Search PubMed⌕ Search

Biomedical subjects

S A Bayer

Publications and source records attributed to S A Bayer.

At least 37 records · Page 2Linked to original sources
PubMed1990

Migration and distribution of two populations of hippocampal granule cell precursors during the perinatal and postnatal periods.

Methacrylate-embedded sections and short-survival thymidine radiograms of the hippocampal dentate gyrus were examined in perinatal and postnatal rats in order to trace the site of origin and migration of the precursors of granule cells and study the morphogenesis of the granular layer. The densely packed, spindle-shaped cells of the secondary dentate matrix (a derivative of the primary dentate neuroepithelium) stream in a subpial position towards the granular layer of the internal dentate limb during the perinatal and early postnatal periods. By an accretionary process, the crest of the granular layer forms on day E21 and on the subsequent days the granular layer of the internal dentate limb expands progressively in a lateral direction. Granule cells differentiation, as judged by the transformation of polymorph, darkly staining small cells into rounder, lightly staining larger granule cells, follows the same gradient from the external dentate limb to the internal dentate limb. The secondary dentate matrix is in a process of dissolution by day P5. This matrix is the source of what will later become the outer shell of the granular layer composed of early generated granule cells. The thicker inner shell of the granular layer, formed during the infantile and juvenile periods, derives from an intrinsic, tertiary germinal matrix. On day E22, the dentate migration of the secondary dentate matrix becomes partitioned into two components: a) the subpial component of extradentate origin, referred to in this context as the first dentate migration, and b) the second dentate migration. The latter is distributed in the basal polymorph layer throughout the entire dentate gyrus and is henceforth recognized as the tertiary dentate matrix. The tertiary dentate matrix is prominent between days P3 and P10. It is postulated that the great increase in granule cell population during the infantile period is principally due to cells derived from this intrinsic matrix of the dentate gyrus. Between days P20 and P30 the tertiary dentate matrix disappears in the basal polymorph layer and henceforth proliferative cells become largely confined to the subgranular zone at the base of the granular layer. The subgranular zone is the source of granule cells produced during the juvenile and adult periods.

Aging↗
PubMed1990

Timetables of cytogenesis in the rat subfornical organ.

Timetables of neurogenesis and ependymal cell production in the rat subfornical organ (SFO) were determined by examining the offspring of pregnant rats injected with [3H]thymidine on E13-E14, E14-E156, ... E21-E22, respectively. The proportion of postmitotic cells originating each embryonic day was determined by analyzing, in the adult offspring, the progressive reduction in the proportion of labeled precursors from the maximum amount seen in the E13-E14 group. Neurogenesis was found to occur over an extended period of time, beginning on E12 and continuing through E21. Ependymal cells were generated E15 through E21. Both neuron and ependymal cell production occurred in a triphasic pattern and followed an anterior (older) to posterior (younger) gradient. The anterior to posterior production gradient may be related to the morphological variation which exists along this plane. A production gradient intrinsic to a particular levels was found only in the posterior SFO, where peripheral neurons form earlier than core neurons. That neurogenetic gradient may be related to the core-periphery topographical patterns found in other studies, and suggests that the core neurons, since they are among the last to be formed, may be interneurons.

Animals↗
PubMed1990

Vertical compartmentation and cellular transformations in the germinal matrices of the embryonic rat cerebral cortex.

Cellular compartmentation was studied in the germinal matrices (the primary neuroepithelium and the subventricular zone) of the rat cerebral cortex at successive stages of embryonic development. Three sets of materials were used: methacrylate-embedded brain sections from normal embryos, autoradiograms from embryos labeled with [3H]thymidine, and methacrylate-embedded sections from embryos exposed to 200 R X-ray. Examination of normal specimens showed that between Embryonic Day 12 (E12) and E15 the cortical germinal matrix consists only of a primary neuroepithelium. By Day E16, a subventricular zone has formed in the early developing ventrolateral aspect of the cortex. The subventricular zone grows in depth for several days, while at the same time the depth of the neuroepithelium decreases. Examination of short-survival thymidine radiograms revealed that the labeled cells do not form a continuous band in the neuroepithelium but aggregate in patches reminiscent of bunches of grapes strung one a line. It is postulated that this vertical periodicity is due to the alternation of cell aggregates with short and long cell cycle times. Finally, examination of the cortical neuroepithelium in rats exposed to 200 R X-ray showed that there is an alternation of radiosensitive (collapsing) and radioresistant (intact) patches that roughly correspond in size to the labeled and unlabeled patches seen in autoradiograms. Additional observations concern the onset of local cell proliferation in the white matter at late stages of fetal development and the transformation of the neuroepithelium into a matrix producing ependymal cells.

Animals↗
PubMed1990

Horizontal compartmentation in the germinal matrices and intermediate zone of the embryonic rat cerebral cortex.

Cellular compartmentation was studied in the germinal matrices and the intermediate zone of the cerebral cortex of rat embryos that survived for 1 or more days after injection with [3H]thymidine. In contrast to the vertical compartmentation seen in the neuroepithelium with short-survival thymidine autoradiography, sequential-survival autoradiography revealed a horizontal compartmentation both in the germinal matrices and the intermediate zone. In the neuroepithelium of embryos that survived for 24 h, the differentially labeled cells form two distinct horizontal bands. The band overlapping with the mitotic zone is composed of heavily labeled cells, whereas the band overlapping with the synthetic zone is composed of lightly labeled cells. This indicates that there are two proliferative cell populations within the neuroepithelium, one turning over fast and the other more slowly. In the cortical intermediate zone of the same embryos several horizontal bands are present. Of these, the dispositions of two bands of heavily labeled cells--the superior band and the inferior band--were followed for several days. The superior band is apparently composed of glial cells that disperse in the direction of the internal capsule and the corpus callosum. In contrast, the inferior band (which overlaps with the subventricular zone where many cells are horizontally oriented) is apparently composed of sojourning young neurons. The cells of the inferior band resume their migration toward the cortical plate after a pause of 1-2 days. These observations call for a reappraisal of the view that young cortical neurons follow a direct radial path to the cortical plate.

Animals↗
PubMed1990

Development of layer I and the subplate in the rat neocortex.

Development of layer I and the subplate of the rat neocortex was examined with [3H]thymidine autoradiography. The experimental animals used for neurogenesis were the offspring of pregnant females injected with [3H]thymidine on 2 consecutive days: Embryonic Day (E) 13-E14, E14-E15, . . . E21-E22, respectively. On Postnatal Day 5, the proportion of layer I and subplate cells originating during 24-h periods were quantified at three anteroposterior levels. Presumptive Cajal-Retzius cells (large horizontal cells) are generated mainly on E14 and subplate cells on E14 and E15 ("outside-in" gradient). Both populations are generated earlier than cells in the cortical plate, which has an "inside-out" gradient. The subplate also has a ventrolateral/older to dorsomedial/younger neurogenetic gradient. The small- to medium-sized horizontal cells in layer I have an extensive period of neurogenesis with an "outside-in" gradient. To study morphogenesis, pregnant females were given single injections of [3H]-thymidine during gestation and embryos were removed in successive 24-h intervals (sequential-survival). On E15 and E16, cells accumulate outside the neuroepithelium in the primordial plexiform layer with older presumptive Cajal-Retzius cells superficial and younger presumptive subplate cells deep. The Cajal-Retzius cells permanently settle superficially among a first system of extracellular channels that appears on E14. Before reaching their final settling sites, subplate cells form the incipient cortical plate in the ventrolateral neocortex on E16. On E17, a seocnd system of extracellular channels appears below the cortical plate. On E18 and E19, subplate cells leave the cortical plate and permanently settle among the deep extracellular channels in a separate layer.

Animals↗
PubMed1990

Development of the lateral and medial limbic cortices in the rat in relation to cortical phylogeny.

[3H]Thymidine autoradiography was used to investigate neurogenesis of the lateral limbic cortex and morphogenesis of the medial and lateral limbic cortices in adult and embryonic rat brains. Ontogenetic patterns in the limbic cortex are unique because some neurogenetic gradients are linked to those in neocortex, others are linked to those in paleocortex. These findings are related to hypotheses of cortical phylogeny. The experimental animals used for neurogenesis were the offspring of pregnant females injected with [3H]thymidine on 2 consecutive days: Embryonic Day (E) 13-E14, E14-E15, ...E21-E22, respectively. On Postnatal Day (P)60, the proportion of neurons originating during 24-h periods were quantified at nine anteroposterior levels and one sagittal level. Similar to neocortex, deep cells are generated earlier than superficial cells throughout the lateral limbic cortex: layer VI mainly on E14-15, layer V on E15-E16, and layers IV-II on E16-E18. There is a ventral/older to dorsal/younger neurogenetic gradient between the ventral agranular insular, dorsal agranular insular, and gustatory cortical areas and between ventral and dorsal orbital areas beneath the frontal pole. Similar to paleocortex below the rhinal sulcus, limbic cortex in the rhinal sulcus has a "sandwich" gradient: the older posterior agranular insular area is sandwiched by anterior and posterior younger areas (ventral agranular insular and perirhinal). To study morphogenesis, pregnant females were given single injections of [3H]thymidine during gestation and embryos were removed in successive 24-h intervals (sequential-survival). Neurogenesis finishes first in ventral limbic areas, later in dorsal limbic areas, and latest in neocortical areas. The cortical plate in the region of the medial and lateral limbic cortices does not have a separate subplate layer as is found in the region of the neocortex. Instead, layer VI in the limbic cortices has unusually older cells that are generated simultaneously with subplate cells.

Animals↗
PubMed1990

Neurogenetic patterns in the medial limbic cortex of the rat related to anatomical connections with the thalamus and striatum.

[3H]Thymidine autoradiography was used to investigate neurogenesis in all areas of the limbic cortex in the medial wall of the hemisphere. The experimental animals were the offspring of pregnant females injected with [3H]thymidine on 2 consecutive days: Embryonic Day (E)13-E14, E14-E15, ...E21-E22, respectively. On Postnatal Day (P)60, the proportion of neurons originating during 24-h periods were quantified at nine anteroposterior levels. Three types of neurogenetic gradients are found. (i) Deep cells are older than superficial cells: layer VI is generated mainly on E15-E16, layer V on E16-E18, and layers IV-II on E18-E20. (ii) There is a ventral/older to dorsal/younger gradient between the dorsal peduncular, infralimbic, and anterior cingulate areas rostral to the genu of the corpus callosum. A ventral/older to dorsal/younger gradient is also found between superficial cells (layers II-IV) in anterior cingulate (CG3/CG1), posterior cingulate (CG2/CG1), and retrosplenial areas (RSG/RSA). (iii) An anterior/older to posterior/younger gradient is found between areas throughout the medial limbic cortex. Some of these neurogenetic patterns correlate with anatomical interconnections between the supracallosal medial limbic cortex (posterior cingulate and retrosplenial areas) and the anteroventral/anteromedial thalamic nuclei: older thalamic cells have longer axons that terminate in cortical areas containing younger cells, while younger thalamic cells have shorter axons that terminate in cortical areas containing older cells. Projections from the medial limbic cortex to the striatum also correlate with neurogenetic gradients: older cortical source cells in the infralimbic area project to the older striatal cells in the enkephalin-rich patches, while younger cortical source cells in the cingulate areas project to younger striatal cells in the surrounding matrix.

Animals↗
PubMed1989

Development of the rat thalamus: IV. The intermediate lobule of the thalamic neuroepithelium, and the time and site of origin and settling pattern of neurons of the ventral nuclear complex.

Short-survival, sequential, and long-survival thymidine radiograms of rat embryos, fetuses, and young pups were analyzed in order to examine the time of origin, settling pattern, migratory route, and site of origin of neurons of the ventral nuclear complex of the thalamus. Quantitative examination of long-survival radiograms established that the bulk of the neurons of the ventral nuclear complex are generated between days E14 and E16 but with statistically significant differences between its three nuclei. The ventrobasal nucleus is the oldest component (97% of the cells are generated on days E14 and E15); the ventrolateral nucleus is next (82% of the cells are generated on days E14 and E15); and the ventromedial nucleus is last (51% of the cells are generated on days E14 and E15). In addition to this caudal-to-rostral (from the ventrobasal nucleus to the ventrolateral nucleus) and lateral-to-medial (from the ventrobasal nucleus to the ventromedial nucleus) internuclear gradients, there are lateral-to-medial and ventral-to-dorsal intranuclear neurogenetic gradients within the ventrobasal and ventrolateral nuclei. Qualitative examination of short and sequential survival thymidine radiograms indicate that the neurons of the ventral nuclear complex originate in the unique intermediate thalamic neuroepithelial lobule, which is distinguished from the rest of the thalamic neuroepithelium by the presence of a mitotically active secondary neuroepithelial matrix. Two sublobules can be distinguished in the intermediate lobule during the early stages of thalamic development. On the basis of their location and chronological pattern of cell production and differentiation, it is inferred that the neurons of the ventrobasal nucleus originate in the earlier differentiating, posteroventrally situated inverted sublobule, and the neurons of the ventrolateral nucleus are produced in the later differentiating, anterodorsally situated everted sublobule. The neurons of the ventromedial nucleus appear to originate from the intermediate neuroepithelial lobule after its two sublobules are no longer distinguishable. The heavily labeled neurons generated soon after injection on day E15 form a wave front that translocates in a lateral direction at a steady rate of 215 microns/day. Examination of methacrylate-embedded materials showed that, in day E15 rats the actively migrating cells are spindle-shaped, with their long axis oriented horizontally. The far-laterally situated differentiating cells (the oldest neurons) become vertically oriented by day E16. Associated with this change in polarity, vertically oriented fibers appear among the cells. These fibers can be traced to the inte

Animals↗
PubMed1989

Development of the rat thalamus: V. The posterior lobule of the thalamic neuroepithelium and the time and site of origin and settling pattern of neurons of the medial geniculate body.

Long-survival, sequential, and short-survival thymidine radiograms of rat embryos, fetuses, and young pups were analyzed in order to examine the time of origin, site of origin, migratory route, and settling pattern of neurons of the medial geniculate body (MG). Quantitative evaluation of long-survival radiograms established that the bulk of MG neurons are generated between embryonic (E) days E13 and E15, with a pronounced peak on day E14. There is an overall lateral-to-medial and caudal-to-rostral chronological gradient in MG neurogenesis. On the basis of significant regional differences in the birth dates of neurons, the MG was divided into several chronoarchitectonic areas. The earliest-generated neurons (with close to 20% of the cells produced on day E13 and a negligible proportion on day E15) form the dorsal and ventral clusters far laterally. Next in sequential order are the neurons of the lateral shell, intermediate shell, and medial shell of the MG. The medial shell with it latest-generated neurons (with over 30% produced rostrally on day E15) corresponds to the medial (magnocellular) subnucleus of the MG. There were no neurogenetic differences between the traditional dorsal and ventral divisions of the MG. Examination of sequential radiograms in rats labeled with 3H-thymidine on day E14 or E15 and killed on successive days brought supportive evidence for our earlier identification, in short-survival radiograms, of a posteroventral thalamic neuroepithelial evagination as the putative source, or committed cell line, of MG neurons. Wave fronts of apparently migrating unlabeled and labeled cells could be traced from this sublobule in a posterolateral direction to the future site of the MG.

Animals↗
PubMed1989

Development of the rat thalamus: VI. The posterior lobule of the thalamic neuroepithelium and the time and site of origin and settling pattern of neurons of the lateral geniculate and lateral posterior nuclei.

Short-survival, sequential, and long-survival thymidine radiograms of rat embryos, fetuses, and young pups were analyzed in order to determine the time of origin, site of origin, migratory route, and settling pattern of neurons of the dorsal lateral geniculate (LGD), ventral lateral geniculate (LGV), and lateral posterior (LP) nuclei of the thalamus. Quantitative examination of long-survival radiograms established that the neurons of the LGD are produced on days E14 and E15. Within the LGD there is an external-to-internal neurogenetic gradient; the majority (77%) of neurons of the external half are generated on day E14, while in the internal half the majority (64%) of neurons originate on day E15. The late-generated LGD neurons are located in the termination field of the uncrossed fibers of the optic tract. Examination of short-survival radiograms indicated that the neurons of the LGD originate in a discrete neuroepithelial eversion situated ventral to the pineal rudiment and dorsal to the putative neuroepithelium of the ventral nuclear complex. In sequential radiograms from rats injected with 3H-thymidine on day E15 and killed on days E16 and E17, the migration of young LGD neurons was followed in a posterolateral direction to the formative lateral geniculate body. By day E17, the day when the optic tract fibers begin to disperse over the lateral surface of the posterior diencephalon, the distribution of early and late-generated neurons of the LGD resembles that seen in young pups. As a whole, the neurons of the LGV are produced earlier than the neurons of the LGD. The bulk of LGV neurons are generated on days E14 and E15 in a caudal-to-rostral intranuclear neurogenetic gradient. Caudal LGV neurons are generated mainly on day E14 (82%), while a substantial proportion of rostral neurons (32%) are generated on day E15. Examination of short-survival and sequential radiograms suggest that the LGV neurons originate in an inverted sublobule situated beneath the putative neuroepithelium of the LGD. At anterior levels the putative inverted sublobule of the LGV merges imperceptibly with the neuroepithelium that produces the neurons of the lateral habenular nucleus. Like the neurons of the LGD and LGV, so also those of the LP are generated on days E14 and E15, but the neurogenetic gradients are different. There is a lateral-to-medial gradient within the LP as a whole. Peak production of neurons is on day E14 laterally (58%) and on day E15 medially (59%).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Cellular aspects of brain development.

The formation of the central nervous system begins early in development with the induction of the neural ectoderm on the dorsal surface of the embryo. Subsequently, the neural ectoderm plate changes its shape to form a neural groove and eventually, a neural tube. The wall of the neural tube is composed of germinal cells, collectively called the neuroepithelium, that produces neurons and glia throughout the central nervous system (CNS). Three points will be made about cellular production in the CNS: (1) The neuroepithelium forms expansions (brain vesicles), folds, and lobules characteristic of particular CNS regions. The hypothesis that neuroepithelial "anatomy" is a blueprint for proper anatomical development of the CNS will be discussed. (2) Using tritiated thymidine autoradiography in the developing rat, we have found that the neuroepithelium generates neuronal populations according to specific timetables during CNS organogenesis. Some populations are produced early in a 1-2 day period, others are produced later during a 5-7 day period, while still others are produced after birth for periods of a few weeks. (3) By exposing perinatal rat pups to low level X-irradiation, we find that killing neuronal precursors and young postmitotic neurons results in permanent reductions in the number of cells that constitute the targeted neuronal populations. Even though some development continues after the X-ray exposures, there is no compensatory increase in cell proliferation to replace the lost cells. The implications of this finding will be discussed in light of the permanence of neurotoxic insults during human CNS development.

Brain↗
PubMed1988

Development of the rat thalamus: I. Mosaic organization of the thalamic neuroepithelium.

Short-survival, sequential, and long-survival thymidine radiograms of rat embryos, fetuses and young pups were analyzed in order to delineate the boundaries of the proliferative thalamic neuroepithelium, describe its early transformations, identify its regional divisions, and, finally, attempt to relate its distinct neuroepithelial components to specific thalamic nuclei that they supply with neurons. On day E13 the thalamic neuroepithelium consists of two divisions, the rostral lobe and the caudal lobe, and interposed between the two is a small transient structure, the reticular protuberance. By day E14 the rostral lobe has become partitioned into the anterior lobule and the reticular lobule, and the caudal lobe into the intermediate lobule and the posterior lobule. By day E15 these four lobules have become further partitioned into sublobules, characterized as regional eversions and inversions (concavities and convexities) of the thalamic neuroepithelium. Several of these sublobules are still recognizable on day E16 but progressively disappear thereafter. In this introductory paper, some evidence is presented in support of the hypothesis that the identified thalamic sublobules represent putative cell lines committed to produce neurons for specific, early-generated thalamic nuclei. Detailed documentation of the evidence on which the identifications are based is provided in subsequent papers of this series which deal with the early development of specific thalamic regions and nuclei. In our attempt to identify these putative cell lines, we sought to meet the following criteria: (1) a good match between the time course of mitotic activity in a neuroepithelial sublobule and the birth days of neurons in the nucleus that it is postulated to supply with neurons, (2) relative proximity between the putative neuroepithelial source and the thalamic target structure, and, where possible, (3) the tracing of migrating cells from the germinal source to its destination. Using these criteria we have made the following tentative identifications. The early derivatives of the anterior thalamic lobules are the sublobules (committed cell lines) of the anterior thalamic nuclei, and of the central lateral and mediodorsal nuclei. The early derivatives of the reticular lobule and reticular protuberance are the sublobules of the reticular nuclear complex. The early derivatives of the intermediate lobule are the sublobules of the ventrolateral and ventrobasal nuclei. Finally, the early derivatives of the posterior lobule are the sublobules of the dorsal geniculate, ventral geniculate, and medial geniculate nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Development of the rat thalamus: II. Time and site of origin and settling pattern of neurons derived from the anterior lobule of the thalamic neuroepithelium.

Short-survival, sequential, and long-survival thymidine radiograms of rat embryos, fetuses, and young pups were analyzed in order to examine the time of origin, settling pattern, and neuroepithelial site of origin of the anterior thalamic nuclei--the lateral dorsal (lateral anterior), anterodorsal, anteroventral and anteromedial nuclei--and of two rostral midline structures--the anterior paraventricular and paratenial nuclei. The neurons of the lateral dorsal nucleus are generated over a 3-day period between days E14-E16 and their settling pattern displays a combined lateral-to-medial and dorsal-to-ventral neurogenetic gradient. The bulk of the neurons of the anteroventral nucleus are generated over a 3-day period between days E15-E17 and settle with an oblique lateral-to-medial and ventral-to-dorsal neurogenetic gradient. The bulk of the neurons of the anteromedial nucleus are generated over a 2-day period between days E16-E17 and show the same settling pattern as the anteroventral nucleus. The neurons of the anterodorsal nucleus are generated over a 3-day period between days E15-E17 and show a lateral-to-medial neurogenetic gradient. The bulk of the neurons of the central part and lateral part of the paraventricular nucleus are generated over a 2-day period (E16-E17 and E17-E18, respectively) and each part displays a ventral-to-dorsal neurogenetic gradient. Finally, the bulk of the neurons of the paratenial nucleus are generated over a 4-day period between days E15-E18 and settle with a lateral-to-medial neurogenetic gradient. Observations are presented that the anterior thalamic nuclei, constituting the distinct "limbic thalamus," derive from a discrete neuroepithelial source. This is the crescent-shaped germinal matrix lining the diencephalic (medial) wall of the hitherto unrecognized anterior transitional promontory, which we call the anterior thalamic neuroepithelial lobule. On day E16 three migratory streams leave the anterior neuroepithelial lobule and, on the basis of their labeling pattern in relation to the neurogenetic gradients of the anterior thalamic nuclei, they are identified, from dorsal to ventral, as the putative migratory streams of the anterodorsal, anteroventral, and lateral dorsal nuclei. On day E17 the putative migratory stream of the anteromedial nucleus appears to leave the same neuroepithelial region that on the previous days was the source of the anteroventral nucleus. Dorsally, two neuroepithelial patches persist after day E17 and these are identified as the putative cell lines of the anterior paraventricular and paratenial nuclei.

Animals↗
PubMed1988

Development of the rat thalamus: III. Time and site of origin and settling pattern of neurons of the reticular nucleus.

Short-survival, sequential, and long-survival thymidine radiograms of rat embryos, fetuses, and young pups were analyzed in order to examine the time of origin, settling pattern, migratory route, and site of origin of neurons of the reticular nuclear complex of the thalamus. On the basis of its chrono-architectonics, the reticular nucleus was divided into a central, medial, and lateral subnucleus. The central subnucleus is the earliest produced component of the entire thalamus with over 50% of its neurons being generated on day E13 and another 40% on day E14. Peak production of neurons of the lateral and medial subnuclei is on day E14. There is a lateral (earlier) to medial (later) neurogenetic gradient between these two components of the reticular complex: only about 12% of the lateral subnucleus neurons, but close to 30% of the medial subnucleus neurons, are generated on day E15. Because the lateral and medial subnuclei display the typical outside-in gradient found in the thalamus, they are considered to constitute a single cytogenetic sector; the early generated central subnucleus, which violates this order, is considered to constitute a separate cytogenetic sector. Observations are presented that neurons of the central reticular subnucleus originate in a unique neuroepithelial region, the reticular protuberance. The migration of heavily labeled cells was traced from this region in rats labeled with 3H-thymidine on day E13 and killed on the subsequent days. The neurons of the lateral and medial reticular subnuclei originate in the reticular lobule of the thalamic neuroepithelium. The migration of heavily labeled, spindle-shaped cells was traced from this region in rats labeled with 3H-thymidine on days E14 and E15 and killed at daily intervals thereafter. The neurogenetic gradient of the reticular thalamic complex seen in postnatal rats is established before birth.

Animals↗
PubMed1987

Neurogenetic and morphogenetic heterogeneity in the bed nucleus of the stria terminalis.

Neurogenesis and morphogenesis in the rat bed nucleus of the stria terminalis (strial bed nucleus) were examined with [3H]thymidine autoradiography. For neurogenesis, the experimental animals were the offspring of pregnant females given an injection of [3H]thymidine on 2 consecutive gestational days. Nine groups of embryos were exposed to [3H]thymidine on E13-E14, E14-E15,... E21-E22, respectively. On P60, the percentage of labeled cells and the proportion of cells originating during 24-hour periods were quantified at six anteroposterior levels in the strial bed nucleus. On the basis of neurogenetic gradients, the strial bed nucleus was divided into anterior and posterior parts. The anterior strial bed nucleus shows a caudal (older) to rostral (younger) neurogenetic gradient. Cells in the vicinity of the anterior commissural decussation are generated mainly between E13 and E16, cells just posterior to the nucleus accumbens mainly between E15 and E17. Within each rostrocaudal level, neurons originate in combined dorsal to ventral and medial to lateral neurogenetic gradients so that the oldest cells are located ventromedially and the youngest cells dorsolaterally. The most caudal level has some small neurons adjacent to the internal capsule that originate between E17 and E20. In the posterior strial bed nucleus, neurons extend ventromedially into the posterior preoptic area. Cells are generated simultaneously along the rostrocaudal plane in a modified lateral (older) to medial (younger) neurogenetic gradient. Ventrolateral neurons originate mainly between E13 and E16, dorsolateral neurons mainly between E15 and E16, and medial neurons mainly between E15 and E17. The youngest neurons are clumped into a medial "core" area just ventral to the fornix. For morphogenesis, pregnant females were given a single injection of [3H]thymidine during gestation, and their embryos were removed either 2 hours later (short survival) or in successive 24-hour periods (sequential survival). The embryonic brains were examined to locate areas of intensely labeled cells in the putative neuroepithelium of the strial bed nucleus, to trace migratory waves of young neurons, and to establish their final settling locations. Two different neuroepithelial sources produce neurons for the strial bed nucleus. The anterior strial bed nucleus is generated by a neuroepithelial zone at the base of the inferior horn of the lateral ventricle from the anterior commissural decussation area forward to the primordium of the nucleus accumbens.(ABSTRACT TRUNCATED AT 400 WORDS)

Amygdala↗
PubMed1987

Development of the preoptic area: time and site of origin, migratory routes, and settling patterns of its neurons.

Neurogenesis and morphogenesis in the rat preoptic area were examined with [3H]thymidine autoradiography. For neurogenesis, the experimental animals were the offspring of pregnant females given an injection of [3H]thymidine on two consecutive gestational days. Nine groups were exposed to [3H]thymidine on embryonic days E13-E14, E14-E15, E21-E22, respectively. On postnatal day P5, the percentage of labeled cells and the proportion of cells originating during 24-hr periods were quantified at four anteroposterior levels in the preoptic area. Throughout most of the preoptic area there is a lateral to medial neurogenetic gradient. Neurons originate between E12-E15 in the lateral preoptic area, between E13-E16 in the medial preoptic area, between E14-E17 in the medial preoptic nucleus, and between E15-E18 in the periventricular nucleus. These structures also have intrinsic dorsal to ventral neurogenetic gradients. There are two atypical structures: (1) the sexually dimorphic nucleus originates exceptionally late (E15-E19) and is located more lateral to the ventricle than older neurons; (2) in the median preoptic nucleus, where older neurons (E13-E14) are located closer to the third ventricle than younger neurons (E14-E17). For an autoradiographic study of morphogenesis, pregnant females were given a single injection of [3H]thymidine during gestation, and their embryos were removed either two hrs later (short survival) or in successive 24-hr periods (sequential survival). Short-survival autoradiography was used to locate the putative neuroepithelial sources of preoptic nuclei, and sequential survival autoradiography was used to trace the migratory waves of young neurons and their final settling locations. The preoptic neuroepithelium is located anterior to and in the front wall of the optic recess. The neuroepithelium lining the third ventricle is postulated to contain a mosaic of spatiotemporally defined neuroepithelial zones, each containing precursor cells for a specific structure. The neuroepithelial zones and the migratory waves originating from them are illustrated. Throughout most of the preoptic area, neurons migrate predominantly laterally. The older neurons in the lateral preoptic area migrate earlier and settle adjacent to the telencephalon. Younger neurons migrate in successively later waves and accumulate medially. The sexually dimorphic neurons are exceptional since they migrate past older cells to settle in the core of the medial preoptic nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Development of the precerebellar nuclei in the rat: I. The precerebellar neuroepithelium of the rhombencephalon.

Short-survival thymidine radiograms from rat embryos aged 13-19 days were analyzed to delineate the precerebellar neuroepithelium of the rhombencephalon. The original definition of the term "rhombencephalon" was modified to refer only to the unique dorsal portion (surface plate) of the medulla and pons where the neural groove fails to fuse and, instead, the medullary velum covers the rhomboid lumen of the fourth ventricle. Initially, the neuroepithelial tissue of the rhombencephalon consists of a pair of rostral and caudal bridgeheads: the former the primary neuroepithelium of the cerebellum and the latter the primary neuroepithelium of the octavo-precerebellar system. The spatial relationship between the cerebellar and precerebellar neuroepithelia soon changes as a result of ongoing morphogenetic events, such that the cerebellar primordium assumes a dorsal position and the precerebellar primordium a ventral position, and the distance between the two decreases. Concurrently the tela choroidea invaginates into the fourth ventricle and a secondary precerebellar neuroepithelium develops. The rostral portion of the secondary precerebellar neuroepithelium grows forward along the choroid plexus and forms the medial recess of the anterior fourth ventricle, while its caudal portion grows in the opposite direction beneath the medullary velum and forms the rostral wall of the posterior fourth ventricle. Evidence will be presented in the succeeding papers that the primary precerebellar neuroepithelium first generates the neurons of the inferior olive that migrate by a circumferential intramural (parenchymal) route to their destination. Next, the neurons of the lateral reticular and external cuneate nuclei are generated. These migrate by a posterior extramural (superficial) route and settle contralaterally. Subsequently, the primary precerebellar neuroepithelium produces the neurons of the nucleus reticularis tegmenti pontis and these form the anterior extramural migratory stream and settle ipsilaterally. Finally, the secondary precerebellar neuroepithelium produces the latest generated neurons of the basal pontine gray that follow the anterior extramural stream and settle ipsilaterally.

Animals↗
PubMed1987

Development of the precerebellar nuclei in the rat: II. The intramural olivary migratory stream and the neurogenetic organization of the inferior olive.

Sequential thymidine radiograms from rats labeled on days E13 and E14, and killed at daily intervals thereafter, were analyzed to trace the migratory route and settling pattern of neurons of the inferior olive. Long-survival thymidine radiograms from perinatal rats injected on day E14 were used to subdivide the inferior olivary complex on the basis of neurogentic criteria. The inferior olivary neurons originate on days E13 and E14 in the primary precerebellar neuroepithelium. The olivary neurons labeled on day E14 (the late generated components) translocate into the inferior olivary premigratory zone on day E15. On day E16 these cells join the olivary migratory stream, which follows an intramural circumferential path between the gray and white matters of the medulla. By day E17 the olivary migratory stream is reduced to a small band near the corpus of the inferior olive, which has been settled by this time by neurons generated on day E13. As a result, the unlabeled cells are situated on day E17 dorsomedially and the labeled cells ventrolaterally. The regional segregation of neurons forming subdivisions of the inferior olive begins on day E18, and by day E19 the major subdivisions are all recognizable. In thymidine radiograms from perinatal rats injected on day E14, four neurogenetic components can be distinguished in the inferior olive, those composed: (1) of unlabeled cells (generated on day E13), (2) of predominantly unlabeled cells, (3) of predominantly labeled cells (generated on day E14), and (4) of labeled cells. By combining these neurogenetic differences with the morphological features of the inferior olivary complex, we propose a modification of the currently accepted classification. The four major divisions of the inferior olive are the successively produced posterodorsal olive, anterolateral (principal) olive, posteroventral olive, and anteroventral olive. The location and configuration of these divisions are illustrated in relation to the traditional classification both in the coronal and the sagittal plane.

Animals↗