the slot's unique ability to rotate its head 180- while climbing upside-dow along horizontal branches so that the head is right-side-up. If it is assumed that the branch directly above the sloth's head needs to be visualized for accurate claw placement then the branch would be imaged on the inferior temporal retina in an area corresponding to the maximum density region

Pattern and extent of demyelination in the optic nerves of mice infected with Semliki Forest virus and the possibility of axonal sprouting.

The optic nerves of all mice infected with Semliki Forest virus (SFV) showed patchy demyelination, although the extent of demyelination varied between animals. There was a significant increase in small diameter unmyelinated fibres in the optic nerves of SFV infected mice, paralleled by a loss of small myelinated fibres, suggesting that the smaller myelinated fibres may be more susceptible to virus-induced demyelination. The small unmyelinated fibres were more numerous in the peripheral region of the optic nerve trunk, where blood vessels are found in greater numbers. In addition, a particularly large increase in the proportion of unmyelinated fibres which had diameters of less than 0.2 microns suggested the possibility of axonal sprouting.

Increase in axonal transport in demyelinating optic nerve fibres in the mouse infected with Semliki Forest virus.

Since the integrity of myelin and axon is closely linked with the transport of substances along the axon, changes in the fast and slow axonal transport in the demyelinating optic nerves of mice infected with Semliki Forest virus were studied. Radioactive analysis of the superior colliculi and the optic nerves was thus made following different survival times after an intravitreal injection of tritiated proline by autoradiographic and liquid scintillation counting techniques. The amounts of both the fast and slow axonal transport of proteins were significantly higher in the optic nerves of mice infected with the virus than those found in the optic nerves of control mice. These results suggest that demyelinating fibres send a signal to the perikarya which then responds by synthesizing more proteins.