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B E Reese

Publications and source records attributed to B E Reese.

At least 37 records · Page 2Linked to original sources
PubMed1995

Cell dispersion patterns in different cortical regions studied with an X-inactivated transgenic marker.

Inactivation of the X-linked lacZ transgene provides a novel and powerful way of distinguishing between clonally related cellular populations in X inactivation mosaics. This ability to distinguish between clonal populations of cells in the mature cortex permits inferences to be made about cellular dispersion patterns during cortical development. The present study addresses the extent to which radial and tangential dispersion patterns contribute to different regions of the cerebral cortex by quantifying the extent of cellular mixing between clonally distinct cells in separate domains of the medial, dorsolateral and lateral cortices. We show that stripes running perpendicular to the cortical layers are more likely to be seen in the medial and dorsolateral regions, and that the appearance of a stripe is attributed to about two-thirds of the cells being of the same colour. Both neurons and glia appeared to exhibit the same ratio of cell mixing. In the lateral regions of the cortex, stripes were not apparent, and cell mixing was roughly equal. In the barrel-field region of the somatosensory cortex we looked for a correspondence between cytoarchitectural features and clonal borders but found no correlation. These results demonstrate, first, that although there is widespread radial dispersion, no cortical region is composed of radially arrayed stripes of cells in which all members of a stripe are derived from a single progenitor. Second, they demonstrate that, within regions containing a sizeable fraction of cells that do migrate radially, the boundaries of individual stripes do not always coincide with single anatomical units of cortical specialization, such as individual barrels.

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PubMed1994

Glial domains and axonal reordering in the chiasmatic region of the developing ferret.

This study has examined the developing glial architecture of the optic pathway and has related this to the changing organization of the constituent axons. Immunocytochemistry was used to reveal the distribution of glial profiles, and DiI was used to label either radial glial profiles or optic axons. Electron microscopy was used to determine the distribution of glial profiles, axons, growth cones, and wrists at different locations along the pathway. Three different glial boundaries were defined: Two of these are revealed as changes in the distribution of vimentin-immunoreactive profiles occurring in the prechiasmatic optic nerve and at the threshold of the optic tract, respectively, and one by the presence of glial fibrillary acidic protein (GFAP)-immunoreactive profiles at the chiasmatic midline. The latter, midline boundary may be related to the segregation of nasal from temporal optic axons. The boundary at the threshold of the optic tract coincides with the segregation of dorsal from ventral optic axons that emerges at this location in the pathway. The segregation of old from young optic axons is shown to occur only gradually along the pathway. Glial profiles are most frequent in the deeper parts of the tract, coursing parallel to the optic axons and orthogonal to their usual radial axis. These are suggested to arise from later-growing radial glial fibers that are diverted to grow amongst the older optic axons. Those glial profiles may subsequently impede axonal invasion, thus creating the chronotopic reordering by forcing the later-arriving axons to accumulate superficially.

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PubMed1994

Birthdates of neurons in the retinal ganglion cell layer of the ferret.

The present study determined the temporal and spatial patterns of genesis for neurons of different sizes in the retinal ganglion cell layer of the ferret. Fetal ferrets were exposed to tritiated thymidine on embryonic days E-22 through E-36. One to 3 months after birth, they were perfused and their retinae dissected, and autoradiographs were prepared from resin-embedded sections throughout the entire flattened retinal ganglion cell layer. Soma size differences in conjunction with separate retrograde labeling and calbindin immunocytochemical studies were used as criteria for identifying different retinal ganglion cell subtypes in juvenile and adult ferrets. Neurons of different sizes in the ganglion cell layer were generated at different stages during development. Medium sized cells were generated primarily between E-22 and E-26; the largest cells were generated between E-24 and E-29; small cells were generated between E-26 and E-32; and very small cells were generated between E-29 and E-36. The former three groups were interpreted to be three subtypes of retinal ganglion cells, while the latter group was interpreted to be displaced amacrine cells. This temporal order of the genesis of ganglion cell classes is consistent with the spatial ordering of their fibers in the mature optic chiasm and tract, and it is consistent with the developmental change in decussation pattern recently shown in the optic pathway of embryonic ferrets. The spatial pattern of genesis suggests that ganglion cells of a particular class are added to the ganglion cell layer in a centroperipheral fashion initiated in the dorsocentral retina nasal to the area centralis. No evidence was found for a wave of ganglion cell addition that proceeded in a spiralling pattern around the area centralis, as has been reported in the cat.

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PubMed1993

Rapid plastic response following early retinal lesions in rats.

Following an early retinal lesion, aberrant uncrossed projections from the opposite, undamaged, retina form in the target visual nuclei. The present study has examined the development of such aberrant projections by making retinal lesions in newborn rat pups, and then examining the nature of the uncrossed retinocollicular projection at different ages following the lesion. Intravitreal injections of horseradish peroxidase were made into the intact eye, and the uncrossed projection was subsequently revealed histochemically. A mature aberrant projection forms as early as postnatal day 9. On postnatal days 5 and 2, aberrant projections are discernable amongst the exuberant uncrossed terminals of normal developing rats, although the former have not matured to form the dense terminal fields characteristic of older projections. Aberrant projections were also detectable as early as 12 h following the lesion, revealed as a relative increase in the density of uncrossed label. These results indicate that lesion-induced plastic responses by intact retinal arbors are initiated shortly after the insult, and they caution the use of retinal lesions in studies of normal retinotopic connectivity during development.

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PubMed1993

Chiasmatic course of temporal retinal axons in the developing ferret.

Recent studies on the distribution of optic axons in the mature visual pathways, as well as on the genesis of their ganglion cells of origin, suggest that the time of axonal arrival at the optic chiasm determines the side of the brain to which a temporal retinal axon will project. The present study has examined this issue directly in fetal ferrets, by determining the projection of the temporal retina at different developmental stages. Fetuses of known gestational age were fixed with paraformaldehyde and subsequently implanted with crystals of the carbocyanine dye, DiI, into either the temporal retina, or into one optic tract. The lipophilic diffusion of the dye within the plasma membrane of the axons revealed the course of temporal retinal fibers through the fetal chiasm, as well as the distribution of ganglion cells across the two retinae projecting to one optic tract. During early fetal stages, the temporal retina extends axons preferentially into the ipsilateral optic tract: the early retinal projection shows a classical partial decussation pattern. During later fetal stages, temporal retinal axons can be traced into both optic tracts, and the distribution of cells with crossed and uncrossed optic axons in the temporal retina is overlapping. These results indicate that the mature decussation patterns of retinal ganglion cell classes are not primarily the consequence of regressive phenomena such as cell death; rather, they are formed as axons navigate the chiasmatic region during development. The differences in decussation pattern between cell classes arise from the fact that the mechanisms producing the segregation of nasal and temporal retinal axons at the chiasm must change as development proceeds.

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PubMed1993

Clinical implications of the fibre order in the optic pathway of primates.

Traditional neuro-ophthalmologic accounts of the optic pathway in primates stipulate that two half-retinal maps, one from each optic nerve, are combined within the chiasmatic region to yield a single, unified representation of the contralateral visual hemi-field in each optic tract. Yet visual disturbances produced by compromise to the visual pathways in the region of the describes recent neuroanatomical studies in monkeys that contradict those classical accounts but are consistent with the incongruous field defects and the functionally selective visual impairments documented in the clinical literature.

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PubMed1992

Time of ganglion cell genesis in relation to the chiasmatic pathway choice of retinofugal axons.

The time of generation of retinal ganglion cells in fetal cats has been related to the course taken later by their axons in the optic chiasm. The ganglion cells were labelled with tritiated thymidine either on embryonic day (E) 26 or on E-30. When the cats were mature, ganglion cells were retrogradely labelled with horseradish peroxidase injected into one optic tract. The distribution of double-labelled cells showed that cells in the temporal retina generated on E-26 all have axons that take an uncrossed course in the chiasm, whereas, of the cells generated on E-30 in the temporal retina, some take a crossed course and others take an uncrossed course. The uncrossed axons of the E-26 cohort come from cells having a central distribution on the retina. For the E-30 cohort, the uncrossed axons come from cells having a relatively peripheral distribution, whereas the crossed axons come from more central cells. The present results suggest that the mechanism which serves to direct temporal retinal axons into the ipsilateral optic tract weakens as development proceeds. In principle, the change may occur in either a chiasmatic signal, read by temporal but not nasal optic axons, or in a retinal label, carried by temporal but not nasal cells and their processes. Since temporal retinal cells born concurrently at different places can project to opposite optic tracts, a retinal signal that deteriorates with time in a centroperipheral fashion is favored by the present results.

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PubMed1992

Position of growth cones within the retinal nerve fibre layer of fetal ferrets.

Optic axons are added to the retinal nerve fibre layer of fish along its vitreal border in a chronotopic manner. Likewise, the optic tract of all vertebrate species acquires axons preferentially along the superficial surface of the pathway. We have examined the developing retina of fetal ferrets (Mustela putorius furo) aged between embryonic day 27 (E27) and E34 to see whether a similar segregation of growth cones is apparent within the mammalian retinal nerve fibre layer. The distributions of growth cone, "wrist" (thick trailing portion of the growth cone), axonal, and glial profiles were determined from electron micrographs, and expressed as a percentage of neural profiles for several retinal locations. The retinal nerve fibre layer of fetal ferrets contains radially elongated bundles of fibres composed of axonal, wrist, and growth cone profiles. Glial processes of varying density divide the adjacent bundles, occasionally subdividing them in the plane of the retina, and give rise to endfeet lining the basal lamina and separating the optic axons from the latter. Growth cones within the developing fibre layer represented about 2.4% of profiles at E28, while at later developmental stages (E34), this value fell to about 0.6%. During this period of axonal outgrowth, growth cones were not preferentially segregated toward the vitreal basal lamina or the glial endfeet within the nerve fibre layer. Rather, they were found scattered throughout the axon bundles of the fibre layer. While there were differences in the proportion of immature profiles found within the vitreal half compared to the scleral half of the fibre layer, such that more growth cones and wrists were found vitreally, there was no clear accumulation of them in association with features of the vitreal margin. The present results show that young and old optic axons course together throughout the depth of the nerve fibre layer. A chronotopic mode of pathway genesis such as seen in the optic fibre layer of fish or in the optic tract of mammals is not present in the nerve fibre layer of ferrets. Differences in growth cone behaviour in the optic fibre layer and tract indicate that the mechanisms governing pathway formation differ along its course.

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PubMed1992

Fiber order in the opossum's optic tract.

The distribution of axons by size in the optic tract of the South American opossum, Didelphis marsupialis was studied. Thin and semi-thin sections were examined, and measurements of axonal diameter were made on electron micrographs taken from various locations across the optic tract of normal opossums. In order to determine the contributions of the different axon diameter classes to the crossed and uncrossed retinofugal pathways, measurements were also made from the tracts of opossums in which one eye had been enucleated 5 weeks previously. Within the opossum's optic tract, the axons are partially segregated by their size: the deepest parts of the tract contain only fine and medium-sized axons, whereas coarse axons are also present superficially. In the middle of the tract, all three size classes are present. At increasingly superficial positions, there is a steady reduction in the proportion of medium-diameter axons, and an increase in the number of the finest axons. Medium and coarse axons contribute to both the crossed and uncrossed pathways, and the uncrossed component is displaced superficially relative to the crossed component. The fine axons in the deeper parts of the tract arise from both retinae, while those in the superficial parts of the tract, near the pial surface, are virtually all crossed. The opossum's optic tract thus displays the segregation of axons by size found in placental mammals, and follows a pattern reminiscent of that found in carnivores. Such a common organizational plan, particularly the similarities between the didelphids and carnivores, is suggestive of an early acquisition of parallel visual pathways in mammalian phylogeny. Since the fiber order in the optic tract of eutherians is a chronological map of axonal arrival during development, these results suggest that a conserved developmental mechanism has led to a common organizational plan.

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PubMed1992

Neurogenesis in the retinal ganglion cell layer of the rat.

The present study has examined the birthdates of neurons in the retinal ganglion cell layer of the adult rat. Rat fetuses were exposed to tritiated thymidine in utero to label neurons departing the mitotic cycle at different gestational stages from embryonic days 12 through to 22. Upon reaching adulthood, rats were either given unilateral injections of horseradish peroxidase into target visual nuclei in order to discriminate (1) ganglion cells from displaced amacrine cells, (2) decussating from non-decussating ganglion cells, and (3) alpha cells from other ganglion cell types; or, their retinae were immunohistochemically processed to reveal the choline acetyltransferase-immunoreactive amacrine cells in the ganglion cell layer. Retinae were embedded flat in resin and cut en face to enable reconstruction of the distribution of labelled cells. Retinal sections were autoradiographically processed and then examined for neurons that were both tritium-positive and either horseradish peroxidase-positive or choline acetyltransferase-positive. Tritium-positive neurons in the ganglion cell layer were present in rats that had been exposed to tritiated thymidine on embryonic days E14-E22. Retinal ganglion cells were generated between E14 and E20, the ipsilaterally projecting ganglion cells ceasing their neurogenesis a full day before the contralaterally projecting ganglion cells. Alpha cells were generated from the very outset of retinal ganglion cell genesis, at E14, but completed their neurogenesis before the other cell types, by E17. Tritium-positive, horseradish peroxidase-negative neurons in the ganglion cell layer were present from E14 through to E22, and are interpreted as displaced amacrine cells. Choline acetyltransferase-positive displaced amacrine cells were generated between E16 and E20. Individual cell types showed a rough centroperipheral neurogenetic gradient, with the dorsal half of the retina slightly preceding the ventral half. These results demonstrate, first, that retinal ganglion cell genesis and displaced amacrine cell genesis overlap substantially in time. They do not occur sequentially, as has been commonly assumed. Second, they demonstrate that the alpha cell population of retinal ganglion cells and the choline acetyltransferase-immunoreactive population of displaced amacrine cells are each generated over a limited time during the periods of overall ganglion cell and displaced amacrine cell genesis, respectively. Third, they show that the very earliest ganglion cells to be generated in the temporal retina have exclusively uncrossed optic axons, while the later cells to be generated therein have an increasing propensity to navigate a crossed chiasmatic course.

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PubMed1991

Position of axons in the cat's optic tract in relation to their retinal origin and chiasmatic pathway.

The positions of the crossed and uncrossed optic axons of distinct diameter classes has been examined in the optic tract of the adult cat. In addition, the retinal origin of axons occupying different positions within the tract has been studied. Since the position of a fibre within the optic tract reflects its time of arrival during development, we have used axonal position as an indicator of age and have related this to the chiasmatic pathway choice of the axons. Cats were either monocularly enucleated, to reveal the position and diameter of surviving crossed and uncrossed optic axons in semithin and thin sections, or implants of horseradish peroxidase (HRP) were placed so as to retrogradely label the ganglion cells giving rise to axons within the deep (early arriving), or superficial (later arriving) parts of the tract selectively. This was accomplished by either 1) surgically implanting HRP into the superficial portion of the optic tract, via a transbuccal approach, or 2) making such a transbuccal transection of the superficial fibres, followed by intracerebral injections of HRP to retrogradely label the surviving, deeper, optic axons from their target nuclei. The deep parts of the optic tract contain fine and medium, crossed and uncrossed axons arising from mainly medium sized cells in the contralateral nasal and the ipsilateral temporal retina; there is a clear line of decussation. In contrast, the superficial parts of the tract contain mainly fine diameter axons arising from small cells in the whole contralateral retina, and a small proportion of large diameter axons arising from large, alpha cells in the whole contralateral retina and in the ipsilateral temporal retina. The likelihood that axons from the temporal retina will project contralaterally therefore increases as development proceeds, since these axons are found in the superficial parts of the tract only. This suggests that a time-dependent signal that weakens with age is responsible for directing early arriving optic axons from the temporal retina to take an exclusively uncrossed course.

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PubMed1990

Cell death and interocular interactions among retinofugal axons: lack of binocularly matched specificity.

Naturally occurring ganglion cell death has been attributed to competitive interactions among axons at their targets during development of the retinofugal pathways. The present study is concerned with the hypothesis that interocular interactions leading to ganglion cell death are restricted to binocularly conjugate terminals in the optic nuclei. We tested this hypothesis in newborn rats by making localized retinal lesions, which denervate a restricted portion of the contralateral optic targets. When these rats reached adulthood, the ipsilaterally projecting ganglion cells of the intact eye were then studied following retrograde labeling with horseradish peroxidase. Results were compared with those from a normal, control group and from rats that had one eye removed on the day of birth. In those retinal loci binocularly conjugate to the lesion in the opposite eye, no localized cell rescue could be found among the ipsilaterally projecting ganglion cells. The same retinal loci, however, showed clear cell rescue after contralateral enucleation. Independent, anterograde, studies of the ipsilateral retino-collicular projection verified that lesions of equivalent size to those used in the retrograde study reliably create aberrant expanded uncrossed terminal fields. The present data suggest that the interocular interactions involved in the diminished ganglion cell loss which follows monocular enucleation are not dependent on topographically specific binocular matching. The phenomena of naturally occurring cell loss and of retinotopically specific interocular interactions may therefore be independent during normal development.

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PubMed1990

Fibre organization of the monkey's optic tract: I. Segregation of functionally distinct optic axons.

The fibre organization of the monkey's optic tract was examined by implanting pellets of horseradish peroxidase into different locations within the tract, or into the superior colliculus and pretectum. Retinae were examined for the distribution, size, and morphological types of retrogradely labelled ganglion cells; optic tracts were examined for the distribution of anterogradely and retrogradely labelled axonal profiles; and lateral geniculate nuclei were examined for the distribution of anterogradely labelled processes within distinct geniculate laminae. Localized implants in the optic tract produced retrograde labelling of ganglion cells across wide regions of the retinal surface. The maximum density of labelled cells was always substantially less than the total ganglion cell density known to be present at those retinal loci. Distinct retinal ganglion cell types were labelled from differing regions within the optic tract: implants into the deep (dorsal) portion of the tract, far removed from the outer, pial, surface, retrogradely labelled predominantly P beta retinal ganglion cells, whereas implants into the superficial (ventral), subpial, part of the tract retrogradely labelled primarily the other retinal ganglion cell types, i.e., the P alpha, P gamma, and P epsilon cells. Within any given class of axon, there is a mapping of the centroperipheral retinal axis across the deep-to-superficial dimension of the tract, but this retinotopy is extremely coarse. Anterograde labelling of axonal terminations within the lateral geniculate nucleus showed a corresponding specificity for distinct geniculate laminae, the deep implants labelling the parvocellular laminae, superficial implants labelling the magnocellular laminae. Implants into the visual centres of the midbrain produced retrograde axonal labelling rostral to the lateral geniculate nucleus only in the superficial part of the optic tract. These results demonstrate that the monkey's optic tract is not a simple topographic mapping of retinal eccentricity. Rather, the primary organizational principle is that of a segregation of functionally distinct optic axon classes. As fibre order in the mammalian optic tract is also a chronological index of axonal arrival during development, the present results provide specific predictions about the temporal order of ganglion call genesis and axonal addition within the visual pathway. They also provide an anatomical basis for the functionally selective visual impairments that may arise following local damage to the optic tract in humans.

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PubMed1990

Fibre organization of the monkey's optic tract: II. Noncongruent representation of the two half-retinae.

The representations of the two half-retinae were examined in the monkey's optic tract. Intravitreal injections of tritiated amino acids were made to reveal the distributions of the crossed and uncrossed populations of optic axons, while localized implants of horseradish peroxidase (HRP) were made into different regions of the optic tract in order to examine the distributions and morphological types of retrogradely labelled cells at corresponding loci in the two half-retinae. Crossed and uncrossed optic axons are intermingled throughout most of the optic tract, but uncrossed axons are very sparse or absent along both the deep and superficial extremes of the tract. Implants of HRP into the deeper regions of the tract demonstrate that the crossed and uncrossed optic axons of the P beta retinal ganglion cells are slightly out of binocular registration, with the uncrossed map being shifted to a slightly superficial location relative to the crossed map. The optic axons for the remaining cell classes, revealed by implants of HRP into the superficial portion of the tract, are much more conspicuously out of binocular registration (in particular, the P alpha optic axons); but in their cases, the uncrossed optic axons are shifted to deeper locations relative to the crossed optic axons. Further evidence that these optic axon classes are markedly out of binocular registration comes from the two optic tracts of a bilaterally destriated monkey, in which most of the P beta optic axons have undergone a transneuronal retrograde degeneration. Following a uni-ocular injection of tritiated amino acids, the distributions of the remaining crossed and uncrossed axonal labelling occupied different positions within the tract rather than being intermingled, with the uncrossed optic axons situated deep to the majority of crossed optic axons. These results demonstrate that the optic chiasm does not combine binocularly corresponding optic axons of similar type. They also demonstrate that noncongruent field defects should be a common consequence of damage to the optic tract in humans. If the fibre order in the mammalian optic tract arises as a consequence of the sequence of axonal addition during development, then differences in the relative times of genesis for nasal and temporal members of any cell class, and/or differences in the relative pathlengths between the eye and two optic tracts, may produce the fibre ordering described herein.

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PubMed1990

Observations on the arrangement of axons according to diameter in the optic tract of the opossum Didelphis marsupialis.

The spectra of fiber sizes at different depths of the optic tract of the opossum Didelphis marsupialis were examined by electron microscopy in order to test for correlations between the eventual location of axons and relevant developmental events. Frequency histograms showed 1) a predominant representation of medium-sized axons and the virtual exclusion of coarse fibers from the deepest portion of that pathway, and 2) a progressive increase in the proportion of thin axons from deep to superficial sites of the tract. These findings are discussed in terms of the view of the optic tract as a chronological map of axon arrival.

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