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At least 1,135 records · Page 63Linked to original sources
PubMed1998

Lectin intravital perfusion studies in tumor-bearing mice: micrometer-resolution, wide-area mapping of microvascular labeling, distinguishing efficiently and inefficiently perfused microregions in the tumor.

Intravital lectin perfusion was combined with computer-guided scanning digital microscopy to map the perfused elements of the vasculature in tumor-bearing mice. High-precision composite images (spatial precision 1.3 micron and optical resolution 1.5 micron) were generated to permit exact positioning, reconstruction, analysis, and mapping of entire tumor cross-sections (c. 1 cm in diameter). Collation of these mosaics with nuclear magnetic resonance maps in the same tumor plane identified sites of rapid contrast medium uptake as tumor blood vessels. Digitized imaging after intravital double labeling allowed polychromatic visualization of two different types of mismatched staining. First, simultaneous application of two lectins, each bearing a different fluorochrome, revealed organ-specific differential processing in the microvascular wall. Second, sequential application of two boluses of one lectin, bearing different fluorochromes successively, distinguished between double-labeled microvessels, representing efficiently perfused vascular segments, and single-labeled microvessels, with inefficient or intermittent perfusion. Intravital lectin perfusion images of blood vessels in the vital functional state thus highlighted biologically significant differences in vessel function and served as high-resolution adjuncts to MR imaging.

Adenocarcinoma↗
PubMed1997

Posterior ventral pallidotomy: techniques and theoretical considerations.

1. Microeletrode mapping of the pallidum and adjacent structures allows for precise target identification and localization of critical structures, i.e., optic tract, internal capsule, and external pallidum, which must be spared from lesioning. 2. Microelectrode mapping has provided physiologic-anatomic correlation of determining the optimal target location as related to clinical outcome and has helped to refine the role of stimulation as a tool for target localization. 3. The improved accuracy of this technique should result in more accurate lesion placement which should improve long-term outcome and decrease morbidity.

Brain Mapping↗
PubMed1995

Wiring up the visual system.

1. In this review we describe some of our recent studies on the developing marsupial visual pathway. The description focuses on retinal ganglion cells, considering the formation of their dendritic trees, the outgrowth of axons and the formation of connections within the brain. 2. Both dendritic trees and outgrowing axons undergo a period of exuberance, followed by one of refinement. The dendritic tree transiently develops a more complex branching pattern than is found in adults. Short side branches, referred to as spines, are a feature of immature dendrites and, to a lesser extent, of axons. These structures are mostly lost as development proceeds. However, they are retained on the dendritic trees of small-field ganglion cells and, for a proportion of axons, on that part within the nerve fibre layer of the retina. Although most axons navigate fairly direct routes towards their targets, a minority follow inappropriate courses, such as doubling back towards the eye or entering the opposite optic nerve at the chiasm. As such errant axons are not seen in the adult, we assume that their parent cell bodies die during development. 3. Throughout development, optic axons are arranged in an approximate retinotopic order along the length of the visual pathway; as a result, axons approach the visual centres aligned to form, at least, a crude retinotopic map. Axons from dorsal and ventral retina exchange locations along the optic nerve and in this way correct for the inversion of the image brought about by the lens.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2003

Distribution of MAP1A, MAP1B, and MAP2A&B during layer formation in the optic tectum of developing chick embryos.

The expression patterns of three microtubule-associated proteins (MAP1A, MAP1B, and MAP2A&B) were investigated in the developing optic tectum. Expression of MAP1B and middle-molecular-weight peptide of neurofilament (NF-M) was first observed in the same mesencephalic cells on day 3 of incubation, indicating that neuroblasts had been produced. At day 5, MAP1A and MAP2A&B expression appeared in the cellular layer containing the first neuroblasts that differentiate into large multipolar cells. The NF-M+ neurites in the striatum album centrale (SAC) and the striatum opticum (SO) were MAP1B+ up to day 19, but the intensity of MAP1B immunoreactivity decreased with development. All three MAPs were expressed in large multipolar neurons in the developing stratum griseum centrale from the beginning of maturation. Stratum griseum et fibrosum centrale cellular layers, containing radially arranged piriform neurons, were MAP1A-/MAP2A&B- on day 11 but became MAP1A+/MAP2A&B+ during later stages. These results suggest that the timing of MAP expression in neuronal maturation of large multipolar cells differs from that of piriform cells. The expression of MAPs has revealed specific cellular events in the developing optic tectum. Based on our observations, the development of the optic tectum can be divided into four periods.

Animals↗
PubMed1989

Distribution of uncrossed axons along the course of the optic nerve and chiasm of rodents.

The distribution of the ipsilaterally projecting population of retinofugal axons has been analyzed following injections of horseradish peroxidase (HRP) into the optic tract of adult hamsters and rats to determine whether the topographical segregation of the cells of origin seen in the retina is maintained by their axons throughout the course of the optic nerve and chiasm. Axons are limited to a roughly appropriate topographic location within the intraorbital course of the nerve but this organization changes at levels progressively closer to the optic chiasm. Immediately rostral to the chiasm labelled profiles are found dispersed across most of the cross-sectional area of the nerve. This dispersal is maintained within the region of the optic chiasm where a complex rearrangement of ipsilaterally projecting axons takes place. The results show that axons are not retinotopically organized along the entire length of the optic nerve. The order of axons changes along the course of the nerve and in the optic chiasm. The change seen within the intracranial course may indicate a chronotopic re-sorting of axons prior to the optic tract where the organization of axons has previously been interpreted as a map of time of axon arrival.

Animals↗
PubMed2000

Two homeobox genes define the domain of EphA3 expression in the developing chick retina.

Graded expression of the Eph receptor EphA3 in the retina and its two ligands, ephrin A2 and ephrin A5 in the optic tectum, the primary target of retinal axons, have been implicated in the formation of the retinotectal projection map. Two homeobox containing genes, SOHo1 and GH6, are expressed in a nasal-high, temporal-low pattern during early retinal development, and thus in opposing gradients to EphA3. Retroviral misexpression of SOHo1 or GH6 completely and specifically repressed EphA3 expression in the neural retina, but not in other parts of the central nervous system, such as the optic tectum. Under these conditions, some temporal ganglion cell axons overshot their expected termination zones in the rostral optic tectum, terminating aberrantly at more posterior locations. However, the majority of ganglion cell axons mapped to the appropriate rostrocaudal locations, although they formed somewhat more diffuse termination zones. These findings indicate that other mechanisms, in addition to differential EphA3 expression in the neural retina, are required for retinal ganglion axons to map to the appropriate rostrocaudal locations in the optic tectum. They further suggest that the control of topographic specificity along the retinal nasal-temporal axis is split into several independent pathways already at a very early time in development.

Animals↗
PubMedDate not supplied

Functional properties of retinal ganglion cells during optic nerve regeneration in the goldfish.

After being severed, optic axons in goldfish regenerate and eventually restore the retinotectal map; refinement of the map depends upon impulse activity generated by the ganglion cells. Because little is known about the changes in activity and receptive-field properties of ganglion cells during regeneration, we made extracellular recordings from them in the intact eye up to 95 days after sectioning their axons in the optic tract. Their receptive fields were classified as OFF-, ON-OFF-, or ON-centers, and their axonal conduction velocities measured by antidromic activation. The rate of encountering single units dropped drastically at 4-8 days postsection when only a few OFF-center units could be recorded, recovering to normal between 42 and 63 days. Receptive-field centers were normal in size, except for the few OFF-centers at 4-8 days which were abnormally large. Maintained discharge rates of all types were depressed up to 42 days, but ON-OFF-center units were more spontaneously active than normal around 42 days. Light-evoked responses in OFF-center units were subnormal at 4-8 days, becoming supernormal at 16 days and normal thereafter. ON-OFF- and ON-center units started to regain responsiveness at 16 days, and became supernormal at 42 days, before returning to normal. Conduction velocities of all fiber groups dropped to a minimum at 8 days, the fastest being affected most. There was a gradual recovery to normal conduction velocity by 63 days. The conduction latencies of OFF- and ON-OFF-center units recovered to normal by 42 days, and ON-center units by 63 days. Recovery of ganglion cell responsiveness correlates with functional recovery in the retinotectal system: OFF-center units recover light-evoked responses at about the time OFF activity first reappears in the tectum. ON- and ON-OFF-center units recover later, exhibiting supernormal spiking activity around the time that ON responses reappear in the tectum.

Animals↗
PubMed1980

[Ontogeny of retinal projections: observation and reflection].

Recent evidence indicates that the retinotectal projection has a field-to-field rather than a point-to-point precision. Therefore, individual fibres can vary their relative position in the fibre pathway to some extent. In addition it is not necessary that retinotopy is maintained throughout the whole pathway; transformations may also occur. In fact, in the chick embryo outgrowing retinal fibres maintain not an absolute but only a high degree of order. Transformations occur at the entrance to the optic nerve and probably also right behind the chiasm. The origin of the map is determined by the fact that central retinal fibres which are formed first connect to tectal neurons near the centre of the optic tectum where neurons mature first. There they immediately invade the cellular tectal layers and form functional synapses soon after. Supernumerary fibres degenerate.

Animals↗
PubMed2005

Mechanisms of retinotopic map development: Ephs, ephrins, and spontaneous correlated retinal activity.

This chapter summarizes mechanisms that control the development of retinotopic maps in the brain, focusing on work from our laboratory using as models the projection of retinal ganglion cells (RGCs) to the chick optic tectum (OT) or rodent superior colliculus (SC). The formation of a retinotopic map involves the establishment of an initial, very coarse map that subsequently undergoes large-scale remodeling to generate a refined map. All arbors are formed by interstitial branches that form in a topographically biased manner along RGC axons that overshoot their correct termination zone (TZ) along the anterior-posterior (A-P) axis of the OT/SC. The interstitial branches exhibit directed growth along the lateral-medial (L-M) axis of the OT/SC to position the branch at the topographically correct location, where it arborizes to form the TZ. EphA receptors and ephrin-A ligands control in part RGC axon mapping along the A-P axis by inhibiting branching and arborization posterior to the correct TZ. Ephrin-B1 acts bifunctionally through EphB forward signaling to direct branches along the L-M axis of the OT/SC to their topographically correct site. Computational modeling indicates that multiple graded activities are required along each axis to generate a retinotopic map, and makes several predictions, including: the progressive addition of ephrin-As within the OT/SC, due to its expression on RGC axon branches and arbors, is required to increase topographic specificity in branching and arborization as well as eliminate the initial axon overshoot, and that interactions amongst RGC axons that resemble correlated neural activity are required to drive retinotopic refinement. Analyses of mutant mice that lack early spontaneous retinal waves that correlate activity amongst neighboring RGCs, confirm this modeling prediction and show that correlated activity during an early brief critical period is required to drive the large-scale remodeling of the initially topographically coarse projection into a refined one. In summary, multiple graded guidance molecules, retinal waves and correlated spontaneous RGC activity cooperate to generate retinotopic maps.

Aging↗
PubMed2005

Development of precise maps in visual cortex requires patterned spontaneous activity in the retina.

The visual cortex is organized into retinotopic maps that preserve an orderly representation of the visual world, achieved by topographically precise inputs from the lateral geniculate nucleus. We show here that geniculocortical mapping is imprecise when the waves of spontaneous activity in the retina during the first postnatal week are disrupted genetically. This anatomical mapping defect is present by postnatal day 8 and has functional consequences, as revealed by optical imaging and microelectrode recording in adults. Pharmacological disruption of these retinal waves during the first week phenocopies the mapping defect, confirming both the site and the timing of the disruption in neural activity responsible for the defect. Analysis shows that the geniculocortical miswiring is not a trivial or necessary consequence of the retinogeniculate defect. Our findings demonstrate that disrupting early spontaneous activity in the eye alters thalamic connections to the cortex.

Animals↗
PubMed2000

Optical Fourier filtering for whole lens assessment of progressive power lenses.

Four binary filter designs for use in an optical Fourier filtering set-up were evaluated when taking quantitative measurements and when qualitatively mapping the power variation of progressive power lenses (PPLs). The binary filters tested were concentric ring, linear grating, grid and "chevron" designs. The chevron filter was considered best for quantitative measurements since it permitted a vernier acuity task to be used for measuring the fringe spacing, significantly reducing errors, and it also gave information on the polarity of the lens power. The linear grating filter was considered best for qualitatively evaluating the power variation. Optical Fourier filtering and a Nidek automatic focimeter were then used to measure the powers in the distance and near portions of five PPLs of differing design. Mean measurement error was 0.04 D with a maximum value of 0.13 D. Good qualitative agreement was found between the iso-cylinder plots provided by the manufacturer and the Fourier filter fringe patterns for the PPLs indicating that optical Fourier filtering provides the ability to map the power distribution across the entire lens aperture without the need for multiple point measurements. Arguments are presented that demonstrate that it should be possible to derive both iso-sphere and iso-cylinder plots from the binary filter patterns.

Eyeglasses↗
PubMed1983

Hypothalamo-retinal centrifugal projection in the dog.

Horseradish peroxidase (HRP)-filled neurons and their processes were consistently detected in the ventral portion of the dog hypothalamus after intraocular injection of HRP. The number of HRP-filled neurons decreased in parallel with the extent of the resection of the optic nerve. HRP-filled neurons were never detected in specimens with a complete resection of the optic nerve. These findings strongly indicate that these HRP-filled neurons in the ventral hypothalamus are the source of centrifugal fibers to the retina.

Animals↗
PubMedDate not supplied

[Functional heterogeneity of lateral geniculate body neurons in the rabbit].

Background and evoked activity of LGB units was studied on immobilized and anaesthetized rabbits. Two groups of projection units were revealed, differing by the level of background activity, latencies and mean frequency of discharges in responses to single photic flashes and to electrical stimulation of the optic nerve. It is assumed that these groups of units belong to the slowly and rapidly conducting paths of sensory information transmission in the visual projection system.

Animals↗